art_10.1007_s10967-007-7079-1-1

DOI: 10.1007/s10967-007-7079-1 Journal of Radioanalytical and Nuclear Chemistry, Vol. 275, No.3 (2008) 487–495

0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2007 Akadémiai Kiadó, Budapest Springer, Dordrecht

Effect of gamma-irradiation on surface and catalytic properties of nanocrystalline CuO, NiO and Fe2O3 supported on alumina

G. A. El-Shobaky,1* M. M. Doheim,2 S. A. Esmail,3 H. A. El-Boohy,3 A. M. Ahmed3

1 National Research Center (NRC), Dokki, Cairo, Egypt 2 Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt

3 National Center for Radiation Research and Technology (NCRRT), Nasr City, Cairo, Egypt

(Received April 6, 2007)

The effect of -irradiation on surface and catalytic properties of CuO/Al2O3, NiO/Al2O3 and Fe2O3/Al2O3 was investigated. The techniques employed were XRD, nitrogen adsorption at –196 °C and catalytic conversion of ethanol and isopropanol at 250–400 °C using micropulse technique. The results showed that the supported solids being calcined at 400 °C consisted of well crystallized CuO, NiO, Fe2O3 and AlOOH phases. The AlOOH crystallized into a poorly crystalline -Al2O3 upon heating at 600 °C. All phases present in different solids calcined at 400 and 600 °C showed that these solids are of nanocrystalline nature measuring an average crystallite size between 6 and 85 nm. The crystallite size of crystalline phases present was found to be much affected by the dose of -rays and the nature of the metal oxide. This treatment resulted in a progressive increase in the specific surface area reaching to a maximum limit at a dose of 0.8 MGy. The dose of 1.6 MGy exerted a measurable decrease in the SBET. A radiation dose of 0.2 to 0.8 MGy brought about a progressive significant decrease in the catalytic activity of all the catalytic systems investigated. All the catalytic systems retained their high activity upon exposure to a dose of 1.6 MGy. The rise in precalcination temperature of the systems investigated from 400 to 600 °C brought about a measurable increase in their catalytic activity in the conversion of alcohols.

Introduction

Supported transition metals or oxides are commonly employed to catalyze several reactions including oxidation-reduction, dehydration, dehydrogenation, cracking, alkylation, etc.1–12 The activities and selectivities for these varieties of solids could be modified by doping with certain foreign oxides.13–19

Ionizing radiations may induce some changes in textural, surface structural, electric and magnetic properties of a large variety of solids. Gamma-irradiation resulted in a decrease in the surface area of graphite as a result of a progressive blocking of pores as bulk expansion took place.20 This treatment caused a significant increase in pore size of steam activated carbon due to possible radiolytic decomposition of complexes located on the carbon surface.21 Gamma-irradiation affected also a decrease in the effective paramagnetic moment of CuO loaded on Al2O3.10

Gamma-irradiation effected also a significant decrease in the concentration of surface OH groups on Al2O3-support material and CuO/Al2O3 solid.16–22

It has been also reported that -rays led to removal of chemisorbed oxygen of unloaded Co3O4 and those loaded on -Al2O3.5,10,23,24 Furthermore, -irradiation effected a progressive decrease in both microstrain and lattice parameters of Co3O4 crystallites supported on -Al2O3 precalcined at 650 °C due to removal of excess

oxygen and fragmentation of it crystallites.25 However, these catalysts undergo deactivation due to the formation of cobalt aluminate via metal oxide-alumina interaction.26–29

* E-mail: [email protected]

The present work reports the results of an intensive study on the effects of -irradiation on physicochemical, surface and catalytic properties of CuO/Al2O3,NiO/Al2O3 and Fe2O3/Al2O3 systems. The techniques employed were XRD, N2 adsorption at –196 °C and conversion of ethanol and isopropanol at 250–400 °C using micro pulse technique.

