摘要
以纯硅和Si/Al比分别为15和10的MCM-41,以及经NH_4NO_3,HAc和NaNO_3的醇溶液交换的MCM-41为载体制得Pt/MCM-41系列催化剂,研究了在甲烷两步同系聚合生成C_(2+)烷烃过程中催化剂的载体效应。载体的N_2吸附和催化剂的TPR显示出各种MCM-41的孔结构和表面性质存在差异;负载Pt催化剂在甲烷反应中的催化性能不同。活性随Si/Al比的增高而增大,其中以纯硅MCM-41负载催化剂活性最高,这来源于它高的比表面及相应的金属Pt在其中的高分散性和它特殊的表面性质;另外,由酸性抽提液处理的含铝MCM-41因载体酸性增加,其负载催化剂的活性也相应提高。同时,在各种Pt/MCM-41催化剂表面CH_x中间物种和其中C_α的生成量与产物C_(2+)生成量随载体变化的规律相同。C_(2+)高碳烃的总生成量和产物选择性取决于MCM-41载体的Si/Al比,Na含量和表面酸碱性。
In order to investigate the support effect on two-step homologation of methane, a series of Pt catalysts supported on MCM-41 mesoporous materials with Si/Al ratio of 10, 15 and oo, as well as that on the MCM-41 ion-exchanged by NH4NO3, HAc and NaNO3, were prepared. The N2 adsorption results of MCM-41 supports reveal that the specific surface area of the support increases with the increase of Si/Al ratio, and the TPR patterns of Pt/MCM-41 catalysts display the different dispersion and reduction degree of metal over pure silica MCM-41. The catalytic activity and selectivity of supported Pt catalysts for methane conversion to higher alkanes through two-step homologation change regularly with the properties of supports. The catalytic activity increases with the increase of Si/Al ratio and acidity of the support. Moreover, the distribution and reactivity of surface carbonaceous species （CHx） generating from the methane decomposition at first step and comisorbed on the catalysts were characterized by temperature programmed hydrogenating （TPH）. The support effect on total amount of CHx （Cα ＋Cβ ） and the Cα species, which is the main resource of C2＋ hydrocarbon products, is the same as that on the formation of C2＋ products. The high metal dispersion and suitable chemical composition of pure silica MCM-41 could be responsible for the high activity of the Pt catalyst supported on the pure silica MCM-41. Also the formation of electron- deficient Pt particles on MCM-41 exchanged by acidic media may account for their higher catalytic activity.
出处
《高校化学工程学报》
EI
CAS
CSCD
北大核心
2007年第3期417-422,共6页
Journal of Chemical Engineering of Chinese Universities
基金
国家重点基础研究发展规划项目(G20000048090)
