摘要
以商品SAPO-11分子筛为基础,通过分子筛草酸脱铝预处理、添加粘结剂、载体预吸附氨、改变金属含量、催化剂活化条件及硫化处理等设计制备了一系列催化剂。在连续流动的反应装置上,以正庚烷为原料的临氢异构化反应评价结果验证了金属与酸功能匹配和相互作用的重要性。提出烷烃异构化需要适宜的酸中心密度,较高的金属分散度,以及较短的金属中心与酸中心距离等有利于提高异构化选择性的观点。在此基础上,对硅、铝、磷的比例和分子筛晶化条件进行调控,合成出酸密度和晶粒均较小的SAPO-11分子筛,获得了金属分散度高、金属中心与酸中心作用密切的Pt/SAPO-11催化剂。临氢异构反应评价结果表明,该催化剂具有较高的异构化选择性,正庚烷转化高达70%时异构化选择性仍可达到90%以上,同时具有优异的稳定性与再生性能,显示出良好的工业应用前景。金属的高分散度、金属与酸中心之间的强相互作用和分子筛择形作用是该催化剂异构化选择性高的根本原因,并推测其作用机制可能与传统的双功能作用机理不同。
A series of hydroisomerization catalysts, using commercially available SAPO-11, were designed and prepared concerning the modification of the original SAPO-11 by oxalic acid leaching, addition of oxides as binder, pre-adsorption of NH_3 on support, and variation of metal loading, as well as catalyst activation and pre-sulfiding. Evaluations of the catalyst samples were performed in a fixed-bed reactor under continuous flow conditions by the hydroisomerization of n-heptane. And the obtained data verified the importance of the matching between metal and acid sites as well as their interaction. So it had been proposed that the hydroisomerization of paraffin need suitable acid density, high dispersion of metal and close proximity between metal and acid sites. Based on this assumption, small crystal SAPO-11 with lower acid density had been synthesized by controlling both the ratios of Si, Al, P and the crystallization conditions. The Pt/SAPO-11 catalyst obtained manifest high Pt dispersion and improved intimacy between Pt and acid sites. Accordingly, the novel Pt/SAPO-11 catalyst has pretty high isomerization activity, and the selectivity was above 90% even at a high conversion of 70%. The catalyst also had good stability and regeneration property, indicating great commercial potentials. The high isomerization selectivity of the new catalyst results from high metal dispersion, strong interaction between metal and acid sites, and shape-selectivity of SAPO-11 molecular sieve. It has been suggested that the classical bifunctional mechanism can not be applied to the new catalysis system.
出处
《石油化工高等学校学报》
CAS
2004年第2期47-53,67,共8页
Journal of Petrochemical Universities