Experimental

Materials

A known mass of finely powdered aluminum hydroxide was impregnated with a known amount of copper nitrate or nickel nitrate or ferric nitrate dissolved in the least amount of doubly distilled water necessary to make paste. This paste was dried at 120 °C to constant weight and then precalcined at 400, 600 °C for 5 hours. The chemicals employed were of analytical grade and supplied by the Fluka company.

The nominal compositions of the prepared calcined mixed solids were 0.2 CuO/Al2O3, 0.2 NiO/Al2O3 and 0.2 Fe2O3/Al2O3. Support samples were prepared by thermal decomposition of aluminum hydroxide at 400, 600 °C for 5 hours. The prepared calcined solids were exposed to different doses of -rays namely 0.2, 0.4, 0.8 and 1.6 MGy. The irradiated samples were kept in sealed tubes for 3 weeks before conducting the different measurements to avoid any temporary effect that may be induced by -irradiation.

G. A. EL-SHOBAKY et al.: EFFECT OF GAMMA-IRRADIATION ON SURFACE AND CATALYTIC PROPERTIES

488

Techniques

X-ray diffractograms of different solids calcined at 400, 600 °C were carried out using a Bruker diffractometer (Bruker D8 advance target). The patterns were run with copper K with a second monochromator ( = 1.5405 Å) at 40 kV and 40 mA with a scanning speed of 2° and 0.2° in 2 .min–1, for phases identification and line broadening profile analysis, respectively. The crystallite size d was estimated using the Scherrer equation:30

d = k /B1/2 cos

where k is the Scherrer constant (0.89), B1/2 is the full width at half maximum (FWHM) of the main diffraction line of different phases present, and is the diffraction angle of the main line of each phase.

The specific surface areas of the variously prepared catalyst samples were determined from nitrogen adsorption isotherms measured at –196 °C using a conventional volumetric apparatus. Before carrying out such measurements, each sample was degassed under a reduced pressure of 10–5 Torr for 2 hours at 200 °C.

A Hewlett-Packard 5890 gas chromatograph fitted with a 30-m HP1 capillary column was used for the chromatographic studies, inj 200 °C, an isothermal oven temperature of 60 °C and an FID 200 °C, with the catalytic conversion of ethanol and isopropanol being followed using nitrogen free-oxygen as the carrier gas at a flow rate of 18 ml/min. These catalytic studies were conducted at temperatures within the range of 250 to 400 °C. The ethanol and isopropanol were introduced as a pulse via a microsyringe, thereby ensuring that only microquantities of the gaseous vapour (1–2).10–3 cm3

were introduced in the form of a pulse over each 50 mg catalyst sample. The reaction products produced were transferred directly by the inert carrier gas to the column.

Results and discussion

XRD investigation of different solids

The X-ray diffractograms of different supported catalytic systems calcined at 400, 600 °C were determined. The diffractograms of samples exposed to different doses of -rays were also determined. The diffractograms of various solids (not given) showed that the solids investigated and calcined at 400 °C consisted of well crystallized AlOOH which decomposed completely by heating at 600 °C yielding a poorly crystalline -Al2O3.

Examination of the XRD data shows the followings: (1) The crystalline phases present in solids calcined at 400, 600 °C are of nano crystalline nature having crystallite size varying between 6–86 nm.

(2) Gamma-irradiation resulted in a measurable change in the crystallite size of different phases. Table 1 summarizes the effects of both calcination temperature and the dose of -rays on the crystallite size of different phases present in various catalytic systems.

(3) It is seen from Table 1 that the rise in the precalcination temperature of CuO/Al2O3, NiO/Al2O3and Fe2O3/Al2O3 from 400 to 600 °C resulted in a significant decrease in the crystallite size of CuO, NiO and -Fe2O3. This thermal treatment should be normally accompanied by an increase and not decrease in the crystallite size of the crystalline phases present. This expectation arises from an enhanced particle adhesion processes due to increasing the calcination temperature from 400 to 600 °C. This expectation has not been verified experimentally (Table 1) this unexpected behavior could be attributed to the role of the nascently formed poorly crystalline -Al2O3 increasing the degree of dispersion of different transition metal oxides present. These results showed that AlOOH is devoted with a dispersion power for various transition metal oxides smaller than that of a poorly crystalline -Al2O3.

