Catalytic partial oxidation of methane to syngas over Ni/Al₂O₃ catalyst

The surface feature and catalytic performance of Ni/Al₂O₃ catalyst for the partial oxidation of methane to synthetic gas were investigated by TPR, XRD and catalytic performance evaluation. It was found that the dispersion capacity of these highly dispersed nickel oxide species was evaluated to be about 9.0% Ni. This catalyst was the best one for CH₄ conversion as well as CO and H₂ selectivity under the conditions of the ratio of V_CH4/V_O1 = 2.0 and high GHSV (11.52 × 10⁵ ml (stp) · g^-1 · h^-1) at atmospheric pressure. As Ni content increased over this limit, the NiO crystals formed made no contribution to the performance of the catalyst. According to TPR results of reduced and unreduced catalysts treated under the reaction conditions, a kind of nickel oxide species, which had lower reduction temperature (520 ∼ 540°C) and smaller reduction peak than the highly dispersed nickel oxide on fresh catalyst, always existed on the catalyst surface during the reaction. It was observed that CH₄ conversion increased with increasing the temperature or GHSV to 11.52 × 10⁵ ml · g^-1 · h^-1. However, a further increase of GHSV led to a decrease of CH₄ conversion and syngas productivity. Selectivity for CO and H₂ was always improved by the increase of GHSV and the temperature. These experimental results indicated that under the nonequilibrium (i. e. using extremely high GHSV), the reaction results were controlled mostly by the process kinetics and the partial oxidation process probably followed a reaction sequence completely different from that considered in the equilibrium process. Moreover, the major part of CO and H₂ products formed directly from CH₄, a little amount of CO₂ seemed to be the product of the deep oxidation of CO and CH₄ especially at low GHSV or low temperature and the disproportionation of CO.