摘要
采用沉淀-沉积法制备出w(Co)=10%、15%、20%和25%的Co/TiO_2催化剂,并用于催化CO_2甲烷化反应。通过XRD、TEM、N_2吸附-脱附、H_2程序升温还原(H_2-TPR)和CO_2程序升温脱附(CO_2-TPD)对催化剂进行了表征与测试。结果表明,Co的负载影响了催化剂中Co3O4晶粒尺寸、比表面积、孔径以及催化剂的还原性能,且Co物种与TiO_2载体发生了强相互作用。其中,w(Co)=20%的Co/TiO_2催化剂中Co颗粒平均尺寸约为8nm,比表面积及孔径分别为40.9 m2/g和6.96 nm,且Co分散度达10.1%,从而更有利于CO_2甲烷化反应。此外,w(Co)=20%的Co/TiO_2催化剂表面具有最大的中强碱位量(28μmol/g),从而可活化更多的CO_2。活性测试结果表明,当反应温度为400℃、压力0.5 MPa、原料气空速3 600 m L/(g·h)、V(H_2)/V(CO_2)=4时,w(Co)=20%的Co/TiO_2催化剂的活性最好,其CO_2转化率和CH_4选择性可分别达到69.9%和98.3%,且在20 h内保持稳定。
A series of Co/TiO_2 catalysts with different Co loadings amounts[w( Co) = 10%,15%,20% and25% ]were prepared by deposition-precipitation method. The catalytic performances for the CO_2 methanation were investigated. These catalysts were characterized by XRD,TEM,N2 adsorption-desorption,temperature programmed reduction of hydrogen( H2-TPR),and temperature programmed desorption of carbon dioxide( CO_2-TPD). The results showed the Co loading amount could affect the crystallite size of Co_3O_4,the BET surface area and reducing properties of catalysts,and a strong interaction was observed between Co species and TiO_2. The Co/TiO_2 catalyst with 20% Co loading amount exhibited a smaller Co particle size of 8 nm and a good Co dispersion of 10. 1%,and the BET surface area and pore size were 40. 9 m2/g and 6. 96 nm,respectively,which would favor the CO_2 methanation. In addition,a maximum medium basicity of 28 μmol/g was observed on the Co/TiO_2 catalyst with 20% Co loading amount,indicating more CO_2 molecules were activated on the catalyst surface. The activity test indicated that the optimal catalytic performance was obtained over Co/TiO_2 catalyst with 20% Co loading amount showed the best catalytic performance and kept stable in 20 h,under the conditions of 400 ℃,0. 5 MPa,a gaseous hourly space velocity of 3 600 m L/( g·h) and V( H2)/V( CO_2) =4,and the CO_2 conversion and methane selectivity were 69. 9% and 98. 3%,respectively.
引文
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