Sulfur-Doped g-C3N4-Supported Ni Species with a Wide Temperature Window for Acetylene Semihydrogenation

The semihydrogenation of acetylene is a vital industrial reaction in C2 hydrorefining. Ethylene selectivity and hydrogenation activity, however, are difficult to optimize simultaneously, naturally leading to a narrow operation temperature window, especially for noble-metal-free catalysts, which are significant for sustainable development. Herein, Ni/g-C3N4-T, i.e., sulfur-doped g-C3N4-T-supported Ni species, is proved to be an excellent Ni catalyst for acetylene semihydrogenation. Full conversion and good selectivity (>63%) are achieved concurrently over Ni/g-C3N4-T in a very wide operation window of 175–300 °C, in sharp contrast to the negative selectivity of Ni/g-C3N4-M, i.e., Ni supported on sulfur-free g-C3N4-M. That is, the introduction of sulfur exerts a significant influence on the catalytic behavior of Ni/g-C3N4 for acetylene hydrogenation. The results of X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) indicate that S-doped g-C3N4-T-supported Ni species exist as Ni cations confined in the cavities of g-C3N4-T or in the form of a Ni-S solid solution with S surface segregation, different from Ni particles for Ni/g-C3N4-M. Accordingly, the continuous Ni ensembles, at least the surface counterparts, are broken up, which, as indicated by C2H4-temperature-programmed desorption (TPD), will promote desorption of weak π-bonded ethylene; therefore, Ni/g-C3N4-T possesses high selectivity. In addition, exclusive Ni2+ species over g-C3N4-T, demonstrated by XPS, will favor the activation of acetylene via their electrostatic interaction; thus, Ni/g-C3N4-T shows a comparable hydrogenation activity with that of Ni/g-C3N4-M. The findings offer an avenue to design cost-effective catalysts with both high selectivity and superior activity over a broad operation window for acetylene semihydrogenation.