Study Of Ni-Based Catalysts For Substitited Natural Gas(SNG) From Synthetic Gas From Coal

Substitute natural gas (SNG) from synthetic gas from coal consists of coal gasification, shift reaction, purification and methanation of synthetic gas, then using for industrial and civil after pipeline transportation, pressure regulating and gas distribution. Methanation of synthetic gas is the one of the most important steps and the key technology of coal chemical industry technology. In order to obtain Ni-based catalysts with high activity and high stability, supports, promoters, preparation conditions, reaction condition are the important aspects of catalyst research.In this paper, the influence of Al2O3 supports, promoters, preparation conditions, reaction condition on the catalytic behaviors (especially the stability) of nickel-based catalysts was investigated. The catalysts were characterized by means of XRD, TPR, BET and SEM-EDS and so on. Main results from this work are as follows.Among the different crystal phases of Al2O3(γ-Al2O3, α-Al2O3), Ni/γ-Al2O3 showed the higher catalytic activity and stability, for γ-Al2O3 possessed the larger specific area and optimal pore diameter. It is found that the properties of different γ-Al2O3 supports(ZT1, ZT2, ZT3, ZT4) have significant effect on the performance of Ni-based catalysts, the catalyst prepared by ZT1 support (pseudoboehmite calcined at 500℃) possessed the highest catalytic activity and stability, followed by ZT2, ZT3, ZT4. The stable structure of ZT1 during the reaction may be the main reason for its good performance. Calcination temperature on the physical and chemical properties and microstructures of A12O3 and catalytic performance of the Ni/Al2O3 catalysts were was investigated. When calcination temperatures were in the range of 500-800℃, the obtained samples were y-Al2O3, and Ni/y-Al2O3 catalysts showed the highest activity and the best stability.Ni-based catalysts prepared by impregnation, solid-mixing and co-deposition method showed good activity and stability, while catalyst prepared with impregnation-deposition is extremely poor. The catalysts with different Ni loading contents (10%,20%,30%, and 40%) showed the good stability, but the optimal Ni loading content is 20%. It is found that the function of reaction temperature and catalytic activity, higher reaction temperature contributes to increase the catalytic activity, but then it will decrease; the optimum reaction temperature interval is 300-425℃.The addition of promoters (La、Fe、Mo、Zr、 Mg、Ba、K) had a great impact on catalysts. La and Mn improved the conversion of H2 and Zr enhanced the selectivity of CH4. When the reaction condition was 350℃, 0.1 MPa,2400 h-1, and H2/CO 3.0, the optimal combination was 10%Ni, 1%La,1%Zr,1%Mn, A12O3 balance.The addition of La could greatly improve the conversion of H2, and the experiments indicated that the optimal addition method of La was co-impregnation. And when the Ni loading content was 10%, the optimal La content was 1.0%. While the Ni loading content was 20%, the optimal La content was 2.0%.