(4) Exposure of different catalytic systems calcined at 600 °C to -irradiation (1.6 MGy) resulted in a measurable increase in the crystallite size of CuO, NiO and -Fe2O3.

(5) This treatment, on the other hand, led to a measurable decrease in the crystallite size of -Al2O3.

(6) The crystallite size of -Al2O3 in CuO/Al2O3calcined at 600 °C measured the minimum crystallite size. It had been reported22 that the -irradiation of Co3O4/Al2O3 calcined at 800 °C resulted in a significant decrease in the crystallite size of Co3O4 due to an energetic fragmentation effect of -rays. In the present work opposite effect was observed. It seems that the nano crystalline nature of CuO, NiO and -Fe2O3 did not permit a further decrease in their crystallite size. The observed significant decrease in the crystallite size of -Al2O3 in Fe2O3/Al2O3 and NiO/Al2O3 precalcined at 600 °C due to the exposure of -rays is expected to be followed by a measurable increase in the specific surface areas of different irradiated solids.

Surface areas of different irradiated systems

The specific surface area of bare alumina that has been used as catalyst's support of the investigated catalytic systems had been already determined and cited in ore of the published papers.34 The alumina support was calcined at 500 °C and its SBET measured 234, 236, 263, 290, 295 and 240 m2/g for unirradiated samples and those exposed to 0.15, 0.3, 0.45, 0.75 and 1.6 MGy, respectively. The most probable pore radius of the above mentioned adsorbents measured 2.1, 2.3, 2.45, 2.75, 3.25 and 4.75 nm, respectively.


489

Table 1. Effect of calcination temperature and dose of -irradiation on crystalline size of different phases present in various solids

Solids Calcination temperature, °C

Crystalline phase present

Crystallite size,nm

Dose of -rays, MGy

400 AlOOH, CuO 62, 72 0.0 600 Al2O3, CuO 9, 46 0.0 600 Al2O3, CuO 6, 48 0.8

CuO/Al2O3

600 Al2O3, CuO 8, 57 1.6

400 AlOOH, NiO 55, 49 0.0 600 Al2O3, NiO 26, 24 0.0 600 Al2O3, NiO 13, 57 0.8

NiO/Al2O3

600 Al2O3, NiO 18, 34 1.6

400 AlOOH, Fe2O3 85, 47 0.0 600 Al2O3, Fe2O3 43, 36 0.0 600 Al2O3, Fe2O3 12, 37 0.8

Fe2O3/Al2O3

600 Al2O3, Fe2O3 11, 45 1.6

The BET-surface areas of NiO/Al2O3, CuO/Al2O3and Fe2O3/Al2O3 precalcined at 400 and 600 °C were determined from nitrogen adsorption isotherms conducted at –196 °C. The obtained isotherms, not given, belong to type II of Brunauer’s classification.31

The different specific surface areas of various adsorbents were determined from linear BET-plots of nitrogen adsorption. The investigated adsorbents were subjected to different doses of -rays namely 0.2, 0.4, 0.8 and 1.6 MGy. The computed values of SBET for various adsorbents are given in Table 2. It is clearly shown from this table that the -irradiation of 0.2 NiO/Al2O3, 0.2 CuO/Al2O3 and 0.2 Fe2O3/Al2O3calcined at 400 and 600 °C resulted in a progressive increase in their specific surface areas reaching to a maximum limit at a dose of 0.8 MGy. Increasing the dose above this limit brought about a measurable decrease in the specific surface areas of variously irradiated solids. These results are very close to those of bare alumina support exposed to different doses of -rays. The maximum increase in the specific surface

areas due to the exposure to a dose of 0.8 MGy attained 28.9%, 27.8% and 21.8 for 0.2 NiO/Al2O3, CuO/Al2O3and Fe2O3/Al2O3, respectively, precalcined at 400 °C, the percentage increase in the SBET of various solids precalcined at 600 °C due to -irradiation at 0.8 MGy was 36.8%, 23% and 30%, respectively.

