Study Of Carbon Deposition On Catalyst During Methane Partial Oxidation To Synthesis Gas By DFT

Partial oxidation of methane (POM) to syngas has been attracting wide attention in recent years. Compared with noble metal catalysts, the Ni-based catalysts have excellent prospects of industrial application for its good catalytic activity in POM and lower cost. The studies on the modification of carbon deposition resistant properties of catalysts by addition of different promoters and the mechanism on carbon species growing both have great theoretical and practical significance.Using the quantum chemical computation method based on density functional theory (DFT), the resistance to carbon deposition on the surfaces of Nickel metal, Platinum metal, Nickel-Platinum alloy and Nickel-Iridium alloy during the process of POM were studied. The possible mechanism on growth process of carbon species on Nickel surface was also investigated.The resistance to carbon deposition over some Ni-based catalysts were compared by studying the reactions of CH→C+H, C+O→CO and C+C→C₂, which play important roles in POM process. The energy barrier, adsorption energy and spatial configurations of some adsorptive species formated during above reactions on metal(111) surfaces were calculated. The results showed that the C species on NiPt(111) surface were less likely to grow than that on Ni(111) surface, NiPt catalyst has distinct inhibitory effect on carbon deposition. It is easy for CH species on NiIr(111) surface to dissociate to C species, further CO was generated, while it is difficult for the C species to grow up. In this way, carbon deposition was inhabited on NiIr(111).In addition, the possible reactions from C species to C₆ species on Ni (111) surface were also studied. The data on adsorption energy and spatial configurations of adsorbed Cx species on Ni(111) surface were calculated. The results indicated that the graphite formation could start from the dissociation of CH species, then C species were accumulatively growing up to C₂, C₃, C₄, C₅ species and finally the cyclic C₆ species stepswise. Because the activiation energy barriers of C₂+C₂→C₄ and C₃+C₃→C₆ reactions were slightly higher than those of C₄ and C₆ species formation through the accumulative growth route, the latter two reactions might also take place during POM process.