Wang Changji, Jiang Feng, Zuo Guangzheng, Liu Bing, Li Hanxu, Liu Xiaohao
College of Earth and Environment, Anhui University of Science and Technology 232001 Huainan China.
Department of Chemical Engineering, School of Chemical and Material Engineering, Jiangnan University Wuxi 214122 China
RSC Adv. 2019 Dec 9;9(69):40618-40627. doi: 10.1039/c9ra08646c. eCollection 2019 Dec 3.
Highly dispersed tungsten species with an isolated tetrahedral WO species structure are substantially beneficial for the metathesis reaction of ethylene and 1-butene to propene. The conventional impregnation method always leads to the formation of inactive crystalline WO thereby notably decreasing the amount of active sites. In this study, we synthesized a highly dispersed W-MCM-41 catalyst using the one-step precipitation method with a Si/W ratio of 30. The prepared catalyst showed excellent catalytic performance with a 1-butene conversion of 92.7% and a propene selectivity of 80.8%. In contrast, the impregnated catalyst with the same W loading as the one-step precipitation method resulted in a much lower 1-butene conversion of 76.5% and propene selectivity of 34.1%. Various characterization techniques including XRD, XPS, ICP-OES, UV-vis DRS, TEM, and Raman spectroscopy were applied to confirm that the one-step precipitation method can efficiently prepare well-dispersed W-MCM-41 catalysts with the desired structure in spite of the fact that the ideal dispersive structure was strongly dependent of the Si/W ratio and stirring time of the reaction mixture of tungstic acid and TEOS. In addition, the introduction of an upstream catalyst onto the W-MCM-41 catalyst could not obviously improve the 1-butene conversion and propene selectivity, which might be due to fast 1-butene isomerization easily occurring on the abundant Si-OH of the W-MCM-41 catalyst. This work provides new insights for the design of metathesis catalysts and reaction processes to efficiently convert ethylene and 1-butene into propene.
具有孤立四面体WO 物种结构的高度分散钨物种对乙烯与1-丁烯复分解生成丙烯的反应极为有利。传统浸渍法总是导致形成无活性的结晶WO，从而显著减少活性位点的数量。在本研究中，我们采用一步沉淀法合成了Si/W比为30的高度分散的W-MCM-41催化剂。制备的催化剂表现出优异的催化性能，1-丁烯转化率为92.7%，丙烯选择性为80.8%。相比之下，与一步沉淀法具有相同钨负载量的浸渍催化剂，其1-丁烯转化率低得多，为76.5%，丙烯选择性为34.1%。采用XRD、XPS、ICP-OES、UV-vis DRS、TEM和拉曼光谱等多种表征技术，证实一步沉淀法能够有效地制备出具有所需结构的高度分散的W-MCM-41催化剂，尽管理想的分散结构强烈依赖于钨酸与TEOS反应混合物的Si/W比和搅拌时间。此外，在W-MCM-41催化剂上引入上游催化剂并不能明显提高1-丁烯转化率和丙烯选择性，这可能是由于在W-MCM-41催化剂丰富的Si-OH上容易发生快速的1-丁烯异构化。这项工作为设计将乙烯和1-丁烯高效转化为丙烯的复分解催化剂和反应过程提供了新的见解。
