Mechanism Insight into Catalytic Performance of Ni12P5 over Ni2P toward the Catalytic Deoxygenation of Butyric Acid

Abstract

The Ni/P ratio of nickel phosphide has an important effect on the catalytic performance toward the deoxygenation of fatty acids to biofuel. The Ni12P5 cluster is preferred to model Ni12P5 catalyst with butyric acid as the reactant model of palmitic acid. The catalytic deoxygenation mechanism of butyric acid over Ni12P5 cluster has been theoretically investigated at GGA-PBE/DSPP, DNP level in dodecane solution. From butyric acid, the hydrodehydration is predominated to form n-butanal. Then, from n-butanal, low temperature benefits the hydroreduction to form butanol and then hydrodehydration to produce n-butane, whereas high temperature favors the direct decarbonylation to yield propane. n-Butane originates from n-butanol through hydrodehydration and not from n-butylene. Propane comes from n-butanal through decarbonylation and not from propanol and/or propylene. Additionally, CO stems from n-butanal through decarbonylation, whereas CO2 is ruled out from butyric acid through decarboxylation. Compared with Ni12P6 cluster, Ni12P5 cluster exhibits higher catalytic activity for the formation of butanal, n-butanol, and n-butane, while it displays lower catalytic activity toward the direct decarbonylation and dehydration to yield propylene. These results can be attributed to less negative charges of Ni-sites over Ni12P5 cluster, compared with Ni12P6 cluster.