Selectivity of bimetallic catalysts

In conclusion, redox reactions allow the surface to be tailored during catalyst preparation, which explains the exceptional catalytic properties, particularly in terms of selectivity, of bimetallic catalysts prepared by these techniques. 

From the studies described above, one can expect that sulphur alters (or poisons) the properties of catalysts that combine gold and transition metals by inducing a reduction in the degree of wetting of the surface of the transition metal by gold. This effect can explain changes induced by sulphur on the activity and selectivity of bimetallic catalysts used for hydrocarbon reforming [7,22,30]. 

The selectivity of bimetallic catalysts can be different than for the component metals. The selectivity of Ni is markedly enhanced by alloying with Cu for scission of C—H bonds because of suppression of C—C bond hydrogenolysis. Other hydrocarbon reactions such as cyclization and skeleton isomerization of paraffins are enhanced by alloying Pt with Au. This enhancement has been ascribed to an increase in the number of isolated Pt atoms in the Au matrix. 

Activities and selectivities of bimetallic catalysts for hydrogenation of carvone are reported in Table 3. The results show a decrease of the specific activity of bimetallic catalysts compared to that of monometallic ones. Gold addition also modifies the selectivity patterns. The partial hydrogenation of the exo double bond is increased on both large and small particles on these catalysts carvotanacetone is the main product. 

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