THE INFLUENCES OF ALLOYING AND SURFACE MODIFICATION ON THE DIRECT SYNTHESIS OF H2O2 ON METAL CLUSTERS

摘要

H2O2 is an environmentally-friendly and selective oxidant useful for epoxidations, bleaching, and disinfection, yet, its use is limited because H2O2 production by the anthraquinone oxidation process is economically viable only at very large scales. Direct synthesis of H2O2 (H2 + O2 → H2O2) could enable H2O2 to be produced cost-effectively on-site, and even in situ, which would curtail the use of chlorine as a selective oxidant in many applications. H2O2 formation rates and selectivities increase when halides or Au are added to Pd clusters. Theoretical investigations have suggested that these additions change energy barriers for elementary steps by modifying the densities of states on surface Pd atoms. Such proposals have not been tested, moreover, the mechanism and identity of the reactive intermediates are a topic of investigation. Here, we combine rate measurements and in situ time-resolved infrared spectroscopy on Pd and Pt clusters and also Pd- and Pt-based bimetallic clusters to determine the mechanism of this reaction and to understand the reasons why changes in the size and composition of metal clusters increase H2O2 selectivities.