Metal Phosphides as High-performance Hydrotreating Catalysts

Experimental and Computational Investigation of the Role of P in Moderating Ethane Dehydrogenation Performance over Ni-Based Catalysts

“…Density functional theory (DFT) calculations relate this improvement to a downshift of the Pt d-band and associated decrease in adsorbate-surface binding, in particular, of ethylene. Several DFT studies also reported that the d-band shift in Pt- and Pd-based alloy surfaces leads to weaker alkene-surface binding compared to that on pure Pd and Pt surfaces. − The energies of alkene desorption and alkene dehydrogenation (and/or C–C bond scission) as computed using DFT have been widely used to predict trends in alkene selectivity across metal alloy catalysts. ,,− For example, Hook et al , used supercell DFT models to compare C–H and C–C bond scission pathways over Pt(111) and Pt x Sn/Pt­(111) ( x = 1, 3) model-ordered surfaces and found that absolute adsorption energies decrease and bond activation energies increase with increasing Sn content. These trends are attributed to a decrease in Pt ensemble size, which suppresses C–C bond scission pathways while maintaining C–H pathways, and modifications of the Pt electronic structure that facilitates ethylene desorption.…”

“…In the high-metal-content regime, phosphides have metallic character, suggesting activities similar to bulk metals. Metal-rich phosphides can also present ensembles similar to those of metal alloys, potentially offering similar selectivity and coke resistance advantages, and tend to be strongly ordering, thus resisting loss of those ensembles at high temperatures. − Metal phosphide catalysts have outstanding hydrogenation activity − and have been explored for hydroprocessing, including hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO). ,− Ni 2 P is known to be the most active and selective phosphide-based hydroprocessing catalyst. − This hydrogenation performance has stimulated some interest in exploring the performance of Ni 2 P for the reverse alkane dehydrogenation reaction. − Wang et al reported that Ni 2 P relative to Ni supported on activated carbon (AC) had increased isobutane dehydrogenation conversion and selectivity to isobutene. The authors speculate that the charge transfer from Ni to P weakens Ni–C bonding and improves selectivity.…”