Nickel Phosphide Nanoparticles for Selective Hydrogenation of SO2 to H2S

Highly mesoporous SiO2-encapsulated Ni x P y crystals, where (x, y) = (5, 4), (2, 1), and (12, 5), were successfully synthesized by adopting a thermolytic method using oleylamine (OAm), trioctylphosphine (TOP), and trioctylphosphine oxide (TOPO). The Ni5P4@SiO2 system shows the highest reported activity for the selective hydrogenation of SO2 toward H2S at 320 °C (96% conversion of SO2 and 99% selectivity to H2S), which was superior to the activity of the commercial CoMoS@Al2O3 catalyst (64% conversion of SO2 and 71% selectivity to H2S at 320 °C). The morphology of the Ni5P4 crystal was finely tuned via adjustment of the synthesis parameters receiving a wide spectrum of morphologies (hollow, macroporous-network, and SiO2-confined ultrafine clusters). Intrinsic characteristics of the materials were studied by X-ray diffraction, high-resolution transmission electron microscopy/scanning transmission electron microscopy-high-angle annular dark-field imaging, energy-dispersive X-ray spectroscopy, the Brunauer–Emmett–Teller method, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and experimental and calculated 31P magic-angle spinning solid-state nuclear magnetic resonance toward establishing the structure–performance correlation for the reaction of interest. Characterization of the catalysts after the SO2 hydrogenation reaction proved the preservation of the morphology, crystallinity, and Ni/P ratio for all the catalysts.