Bimetallic Pd-Au nanoclusters were prepared on SiO2/Si(100) via amorphous solid water (ASW) as buffer layer. Selective growth pathways have led to segregated palladium and gold clusters or alloy bimetallic crystallites. Morphology and chemical composition were determined by AFM, SEM, and HR-TEM coupled to EDX analysis. Correlation between clusters morphology and composition to their chemical reactivity is reported for the first time. Temperature programmed reaction studies revealed that conversion of acetylene to ethylene and trimerization to benzene are significantly enhanced over crystalline alloy Pd-Au clusters when compared to clean Pd. A remarkable selectivity toward ethylene formation over benzene is unique to the alloy bimetallic clusters grown via ASW buffer layer on silica, presumably due to suppression of the trimerization pathway. The intrinsic, modified electronic properties of the bimetallic alloy clusters are believed to drive their enhanced chemical reactivity when compared with the pure Pd clusters.