The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO （La/Ca = 0.05） catalysts, prepared using different precursor salts for CaO and La2O3 （viz. acetates, carbonates...The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO （La/Ca = 0.05） catalysts, prepared using different precursor salts for CaO and La2O3 （viz. acetates, carbonates, nitrates and hydroxides） and catalyst preparation methods （viz. physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent）, under different reaction conditions （temperature： 700-850 ℃, CH4/O2 ratio： 4.0 and 8.0, and GHSV： 51360 cm^3·g^-1·h^- 1）. The surface area and surface basicity/base strength distribution of the catalysts have also been investigated. The surface properties and catalytic activity/selectivity of the La-promoted CaO catalysts vary from catalyst to catalyst depending on the catalyst precursors used and catalyst preparation method. The basicity/base strength distribution is strongly influenced by the precursors （for CaO and La2O3） and catalyst preparation method. Basicity （total and strong basic sites measured in terms of CO2 chemisorbed at 50℃ and 500 ℃, respectively） observed for the catalyst prepared by co-precipitation method is higher than that of the catalysts prepared by physical mixing method. The catalysts prepared by the nitrates of La- and Ca- and co- precipitated by the solution of sodium carbonate and ammonium carbonate exhibit different catalytic performance in OCM. The finding that no direct relationship between the surface basicity and catalytic activity/selectivity in OCM exists indicates that basicity is not solely responsible for obtaining high selectivity to C2 hydrocarbons.展开更多
The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, s...The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 adsorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.展开更多
文摘The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO （La/Ca = 0.05） catalysts, prepared using different precursor salts for CaO and La2O3 （viz. acetates, carbonates, nitrates and hydroxides） and catalyst preparation methods （viz. physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent）, under different reaction conditions （temperature： 700-850 ℃, CH4/O2 ratio： 4.0 and 8.0, and GHSV： 51360 cm^3·g^-1·h^- 1）. The surface area and surface basicity/base strength distribution of the catalysts have also been investigated. The surface properties and catalytic activity/selectivity of the La-promoted CaO catalysts vary from catalyst to catalyst depending on the catalyst precursors used and catalyst preparation method. The basicity/base strength distribution is strongly influenced by the precursors （for CaO and La2O3） and catalyst preparation method. Basicity （total and strong basic sites measured in terms of CO2 chemisorbed at 50℃ and 500 ℃, respectively） observed for the catalyst prepared by co-precipitation method is higher than that of the catalysts prepared by physical mixing method. The catalysts prepared by the nitrates of La- and Ca- and co- precipitated by the solution of sodium carbonate and ammonium carbonate exhibit different catalytic performance in OCM. The finding that no direct relationship between the surface basicity and catalytic activity/selectivity in OCM exists indicates that basicity is not solely responsible for obtaining high selectivity to C2 hydrocarbons.
基金supported by the Key Project of Chinese National Programs for Fundamental Research and Development(973 Program 2005CB221204)the Natural Science Fund of China(20676087)
文摘The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 adsorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.
