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.

Keywords: dehydrogenation; density functional theory; fuel cells; methanol decomposition; nickel phosphides; steam reforming.