PLATINUM METALS REVIEW · High Pressure Research on Palladium-Hydrogen Systems Platinum Compounds in Cancer Research ... unlike the old ones, have reference tables derived from them

PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and of developments in their application in industry

V O L . 1 6 J A N U A R Y 1 9 7 2 NO. 1

Contents

Platinum Metal Thermocouples

Iron-Rhodium Resistance Thermometers

High Pressure Research on Palladium-Hydrogen Systems

Platinum Compounds in Cancer Research

Low Temperature Catalytic Heaters

Platinum Metals in Organometallic Chemistry

Rhodium Coating on Plastics

Abstracts

New Patents

2

9

10

15

16

22

26

27

35

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, Matthey & Co Limited, Hatton Garden, London EClP 1AE

Platinum Metal Thermocouples NEW INTERNATIONAL REFERENCE TABLES

By T. J. Quinn and T. R. D. Chandler National Physical Laboratory, Teddington, Middlesex

As a result of a remarkable piece of international collaboration between three national standards laboratories and seven United States and United Kingdom manufacturers, new reference tables have now been completed for platinum : 10 per cent rhodium-platinum and platinum: 13 per cent rhodium-platinum thermocouples. These new tables take into account the changes in the temperature scale resulting from the introduction of the International Practical Temperature Scale of 1968 (IPTS-68) and also provide reference tables which will be common to both U.S. and U.K. manufacturers and users of thermocouples.

The changes in the temperature scale ( I ) when IPTS-68 was introduced highlighted the problem hitherto of the two conflicting reference tables for rhodium-platinum thermocouples. One table was based on work done in 1933 at the National Bureau of Standards (NBS) by Roeser and Caldwell (2) and was published as NBS 561, and the other was based on work done at the National Physical Laboratory (NPL) in 1950 by C. R. Barber (3) and was published in the United Kingdom as BS 1826. These tables differed from one another as a result of differences in both the realisation of the temperature scales in the original calibrations and in the compositions of the platinum and rhodium- platinum wire. Since the original measurements were made, particularly those in 1933, there have been substantial improvements in the purification of both platinum and rhodium and thus, in order to continue to meet the old tables, changes were made in the composition of the alloy arms of the thermocouples. The result was that differences between thermocouples made to meet NBS 561 and those made to meet BS 1826 have become quite substantial. It has been clear for some time that it was uneconomic for manufacturers to have to make material of

nominally the same composition to these two specifications.

In September 1967 an informal meeting took place at the NBS between representatives of the NBS, National Research Council of Canada (NRC) and the NPL. At this meeting it was agreed that the introduction of the IPTS-68 would provide an excellent op- portunity to unify the reference tables €or platinum thermocouples. It was agreed that a joint approach should be made by the three national laboratories to all the U.S. and U.K. manufacturers with a view to carrying out a programme of research leading to new reference tables. This was welcomed by the manufacturers, many of whom had been aware of and had encouraged the proposals discussed at this meeting, and it was agreed that the terms of reference for the project would be as follows:

(i) Each of four American and three British manufacturers would contri- bute 24 metres of pure platinum wire and 12 metres each of ID per cent rhodium-platinum and 13 per cent rhodium-platinum wire.

(ii) Each of the three types of wire would have nominal diameter 0.5 mrn and be supplied in a continuous length.

Platinum Metals Rev., 1972, 16, (l), 2-9 2

Fig. 1 Experimental work at the National Physical Laboratory to provide the data for new reference tables for platinum : 10 per cent rhodium-platinum and platinum : 13 per cent rhodium-platinum thermorouples above the gold point was carried out using the NI’L photoelectric pyrometer. The standard lamps and furnace are seen here also and the furnace containing a gold point black-body as CL reference is on the right

(iii) The pure platinum wires should have a steam point to ice point resistance ratio not less than 1.3924.

(iv) The two alloy wires would contain as closely as possible 10 per cent rhodium and 13 per cent rhodium respectively, rather than have the rhodium contents adjusted to match particular specified e.m.f.s of the gold point. It was generally acknowledged that this would lead to slightly higher values of e.m.f. for given temperatures than in existing tables.

I t was decided also to split the experimental work among the three national laboratories in the following way :

(i) The materials would be collected and the thermocouples assembled by NBS, then half of the completed thermocouples would be sent to NRC.

(ii) NBS and NRC would perform primary calibrations on some and comparison calibrations on all of their thermocouples from 0°C to the gold point.

(iii) A selected number of thermocouples from each of the NBS and NRC groups would then receive primary calibrations at NPL from the gold point to the platinum point against a photoelectric optical pyrometer using a suitable black-body cavity. Enough calibrations would be done at the gold point to ensure agreement with the NBS and NRC calibrations.

(iv) The thermocouples retained by NBS and NRC would be intercompared from the gold point to the platinum point and also be compared with those from NPL upon their return.

(v) NBS and NRC would ensure agreement with the NPL by a limited number of high temperature calibrations obtained by measuring palladium and platinum points by the wire method.

The Reference Tables This work has now been completed and the

new reference tables were presented at the

Platinum Metals Rev., 1972, 16, (1) 3

Table I

The New Platinum : lo?/, Rhodium- Platinum Reference Table Defined by

Sets of Polynomial Functions

Tem peratu r e Range

-50°C to 630.74"C

630.74"C t o 1064.43"C

1064.43"C t o 1665°C

1665°C to 1767.6"C

Polynomial

6 E=2; ai tib8 yV

i -0 where a,=O

a,= 5.399578 aZ=1.251977x lo-, a,= -2.244822 x I 0-5 aA-2.845216x 10-8 a,=-2.244058~10-~~ a = 8.50541 7 x I O-l5

2

where go--298.245

g2=1.645391 x g, =8.237553

3

i = O E=C b;(t*)i pV

where t*-(tb8-l 365)/300

b,=l3943.439 b, -3639.869 b, 7-5.028 b3=-42.451

where t* =(t68-1715);50

c0 = 181 1 3.083 C, -=567.954 c,=--12.112 c,=-2.812

Table II

The New Platinum : 1304 Rhodium- Platinum Reference Table Defined by

Sets of Polynomial Functions

Temperature Range

-50°C t o 630.74"C

630.74"C t o 1064.43"C

1064.43T t o 1665°C

1665°C t o 1767.6"C

Polynomial

7

i -0 E=Z d, ti6@ pV

where d,=O d, -5.289139 d,~1.391111 x I O - ' d, --2.400524x d,- 3.620141 x IC-'

d = 3.849769 x I d5--4.4645C2x 10 "

d,- -1.537264~ lo-"

where h,=264.180 h,=8.046868 h,-=2.989229 x 10- h,= -2.687606 x lo-'

3

where t*=(t,,- -1365)/300

eo:l554O.4I4 e, =4235.777 e,=14.693 e,--52.214

3

i- 0 E- cf,(t*)l pV

where t*-(t,,-1715)~ 50

f,-=2041 6.695 f, -668.509 f2---12.301 f3--2.7a6

5th Symposium on "Temperature" held in of the experimental work. These functions Washington in June 1971." These new are listed in Tables I and I1 and skeleton reference tables, unlike the old ones, have reference tables derived from them appear in been produced by means of agreed sets of Tables I11 and IV. The differences between polynomial functions fitted to the results the new tables and the old are shown in * The Proceedings of the 5th Symposium on Figs. 2 and 3, which also clearly indicate the "Temperature Measurement and Control in differences between the NBS 561 and BS Science and Industry" are to be published in 1972. 1826 tables.

Platirium Metals Rev., 1972, 16, (1) 4

Table Ill

Skeleton Reference Table for Platinum : 10 per cent Rhodium-Platinum (Type S) Thermocouples

Temperatures in Degrees Celsius (IPTS-68) Reference Junction at 0°C

Temp. I 0 10 20 30 40 50 60 70 80 90

0

0 100 200 300 400

500 600 700 800 900

1000 1100 1200 1300 1400

1500 1600 1700

I Absolute E.M.F. in Microvolts 0

0 645

1440 2323 3260

4234 5237 6274 7345 8448

9585 10754 11 947 13155 14368

15576 16771 17942

- 53

55 71 9

1525 241 4 3356

4333 5339 6380 7454 8560

9700 10872 12067 13276 14489

15697 16890 18056

-103

113 795

1611 2506 3452

4432 5442 6486 7563 8673

981 6 10991 121 88 13397 1461 0

15817 17008 181 70

-150

173 872

1698 2599 3549

4532 5544 6592 7672 8786

9932 11110 12308 13519 14731

15937 171 25 18282

-194

235 950

1785 2692 3645

4632 5648 6699 7782 8899

10048 11 229 12429 13640 14852

16057 17243 18394

-236

299 1029 1873 2786 3743

4732 5751 6805 7892 901 2

101 65 1 1348 12550 13761 14973

161 76 17360 18504

365 1109 1962 2880 3840

4832 5855 691 3 8003 91 26

10282 1 1467 12671 13883 15094

16296 17477 1861 2

432 1190 2051 2974 3938

4933 5960 7020 8114 9240

10400 11587 12792 14004 1521 5

1641 5 17594

502 1273 21 41 3069 4036

5034 6064 71 28 8225 9355

1051 7 1 1707 1291 3 14125 15336

16534 1771 1

573 1356 2232 31 64 4135

51 36 61 69 7236 8336 9470

10635 11 827 13034 14247 15456

16653 17826

Table IV

Skeleton Reference Table for Platinum : 13 per cent Rhodium-Platinum (Type R) Thermocouples

Temperatures in Degrees Celsius (IPTS-68) Reference Junction at 0°C

Temp. I 0 10 20 30 40 50 60 70 80 90

0

0 100 200 300 400

500 600 700 800 900

1000 1100 1200 1300 1400

I Absolute E.M.F. in Microvolts 0

0 647

1468 2400 3407

4471 5582 6741 7949 9203

10503 11 846 13224 14624 16035

- 51

54 723

1557 2498 351 1

4580 5696 6860 8072 9331

10636 11 983 13363 14765 161 76

-100

111 800

1647 2596 3616

4689 581 0 6979 81 96 9460

10768 12119 13502 14906 1631 7

-145

171 879

1738 2695 3721

4799 5925 7098 8320 9589

10902 12257 13642 15047 16458

-188

232 959

1830 2795 3826

491 0 6040 721 8 8445 971 8

11 035 12394 13782 15188 16599

-226

296 1041 1923 2896 3933

5021 61 55 7339 8570 9848

11170 12532 13922 15329 16741

363 1124 201 7 2997 4039

51 32 6272 7460 8696 9978

11304 12669 14062 15470 16882

431 1208 2111 3099 41 46

5244 6388 7582 8822

10109

f 1439 12808 14202 1561 1 17022

501 1294 2207 3201 4254

5356 6505 7703 8949

10240

11574 12946 14343 15752 17163

573 1380 2303 3304 4362

5469 6623 7826 9076

10371

11710 13085 14483 15893 17304

1500 17445 17585 17726 17866 18006 18146 18286 18425 18564 18703 1600 18842 18981 19119 19257 19395 19533 19670 19807 19944 20080 1700 20215 20350 20483 20616 20748 20878 21006


Experimental Work reference tables above the gold point was undertaken using the NPL photoelectric

The experimental work carried out at pyrometer (Figure I). This was used to measure the temperature of a black-body NPL that provided the data for the new


Fig. 4 The platinum black-body constructed b-y Johnson Matthey before assembly and use

cavity which could accommodate up to four thermocouples at a time. The cavity used from the gold point up to 1748°C was made from solid platinum and was loaned to NPL for this work by Johnson Matthey. It is illustrated in Figs. 4 and 5. Using a furnace wound with pure rhodium ribbon and 40 per cent rhodium-platinum wire internal end heaters, a temperature uniformity, at about 15oo0C, of within 0.3 deg C was achieved over the whole length of the block.

