Scaling-Relation-Based Analysis of Bifunctional Catalysis: The Case for Homogeneous Bimetallic Alloys

We
present a generic analysis of the implications of energetic
scaling relations on the possibilities for bifunctional gains at homogeneous
bimetallic alloy catalysts. Such catalysts exhibit a large number
of interface sites, where second-order reaction steps can involve
intermediates adsorbed at different active sites. Using different
types of model reaction schemes, we show that such site-coupling reaction
steps can provide bifunctional gains that allow for a bimetallic catalyst
composed of two individually poor catalyst materials to approach the
activity of the optimal monomaterial catalyst. However, bifunctional
gains cannot result in activities higher than the activity peak of
the monomaterial volcano curve as long as both sites obey similar
scaling relations, as is generally the case for bimetallic catalysts.
These scaling-relation-imposed limitations could be overcome by combining
different classes of materials such as metals and oxides.