The effects of -rays on the specific surface areas of a big variety of solids had been investigated by EL-SHOBAKY et al.13–18,26 These authors claimed that the -irradiation of Co3O4, Co3O4/Al2O3, Co3O4/MgO,

CuO/Al2O3, CuO/MgO, NiO/Al2O3, NiO/MgO, CuO-ZnO/Al2O3, Cr2O3/Al2O3, Fe2O3-Cr2O3/Al2O3,Fe2O3/Al2O3 and Mn2O3,13–18,26 resulted in a measurable increase in specific surface areas of the previously mentioned solids. The extent of the increase of the

specific surface areas depends on the nature of irradiated solids and their calcination condition. The observed increase in the specific surface areas of different solids exposed to -irradiation has been attributed to creation of new pores and also to splitting of the crystallites of the irradiated solids. In fact, it has been shown in the present work in the XRD section that the -irradiation of different solids calcined at 400 and 600 °C resulted in a measurable significant decrease in the crystallite size of their constituting oxides (NiO, CuO, Fe2O3 and Al2O3)as been shown in Table 1. The measurable decrease in the SBET of different catalytic systems due to irradiation at a dose of 1.6 MGy could be attributed to an effective pore widening as being evidenced from the results of bare alumina support.34

Catalytic conversion of ethanol and isopropanol

The catalytic conversion of ethanol and isopropanol was carried out over different catalytic systems precalcined at 400 and 600 °C and subjected to different doses of -rays within 0.2–1.6 MGy.

Tables 3 to 5 include the activities and selectivities of CuO/Al2O3, NiO/Al2O3 and Fe2O3/Al2O3 calcined at 400 °C, respectively. These tables include the percentage of total conversion for both alcohols and the selectivity towards dehydration and dehydrogenation as being influenced by reaction temperature and dose of -rays.

Figures 1 and 2 depict the effect of reaction temperature on total conversion of both alcohols carried out over different solids calcined at 600 °C.

Figures 3 to 6 show the effect of reaction temperature and -irradiation on the selectivities of various solids calcined at 600 °C towards dehydration and dehydrogenation of both alcohols.


490

Table 2. Specific surface areas of different solids

Solid Calcination temperature, °C

Dose of -rays, MGy

SBET,m2/g

400 0.00.20.40.81.6

225265275290230

0.2 NiO/Al2O3

600 0.00.20.40.81.6

190228240260195

400 0.00.20.40.81.6

228263275290237

0.2 CuO/Al2O3

600 0.00.20.40.81.6

195205215240180

400 0.00.20.40.81.6

238252275290240

0.2 Fe2O3/Al2O3

600 0.00.20.40.81.6

210285253273203

Examination of Tables 3 to 5 and Figs 1 to 6 shows the followings: (1) The catalytic activity of various systems, expressed as total conversion decreases progressively by increasing the dose of -rays falling to a minimum value at a dose of 0.8 MGy.

(2) All catalysts retained their initial high catalytic activity upon exposure to a dose of 1.6 MGy.

(3) All investigated catalytic systems are highly selective towards dehydration of ethanol and isopropanol yielding ethene and propene, respectively. The dehydrogenation selectivity which is quite smaller than that of the dehydration selectivity increases progressively by increasing the reaction temperature.

(4) The rise, in precalcination temperature of all catalysts investigated from 400 to 600 °C brought about a significant increase in their catalytic activity.

(5) The comparison between the catalytic activities of various systems calcined at 400 and 600 °C in dehydration and dehydrogenation of ethanol and isopropanol vary according to the sequence NiO/Al2O3 CuO/Al2O3>Fe2O3/Al2O3. This sequence turned to CuO/Al2O3>NiO/Al2O3>Fe2O3/Al2O3 for isopropanol conversion carried out over various catalysts calcined at 400 °C.