It was found that the reproducibility of platinum : 13 per cent rhodium-platinum thermocouples was significantly better than that of platinum : 10 per cent rhodium- platinum thermocouples over the whole temperature range. For example, the mean gold point e.m.f. determined by NPL for eight platinum : 13 per cent rhodium-

Fig. 5 The platinum black- body afer prolonged use at temperatures up to 1748°C. One of the thermocouples used for this work is also shown

platinum thermocouples was 0.4 microvolts above the NBS and NRC mean ingot value, while that of the platinum : 10 per cent rhodium-platinum thermocouples was 2 microvolts higher. A difference in behaviour of this sort can be reasonably accounted for by the fall in slope, between 10 per cent rhodium and 13 per cent rhodium, of the e.m.f./composition curve for rhodium-platinum alloys. It would seem reasonable therefore to hope that in due course the platinum : 13 per cent rhodium-platinum thermocouple would supersede the platinum: 10 per cent rhodium-platinum thermocouple in general use, particularly if the IPTS-68 between 630.74"C and 1064.43T is eventu-


ally defined in terms of the platinum resistance thermometer rather than the platinum: 10 per cent rhodium-platinum thermocouple.

To cover the range between 1748°C and the melting point of platinum further measurements were made using a black- body cavity made from alumina. It was found with this cavity that there is a significant drop in the thermoelectric power both of platinum : 10 per cent rhodium-platinum and platinum : 13 per cent rhodium-platinum thermocouples above 1700'C. Figures 6 and 7 show the results of these high tem-

perature measurements of thermoelectric power. The change in slope of the thermoelectric power/temperature curve above about IIOO'C can be accounted for qualitatively by the effects of the increasing concentration of lattice vacancies at high temperatures. The drop above 170o0C, however, seems too steep to be accounted for solely by lattice defects; there must be another factor which is becoming important. One such factor could be the conductivity of the alumina refractory which is increasing at a significant rate at these temperatures.

Platinum Metals Rev., 1972, 16, (1)

Fig. 8 An ingot of platinum after melting. Neither the alumina crucible nor black- body were damaged during heating or cooling from room temperature to the melting point. The crucible was broken after the measurement so that the melted platinum could be examined

The Freezing Point of Platinum It became apparent during the course of

this work that a temperature of 1772~C (IPTS-68) for the freezing point of platinum would not be consistent with the results of measurements made in the two black-bodies from the gold point upwards. The e.m.f.1 temperature curve thus obtained showed that the temperature at which the platinum arm of the thermocouple melted was some 4 deg C below 1772OC. A similar result was obtained from platinum wire-point measurements made at NRC. That the freezing point of platinum was lower than the previously accepted value was subsequently confirmed at NPL by measurements made with the photoelectric pyrometer using substantial ingots of pure platinum (4). Three series of measurements were made, two ingots being supplied by Engelhard (U.K.)

and one by Johnson Matthey. There was no significant difference found between the results from the three ingots, nor between the melts and the freezes. The final value for the freezing point of platinum was found to be 1767.6to.3"C (IPTS-68).

The authors are pleased to acknowledge the generous assistance given by Johnson Matthey & Co Ltd, throughout this work by the supply of the platinum and rhodium-platinum wire, the construction and loan of the platinum black- body, the machining and loan of one of the ingots of platinum used for the melting point work, and for spectrographic analysis of pieces of the platinum before and after melting.

Much of the impetus behind this work, together with invaluable advice and encouragement during its execution, came from the late C. R. Barber of NPL.

References I C . R. Barber, Nature, 1969, 222, 929 2 W. F. Roeser and H. T. Wensel, J . Res. Nat.

3 C. R. Barber, Proc. Phys. Soc., 1950, B63, 492 4 T. J. Quinn and T. R. D. Chandler, Metrologia,

Bur. Stds., 1933, 10, 275

1971, 7, 132

Iron-Rhodium Resistance Thermometers Cryogenic engineering is becoming much

more important as work with liquid gases and on the applications of superconductivity increases. Special thermometers are needed at these very low temperatures because although platinum resistance thermometers are satisfactory for use down to 20 K they cannot be used below 10 K.

The use of 0.5 atomic per cent iron- rhodium alloy as a resistance thermometer material at very low temperatures was proposed by Professor B. R. Coles of Imperial College, London in 1964 (Phys. Lett., 1964, 8, (4), 243-24). Tests have since shown that it is suitable for use between 0.35 and 40 K. It is now available from Johnson Matthey Metals in the form of wire 0.13 mm diameter in either a hard-worked or an annealed condition,


The rate of increase of resistance of the wire varies somewhat over the range of temperature from 0.35 up to 40 K. Calibration is therefore necessary and this should take place in the position in which the instrument is to be used.

Strong magnetic fields occur in work on superconduction but the iron-rhodium alloy remains virtually unaffected so that the change in resistance per deg K is small and predictable. At temperatures in the liquid helium range a one per cent change in the resistance is produced by a field of 10 kOe. The change in resistance per deg K is not altered by work-hardening. Accuracy of 31 ~ o - ~ d e g K in the range is possible with 20 cm of 0.13 mm diameter wire used with conventional potentiometric measuring equip- ment.

9

High Pressure Research on Palladium-Hydrogen Systems By B. Baranowski Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw

High pressure studies involving hydrogen gas present considerable technological di@culties because of the embrittling efect of hydrogen on constructional materials. In recent work in Warsaw, however, it has been possible to study the absorption of hydrogen by palladium and by a series of palladium alloys at pressures of up to 25,000 atmospheres of hydrogen, and interesting results have been obtained.

The very great majority of results published for the palladium-hydrogen and palladium alloy-hydrogen systems have been obtained with low pressures of gaseous hydrogen or, in the case of electrochemical studies, a t electrode potentials corresponding to relatively low pressures of hydrogen (I).

Of the studies with high pressures of gaseous hydrogen one must first mention the paper of Frumkin and co-workers (2) where isotherms of the palladium-hydrogen system have been measured at temperatures from -18.5 to 30°C up to 1700 atmospheres of gaseous hydrogen. An important finding of this study was that in purely P-phase ranges of hydrogen content a linear relationship exists between hydrogen content (expressed for example as the atomic ratio, H/Pd) and the logarithm of hydrogen pressure. A later study (3) by Levine and Weale, using pressures of up to 1000 atmospheres was carried out at temperatures adjacent to the critical region of the palladium-hydrogen system- for which T, is w 300°C.

Experimental Arrangements for High Pressure Studies

The handling of gaseous hydrogen at high pressures is especially complicated because of its extremely damaging effect on steel vessels or components. Figure I shows a schematic diagram of a device designed to

counteract this difficulty which is in current use in this laboratory (4, and which also represents an improvement in regard to this general problem over arrangements which we have employed earlier (5). The device described has allowed us to reach hydrogen pressures up to 25,000 atmospheres at room temperature.

Initiatives for High Pressure Research Studies

Interest or need for working with high pressures of hydrogen in metal-hydrogen systems can arise for different reasons :

(i) With clean surfaces the upper limit of hydrogen pressure which can be obtained at an electrode does not generally exceed the range 10 to 50 atmospheres (6). One can achieve much higher hydrogen activities (under irreversible kinetic conditions) at the electrode by adding promoting agents to the electrolyte (7) but this makes any equilibrium study impossible due to the non-reversible character of the electrode surface.

(ii) There are several metals which exhibit hardly any solubility of hydrogen under low pressures of the gas. And this low solubility is generally accompanied by only rather uninterestingly small changes of physical parameters. In the case of nickel, however, it has already been shown (8) that at pressures of % 8000 atmospheres a hydride phase


1 2 3

Fig. I l h e high pressure apparatus used for the studies of pnlladium- iydrogen and palladium alloy-hydrogen systems. The pressure vessel is he internal conical steel cylinder 1 supported by two steel rings 2 and 3. rhe reaction vessel inside the cylinder i s shown in more detail on the right. rhe bottom of the rylinder i s closed by a steel stopper 6 with O-ring 10 and irass ring 4 seals. Electrical connections are introduced at 7. The internal eaction vessel 11 i s located on the steel stopper by arrangements shown 1s 8 and 9. In operation the internal reaction vessel 11 i s first filled with :aseous hydrogen outside the pressure vessel u p to a pressure of -400 ttmospheres. Higher pressures are then attained by transmission of a n xternally applied force by the piston 5 to the organic liquid piling u p the pace between the pressure vessel and the hydrogen container so that the )iston inside the hydrogen container i s operated on by hydrostatic force. I'ressure i s measured by a manganin resistance gauge placed in the irganic liquid

(5 , 8, g, 10) can be formed with a composition corresponding to an atomic ratio H/Niwo.7 to 0.9 - as compared with a solubility corresponding to a value of H/Ni of only w I O - ~ under a hydrogen pressure of one atmosphere. This suggests the interesting possibility that other metals might exhibit comparable behaviour in hitherto unstudied high pressure regions.

