IN SITU METHODS OF CATALYST CHARACTERIZATION

Submitted to:

Deepak Pandey Dr. Prateek Jha

14514013 Assistant Professor

IIT ROORKEE

BACKGROUND

catalyst under action Catalyst undergoes many changes when in

action

These changes may lead to change in catalytic properties that we are interested in.

Characterization involves determination of parameters like porosity, surface area ,density, selectivity etc.

X-RAY DIFFRACTION

Governed by Braggs law

X ray have wavelength of same order of inter atomic spacing , hence can be used for diffraction

Different diffraction pattern - single crystal - more than one crystal -mixture of crystals (PXRD)

XRPD patterns, diffraction cones

Random orientation of crystals ,so powdered sample generates cones instead of single spots

Cones intersect strip of photographic film to produce characteristic sets of arcs.

Detector converts this signal into count rate versus 2 plot.

Plot compared with reference data available for different materials

More information

Diffraction peak broadening may contain info about sample microstructure

Peak position can be used to calculate unit cell dimensions.

CASE STUDY-1

Discusses about importance of XRPD Zn/Cr oxides are well known catalysts for

synthesis of methanol from syn-gas For long time its active component was

considered to be ZnO. XRPD revealed active species non-

stoichiometric spinel-like phase of ZnCr2O4 Earlier it was known that Zn ion occupy

tetrahedral while Cr ions octahedral spaces Residual ZnO is expected when Zn/Cr above 0.5 But XRPD showed pure spinel- phase existence

at least up to Zn/Cr =1 due to nonstoichiometric spinel- where Zn ions occupy some octahedral sites randomly with Cr ions.

Common catalysts for WGS reaction are CuMoO4, NiMoO4 , CuO-ZnO .XRD studies have been done before

XRD studies of CuFe2O4 inverse spinel structure Contains both octahedral and tetrahedral sites ,Cu ion

sits on octahedral while iron on both.

CuFe2O4 is cubic at elevated temp(>400) and tetragonal at room temp.

As temperature was raised , tetragonal diffraction lines disappeared at 380 ,only cubic lines left

200 no WGS activity 200-300 CO attacks oxide and partial reduction leads

to metallic Cu ,onset of WGS activity

At 35o active WGS catalyst mixture of Cu,CuFe5O8 and Fe3O4

These XRD results point to metallic copper as an active species for the WGS.

References :

[1] Giovanni Perego, Characterization of heterogeneous catalysts by X-ray diffraction techniques, catalysis today(1998)

[2] Jose A. Rodriguez , Jonathan C. Hanson , Wen Wen, Xianqin Wang, Joaqun L. Brito , Arturo Martnez-Arias , Marcos Fernandez-Garc, In-situ characterization of watergas shift catalysts using time-resolved X-ray diffraction,catalysis today (2009)

[3]Scott A Speakman, Introduction to X-Ray Powder Diffraction, Data Analysis, Centre for Materials Science and Engineering at MIT.

[4] Andrew M. Beale , Eli Stavitski, Bert M. Weckhuysen, Characterization of catalysts : Surface and In-situ methods, Department of Chemistry, Utrecht university, The Netherlands