Theoretical insights into the catalytic activity of nanostructured polyoxometalates

Acid catalysis is the hallmark of many energy intensive hydrocarbon conversion processes including alkylation. Supported heteropolyacids (HPAs) have been shown to actively carry out this reaction an but were found to undergo very rapid deactivation. HPA offer unique catalytic functionality as their nanometer architectures allow them to be readily tuned by altering the addenda metal atoms or the central ions to improve both their catalytic activity as well as their stability. Herein we use first principle density functional theoretical calculations to follow the catalytic cycles involved in the alkylation of isobutene and isobutene. Systematic studies have been carried out over a range of different HPA structures in order to establish those which demonstrate the best activity. The results were found to nicely correlate with the charge on the central ion. Hydrocarbon coupling of the alkene predominates and subsequently leads to lower selectivity. We discuss possible ways of improving these materials.