(6) All investigated solids calcined at 600 °C showed high and comparable activity in alcohols conversion.

The observed measurable increase in the catalytic activity of various systems upon increasing their calcination temperature from 400 to 600 °C can be discussed in terms of the following parameters: (a) conversion of AlOOH into poorly crystallized -Al2O3;(b) an effective decrease in the crystallite size of NiO, CuO and Fe2O3; (c) the decrease in the specific surface areas of different catalytic systems; (d) the possible decrease in surface OH groups.

Parameters (c) and (d) are normally accompanied by a decrease in the catalytic activities of the systems investigated due to increasing their calcination temperature from 400 to 600 °C. While parameters (a) and (b) should increase the catalytic activities of different systems. The fact that the catalytic activity of various solids were found to increase by increasing the calcination temperature from 400 to 600 °C points out that parameters (a) and (b) dominante and counteract the other two parameters.

The observed significant decrease in the catalytic activity of various systems investigated due to treating with -rays from 0.2–0.8 MGy could be attributed to an effective decrease in the concentration of Brönsted acidity (surface OH groups) acting as catalytically active sites. This treatment, however, brought about an effective increase in the specific surface area of all systems investigated. So, the induced effects of -irradiation were operating against each other.

However, the role of decreasing the concentration of the surface OH groups was dominant.

All investigated catalysts gained their initial high activities upon exposure to a dose of 1.6 MGy. This finding had been attributed to the reaction of water molecules liberated in the early stage of the dehydration reaction of alcohols with the surface of the treated solids yielding OH groups, which retained on the catalyst surface.13–18 This phenomenon did not take place in the case of catalysts exposed to doses smaller than 0.8 MGy. Simply because a dose of 0.8 MGy removed more than 80% of surface OH groups in different solids.34 This situation favored the creation of these surface OH groups via an interaction between the liberated water molecules with the irradiated catalyst surfaces.

Similar results have been reported by EL-SHOBAKYet al. for the conversion of ethanol and isopropanol carried out over CuO/MgO, Na2O–Mn2O3/Al2O3,Co3O4/Al2O3, ZnO–Co3O4/Al2O3, Co3O4/MgO, NiO–Co3O4, CeO2/NiO/Al2O3 and manganese oxides systems.13–18,26,32–34


491

Table 3. Total conversion (activity) and selectivities of alcohols over unirradiated and various -irradiated CuO/Al2O3 solid catalysts precalcined at 400 °C

Ethanol Isopropanol Dose, MGy Temperature, °C TC S1 S2 TC S1 S2

250 5 100 0 18.2 100 0 300 25.6 18.5 81.5 89.6 16 83 325 60.9 7.4 92.6 94.5 13 87 350 70.2 2.6 92.6 95.1 11 88.3 375 77.9 1.5 95.3 97.4 7.3 89.4

0.0

400 85.9 0.9 96.3 98.7 5.6 90.3 250 3.2 100 0 8.9 100 0 300 15.2 19.7 80.3 55.5 9.2 90 325 38.2 7.1 42.9 61.2 7.7 91 350 42.6 5.9 94 65.1 3.4 93 375 55.2 3.8 96 66.4 2.0 94.8

0.2

400 60.2 0 97.7 68.7 0.70 96 250 2.1 100 0 5.8 100 0 300 9.1 20.9 79.1 32.5 87.4 12 325 30.2 5.6 94.4 33.5 80.2 17.6 350 32.1 4.7 95 38.7 73.4 20.7 375 39.5 3 95.9 39.9 70 27.8

0.4

400 43.6 1.8 97.7 42.5 62.4 35.4 250 0 0 0 2.1 100 0 300 4 100 0 9.8 19.4 80.6 325 6.1 57.4 42.6 11.2 10.7 88.3 350 8.1 39.5 56.8 13.8 8 90.6 375 6.3 20.6 74.6 16.8 2.4 95.2

0.8

400 11.1 10.8 85.6 19.7 0.5 95.9 250 4.3 100 0 16.5 97.6 2.4 300 24.5 15.5 84.5 87.5 16.2 83.8 325 60.1 5.5 94.5 94.1 12.9 87.1 350 69.1 4.3 95.5 94.5 10.7 88.9 375 76.2 3.7 93.8 96.5 5.9 92.2

1.6

400 84.2 3.1 94.6 97.9 4.2 92.9

TC: Total conversion. S1: Selectivity towards dehydration. S2: Selectivity towards dehydrogenation.

