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

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 Ni 12 P 5 (001) surfaces was explored and contrasted to our previous results from research on Ni 2 P(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 CH 3 OH* → CH 3 O* → CH 2 O* → CHO* → CO*. On the other hand, Ni 12 P 5 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 CO 2 through a sequence of reactions involving CH 2 O*→ H 2 COOH* → HCOOH* → HCOO* → CO 2 . 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 Ni 2 P 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 CO 2 through the MSR route, offering valuable insights into optimizing nickel phosphide catalysts for desired chemical transformations.