摘要
用元素分析、热脱附和H_2还原脱附等方法分析了Pd/γ-Al_2O_3、Pd/MgO、Pd/TiO_2溶剂化金属原子浸渍(SMAI)催化剂的表面组成和孔结构。结果表明Pd颗粒表面覆盖着一些有机碎片,这些碎片主要由C_1和少量C_2,C_3及C_3以上物种组成。SMAI催化剂的比表面积均高于相应纯载体的比表面积。而平均孔径均小于后者,CO_2甲烷化反应中,SMAI催化剂的活性均高于相应的普通浸渍法(CI)催化剂,而活化能却低于后者。在SMAI催化剂上CO_2甲烷化反应机理与Solymosi机理相同。
The surface compositions of Pd/rrrrrrrrrrrrrrr-Al2O3, Pd/MgO, Pd/TiO2 catalysts prepared by the Solvated Metal Atom Impregnation(SMAI) technique were analysed by elemental analysis, thermal desorption and H2 reduction desorption methods. The results show that the surfaces of Pd particles are covered by some carbonaceous fragments. These fragments are primarily composed of C1 species. There are also small amounts of some C2 and C3 species on the surface. The carbonaceous fragments serve to halt the growth of Pd particles and provide thermal stability to the Pd powders. Therefore the SMAI Pd catalysts have very small particle sizes and are characterized by very high dispersion.
The pore structure measurements show that the specific areas of SMAI catalysts are all larger than and their average pore diameters are smaller than those of the pure supports. In contrast, the specific areas of conventional impregnation (CI) catalysts are all smaller than and their average pore diameters are approximately the same as those of the pure supports.
The experimental results indicate that the catalytic activities of all SMAI Pd catalysts are greater than those of the corresponding CI Pd catalysts while the activation energies of SMAI catalysts are lower than those of CI catalysts in the CO2 methanation reaction. This difference between SMAI and
CI catalysts is attributed to the larger specific areas and higher dispersion of the SMAI catalysts.
The kinetic experimental data also show that the reaction order for the two kinds of catalysts are similar(CO2, 0. 9-1.1; H2, 0. 35-0. 45). The mechanism of CO2methanation on SMAI Pd catalysts is believed to be the same as that proposed by Solymosi.
出处
《分子催化》
EI
CAS
CSCD
1992年第2期120-127,共8页
Journal of Molecular Catalysis(China)
关键词
催化剂
金属蒸气合成
负载型
钯
Metal vapor synthesis, Pd catalysts, CO2 methanation reaction.