Fig. 1. Effect of reaction temperature and -irradiation on ethanol total conversion of over various catalysts precalcined at 600 °C


492

Fig. 2. Effect of reaction temperature and -irradiation on isopropanol total conversion of over various catalysts precalcined at 600 °C

Table 4. Total conversion (activity) and selectivities of alcohols over unirradiated and various -irradiated NiO/Al2O3 solid catalysts precalcined at 400 °C


250 10.5 89.5 10.5 10.5 100 0 300 69.5 11.9 88.1 69.6 14.7 85.3 325 73.6 10.2 89.8 73.8 13.3 86.7 350 75.8 8 91.1 75.9 11.7 87 375 98.9 5.3 92.9 98.9 6.5 87.7

0.0

400 99.9 1.9 93.5 99.1 4 88.6 250 6.1 100 0 5.2 96.2 3.8 300 42.1 14 86 32.5 14.8 85.2 325 50.4 8.2 91.7 36.1 11.9 88.1 350 55.6 6.5 93.7 40.2 9.7 89.8 375 60.2 3 96.3 41.5 1.2 96.7

0.2

400 62.2 0.2 96.6 44.1 0 97.6 250 4.2 98 1.4 2.1 100 0 300 32.4 11.7 88.3 19.5 9.2 90.8 325 38.1 6.8 93.2 22.3 5.8 94.2 350 42.9 5.3 93.5 25.8 3.1 94.6 375 48.2 2.5 94.8 27.8 1.8 95.3

0.4

400 51.5 1 95.5 30.1 0 95.7 250 0 0 0 0 0 0 300 3.4 100 0 2.1 100 0 325 7.2 44.4 55.6 3.5 51.4 48.6 350 11.2 27.7 66.6 5.8 20.7 77.6 375 13.5 21.5 75.6 6.7 11.9 85.1

0.8

400 15.8 10.1 86.1 8.9 0 94.4 250 10.1 100 0 9.5 89.5 10.5 300 68.1 14.4 85.6 58.8 13.9 86.1 325 72.1 13.2 86.8 71.8 9.3 90.5 350 73.6 11 87.2 74.1 7 90.6 375 77.2 9.3 88.5 77.5 6.2 91.5

1.6

400 78.4 5.4 89.4 78.7 4.7 91.9



493

Table 5. Total conversion (activity) and selectivities of alcohols over unirradiated and various -irradiated Fe2O3/Al2O3solid catalysts precalcined at 400 °C


250 8.1 99 1 5.2 94.2 5.2 300 35.4 22 77.9 20.6 20.9 79.1 325 46.7 15.6 84.5 57.3 7.1 93 350 55.7 11.1 89 67.8 4.6 94.2 375 57.4 9.4 88.2 70.2 3.4 95.4

0.0

400 60.3 6.8 91.2 75.1 2.8 96.4 250 5.2 96.2 3.8 2.3 100 0 300 25.3 19.4 80.6 11.2 18.8 81.3 325 32.8 14.3 85.7 30.2 6 84 350 40.2 10.2 86.3 39.5 3 96.2 375 43.8 8.4 87.7 42.1 1.9 96.7

0.2

400 45.2 0 94 46.9 0 97 250 4.1 100 0 0 0 0 300 15.5 25.2 75 6.3 95.2 4.8 325 19.5 18 82.1 19.8 28.8 71.2 350 24.8 12.5 85.1 23.5 21.7 72.8 375 30.2 9.3 87.4 26.9 16.7 79.9

