Mechanistic insights into the adsorption and dissociation of nitrogen oxides on nickel phosphide (Ni₂P) catalysts

The escalating concern regarding nitrogen oxides (NOx) emissions, linked to environmental challenges like smog, acid rain, ozone depletion, and global warming, necessitates effective strategies for their mitigation. DeNOx processes, including selective catalytic reduction (SCR), offer potential solutions, but costly precious metal catalysts hinder a widespread implementation. Alternatively, earth-abundant element compounds, particularly transition metal phosphides (TMPs), such as nickel phosphides (Ni₂P), have garnered interest due to their promising catalytic performance. This study employed first-principles density functional theory (DFT) methods to investigate the catalytic properties of the (0001) Ni₂P surface concerning NOx adsorption and dissociation. Both NO and NO₂ are found to exhibit strong reactivity towards Ni₂P-(0001)’s surface at the hollow triple-Ni sites, forming stable conjugated structures. Bader charge analysis indicates significant charge transfers during NOx adsorption from the interacting surface to the NOx, resulting in elongated N–O bond lengths, confirmed by vibrational frequency analyses. The dissociation process of NO₂ was found to be both thermodynamically and kinetically favorable, with more heat being released than the subsequent NO dissociation's activation barrier, resulting in a self-sustaining overall reaction. These insights provide valuable knowledge for designing efficient and sustainable Ni₂P-based catalytic systems to address NOx emissions in environmental and industrial applications.