(iii) In higher pressure regions, gaseous hydrogen exhibits large deviations from ideal behaviour (11), in that increases of chemical potential are larger than those calculated on an assumption of


5

11

9

6

10

4

1': ,'

ideality for complementary incremental increases of hydrostatic pressure. Although direct experimental evidence is only available up to ~ 3 0 0 0 atmospheres, Fig. z indicates that, if the constants used for extrapolation are pressure independent, a hydrogen pressure of 21,000 atmospheres should correspond to a fugacity of about log atmospheres.

Changes of Electrical Resistance and Other High Pressure Studies of the Palladium-Hydrogen System

It has been known for a long time that electrical resistance is quite a sensitive function of hydrogen content at compositions

obtainable with relatively low pressures of hydrogen (I) . (Changes of resistance are usually expressed for generality in terms of the relative resistance, R/RPd.) At room temperature R/Rpd exhibits a gradual increase with increasing hydrogen content up to a fairly constant value at values of HjPd of mo.7, which can be reached at equilibrium pressures only slightly above atmospheric. As illustrated in Fig. 3, recent results (12, 13) have shown that additional hydrogen introduced under high pressure causes a subsequent substantial lowering of resistance until it eventually decreases to slightly below the initial value of hydrogen-free palladium.


In studies at very high pressures it is not, however, easy to make direct concurrent measurements of changes of hydrogen content. Estimates of H/Pd can nevertheless be obtained by using extrapolations of relationships between pressure and content derived (14) over lower ranges of pressure. Figure 4 indicates that if these relationships were reasonably correct, then the decrease of R/R,, with increasing HjPd would remain of the same form up to values of the atomic ratio H/Pd of close to a stoichiometry of I :I. It seems from Fig. 3, however, that the linear dependence between relative resistance and the logarithm of hydrogen fugacity only holds up to w 16,000 atmospheres.

At higher pressures there is a change of slope to a further linear relationship which seems to extend up to w 25,000 atmospheres, which represents the upper limit of pressure so far attained. At the highest pressures the extrapolated relationships would suggest that HjPd had reached values of w 1.2 as indicated in Fig. 4. Attempts have been made to estimate directly the maximum contents of hydrogen which can be absorbed, by outgassing specimens in vacuo after their removal

from the high pressure apparatus following a cooling to -40°C (mass spectrometry was used for the quantitative analysis of hydrogen). Indications are, however, that some loss of hydrogen always occurs from such specimens as compared to the volume which had been absorbed under very high pressure. Never- theless, specimens with compositions ap- proaching H/Pd = I have been isolated; and values of the lattice constant of such specimens have been shown to be consistent with general relationships between lattice constant and hydrogen content which have recently been discerned (15) for the palladium-hydrogen and a number of palladium alloy-hydrogen systems.

Specimens containing the larger contents of hydrogen introduced under high pressure have also recently been employed in studies (16) of the anomaly in relationship between electrical resistance and temperature in the region of 60 K.

Thus, as illustrated in Fig. 5, the interesting information has been found that a sample with H/Pdwo.89 showed little evidence of an anomaly whilst effects of a maximum degree


are obtained for specimens for which H/Pd=:0.7. The relevance of these findings to alternative explanations of the anomaly in terms either of transitions of hydrogen between octahedral and tetrahedral interstices (17) or the existence of islands of stoichio- metric PdH (IS) has been discussed. At present it seems that additional experimental information is still necessary to resolve this problem, such as determinations of the lattice structures of samples with high contents of hydrogen, at higher temperatures than it has been convenient to use so far.

High Pressure Research on Various Palladium Alloys

An initial study (13) with a single Pd-Au alloy ( z 35 atom per cent Au) at 25°C showed that electrical resistance continued to increase linearly as a function of logarithm of hydrogen fugacity up to 24,000 atmospheres after passing through a minimum below 300 atmospheres.

Recently systematic investigations have been in progress for comprehensive series of Pd-Ag, Pd-Pt and Pd-Rh alloys. It has again been found that a substantial proportion of hydrogen introduced at high pressure can be retained after removal from the high pressure apparatus by using a similar cooling procedure to that discussed above for the Pd-H system. It has therefore been possible to show that values of lattice parameters derived at these high hydrogen contents also correspond with the general relationships for the palladium and other palladium alloy- hydrogen systems (15) to which attention has recently been drawn, as mentioned earlier above.

The course of changes of electrical resistance in the high regions shows a rich variety of behaviour for these alloy systems. The palladium-platinum series of alloys (19) exhibits a gradual modification of the behaviour of the Pd-H system in that, for rising overall platinum content, electrical resistance still increases as a function of pressure to a maximum value, which, how-

ever, is attained at progressively higher pressures. Furthermore, in the regions of decreasing resistance following the maximum, the relationship between relative resistance and the logarithm of fugacity finally again becomes linear for those alloys (containing 70 per cent silver might absorb significant amounts of hydrogen was not paralleled in the Pd-Pt series; for example, up to pressures as high as 24,000 atmospheres an alloy with 70 atom per cent platinum exhibited virtually no changes of electrical resistance -which seems reasonably indicative of a correspond- ingly very low hydrogen solubility.

Despite the indications of significant solubility of hydrogen in alloys with >70 per cent silver, the overall indications from the changing form of the relationships between relative resistance and pressure are that making comparisons at any given pressure over the whole range of higher pressures, the solubilities of hydrogen in both the Pd-Pt and Pd-Ag series of alloy decreased con- tinuously as a function of either platinum or silver contents at 25°C. This did not seem to indicate a very active participation of the


platinum or silver atoms in hydride formation. A considerably contrasting behaviour has, however, been found in the case of the Pd-Rh series of alloys. Here alloys with contents of rhodium extending up to 40 per cent have been found to exhibit solubilities corresponding to ratios of hydrogen to palladium atoms greater than one (21). These high contents have been measured directly by outgassing specimens removed from the high pressure apparatus after cooling and pressure reduction; the contents are also in keeping with measurement of changes of lattice parameters (15). Data are as yet incomplete over the whole range of alloy compositions but the results available seem to indicate either supplementation by rhodium in certain concentration ranges of the ability of palladium to form distinct hydride phases or the possibility of rhodium itself being able to form a hydride phase. The author wishes to thank Dr F. A. Lewis, Chemistry Dept, Queen’s University, Belfast for editorial revision of this article.

References F. A. Lewis, The Palladium Hydrogen System, Academic Press, London and New York, 1967 P. S. Perrninov, A. A. Orlov and A. N. Frumkin, Dokl. Akad. Nauk S.S.S.R., 1952, 84,749

3 P. L. Levine and K. E. Weale, Trans. Faraduy SOC.J 1960, 56, 357

4 B. Baranowski and W. Bujnowski, Roczniki Chem., 1970,44,2271

5 B. Baranowski and R. WiSniewski, Bull. Polon. Acad. Sci., 1966, 14, 273

6 J. A. S. Green and F. A. Lewis, Trans. Faraday Soc., 1964, 60, 2234

7 R. J. Smith and D. A. Otterson, J . Phys. Chem. Solids, 1970, 31, 187

8 B. Baranowski, K. Bocheriska and S. Majchrzak, Roczniki Chem., 1967, 41, 2071

9 A. Stroka and A. Freilich, Roczniki Chem.,

10 B. Baranowski and M. Smialowski, J. Phys. Chem. Solids, 1959, 12, 206

11 W. de Graaff, Compressibility Isotherms and Thermodynamic Functions of Hydrogen and Deuterium, Diss., Amsterdam, 1960

12 B. Baranowski and R. WiSniewski, J . Phys. Chem. Solids, 1968, 23, 1275

13 B. Baranowski and R. WiSniewski, Phys. Status Solidi, 1969, 35, 593

14 E. Wicke and G. Nernst, Ber. Bunsen. Phys. Chem., 1964,68,224

15 B. Baranowski, S. Majchrzak and T. B. Flanagan, J . Phys. F, Metal Phys., 1971, I, 258

16 T. Skoikiewicz and B. Baranowski, Phys. Status Solidi, 1968, 30, K33

17 G. A. Ferguson, A. J. Schindler, T. Tanaka and P. Morita, Phys. Rev., 1965, 137, 483

18 H. Brodowsky, 67 Hauptversamml. der Deutsch. Bunsenges., Augsburg, May 1968

19 B. Baranowski, R. WiBniewski, S. Majchrzak and F. A. Lewis, to be published

20 B. Baranowski and A. Szafrariski, to be published

21 T. B. Flanagan, B. Baranowski and S. Majchrzak,J. Phys. Chem., 1970, 74, 4299

I97OJ 44, 235

Platinum Compounds in Cancer Research Professor B. Rosenberg of Michigan State

University has reported previously that certain platinum compounds are very potent anti-tumour agents against a wide variety of tumours (Platinum Metals Rev., 1971, 15, (2), 42-51). Tests were carried out initially on laboratory mice but trials of cis-dichlorodiamminoplatinum(I1) have now been extended to human patients at six hospitals and institutes in the U.S.A. and at one in London.

B. J. Leonard and co-workers of I.C.I. Pharmaceuticals and Dyestuffs Divisions, Macclesfield, Cheshire have also now reported that cis-dichlorodiamminoplatinum(I1) and cis-tetrachlorodiamminoplatinum(1V) have strong antileukaemic effects in rats on myeloid and lymphatic leukaemias (Nature,

1971, 234, (Nov. 5), 43-45). Although the effects are accompanied by uraemia, these two compounds seem to be superior to those in clinical use as they have no undesirable side effects on the normal cells of the marrow, gonads and intestine. These antileukaemic and nephrotoxic properties seem to be related to the molecular configuration of the platinum compounds because the corresponding trans compounds had no effect on either type of rat leukaemia or on the kidneys of mice, rats and marmosets. The I.C.I. team suggest that it is not clear whether the antileukaemic effect of the compounds is direct and selective on the tumour cells or indirect and perhaps mediated through the immunological system but they believe that clinical trials on human tumours and leukaemias would be justified.


17

21

Low Temperature Catalytic Heaters THE CATAHEAT RANGE OF FLAMELESS COMBUSTION SYSTEMS

By J. D. MacConnell Matthey Bishop Inc., Malvern, Pennsylvania

Platinum group metal catalysts are incorporated in the Cataheat flameless Combustion systems designed by Matthey Bishop to burn hydrocarbon fuels. These systems are safer and more escient than radiant heaters with an openflame. They are used in portable heaters for a wide range of agricultural, industrial and recreational purposes.