0.4

400 32.7 5.8 89 29.9 12.7 82.6 250 3.1 100 0 0 0 0 300 5.4 89.6 10 2.3 87 13 325 6.7 87.8 11.2 4.5 40 60 350 8.2 79.1 14.6 6.5 24.6 72.3 375 10.5 68 20.4 7.8 15.4 80.8

0.8

400 12.3 59 36 9.1 9.9 86.8 250 7.1 100 0 4.5 91.1 8.9 300 34.1 14.9 84.1 20.1 18.4 81.6 325 46.1 2.9 97.1 55.7 5.7 94.3 350 54.2 1.7 98 67.1 4.5 94.6 375 57.2 0.9 95.6 69.2 3.6 95.5

1.6

400 60.1 0 96.7 73 2.6 95.8


Fig. 3. Effect of reaction temperature and -irradiation on the dehydration of ethanol on various catalysts precalcined at 600 °C


494

Fig. 4. Effect of reaction temperature and -irradiation on the dehydrogenation of ethanol on various catalysts precalcined at 600 °C

Fig. 5. Effect of reaction temperature and -irradiation on the dehydration of isopropanol on various catalysts precalcined at 600 °C

Fig. 6. Effect of reaction temperature and -irradiation on the dehydrogenation of isopropanol on various catalysts precalcined at 600 °C

Conclusions

The followings are the main conclusions that may be drawn from the results obtained.

CuO/Al2O3, NiO/Al2O3 and Fe2O3/Al2O3 prepared by imprignation method and calcined at 400 and 600 °C are nanocrystalline solids measuring particle size varying between 6 and 85 nm.

The transition metal oxides loaded on aluminium substrate consisted of well crystallized metal oxides and a mixture of aluminum oxihydroxide and a poorly crystalline -Al2O3.

Increasing the calcination temperature of various catalytic systems from 400 to 600 °C brought about a measurable decrease in the crystallite size of the CuO,

NiO and Fe2O3 and the conversion of AlOOH into a poorly crystalline -Al2O3.

Gamma-irradiation changed the crystallite size of different catalysts constituents. The change is dependent of the dose of -rays and the nature of the oxide.

The specific surface areas of different catalytic systems were found to increase by increasing the dose of -rays reaching to a maximum limit at a dose of

0.8 MGy.The different catalytic systems calcined at 400 and

600 °C were highly selective towards dehydration of alcohols especially for the reaction carried out at a temperature below 300 °C.

The catalytic activities of different solids investigated much increase by increasing their calcination temperature from 400 to 600 °C.


495

Gamma-irradiation led to a progressive decrease in the catalytic activity of different solids falling to minimum values at a dose of 0.8 MGy.

All catalysts investigated retained their initial highly activity upon exposure to a dose of 1.6 MGy.

References

1. N. Z. MURADOV, Intern. J. Hydrogen Energy, 18 (1993) 211. 2. A. C. B. DOS SANTOS, W. B. KOVER, A. C. FARO, Appl. Catal.,

A153 (1997) 83. 3. T. ZHANG, M. D. AMIRIDIS, Appl. Catal., A163 (1998) 161. 4. S. VELU, M. F. STEPHANOPOLOULOS, Appl. Catal., A162 (1997)

81. 5. G. A. EL-SHOBAKY, A. N. AL-NOAIMI, Appl. Catal., A29 (1987)

235. 6. M. F. LUO, Y. J. ZHONG, X. X. UAN, X. M. ZHENG, Appl. Catal.,

A162 (1997) 121. 7. G. A. EL-SHOBAKY, A. S. AHMED, M. M. MOKHTAR,

J. Radioanal. Nucl. Chem., 219 (1997) 89. 8. G. A. EL-SHOBAKY, F. M. RADWAN, A. M. TURKY,

A. ABD-EL-MOEMEN, Adsorb. Sci. Technol., 19 (2001) 779. 9. A. GOLCHET, J. M. WGITE, J. Catal., 53 (1978) 266. 10. A. M. YOUSSEF, S. A. EL-HAKAM, G. A. EL-SHOBAKY, Radiat.

