Catalytic Behaviors and Stability of Aerogel Silica-Supported Ni Catalysts for the Partial Oxidation of Methane into Synthesis Gas

Two types of aerogel silica, denoted as SiO2-A(or B) G are synthesized with either solvent substitution (A) or solvent substitution-surface modification (B) under atmospheric conditions. Aerogel silica-supported Ni catalysts are then prepared via impregnated (IM) and polyvinylpyrrolidone (PVP)-added IM methods, and their performances for the partial oxidation of methane (POM) are investigated. The similar initial catalytic performances (activity and selectivity) are observed over the different Ni/SiO2 catalysts. With respect to POM stability, Ni/SiO2-BG is significantly worse than Ni/SiO2-AG, while catalysts with PVP addition (during preparation) exhibit a significant improvement. In this case, Ni/SiO2-BG-PVP is comparable to Ni/SiO2-AG-PVP. We characterize the catalysts with X-ray diffraction (XRD), temperature-programmed hydrogen reduction (H-2-TPR), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. We find that there are hydroxyls on the SiO2-AG surface that favor their interaction with hydrophilic metal species, while on the SiO2-BG surface there are organic groups that do not interact with hydrophilic metal species. In addition, with the help of PVP, metal species can access the deep pores of hydrophilic/hydrophobic silica gels. Then, the contraction of the silica framework and the growth of metal particles are inhibited during calcinations, enhancing interactions between Ni and the silica gels. These (benefits from surface hydroxyls and PVP) result in significant improvements in the catalysts with respect to POM stability.