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

The semihydrogenation of acetylene is a vitalindustrial reaction in C2hydrorefining. Ethylene selectivity andhydrogenation activity, however, are difficult to optimizesimultaneously, naturally leading to a narrow operation temper-ature window, especially for noble-metal-free catalysts, which aresignificant for sustainable development. Herein, Ni/g-C3N4-T, i.e.,sulfur-doped g-C3N4-T-supported Ni species, is proved to be anexcellent Ni catalyst for acetylene semihydrogenation. Fullconversion and good selectivity (>63%) are achieved concurrentlyover Ni/g-C3N4-T in a very wide operation window of 175-300 degrees 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, theintroduction of sulfur exerts a significant influence on the catalyticbehavior of Ni/g-C3N4for acetylene hydrogenation. The results of X-ray diffraction (XRD), high-resolution transmission electronmicroscopy (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 solutionwith S surface segregation, different from Ni particles for Ni/g-C3N4-M. Accordingly, the continuous Ni ensembles, at least thesurface counterparts, are broken up, which, as indicated by C2H4-temperature-programmed desorption (TPD), will promotedesorption of weak pi-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 acomparable hydrogenation activity with that of Ni/g-C3N4-M. Thefindings offer an avenue to design cost-effective catalysts withboth high selectivity and superior activity over a broad operation window for acetylene semihydrogenation.