The small radiant heaters that burn hydrocarbon fuels - propane, butane, methane/natural gas and liquid hydrocarbon fuels - are used widely because of their simple design, their portability, and the ready availability of fuels. The open flame heater presents obvious disadvantages as follows. An upset heater is a grave fire risk where the surroundings are flammable and this restricts usage in, for example, farm buildings. If there is incomplete combustion of the fuel then the flame tends to smoke and a build-up of soot occurs on the heater. And, most important, the temperature of the flame may exceed IOOO'C with much energy being wasted in heating the surrounding atmosphere and in the emission of visible light energy.

To avoid these problems it is necessary to suppress the flame, to ensure efficient combustion and to reduce emission of useless energy. The solution is to use a catalyst that permits combustion of the hydrocarbon fuels at much lower temperatures. A suitable catalyst enables oxidation of the fuel to take place at a much lower energy level than would otherwise be possible. For example, using propane as fuel, combustion can take place on a catalyst at about 400"C, much lower than the 1000°C quoted above for a naked flame.

The properties of the platinum group metals have led to their wide use as catalysts

in oxidation reactions, including the oxidation of hydrocarbons. Technical staff in the Chemicals Division of Matthey Bishop have studied how these properties can best be adapted to construct low temperature catalytic heaters. They have developed a range of such platinum group metal catalysts, which are known as Cataheat, each of which is designed to operate with a specific type of fuel. Basically the Cataheat systems consist of platinum group metals supported on new and improved substrates to produce catalytic burning surfaces suitable for use with each fuel. The characteristics of three types of Cataheat unit are summarised in the table opposite. Cataheat L has been developed for the combustion of liquid fuel such as white gasoline, Cataheat P for the combustion of propane or butane, and Cataheat M for combustion of methane/natural gas.

Cataheat systems reduce the temperature at which the oxidation reaction of combustion takes place to well below that at which combustion occurs in a flame. The reaction is still, of course, exothermic but the heat that is emitted is radiant. The infra-red radiation warms surfaces exposed to the catalytic heater whileleaving the air around the heater virtually unaffected. Thus the efficiency of heating is higher than where there is an open flame. Heat is directed only where it is wanted. Improved safety is an added bonus. There is 98.6 per cent conversion of hydro-


Fig. 1 The Super-Ray propane gas catalytic heater was developed mainly f o r chicken brooders. Made by Impala Industries Inc. f o r sale to farmers by the Anderson B o x Company of Indianapolis, it incorporates a tubular Catahsat jlameless combustion system .fafabricated by Matthey Bishop Inc. This type of unit is particularly economic in fue l consumption. Although the air in the brooder p e n does not feel very warm the chicks are penetrated by the infra-red radiation and hence feel comfortable

carbon fuel to carbon dioxide and water during combustion on a Cataheat system.

The general design of Cataheat units is clear from Figs. z and 3. In a typical unit the gaseous fuel is fed in through an orifice in the metal dish which serves as a reservoir of gas behind the catalyst pad. The dish is designed to spread the gas evenly to all

parts of the pad, otherwise there may be a temperature gradient across the face of the pad of something like IOO deg C while combustion is taking place. The combustion takes place on the surface of the fibres of the catalyst pad. A filter pad may be included as well. The front face of the catalyst pad is protected by strong wire mesh or by a

Operating Characteristics of Cataheat Units

Rating J/m2 (Btu/i n2)

Cataheat L 123 x106 (liquid) (75)

Cataheat P 123 x106 (HD5 propane) (75)

Cataheat M 123 x106

West Texas natural gas)

(methane- (75)


Air-free CO Measured by A.G.A. Pro- cedu res, p.p.m.

125

100

150

17

Approx. Ignition Temp., "C

250-280

250

330

Approx. Unburned Surface Hydrocarbons Temp., as Hexane, "C p.p.m.

300-420 6000

290-500 1500

360-470 5000

Life, h

5000 +

1 0 , ~ +

1 o,ooo+

Type

bustion can take place. Starting up with complex pilot lights or automatic electric ignition may be used but simple ignition with a match is normally sufficient with small heaters. In those heaters fuelled with a liquid hydrocarbon, the vapour, which is heavier than air, must permeate the pad from below before it can be ignited. The catalyst must be preheated by one or other ignition method to about 120°C, at which temperature catalytic combustion commences.

The life of a Cataheat system, apart from gross physical damage, has proved to be the life of the catalyst. Eventual failure of the catalyst depends upon the quality of the fuel, impurities in which may be adsorbed on to active catalytic sites on the surface of the platinum group metals in the Cataheat system. Thus if pure fuel is used the life of a catalyst pad should be infinite. What deactivation does occur is unlikely to be due to sulphur in these strongly oxidising conditions but rather to traces of volatile metals in the fuel. Such traces accumulate on the catalyst and eventually have a deleterious effect. Signs of catalyst deactivation are evidenced by in-

perforated metal screen. The most common shape of catalyst pad (and therefore of heater) is rectangular,

Most heaters based on Cataheat units operate at gas pressures between four inches (10 cm) of water column and 15 p.s.i.g. (1.0 bar). T o commence operation the units must be heated to raise the catalyst temperature to that at which catalytic com-

Fig. 3 Construction of a rectangular propune or methane catalytic heater. In the foreground is the metal plate through which the gas enters and is distributed evenly ouer the catalyst pad. Left is the back of the plate, showing the gas orifice and right is the inside of the plate. The white pad i s a .filter pad through which the gas permeates to the catalyst pad, the front face of which is protected by the wire mesh screen


Fig 4 . The Trailblazer by Wznchester propane cataZytic heater manufactured by the Turner Corporation Division of Olirt Corporation for outdoor use. This model, which has a rectangular Cataheat system, operatw on gaseous propane with electric ignition. The Cataheat pad can be seen behind the protective grill

creasing difficulty in lighting and by some parts of the pad surface ceasing to radiate heat. When this happens it is a simple matter to replace the pad with a new one.

Heater Standards Although catalytic heater units have been

developed in the United States, regulations governing their operation have not yet been finalised. Therefore Matthey Bishop along with heater manufacturers are applying standards which were designed for the traditional type of radiant heater with the open flame. The American Gas Association (A.G.A.) standards specify that the concentration in free air of carbon monoxide from such a heater should not exceed 200 p.p.m., air free basis. In closed rooms with low

oxygen levels (15.1 per cent) the carbon monoxide level should not exceed 500 p.p.m. Tests by Matthey Bishop over long periods of operation of Cataheat systems have indicated unburned hydrocarbon concentrations on the face of the catalyst pad of less than 1500 p.p.m., air free basis as hexane, and of carbon monoxide of less than IOO p.p.m. A.G.A. pro- cedures confirmed that the closed-room concentration of carbon monoxide was less than 50 p.p.m. The above tests were carried out using HD5 grade propane gas as fuel with heat emission of 123 x 106 J/mz (10,000 Btu/ftz). The emission readings remained unchanged over 2500 hours.

Combustion requires, of course, a continuous supply of oxygen from the air. Provided that ventilation is adequate to

Platirium Metals Rev., 1972, 16, (1) 19

Fig. 5 The Coleman Company propane catalytic heater in use in camp for keeping a tent warm with complete safety

replace the oxygen burned up the combustion reaction will continue as long as fuel is supplied to the Cataheat system. However, the total reaction at any one moment depends on the catalyst surface area. Hence, once the catalytic surface is fully operational, the rate of air flow is unimportant and the Cataheat system cannot be blown out. The unit is turned off by stopping the fuel supply. It is advisable, therefore, to fit a regulator to control this supply.

Cataheat Applications Cataheat flameless combustion units have

been incorporated in heaters produced for the American market by several manufacturers. Designs of heater based on the catalyst principle can be broadly classified into three major fields of application. These are recreational, agricultural and industrial.

The recreational applications cover the smallest types of heater, used for example in the heating of tents, cabins and any outdoor


use where heat is necessary for body comfort. In addition such heaters can be used for boats and for small vehicles such as golf carts. Figures 4, 5 and 6 show typical units for the above applications.

In the agricultural industry the advantages of Cataheat units are particularly apparent, especially in animal raising.

Animal raising benefits from warm conditions for stock and the first usc of catalytic heaters for this work 'was in 1969. Results were good and there has since been considerable demand for these heaters from farmers, particularly because of their reduced fire risk in farm buildings.

Tubular Cataheat systems have been developed for poultry brooders as shown in Fig. I. Heaters of this type provide better, more efficient combustion in certain applications in comparison with flat heaters. The tubular element permits free movement of air over the entire tubular catalytic surface. Recently the Missouri State Poultry Experi-

Fig. 6 A Coleman liquid fuel (pure naphtha) unit which uses a Matthey Bishop Inc. Cata- heat L system. This type of camp heater has become very popular with outdoor en- thusiasts and is made in two sizes

ment Station has reported the results of tests demonstrating the superiority of flameless catalytic heaters over other gas-fuelled brooders and over electric units. These tests have revealed that the amount of propane consumed in comparison to other types of gas heaters was far less, while there were no major differences between the temperature of pens, the mortality of birds, or the feed efficiency. The advantages of catalytic heaters in this connection are stated as: almost complete combustion of gases with no emission of harmful fumes, the lightweight portable units enable easy observation of the poultry, the infra-red heat is directed down- wards and does not heat up the rest of the brooder houses, the flameless heater Is practically fireproof. Tests showed that day-old chicks moved about more freely under a tubular catalytic heater than under traditional units. The air in the pens did not feel as warm but the infra-red radiation

penetrated the chicks and they felt comfortable.

Industrial uses include heaters for small factory vehicles. Trolley-borne units can be installed wherever heat is wanted tem- porarily, on a building site, for example, or elsewhere when public utility workers are out of doors. Further industrial uses extend to drying operations such as paint application, and to anywhere that safe radiant energy is needed.

Matthey Bishop has developed many successful commercial Cataheat systems. However, the field of industrial and household heating has scarcely been touched and offers a significant incentive to continue a concentra- ted development programme in this direction. New Cataheat systems, some of which are at present in an advanced stage of development, are geared towards other fuel systems and towards yet greater safety. The future of catalytic combustion appears unlimited.


