Synergic promotion

It appears probable, and will be substantiated below, that the effects of C02 and the synergic promotion of one catalyst component by another are but two facets of the formation of an active catalyst through the interactions among its components and the surrounding gas phase. It is the purpose of this article to review the recent observations and interpretations concerning the distribution of phases and elements, the physicochemical state of the catalyst components, the mode of activation of the reactants, and to show that a consistent picture is emerging that elucidates the function of the copper-based catalysts in the synthesis mechanism. 

Further, since the activity of zinc oxide has been found to be higher than that of other oxides such as alumina or chromia, no single-component catalyst, oxide, or metal is known at the present time that would effectively catalyze methanol synthesis at low temperatures and pressures, i.e., below 250°C and 100 atm. It is the synergic promotion in multicomponent catalysts that brings about greatly enhanced activity at low temperatures. 

Mechanism for synergic promotion of hydrogen evolution in the dehydrogenation of organic hydrides such as cyclohexane on bimetallic Pt-M catalysts (M = Rh, Ir, Pd, Re, Mo, etc.). 

Promotional effects of sulfide can evidently be explained, because exposure of reduced metals Is Increased on reduced sulfided catalysts. The role of cobalt Is less clear. It Is normally not fully reduced. It apparently does not promote greater exposure of Mo In any form detected, either In the presence or absence of sulfide. On the contrary. It evidently only decreases the concentration of exposed Mo atoms, although, at concentrations typically used, most. Mo atoms are unaffected by Co. Either some property of Co alone or some local cooperative effect of adjacent Co and Mo must explain promotion. Simple mechanical mixtures will not give the synergism observed, however (1-4). 

Simple passive immunization with Tyv-specific antibodies does not protect adult rats against T. spiralis, however, it has been shown that prior infection with an unrelated intestinal nematode (Heligmosomoides polygyrus) in combination with passive immunization with Tyv-specific antibodies promotes expulsion of T. spiralis larvae (Bell et al, 1992). The way(s) that II. polygyrus infection synergizes with antibodies is not known. 

Murphy, M.N., Smith, M.C., and Juergens, J.P, The synergic impact of promotion intensity and therapeutic novelty on market performance of prescription drug products, J. Drug Issues, 22, 305-316, 1992. 

Rh, are the base of active catalysts for CO hydrogenation and the hydroformylation of olefins. The presence of several promoters modifies their catalytic behavior and synergic effects on the base-metal have been observed Table 8.5 illustrates several examples in which homonuclear or heteronuclear carbonyl compounds have been used in the preparation of Co- or Co-Rh-based catalysts for the CO hydrogenation and/or hydroformylation reactions. 

When acid chelators are combined with one of the phenolic-type antioxidants, they can act synergistically. This type of synergism has been referred to as acid synergism (S). In this case, the primary role of a chelator is to bind metals, or metalloproteins that promote oxidation and thus, allow the antioxidant to perform its function and capture free radicals. In this manner, acid synergism is different than the BHA/BHT system. 

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