Effects of P:Ni Ratio on Methanol Steam Reforming on Nickel Phosphide Catalysts

Abstract

This study investigates the influence of the phosphorus-to-nickel (P:Ni) ratio on methanol steam reforming (MSR) over nickel phosphide catalysts using density functional theory (DFT) calculations. The catalytic behavior of Ni(111) and Ni12P5(001) surfaces was explored and contrasted to our previous results from research on Ni2P(001). The DFT-predicted barriers reveal that Ni(111) predominantly favors the methanol decomposition route, where methanol is converted into carbon monoxide through a stepwise pathway involving CH3OH* → CH3O* → CH2O* → CHO* → CO*. On the other hand, Ni12P5 with a P:Ni atomic ratio of 0.42 (5:12) exhibits a substantial increase in selectivity towards methanol steam reforming (MSR) relative to methanol decomposition. In this pathway, formaldehyde is transformed into CO2 through a sequence of reactions involving CH2O*→ H2COOH* → HCOOH* → HCOO* → CO2. The introduction of phosphorus into the catalyst alters the surface morphology and electronic structure, favoring the MSR pathway. However, with a further increase in the P:Ni atomic ratio to 0.5 (1:2) on Ni2P catalysts, the selectivity towards MSR decreases, resulting in a more balanced competition between methanol decomposition and MSR. These results highlight the significance of tuning the P:Ni atomic ratio in designing efficient catalysts for the selective production of CO2 through the MSR route, offering valuable insights into optimizing nickel phosphide catalysts for desired chemical transformations.