Platinum Metals in Organometallic Chemistry THE INTERNATIONAL CONFERENCE IN MOSCOW

By F. R. Hartley Department of Chemistry, The University of Southampton

At the Fifth International Conference on Organometallic Chemistry, held in Moscow in August 1971, no fewer than 463 papers were presented, of which 189 were actually delivered orally, together with 11 section lectures, in three parallel sessions. This review can therefore give only a brief account of such a conference and of the concerned the platinum metals.

many contributions that

A highlight of the Conference came on the first day when Professor Geoffrey Wilkinson (Imperial College, London) cast aside many time-honoured ideas about the factors respon- sible for the formation of strong metal-carbon u-bonds. Wilkinson emphasised that, before these factors can be meaningfully discussed, it is necessary to have criteria for deciding how to measure bond strength. The ideal source of data, namely thermodynamic measurements, is at present insufficient to be of any value in comparing bonds. In addition, relatively few metal-carbon a-bond lengths are known with sufficient accuracy for them to be used. One possible way of comparing bond strengths is to compare the thermal stabilities of complexes, although for this to be used it is essential to understand the mode of decomposition of the complex which Wilkinson suggested was by an "alkene- elimination hydride transfer" mechanism :

H '\L/" I I

H \c,R other similar ligand is necessary for [ Y.H>.;'] H I 11 the formation of stable metal-carbon a-bonds.

F. J. McQuillin (University of Newcastle upon Tyne) reported

M-C-H M - - - - - C -3 M + C / \ / \

H H H

stabilised against such a reaction. This may be achieved by :

(i) the formation of complexes with alkyl ligands of the type -CH,Y where Y is an atom that cannot form a double-bond to carbon (e.g., Y=H, CMe,, SiMe, or Ph),

(ii) blocking all the coordination sites around the metal atom with strong ligands such as triphenylphosphine, pyridine, or even carbon- bonded ligands themselves, thus preventing a second coordination site being available for the hydride to transfer to. This new approach, which satisfactorily explains many of the anomalies that have recently arisen in connection with Chatt's electronic theory of the stabilisation of metal-carbon a-bonds by tertiary phosphine ligands has enabled Wilkinson to prepare a number of binary alkyl complexes of such species as V", CrIV, Mo", WIV, etc., with ligands such as -CH,SiMe,. The stability of these com-

plexes dispels the suggestion that the presence of a tertiary phosphine or

on the reaction of substituted cyclo- The formation of a stable metal-carbon propanes with platinum(I1) complexes to a-bond requires the formation of a complex form analogues of Tipper's Compound:


[ ‘\Pd/’] + ZC,H4NH2 i,z dichloromethane YC,H,NC/ ‘X ZC,II,NH/ Crociani (CNR, Bol-

ogna) reported a study of the kinetics of forrna-

reflux i n e the r

for 2 hours R+ + [(C,H,)PtCl,I, -

It was found that the reactivity of the cyclopropane increased with increasing electron density in the ring (with electron withdrawing groups such as CN or OCH, no reaction occurred). When R was H, n-C,H,,, Ph, o-NO,CBH,, PhCH,, the resulting product

indicated that ring opening had occurred at the least substituted bond, probably due to electronic rather than steric effects since the bulky p-tolyl group gave

r C6H4CH31

[L,Pt(CO)Cl]+ + 2HNRR’ [L,Pt(c 4’ )ci] + H p w + HC1 “RR’ Although with trans-

tion of carbene corn- plexes of palladium(I1)

according to the above reaction. It was found that the rate increased with both increasing a-donor ability of the amine nitrogen and increasing electron-withdrawing ability of the substituent Y on the isocyanide ligand indicating that the reaction proceeds by nucleophilic attack of the amine on the coordinated isocyanide.

R. J. Angelici and his colleagues (Iowa State University) reported two routes for the preparation of carbene complexes of platinum(I1) and palladium(I1):

(i) Nucleophilic attack of amines on cationic carbonyl complexes.

* ~ ~ - d ~ s ~ ~ ~ ~ ~ ~ u t e d cYclo-ProPanes ring opening Occurred to

This reaction, which can be reversed by addition of hydro- chloric acid, is only applicable to cationic carbonyl complexes, since in neutral carbonyls the arnine substitutes the carbonyl ligand.

give 0 S :/ l /

(ii) Oxidative addition of C1C-NMe, and C1C-NMe, to b q .] I, platinum(0) and palladium(0) complcxes. Ft 4 //E

[M(PPh,),] t ClC-NMe,* [(PPh3),M(C-NMe,)C1] + 2PPh, with cis-r,z-disubsti- (M=Pd, Pt; tuted cyclopropanes, E=O, S) the cyclopropane was isomerised to olefin. No The triphenylphosphine complex shows no platinocyclopropane ring complex was formed. rotation about the C-N bond even on heating

H. M. Walborsky (Florida State Univer- to zoo°C, although with less bulky tertiary sity) reported a study of the decarbonylation phosphine such rotation is observed. of acyl complexes of the “Wilkinson Catalyst”. Professor Abel read a paper by M. F. The reaction was stereoselective but not Lappert and his co-workers (University of stereospecific, and consistent with the forma- Sussex) on the use of electron-rich olefins tion of a radical pair intermediate:

R [ C1/ H,Rh/!=O] I ‘PPh, - [ C l / y \ P P h 3 H, . /@’] RH + [(PPh,),Rh(CO)Cl] PPh, PPh,


in the synthesis of carbene complexes in which the published range of olefins that can be used in the reaction

Y Y

was extended to include

P h M e

x l c = c c , p c and a4.. N/ P h

Y' N' Ph &I e

The bis(dibenzy1ideneacetone) complexes of both platinum and palladium were described by two groups of workers, Professor Maitlis of McMaster University, and Ito and his colleagues from Nagoya University, Japan, as useful air-stable starting materials for the preparation of other complexes of these metals. The complexes are prepared by treating Na,PdCl, or Na,PtCl, with dibenzyl- ideneacetone (DBA) in an alcoholic solvent in the presence of sodium acetate. The structures of the complexes [M(DBA),] are unknown, the Canadian group favouring bonding of the carbonyl group to the metal and the Japanese bonding of the olefin group to the metal.

Professor Maitlis, in a masterly section lecture, reviewed his work on the cyclo- oligomerisation of acetylenes by palladium

salts and emphasised the importance of the oxidation state of the metal on the mechanism of the cyclotrimerisation of acetylenes. This is not unexpected, since acetylene complexes of palladium(0) involve strong n-back donation of electron density from the metal to the acetylene so that the acetylene is susceptible to electrophilic attack whereas, in the acetylene complexes of palladium( 11), a-donation of charge from the acetylene to the metal is more important than the reverse n-back donation so that the acetylene is susceptible to nucleophilic attack. These and other differences in the properties of olefin and acetylene complexes of transition metals were considered by the present author, who suggested that olefin complexes fell into one of two classes, whose similarities and differences are shown in the table.

In other papers on olefin complexes Panunzi (University of Naples) reported extensions of his work on the attack of nucleophiles on olefin complexes to include

Classification of Olefin Complexes

Model complex

Coordination number of the metal

Rotation of the olefin about metal-olefin bond?

Angle between axis of double-bond and square-plane of metal

Multiple bond lengthening on coordination

Angle at which substituents on multiple bond bent back away from metal

Examples of metal ions giving each class of complex


Class S

K+[ Pt(C,H ,)CI ,I- 4 or 6

Yes

77-90" -0.028,

-1 5'

Pt", Pd", Fell, Rhl, Re', Mnl

24

Class T

No

0-24"

-0.1 5A

-35"

Pto, Pdo, FeO, Id, W1, Mot

3 or 5

both cis- and tram-[Pt(olefin)LCl.J and cationic [Pt(olefin)C1LL'] 1- complexes (L is a ligand that enables the initial platinum(I1)- alkyl complex to be isolated). I t was found that the stereochemical route of the reaction of the trans-complexes was less dependent on the nature of L than in the cis-complexes.

H. Thyret of Munich described evidence which suggested that an earlier report of a vinyl alcohol complex of platinum(II), [(CH, =CHOH)PtCl,],, was incorrect and described the preparation of complexes of Fe(CO), with vinyl alcohol and vinyl alcohol derivatives. H. A, Tayim (American Univer- sity of Beirut) has prepared complexes of 1,4-cyclooctadiene ( 1,4-COD) with Pt", Pd", Rh', Ag', and Cu' and found that the properties of 1,4-COD are intermediate between 1,3-COD and 1,5-COD.

Y . Fujiwara of Osaka University reported a detailed study of the reaction of styrene and benzene in the presence of palladium(I1) acetate to give trans-stilbene. The electronic effects of substituents in the aromatic rings (electron-donating substituents in the benzene give ortho, para-substitution; electron-withdrawing give metu-substitution; electron- withdrawing substituents on the styrene make it more reactive), the steric effect of groups on the olefin, which lead to the aryl group being introduced on to the least substituted carbon atom of the olefin, and the fact that no hydride shift occurs during the reaction are consistent with the mechanism shown here :

Professor Stone of Bristol discussed the ability of unsaturated fluorocompounds to form 3- and 5-membered rings with zero- valent platinum, palladium, and nickel. Thus, for example, while most unsaturated fluoro-compounds such as CF, =CF,, (CF,),C=O, (CF,),C =NCH, form 3-membered ring compounds of the type

some of these compounds can react further to give 5-membered ring compounds :

r 1

Stone showed that such ring expansion depended in a complex way on the electronic properties of the phosphine ligand, which should be a strong, but not too powerful, a-donor. Nickel(0) appears to give ring expansion more readily than platinum(0).

A. P. Belov (Kurnakov Institute, Moscow) described the chemical oxidation of x-ally1 palladium halides in aqueous solution and showed that the redox potential decreases as

c P h H \ /

/ \ H Ph

PdO + 2HOAc f C=C i-


HOAc

~ + i - H o * c

25

the halide is altered in the order chloride:> bromide >iodide.

F. Glockling (Queen’s University, Belfast) reported the preparation of platinum(1V) complexes of trimethylstannane which, although widely implicated as intermediates

[(diPhos)k’tl f excess Me8nH-

[(diphos)PtCl,] + Me,SnH -> [(diphos)Pt(SnMe,),H]

[jdiphos)Pt( SnMe,),HCl]

M. I. Bruce (Bristol University), described a number of interesting complexes in which iron, ruthenium, or osmium were co-ordinated directly to platinum(I1).

and PMe,Ph)

(M = RU o r 0s) (M =Ru or 0s) (M=Os only; positions of hydrides uncertain)

J. Dehand (Institute of Chemistry, Stras- in the reactions of platinum(I1) complexes of bourg) discussed the vibrational spectra of trimethylstannane, had not been isolated the related compounds [(pyr),M(M’(CO),),], until recently. Two main routes both where M Pd or Pt, M’(CO), - Mn(CO),, involving oxidative-addition reactions were Co(CO), or Mo(CO),(x-C,H,) and pyr = reported for the preparation of these com- pyridine, 3-methylpyridine or +methyl- plexes : pyridine.

