关键词: 催化剂, 分子筛, 扩散, 活性位, 异构化, 贵金属

Abstract:

Metal-zeolite bifunctional catalysts have two kinds of active sites, which is suitable for promoting the catalytic efficiency of complex reactions such as alkane isomerization. Based on our understanding of the mechanisms of hydrogenation/dehydrogenation on metal sites and carbon chain isomerization on acid sites, several typical cases in frontier researches and the study strategies were summarized in order to provide fundamental insight for the research and development of novel efficient catalysts for alkane isomerization. Regarding the control of the proximity of bifunctional sites, the spatial distribution control strategies of metals, zeolites and binders are introduced, and it is pointed out that the appropriate distance between the two sites is beneficial to the diffusion of olefin intermediates. For improving the utilization of acid sites, the hierarchically structured zeolites with micro-meso porous structure or short diffusion distance are introduced, and it is pointed out that the enhanced diffusion and mass transfer can help to inhibit the side reaction of olefin cracking. To improve the utilization of metal sites, the highly dispersion method of precious metals is introduced, and the strategy of using light transition metals to replace precious metals is briefly described. In view of the future development, it is necessary to further study the proximity of bifunctional sites in the forming process of industrial catalysts, to improve the utilization of acid sites and metal sites, and to reduce the cost of precious metals in catalysts.

Key words: catalyst, zeolite, diffusion, active site, isomerization, precious metals