标题：Methanation of CO2: Impacts of modifying nickel catalysts with variable-valence additives on reaction mechanism
作者：Liang, Chuanfei ;Ye, Zhengmao ;Dong, Dehua ;Zhang, Shu ;Liu, Qing ;Chen, Guozhu ;Li, Cuncheng ;Wang, Yi ;Hu, Xun
作者机构：[Liang, Chuanfei ;Ye, Zhengmao ;Dong, Dehua ;Hu, Xun ] School of Material Science and Engineering, University of Jinan, Jinan; 250022, China;[Liu, Qin 更多
摘要：In this study, in total 16 additives ranging from Na to Zn in the periodic table of elements were added respectively to Ni/Al2O3 catalyst to understand their impacts on the physiochemical properties and reaction behaviors of the catalysts in methanation of CO2. The results showed that the additives, except Sc, Ti, V, Mn, Zr, La and Ce, all led to the enlarged pores and the decreased surface area of the catalysts, especially for Na and K. Na or K reacted with alumina, forming Al(OH)3 phase and leading to re-structure of the catalysts. MnO2 reacted with NiO and formed NiMnO3 structure. The additives also significantly affected the reduction behaviors of nickel oxide and the distribution of the basic sites on surface of the catalysts. V, Cr, Mn, Fe, Co, La and Ce modified catalysts showed good activity for methanation, resulting from that the multiple valences or oxygen vacancies (verified by EPR analysis of the Fe or Ce modified catalyst) in oxide form helped to absorb/activate CO2. The in-situ DRIFTS studies indicated that *CO2, *CO, formate, H2CO*, *CH3OH, hydrogen carbonate and carbonate were important reaction intermediates. The KNiAl catalyst showed strong absorption of carbonate and H2CO* intermediates, negatively affecting their further conversion to form methane. The strong absorption of *CO over CuNiAl also prevented the further conversion of the intermediates to the downstream products. The Cr, Mn, Fe, La and Ce modified catalysts had milder absorption of the crucial formate intermediate, and no strong absorption of *CO or H2CO* intermediates were observed, which were responsible for their high activities for methanation.
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