Rhodium Coating on Plastics RADIO FREQUENCY SPUTTERING TECHNIQUE

Techniques developed by Precision In- strument Company of Palo Alto, California, have made it possible to coat heat-sensitive substrates with a variety of metals by sputtering. This work grew out of the need to coat strips of polyester with thin films of rhodium. The rhodium-coated strips form part of a mass memory computer core but any distortion renders them useless for this purpose. The sputtering technique used by the company ensures that substrate temperatures do not exceed 50°C, thus avoiding thermal distortion. This enables pin hole-free metal coatings zooA thick or less to be deposited uniformly over the whole surface of the substrate to ~ I O per cent accuracy.

The apparatus was developed from work carried out at Argonne National Laboratory.

It consists of a supported glow discharge system. The rhodium or other metal to be coated is fixed to a cathode connected to a radio frequency or d.c. power supply and is enclosed in a vessel capable of withstanding a high vacuum. The substrate is supported some 10 cm below the cathode. Between the cathode and the substrate is a double coil of wire connected to a 1.2 kW, 13.5 MHz R.F. power source. After evacuation to I O - ~ torr and backfilling to I O - ~ torr with argon, power in the double coil stimulates a glow discharge in the argon, so that argon ions strike the cathode metal target and displace metal atoms, which are deposited on the substrate. The substrate temperature remains low because it is not connected to the electrical system.


ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Electrical Resistance of Platinnm Wires during Annealing and Quenching in Air and Helium J. POLAK and L. KUNZ, Czech. J . Phys., 1971,

The electrical resistance of Pt wires annealed and quenched in air and He was measured. Irreversible changes in the resistance were observed in specimens treated in air, but not in those treated in He. The changes are partly due t o dimensional changes on oxidation, for which the activation energy is 1.7950.04 eV.

Dispersion Hardened Platinum and Gold Alloys for Electrical Applications

23, (61, 39-44 Dispersion hardened alloys of Pt and Au containing T h o , and A1,0, were made by pre- cipitating the elements from solution on to a suspension of oxide particles. The alloys showed good homogeneity but contained large amounts of adsorbed gases which were removed by heating in vacuo. Optimum mechanical properties were obtained with 1-2 vol.:(, dispersoid. Dispersion strengthening slightly increases resistivity.

Reaction of Sulphur and Sulphur-containing Substances with Platinum, Rhodium and Platinum-Rhodium Alloys

25, (IO), 1121-1123 Pt-Rh alloys and pure Rh react at Soo-rzoo"C rapidly with H,S, but only slowly with SO, with formation of sulphides. No reaction occurs with K,SO,.

Processes of Ordering and the High Co- ercivity State of Copt Alloy G. v. IVANOVA, L. M. MAGAT, L. v. SOLINA and YA. s. SHUR, Fiz. Metal. Metalloved., 197X, 32, (3), 543-548 The greatest coercivity of Copt is related to the state in which mainly the ordered phase is present. Annealing in two stages at 700 and 600°C gives better magnetic properties than single- stage annealing because a homogeneous structure is formed during the first stage with further ordering during the second stage.

Interaction of Hydrogen with Palladium

1971, 22, (2 ) , 260-265 The adsorption and absorption of H, on Pd

21, (31, 269-274

M. L. GIMPL and N. FUSCHILL0,J. Metals, 1971,

G . ZWINGMANN and E.-M. WENZEL, Metall, 1971,

A. W. ALDAG and L. D. SCHMIDT, J. CatabSiS,

wires was studied using flash filament desorption. The initial H sticking coefficient was 0.13. At ZOO K three states, PI, j3, and p3, were observed with binding energies of 22, 25 and 35 kcall mole. At roo K an a state was observed. The amount of H, taken up in the CI state greatly exceeds that of the /3 state; the former probably corresponds to solution of H in Pd.

The Effect of Hydrogen on the Tensile Properties of Palladium R. J. SMITH and D. A. OTTERSON, J . Less-common Metals, 1971, 24, (4), 419-426 Tensile properties of annealed and non-annealed Pd wire were measured as a function of H content. The yield stress, ultimate tensile stress and elongation at maximum stress showed abrupt changes with respect to H content near phase diagram boundaries. The dependence of tensile properties on H content within a single phase region was interpreted in terms of electronic structure and work hardening.

Magnetic and Electrical Properties of Pd-Rh and Pd-Ag Alloys

CHENKO, Ukr. Fiz. Khini., 1971, 16, (61, 915921 Magnetic and electrical properties of annealed and deformed Pd-RhJ Pd-Ag and I at.?;, Fe-Pd-Rh alloys were studied. Plastic deforma- tion increases the magnetic susceptibility of alloys with more than 5 at.% Rh, and also increases the electrical resistivity, particularly in binary alloys.

Ordering in PtFe-PdFe and PtFe-PtNi Alloys and Their Magnetic Properties s. SHIMIZU and E. HASHIMOTO, J . Japan Inst. Metals, I97IJ 35, (9h 902-907 Order-disorder transformations in Pt,, Pd, Fe,, and Pt,, Fe50-x Nix were studied. Both systems form solid solutions and undergo transformation from disordered f.c.c. to ordered f.c.t. Alloys containing more than 20 at.76 Pd show magnetic hardening phenomena and are the most suitable for use as permanent magnetic alloys.

Vapour Pressure of Palladium-based Liquid Alloys N. A. VATOLIN, A. I. TIMOFEEV and E. L. DUBININ, Zh. Fiz. Khim., 1971, 45, (S), 2027-2029 The vapour pressures over Pd-Ag, Pd-Cu, Pd-Co, Pd-Ni, Pd-Fe, and Pd-W were measured using the Knudsen effusion method. The thermodynamic activities of the components in the alloys were found.

I. YA. DEKHTYAR, E. G. MADATOVA and R. G. FED-


Study of the Activity of the Components in Some Palladium-based Liquid Metal AUoys hy the E.M.F. Method N. A. VATOLIN, A. I. TIMOFEEV, 0. A. ESIN and E. L. DUBININ, Ibid., 2021-2026 The concentration and temperature dependences of e.m.f.s of melts of Pd with Ni, Co, Fe, Cu, Mn and Si were measured. With Ni, Fe, Co and Cu at 1600'C a positive deviation from Raoul's law is observed; a negative one occurs in Pd-Mn and Pd-Si. The two latter alloys show the presence in the melt of ordered groups of compositions close to Pd,Mn, and PdSi.

On the Magnetic Properties of Powders of Alloys of the System Iron-Palladium

KANDAUROVA and G . M. MAKAROVA, Fiz. Metal. Metallowed., 1971, 32, (3), 562-568 Studies of the magnetic properties and phase compositions of FePd and Fe,.,Pd,., powders with grain sizes from 3 to 400 EL, previously treated by crushing, annealing and pickling, indicate the mechanism of magnetisation and magnetic reversal in these powders.

On the Composition of the Vapour above Pd-Ba and Pt-Ba Alloys

N. P. ESAULOV and v. M. ROZHDESTVENSKII, Zh. Fiz. Khim., 1971, 45, (8), 2064-2065 The composition of the vapours over 2.0 and 32.0 wt."/,, Ba-Pd at 1515-1720 K and 1.5 w t . O i 0 Ba-Pt at 1980 K was investigated by mass spectroscopy. The vapour consists of Ba and BaO. The partial pressures of the components and the rate of vaporisation over 2.0 wt.7; Ba-Pd were measured.

Variation of Thermal Expansion Coefficient with the Applied Stress in an Amorphous Metallic Alloy

YA. S. SHUR, V. S . BOIDENKO, L. M. MAGAT, G. S.

D. M. CHIZHIKOV, W. V. TSVETKOV, E. K. KAZENAS,

D. LESEUR, J. Y. THOMAS and V. VENDITTI, Rev. phys. APPl., I971,6, (I), 91-94 The linear thermal expansion coefficient of 20

Si-Pd at 15-100" above ambient increases linearly from 1.95 x 10-5 to 2.08 x ~o-,/deg K for stresses up to 80 kgjmm2. Young's modulus is 5300 kg/mm?, the temperature coefficient of electrical resistance is 1.20 x 10 4[deg K and the elastoresistance coefficient is 1.710.1.

The Influence of Transition Metal Additions on the Sintering Behaviour of Tungsten G . v. SAMSONOV and v . I. YAKOVLEV, Z . Metall- hunde, 1971, 63, (8), 621-626 The effect of additions of 0.05-1.0 wt.% transition metals, including Pt group metals, on the sintering behaviour of W at 1000-2000°C was studied. The Pt metals promote sintering with the exception of Os, which has no effect. The

activation is probably due to electron exchange between the metals; the free energy is lowered with an increase in d bonds in the system. The sintering diffusion is accelerated by alloying additions for which W acts as an electron donor.

CHEMICAL COMPOUNDS Thermodynamics of the Gaseous Platinum Oxide PtQ, I . LAUDER, 3. Chem. Thermodyn., W I , 3, (3), 407-408 The Pt+O, system at 1579"C, which contains two oxides, PtO, and PtO, is discussed in terms of the Gibbs-Duhem equation.

The Volatilisation and Deposition of Ruth- enium Dioxide in Relation to the Fingal Process

1971, (May), 25 PP The mechanism of Ru volatilisation at high temperatures was studied. Ru transport is due to formation of gaseous RuO, and RuO, due to 0, in the system at concentrations :> the dis- sociation pressure of RuO,. When 0, is absent or at a lower pressure, RuO, dissociates to Ru and 0, and no Ru is lost. The deposition of RuO, was studied using lo3Ru.

Preparation and Crystal Structure of Qs- mium Pentafluoride s. J. MITCHELL and J. H. HOLLOWAY, J . Chem. SOC., A, Inorg. Phys. Theor., 1971, (17), 2789-2794 The preparation of OsF, is described. Crystals of the solid are monoclinic, space group Pz,/C with ac5.53, b-9.91, c =12.59 A, 8=99.5". OsF, is isostructural with RuO,. The structural unit is a tetramer with 0 s atoms at the corners of a rhombus, linked by binding F atoms.