Phys. Chem., 40 (1992) 575. 11. F. M. T. MENDES, M. SCHMAL, Appl. Catal., A163 (1997) 153. 12. H. LI, J. F. DING, Appl. Catal., A193 (2000) 9. 13. H. G. EL-SHOBAKY, H. A. EL-BOOHY, M. M. DOHEIM, Adsorp.

Sci. Technol., 18 (2000) 749. 14. G. A. EL-SHOBAKY, M. M. DOHEIM, A. M. GHOZZA,

H. A. EL-BOOHY, Mater. Lett., 57 (2002) 525. 15. G. A. EL-SHOBAKY, M. M. DOHEIM, A. M. TURKY,

H. A. EL-BOOHY, J. Radioanal. Nucl. Chem., 256 (2003) 107. 16. H. A. EL-BOOHY, M. M. DOHEIM, G. A. EL-SHOBAKY, Afinidad,

59 (2002) 497.

17. M. M. DOHEIM, H. A. EL-BOOHY, G. A. EL-SHOBAKY, Adsorp. Sci. Technol., 19 (2001) 635.

18. M. M. DOHEIM, H. A. EL-BOOHY, M. MOKHTAR,G. A. EL-SHOBAKY, Adsorb. Sci. Technol., 19 (2001) 751.

19. M. M. DOHEIM, A. S. AHMED, H. A. EL-BOOHY,G. A. EL-SHOBAKY, J. Radioanal. Nucl. Chem., 254 (2002) 583.

20. A. ANDREEV, V. KAFEDZHIISKI, T. KUNEV, V. KALCHEV, Appl. Catal., 78 (1991) 99.

21. C. N. SPALARIS, L. P. BUPP, E. C. GILBERT, J. Phys. Chem., 61 (1957) 350.

22. N. H. AMIN, G. A. EL-SHOBAKY, G. A. FAGAL, J. Radioanal. Nucl. Chem., 177 (1994) 211.

23. G. A. EL-SHOBAKY, G. A. FAGAL, N. PETRO, A. M. DESSOUKI,Radiat. Phys. Chem., 29 (1987) 39.

24. G. A. EL-SHOBAKY, A. S. AHMED, H. G. EL-SHOBAKY,J. Radioanal. Nucl. Chem., 185 (1994) 23.

25. G. A. EL-SHOBAKY, A. M. EL-SHAABINY, A. A. RAMADAN,A. M. DESSOUKI, Radiat. Phys. Chem., 34 (1989) 787.

26. G. A. EL-SHOBAKY, A. M. EL-SHAABINY, A. A. RAMADAN,A. M. DESSOUKI, Radiat. Phys. Chem., 30 (1987) 233.

27. P. H. BOLT, S. F. LOBNER, T. P. BOUT, J. W. GEUS,F. H. P. M. HABARKEN, Appl. Surf. Sci., 70/71 (1993) 196.

28. P. H. BOLT, F. H. P. M. HARBARKEN, J. W. GEUS, Catal. Deactiv., 88 (1994) 425.

29. P. H. BOLT, M. E. VAN IPENBURG, J. W. GEUS,F. H. P. M. HABARKEN, Mater. Res. Symp. Proc., 334 (1994) 15.

30. B. D. CULLITY, Elements of X-ray Diffraction, 3 ed, Addison-Wesley, Reading MA, 1967.

31. R. BRUNAUER, E. MIKHAIL, E. BODOR, Colloid Interface Sci., 24 (1967) 351.

32. G. A. EL-SHOBAKY, M. M. DOHEIM, A. M. GHOZZA, Radiat. Phys. Chem., 69 (2004) 31.

33. M. R. MOSTAFA, A. M. YOUSSEF, A. M. HASSAN, Mater. Lett., 12 (1991) 207.

34. A. M. YOUSSEF, G. A. EL-SHOBAKY, TH. EL-NABARAWY,N. H. AMIN, J. Serbian Chem. Soc., 55 (1990) 121.

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