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Downloaded by UNIV OF ROCHESTER on November 16, 2016 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0121.ch043
Adsorption and Catalytic Properties of Palladium Supported by Silica, Alumina, Magnesia, and Amorphous and Crystalline Silica-Aluminas 1
F. FIGUERAS, R. GOMEZ, and M. PRIMET C.N.R.S., Institut de Recherches sur la Catalyse 39, boulevard du 11 Novembre 1918, 69100, Villeurbanne, France Some properties of palladium deposited on different amorphous or zeolitic supports were determined, including catalytic activity per surface metal atom (N) for benzene hydrogenation, number of electron-acceptor sites, and infrared spectra of chemisorbed CO. A n increase of the value of Ν and a shift of CO vibration toward higher frequencies were observed on the supports which possessed electron-acceptor sites. The results are interpreted in terms of the existence of an interaction between the metal and oxidizing sites modifying the electronic state of palladium.
hough industrial metallic catalysts are commonly used in the supported form, the influence of the carrier on the intrinsic catalytic activity is still controversial. The literature shows that most authors who found no sup port effect were using alumina or silica as carriers (1-5). Those authors who obtained an effect of the support on catalytic activity used acidic oxides (6, 7). Zeolites form an interesting class of supports since good metal dispersions may be obtained (8) and the acidic properties can be controlled by the cations exchanged into the initial sieve. Thus, the problem was to determine if the catalytic activity per metal atom was the same in a series of zeolites differing in their majority cation. Recently, Dalla Betta and Boudart (9) proved that the catalytic activity of platinum for ethylene hydro genation was higher on a Y zeolite than on silica. The present work is devoted to the study of palladium. Since the ionization potential is lower for palladium than for platinum, it should be easier to prove a possible interaction of this metal with a support. We Present address: Instituto Mexicano del Petroleo, Mexico.
1
480 Meier and Uytterhoeven; Molecular Sieves Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
43.
FiGUERAs E T A L .
481
Supported Palladium
s t u d i e d the h y d r o g e n a t i o n of benzene w h i c h is slow, c h a r a c t e r i s t i c of t h e m e t a l , a n d facile b y B o u d a r t ' s d e f i n i t i o n (1).
A n o t h e r a d v a n t a g e is t h a t
c a t a l y s t a g i n g is s m a l l i n t h i s r e a c t i o n . Experimental M a t e r i a l s . A series of zeolites was p r e p a r e d f r o m N a Y b y e x c h a n g i n g p a r t of t h e N a + ions b y N H + , C a , C e + , M g + , a n d L a . Palladium was exchanged i n t o these zeolites f r o m a Ρ d ( Ν Η ) 0 1 aqueous basic s o l u t i o n t o y i e l d a p a l l a d i u m c o n t e n t of a p p r o x i m a t e l y 2 w t % ( a p p r o x i m a t e l y 2 Pd ions p e r u n i t cell). T h e c h e m i c a l c o m p o s i t i o n s of t h e c a t a l y s t s so o b t a i n e d are g i v e n i n T a b l e I . D u r i n g t h e exchange b y t h e p a l l a d i u m salt p a r t of the s o d i u m is r e p l a c e d b y a m m o n i u m ions. 2 +
4
3
2
3
2
3 +
2
Downloaded by UNIV OF ROCHESTER on November 16, 2016 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0121.ch043
2 +
T a b l e I. C h e m i c a l C o m p o s i t i o n a n d D i s p e r s i o n of the M e t a l l i c P h a s e after R e d u c t i o n at 300°C of the P a l l a d i z e d Z e o l i t e s U s e d % Exchange Initial % wt Na Cation M in Sieve Remaining % Dis %Pd Initial Catalyst Support M-Y in Catalyst persion (wt) Denomination HY-1.2 HY-0.62 HY-0.20 NaX-4.6 NaX-2.0 NaY-5.1 NaY-1.7 CaY-1.9 CeY-2 0 CeY-1.77 LaY-1.86 MgY-1.84
1.2 0.62 0.20 4.6 2.0 5.1 1.7 1.9 2.0 1.77 1.86 1.84
100 100 100 100 100 100 100 70 15 70 70 58
NH Y NH Y NH Y NaX NaX NaY NaY CaY CeY CeY LaY MgY 4
4
4
— — —
7.5
12 16 12 13
—
—
4.1 6.5
