TY - JOUR
T1 - The structure of reactive sites on platinum metal catalysts for the hydrogenation of unsaturated hydrocarbons
AU - Siegel, Samuel
AU - Outlaw, James
AU - Garti, Nissim
PY - 1978/3/30
Y1 - 1978/3/30
N2 - The reactive sites, on platinum metal catalysts for the hydrogenation of unsaturated hydrocarbons and related reactions, are proposed to be the most coordinatively unsaturated exposed metal atoms. To simplify the discussion, the surface atoms are divided into three groups with one, two, or three units of coordinative unsaturation (corresponding to the number of monodentate ligands which may become attached) and are symbolized by 1M, 2M, and 3M. When exposed to hydrogen the first structures formed are 2MH2 and 3MH2 which are transformed, in part, to 2MH and 3MH by diffusion of hydrogen from the edge to other surface sites or to the interior of the crystallite. The proportions of 3M and 3MH present during a reaction are a function of the metal and the conditions of preparation and use. These structures bear a formal relationship to the structure of the complexes ClRh(PPh3)2(1) and HRhCO(PPh3)2(2) which are formed through the dissociation of ClRh(PPh3)3 and HRh(CO)(PPh3)3, respectively. The catalytic functions of both 1 and 2 appear to involve the same kinds of elementary processes, but the presence of the hydrido group in 2 leads to recognizably different phenomena (kinetics, stereochemistry, deuterium exchange reactions). Accordingly, the characteristics of hydrogenations catalyzed by platinum metals may be rationalized by considering the elementary processes which may occur at each category of site.
AB - The reactive sites, on platinum metal catalysts for the hydrogenation of unsaturated hydrocarbons and related reactions, are proposed to be the most coordinatively unsaturated exposed metal atoms. To simplify the discussion, the surface atoms are divided into three groups with one, two, or three units of coordinative unsaturation (corresponding to the number of monodentate ligands which may become attached) and are symbolized by 1M, 2M, and 3M. When exposed to hydrogen the first structures formed are 2MH2 and 3MH2 which are transformed, in part, to 2MH and 3MH by diffusion of hydrogen from the edge to other surface sites or to the interior of the crystallite. The proportions of 3M and 3MH present during a reaction are a function of the metal and the conditions of preparation and use. These structures bear a formal relationship to the structure of the complexes ClRh(PPh3)2(1) and HRhCO(PPh3)2(2) which are formed through the dissociation of ClRh(PPh3)3 and HRh(CO)(PPh3)3, respectively. The catalytic functions of both 1 and 2 appear to involve the same kinds of elementary processes, but the presence of the hydrido group in 2 leads to recognizably different phenomena (kinetics, stereochemistry, deuterium exchange reactions). Accordingly, the characteristics of hydrogenations catalyzed by platinum metals may be rationalized by considering the elementary processes which may occur at each category of site.
UR - http://www.scopus.com/inward/record.url?scp=0008967652&partnerID=8YFLogxK
U2 - 10.1016/0021-9517(78)90127-6
DO - 10.1016/0021-9517(78)90127-6
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AN - SCOPUS:0008967652
SN - 0021-9517
VL - 52
SP - 102
EP - 115
JO - Journal of Catalysis
JF - Journal of Catalysis
IS - 1
ER -