Crystal Structure of Iridium Trisilicide, IrSi,

1971, 10, (9), 1934-193s

M. 1. HOLDOWAY, A.E.R.E. Rept. R-6418,

J. G . WHITE and E. F. HOCKINGS, Inorg. Chem.,

Single crystals of IrSi, were prepared. The crystals are hexagonal, space group P6,mc with a=4.351*0.001, c=6.622~0.002 A and z=2. The structure contains infinite, planar, four- connected layers of Si atoms perpendicular to the c axis with each Ir atom spaced at unequal distances between two Si layers to make equal contacts with Si atoms. The Si-Si distance is 2.175 A.

Ternary Hydrides of Calcium and Stron- tium with Iridium, Rhodium and Ruthenium

Solid State Chem., 1971, 3, (4), 541-549 The ternary hydrides, Ca,IrH,, Sr21rH6, Ca,RhH,, Sr,RhH, and Sr,RuH, were prepared

R. 0. MOYER, C. STANITSKI and J. T.4NAKA, 3.


by reacting the alkaline earth hydride with a Group VIII metal at high temperature under a H, atmosphere. The two metal atoms are arranged in the fluorite structure. The H atoms octahedrally coordinate the Group VI I I metal atom; random vacancies of H sites were indicated for the I r compound.

cis-Dichlorodiammineplatinum(I1) : Inhibi- tion of Nucleic Acid Synthesis in Lym- phocytes Stimulated with Phytohemagglutin J. A. HOWLE, H. S. THOMPSON, A. E. STONE and G. R. GALE, Proc. SOC. Biol. Mid., 1971, 137, (3), 820-825 cis-Pt(NH,),Cl, inhibited DNA synthesis in human lymphocyte cultures stimulated with phytohemagglutin. Selectivity was evident at low concentration (3 x IO-~MM). The complex may undergo two sequential transformations, losing C1- at each step, the resulting species acting bifunctionally to cross-link adjacent nucleophilic centres.

Immunosuppression by Platinum Diammines M. C. B E R E ~ ~ A U M , Br. j. Cancer, 1971, 75, (91, 208-211 Pt(NH,),Cl, and, to a lesser extent, Pt(NH,),CI, inhibit antibody-forming cells in mouse spleen after injection of sheep red cells. The rapidly proliferating cells were most sensitive to the dichloride. The complex acts like an alkylating agent. Pt-en-C1, and Pt-en-C1, were ineffective.

Antitumour and Antimitogenic Properties of cis-Dichloro(dipyridine)platinum(II) G. R. GALE, J. A. HOWE and E. M. WALKER, Cancer

cis-Pt(py),CI, showed less potential antitumour and antimitogenic activity than cis-Pt(NH,) ,C1, but was less toxic to mice. The py complex inhibited the growth of E. coli and increased the survival time of mice bearing Ehrlich ascites tumour. In vitro, it also inhibited protein and nucleic acid synthesis by turnours, and DNA synthesis in phytohemagglutin-stimulated cultures of human lymphocytes.

Res., 1971, 3 IJ (7), 950-952

ELECTROCHEMISTRY EIectrochemical Activity of Electrodeposited and Heat-treated Platinum Electrodes S. SHIBATA and M. P. SUMINO, Electrochim. Acta,

The electrochemical activity of a platinised Pt electrode is decreased by annealing in vacuo due to the rearrangement of superficial, metastable Pt atoms to stable lattice positions. The annealed electrode may be activated by oxidation-reduction treatment or by short exposure to air. Activation probably results from the formation of a superficial active monolayer of Pt atoms.

1971, 16, (91, 1511-15V


Chemisorption on Platinum and Tungsten J. M. SALEH, Trans. Faraday soc. , 1971, 67, (6),

Adsorption of H,S, H,Se, SO2 and CS2 on Pt films at -80 to 250°C was studied. Fast dis- sociation chemisorption of H,S and H,Se OC- curred on Pt films at -80°C. Further slow, dissociating adsorption occurred above 30°C, the activation energies =46 and 24 kJ/mol respectively. Adsorption of SO, and C S , was molecular and completely reversible.

1830-1836.

ELECTRODEPOSITION AND SURFACE COATINGS Deposition of Platinum on Teflon and Parylene by Sputtering

Instrum., 1971, 42, (7), 1076-1077 The manufacture of a microelectrode by sputter deposition of Pt on a 0.08-0.13 mm thick film of teflon or parylene is described. The target is a 99.9876 pure Pt sheet. Good adhesion of the I!L thick Pt coating was obtained.

Photoselective Metal Deposition

Hydrated SnO, is produced when substrates, previously wetted with a dilute SnCl, solution, are hydrolysed in water. This layer can be photo-oxidised by a U.V. image and activated by immersion in dilute PdCI,, thereby depositing Pd on to the unexposed areas. The Pd image catalyses the reduction of metal from electroless plating baths. This method could be used to manufacture printed circuits.

Electrodeposition of Palladium-Cobalt Alloy from Complcx Electrolytes with Mixed Ligands s. N. VINOGRADOV, N. T. KUDRYAVTSEV and G. G. ARTANOVA, Zashchita Metal., 1971, 7, (5), 612-613 To eliminate the high internal stress of Pd-Co alloys deposited from ammino-chloride complexes Co pyrophosphate was added to the electrolyte. Dense bright fine-crystal deposits of Pd-Co with up to 25"/0 Co and low internal stress were produced using the following electrolyte (gll): [Pd(NH,),]Cl, (on conversion to metal) ~3-IS; K,Co(P,O,), (on conversion to metal) r3-15; K4P,0,.3H,O (total) 6 0 5 6 5 0 ; NH,Cl 25-35; NH,NO, 20-30. Recommended conditions are: electrolyte at 35-4Ooc, pH 9-9.5; current density 0.8-1 A/dm2; insoluble C anode.

Electrodeposition of Osmium L. GREENSFAN, Plating in the Electronics Industry - Third Symposium of American Electroplaters Society Znc., 1971, (Feb 3-4, ~ ~ I - z z g The electrodeposition of 0 s from an alkaline solution of osmic acid containing conducting

M. SONN, G. J. JAKO and W. M. FEIST, RW. SCi.

D. J. SHARP, Plating, 1971, 58, (8), 786-790

salts is described. The deposits are bright up to 50 pin thick, and have excellent adhesion. A study of the use of 0s-plated reeds for reed switches shows that 0 s is superior to Rh.

LABORATORY APPARATUS AND TECHNIQUE Use of the Macroprobe for the Study of a Corroded Platinum Crucible M. GRASSERBAUER, Microchim. Acta, 1971, (2), 335-340 The macroprobe, an X-ray analyser with electron beam excitation, was used to study corroded Pt crucibles. The pits in the corroded crucible consisted of a Pt-Si alloy; the development of pit-forming corrosion sites and the formation of cracks is discussed.

JOINING Strength Behaviour of Vacuum-brazed Creep-resistant Materials H. LANGE, Schweissen Schneiden, 1971, 23, (I), 14-17 Samples of heat resisting alloys of type Ni-Cr-Ti-A1 were vacuum brazed with filler metals including 21~/,Pd-31”&Mn-Ni and 40‘:/v Ni-Pd. The tensile strength decreased with increasing temperature for all brazed joints except those with Pd-Mn-Ni.

HETEROGENEOUS CATALYSIS Nitric Acid Development Aims at Cutting Pollution and Catalyst Loss D. J. NEWMAN and B. J. HULBERT, Eur. Chem. News Large Plants Supp., 1971, (Sept. 24),

Methods for the reduction of Pt loss from catalysts for NH, oxidation plants are described; they include filters and Pd-Au “getter” gauzes. Catalysts for the combustion of pollutants from HNO, manufacture, such as Pt or Pd on wire, A1,0, pellets or honeycombs are described.

Hydrogenation of Cyclohexene, cis -Cyclone- nene and cis-Cyclododecene over Pt Black E. s. BALENKOVA, v. I. ALEKSEEVA and s. I. KHROMOV, Neftekhimiya, 1971, XI, (4), 483-486 Liquid-phase hydrogenations of cyclohexene, cis-cyclononene and cis-cyclododecene over Pt black were studied at 21-75’C. The rate of hydrogenation varied with ring size.

Transannular DehydrocycIisation of Dimethylcyclooctanes

Neftekhimiya, 197r, 11, (4), 528-532 The reactions of 1,2-, 1,3-, 1,4-, and r,s-di-

26, 28, 30, 32, 36

V. M. MAKUSHINA, 0. A. AREF’EV and A. A. PETROV,


methylcyclooctanes over Pt catalysts were studied at 260-300’C. The chief reaction is transannular dehydrocyclisation to form the respective dimethylbicyclo- [3.3 .o]-octanes.

The Effect of Heat Treatment on the Catalytic Properties of Platinum Adsorption Catalysts ZH. v. STREL’NIKOVA and L. E. MARTYSHKINA, Vest. Moskov. Univ., Ser. I I , Khim., 1971, (4),

Heat treatment of Pt adsorption catalysts does not affect the composition of the active centre, but changes the magnitude of the absorptive capacity.

On the Distribution of Hydrogen Adsorbed from Solutions on the Surface of Some Hydrogenation Catalysts. 111. Effect of Mercury Poisoning on the Form of the Differential Isotherms of Hydrogen Ad- sorption on Platinum YU. A. PODVYAZKIN, 0. R. SERGUTKINA and N. A. DUGIN, Kinet. Kataliz, r97x, 12, (4), 1068-1070 The effect of Hg poisoning of Pt for 2, 10 and 400,; surface coverage and 0-4oO’C on the form of the differential isotherm of H, adsorption is caused by Hg displacing H, bonded to the Pt.

Physical and Chemical Characterisation of Platinum-Rhodium Gauze Catalysts L. D. SCHMIDT and D. LUSS, J. Catalysis, 1971, 22,

IO~J; Rh-Pt gauze catalysts for NH, oxidation and HCN production were studied using scan- ning electron microscopy, Auger spectroscopy and sputtering techniques. Normal activation produced surface area increases and the formation of randomly oriented facets. Catalysts treated with H,S for higher activity showed crystalline surfaces consisting predominantly of (I o 0) planes. The gauze wires were permeated by rectangular-shaped channels -3 p in width.

