Chapter 27
Factors Affecting X-ray Diffraction Characteristics of Catalyst Materials Wayne J. Rohrbaugh and Ellen L . W u
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Mobil Research and Development Corporation, Paulsboro Research Laboratory, Paulsboro, N J 08066-0480
X-ray diffraction (XRD) is a major tool employed to identify and characterize catalytic materials. A brief review of the diffraction phenomenon and the effect of crystallite size is presented. Appli cations of XRD to catalyst characterization are illustrated, including correlation of XRD powder patterns to molecular structural features, deter mination of Pt crystallite size and others. Factors that affect the appearance of XRD powder patterns, such as framework structure perturbations, extra framework material, crystal morphology, impurities, sample preparation, instrument configurations, and x-ray sources, are discussed.
X-ray d i f f r a c t i o n (XRD), i n p a r t i c u l a r x - r a y powder d i f f r a c t i o n , has been used e x t e n s i v e l y t o i d e n t i f y and c h a r a c t e r i z e m a t e r i a l s used as c a t a l y s t s i n t h e p e t r o l e u m r e f i n i n g and p e t r o c h e m i c a l i n d u s t r i e s . T h i s i s n o t s u r p r i s i n g , s i n c e many o f t h e m a t e r i a l s are c r y s t a l l i n e ; i . e . , t h e atoms c a n be a r r a n g e d i n t h r e e d i m e n s i o n a l p e r i o d i c a r r a y s . E v e r y atom i n a c r y s t a l l i n e s o l i d c o n t r i b u t e s t o t h e o b s e r v e d XRD p a t t e r n , t h u s making t h e p a t t e r n c h a r a c t e r i s t i c o f t h e m a t e r i a l - a v i r t u a l f i n g e r p r i n t . The d i f f r a c t i o n d a t a o b t a i n e d f o r c a t a l y t i c m a t e r i a l s can t e l l us many t h i n g s about t h e s e m a t e r i a l s , r a n g i n g from t h e s t r u c t u r a l n a t u r e o f the c r y s t a l l i n e components t o t h e average P t c r y s t a l l i t e s i z e on a s u p p o r t e d - m e t a l c a t a l y s t . I t can be used t o m o n i t o r and c o r r e l a t e m o l e c u l a r s t r u c t u r a l f e a t u r e s t o c a t a l y t i c p r o c e s s and r e a c t i o n v a r i a b l e s , o r t o specify composition f o r patent d e f i n i t i o n . I n s h o r t , XRD i s an i n v a l u a b l e t e c h n i q u e i n c a t a l y s t r e s e a r c h and development. T h i s d i s c u s s i o n w i l l i l l u s t r a t e some o f t h e a p p l i c a t i o n s o f XRD t o c a t a l y s t c h a r a c t e r i z a t i o n and p o i n t o u t some of t h e f a c t o r s t h a t a f f e c t t h e appearance o f x - r a y powder d i f f r a c t i o n patterns of these m a t e r i a l s . 0097-6156/89/0411-0279$07.00/0 © 1989 American Chemical Society
In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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XRD
CHARACTERIZATION AND CATALYST DEVELOPMENT
Fundamentals
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In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
X-ray Diffraction Characteristics of Catalysts
ROHRBAUGH & WU
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Downloaded by GEORGETOWN UNIV on August 20, 2015 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch027
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