摘要
采用脉冲微反技术研究了添加CeO2 和Co3 O4助剂对镍基催化剂上CH4积碳和CO2 消碳性能的影响 ,并用BET ,TGA ,XPS及CO2 TPSR等技术对催化剂进行了表征 .结果表明 ,添加CeO2 可以提高活性原子Ni0 中d电子的密度 ;Ni0 原子中d电子密度的增加在一定程度上抑制了CH4分子中C H键σ电子向d轨道的迁移 ,降低了CH4裂解积碳性能 ;同时加强了Ni0原子d轨道向CO2 空反键π轨道的电子迁移 ,促进了CO2 分子的活化 ,提高了CO2 的消碳活性 .助剂Co3 O4的添加则促进CH4的裂解积碳 ,抑制了CO2 的消碳 .分析表明 ,活性金属与半导体助剂之间存在的金属 半导体相互作用是影响这种机制的主要因素 .
The influence of the addition of CeO 2 or Co 3O 4 promoter on carbon deposition by CH 4 and carbon elimination by CO 2 over nickel based catalysts was studied by using pulse reaction as well as BET, TGA, XPS, H 2 chemisorption and CO 2 TPSR techniques. The addition of n type semiconductor CeO 2 decreased carbon deposition activity of CH 4 and increased carbon elimination ability of CO 2. However, the addition of Co 3O 4 improved carbon deposition by CH 4 and resisted carbon elimination by CO 2. Compared with Ni/Al 2O 3 catalyst, the modified catalysts Ni/CeO 2 Al 2O 3 and Ni/Co 3O 4 Al 2O 3 show no change in specific surface area and pore volume. Thereby, it should be considered that there is no any relation between the carbon deposition or carbon elimination and the specific surface area or the pore volume of the catalysts. Also, the changes in particle size and metallic surface area by the adding of metal additives were not remarkable compared with Ni/Al 2O 3 catalyst. There is an interaction between active metal Ni and semiconductor oxide CeO 2 and the addition of CeO 2 can increase the d electron density of active atom Ni, which would inhibit the migration of C H σ electron from CH 4 molecule to d orbital of Ni atom, thus decreasing the amount of CH 4 adsorbed on Ni 0 sites and the extent of carbon deposition. On the contrary, in the case of CO 2, the electron rich character of Ni sites, which is strengthened by the addition of n type semiconductor CeO 2, is beneficial to CO 2 adsorption, thus leading to an enhancement of carbon elimination. Metal semiconductor interaction is the most important factor for the above phenomenon.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2002年第6期517-520,共4页
基金
国家重点基础研究发展规划资助项目 (G19990 2 2 40 1)