Effect of Chlorine and Water on Benzene Reforming on a Platinum Catalyst 0. SVAJEL, Chem. prumysl, 197X, 21, (7), 315-319 Pt/A1,0, catalysts for C,H, reforming contained 0.1-1.2 wt.06 C1, the optimum concentrationbeing 0.3-0.7 wt.71;. Lower concentrations decrease the dehydrocyclisation reaction so that low octane petrol is formed. Higher concentrations show hydrocracking properties and are unstable.

Peculiar Effect of Hydrogen Pressure and Adsorption of Water on the Activity of Platinum:‘Alumina Catalysts in the Hydro- genolysis of Methylcyclopentane

UDAL’TAOVA, Izv. Akad. Nauk S.S.S.R., Ser.

Studies of the effects of pH9 and H,O adsorption

486-488

(2), 269-279

I. I. LEVITSKII, KH. M . MINACHEV and E. A.

Khim., 1971, (91, 1913-rg17

on the activity of 0.3% Pt/Al,O, in the hydro- genolysis of methylcyclopentane showed that, as PH, increased from g to 49 atrn, catalyst activity decreased when the catalyst contained adsorbed HzO but rose when the catalyst was free of H,O. Activity also decreased during the elimination of H,O from the catalyst at a total pressure of 10 atm but rose during the same process at 50 atm total pressure. Two mechanisms form the basis of the changes in opposite directions of catalytic activity as pHz increases or as H, adsorption decreases.

Effect of Rare-earth Elements on Activity of Aluminoplatinum Catalysts N. s. KOZLOV, v. A. POLIKARPOV and G. M. SEN’KOV, Vestsi Akad. Navuk Belaruss. S.S.R., Ser. Khim. Navuk, 1971, (2), 110-114 Addition of 0.1-104, Ce, Nd, Y, Gd or Yb improves the catalytic activity of Pt /A1,0, for C,H,, conversion. The yield of cracking products is reduced, and the yield of isomers increased at 4oo--q50cC; the cyclisation activity is unchanged.

Aromatisation of 2-Methylheptane and 2,P- Dimethylhexane in the Presence of Platinum! Alumina Catalyst in Pulsed Conditions v. G. VLASOV, YU. v. FOMICHEV and B. A. KAZANSKII, Neftekhimiya, 1971, 11, (4, 510-516 The aromatisation of 2-methylheptane and of aJ4-dimethylhexane in the presence of 0.6‘;;;~ Pt!y-Al,O, and o.6u~~Pt+o.8~~Na20/A1,0, was studied. C,-dehydrocyclisation occurs during aromatisation. Introduction of Na,O reduces the yield of C, aromatics and decreases the amount of isomers. Aromatisation probably occurs by C,-dehydrocyclisation.

On the Effect of Sulphurisation on the Activity of Platinum/Alumina Catalysts

and T. M. KLIMENKO, Kinet. Kataliz, 1971, 12, (4), 1060-1061 S added to Pt/Al,O, in one or another stage reduces the activity of the catalyst for C,H, hydrogenation but increases its thermal stability. The treated catalyst has maximum activity for reduction at 800°C.

Effect of the Nature of the Initial Platinum- containing Compounds on the Properties of Platinum/Alumina Catalysts for Aro- matisation of Hydrocarbons

G. N. MASLYANSKII, B. B. ZHARKOV, A. 2. RUBINOV

S . B. KOGAN, T. S. KISELEVA and N. R. BURSIAN, Z b 4 (s), 1338-1341 Pt/A1,0, catalysts prepared from various Pt(1V) ammoniates and from H,PtCl, (0.6 wt.%, Pt) were tested in aromatisations of n-C,H,,, cyclohexane and methylcyclopentane, and in decomposition of H,O,. The concentration of Pt ions was determined. The catalyst activity in

n-C,H aromatisation depended on the nature of the initial Pt compound. Those based on mono- and dichloroamino complexes had the greatest activity. No analogous maximum activities were observed in the other reactions. An explanation of this effect is given.

Vapour-phase Catalytic Synthesis of Xylenes from Toluene and Formaldehyde

Gakkai Shi, 1971,14, (2), 113-118 The vapour phase synthesis of xylenes from PhCH, and HCHO in the presence of Ha was studied over various catalysts. I wt.”. PtlSi0,- A1,0, catalyst was the most selective for pro- ducing p-xylenes. The stability of this catalyst was greater than that of SiCJ2-AlaO3.

Investigation of Mixed Platinum Group Metal Catalysts on Supports for the Reduc- tion of Nitro Compounds

v. F. PECHENKINA, Zh. Fiz. k’him., 1971,45, (IO),

Studies of activity of binary supported Pt group metal catalysts during hydrogenations of o-nitro- anisole and nitrobenzene showed that significantly increased activity is connected with an increase in the rate of production of active components on their surfaces.

Kinetics and Mechanism of the Oxidation of Carbon Mvnoxide vn Pure Palladium I. I. TRET’YAKOV, A. v. SKLYAROV and B. R. SHW, Kinet. Kataliz, 1971, 12, (4), 996-lo02 Oxidation of CO by 0, on Pd in IO-”-IO-’ torr vacuum at 80-50orC proceeds by gas phase reaction of adsorbed 0 with CO. The reaction is retarded where the gases are present in excess amounts because there is concurrent chemisorption of 0 and 0,.

Kinetics of Dehydrogenation of Cyclo- hexane on Palladium Foil

ROSEN and E. KHAURES, Ibid, (s), 1197-1202 Studies of the kinetics of the dehydrogenation of cyclohexane in C,H, on Pd foil at 250-322”C, pHI = c-500 mm Hg, pCoHj2 = IO-IOO mm Hg show that the reaction rate rises as p ~ ? and PC,H,> increase. The kinetic equation is derived and is related to the reaction mechanism. The apparent activation energy is calculated from the temperature dependence of the reaction rate.

Hydrogenation of Nitrobenzene over Pal- ladium-Silver Catalysts A. METCALFE and M. w. ROWDEN, J. Catalysis,

The rates of hydrogenation of nitrobenzene in n-butanol were measured over I’d-Ag alloy catalysts. The activation energy varied from -5 kcal,’

M. OKADA, Y. ASAMI, Y. KAKU and K. UOYA, Sekiyu

N. I. POPOV, D. V. SOKOL’SKII, F. B. BIZHANOV and

2637-2640

V. M. GRYAZNOV, L. F. PAVLOVA, P. RIVERA, A.

1971, 22, (I>> 30-34


mole on Pd-rich alloys to -25 kcal/mole on Ag-rich alloys. This is consistent with the theory that promotion of electrons from within the con- duction band to the Fermi surface of the solid is rate determining.

Dehydrocyclisation of Alkenes and of Alka- dienes in the Presence of Palladium/Aluxnina Catalyst v. s. FADEEV, I. v. GOSTUNSKAYA and B. A. KAZANSKII, Nefiekhimiya, 1971, 11, (4), 523-527 The aromatisation of 1-hexene, hexa-~,s-diene, hexa-2,4-diene and methylcyclopentane and I - methylcyclopentene-a over Pd /Al,O, was studied. The degree of aromatisation increases with the degree of unsaturation of the olefin, and for hexene and hexadiene is greater in He than in H2.

Exchange with Deuterium of Some Cyclic Hydrocarbons Catalysed by Palladium H. A. QUINN, J. H. GRAH+ M. A. MCKERVEY and J. J. ROONEY, J . Catalyszs, 197x, zz, (I), 35-40 The isotopic DIH exchange in cyclic hydrocarbons catalysed by Pd was investigated. Pd/SiO, and Pd films were used. The results indicate that the exchange proceeds via roll-over of intermediate olefins.

The Structure and Activity of Supported Metal Catalysts. VI. Measurement of Dispersion in Palladium-Charcoal Catalysts D. POPE, w. L. SMITH, M. J. EASTLAKE and R. L. MOSS, 3. Catalysis, 1971, 22, (I), 72-84 The metal dispersion in P d K catalysts was estimated from X-ray line broadening and in- tensity measurements, as this method avoids surface cleaning. The mildest surface cleaning can induce sintering, but the extent is mini- mised at low Pd content and uniform Pd distribution. The feasibility of using CO chemisorption as a measure of Pd area is discussed.

A Study of the Active Site of the Catalyst Composed of Palladium and Active Charcoal

KUNUGI, Kogyo Kagaku Zasshi, 1971, 74, (6), 1076-1080 A deactivated Pd salt/C catalyst was reactivated by HCl so that CzHa oxidation gave four times the amount of acetaldehyde produced using the deactivated catalyst. When 0, was added the catalytic activity increased to 70-80 standard activity. Surface oxides on the active C are not effective for the reoxidation of Pd.

K. FUJIMOTO, T. TAKAHASHI, Y. NEGAMI and T.

The Effect of Alkali Additions on the Properties of Palladium/Polyacrylonitrile Catalysts 0. A. TYURENKOVA and L. A. CHIMAROVA, Zh. Fiz. Khim., 1971,45, (9), 2216-2219 Small additions of alkali to Pdipolyacrylonitrile

increase its activity in hydrogenation of dimethyl- ethynylcarbinols. The maximum rate of reaction occurs when Pd:KOH = I: 0.39. The 39% added alkali arises from the need to convert all Pd to Pd(OH),. Further addition of KOH leads to a less active catalyst.

Stereospecific Hydrogenations. V. Hydro- genation Rates Using Palladium-on-Poly- S-leucine and Palladium-on-Poly-S-valine R. L. BEAMER and w. D. BROWN,^. Pharm. Sci.,

Hydrogenations of cr-methylcinnamic acid and a-acetamidocinnamic acid were more rapid on Pd Ipoly-S-leucine (helical catalyst) than on Pd/poly-S-valine (non-helical catalyst). The reactants occupy different sites on the catalyst surface. Inhibition studies were carried out, from which mechanisms are proposed.

Hydrogenation of Fatty Acids from Cotton- seed Oil K. K. DOMANSKAYA, A. I. GLUSHENKOVA and A. L. MARKMAN, Maslo-Zhir. Prom., 1971, 37, (4), 23-26 Hydrogenation of fatty acids on a supported Pd catalyst followed a zero order reaction relative to the acids. Isomerisation took place, forming conjugated systems in linoleic acids.

Catalytic Oxidation. 111. The Mechanism of Ethylene and Propylene Oxidation over Supported Rhodium and

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