Preparation Of Transition Metal Carbides And Their Catalytic Performance For CO_2 Hydrogenation

CO₂ is not only a major greenhouse gas, but also an abundant C1 resource. Realizing the fixation and chemical conversion of CO₂ is of great significance. In this thesis, WC catalysts were prepared using different carbon sources（C3H6 and CO） by temperature programmed carbonization method, and their effects on the morphology of WC and catalytic performance in the hydrogenation of CO₂ to methanol were investigated. The results showed that the similar catalytic performances were obtained in the presence of both WC catalysts with different morphology. Under the optimal reaction conditions（reaction temperature 240 ℃, pressure 3.0 MPa and GHSV 3600 m L/（h·g））, the selectivity of 61.7% for methanol at CO₂ conversion of 5.6% was obtained after 18 h over the catalyst WC-C4/Si O2 prepared by CO as carbon source and mixed with equal mass of Si O2 inert support.In order to improve the catalytic performance, a series of Cu and metal oxide（La2O3、Ga2O3、Al2O3、Ca O） promoted WC were prepared by mechanical mixing and impregnation method, and their catalytic performances in the hydrogenation of CO₂ to methanol were also studied. When different kinds of metal oxide were introduced by mechanical mixing method, there was a great effect on the catalytic performance of WC. Owing to the mild basicity of Ca O, which improved the properties of adsorption and activation of CO₂, the highest selectivity for methanol was reached. The CO₂ conversion of 8.2% and selectivity for methanol of 69.5% were achieved after 18 h over M-10 Ca O/WC-C4/Si O2 catalyst. Compared to mechanical mixing method, the stronger synergistic effect was obtained when Cu was introduced to WC by impregnation method, which markedly increased the selectivity for methanol in CO₂ hydrogenation. When the introducing amount of Cu promoter was 8%, the selectivity of 75.3% for methanol at CO₂ conversion of 7.1% was obtained when the reaction was carried out for 18 h.WC and Mo₂C catalysts on the support MCM-41 promoted by Cu were prepared by co-impregnation method and their catalytic performance in the hydrogenation of CO₂ to methanol were investigated. Results indicated that their catalytic performance could be adjusted by loading proper amount of WC/Mo₂C and Cu promoter. Both 20Cu20Mo₂C/M41 and 20Cu30WC/M41 catalysts showed excellent catalytic performance, and the 20Cu30WC/M41 catalyst showed higher methanol selectivity in initial reaction period.