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Discrimination of the Synergistic Effect of Different Zinc Active Sites with a Brønsted Acid in Zeolite for Dehydrogenation Cracking of n-Octane and Ethane Dehydroaromatization
Langmuir ( IF 3.7 ) Pub Date : 2024-12-17 , DOI: 10.1021/acs.langmuir.4c03769
Xin Guo, Xiaoqiao Zhang, Guiying Wu, Jianhong Gong, Fang Jin

The synergetic effect of different zinc active sites with a Brønsted acid site (BAS) in Zn-MCM-22 for n-octane dehydrogenation cracking and ethane dehydroaromatization was investigated. Zn-MCM-22 catalysts containing ZnO were prepared via incipient wetness impregnation (IM) using liquid ion grafting, whereas those containing [ZnOx]2+ were prepared via atom-planting (AP) using the gas dechlorination reaction. The synergetic effects of BAS with micropore incorporated [ZnOx]2+ and external surface ZnO species on the dehydrogenation of different molecule size reactants n-octane and ethane were compared. The synergistic effect of ZnO and BAS can improve ethane dehydrogenation through aromatization, whereas [ZnOx]2+ as the introduced Lewis acid site (LAS) can override the bridge Si-OH-Al hydroxyl group BAS to inhibit the generation of benzene–toluene–xylene (BTX) and is more favorable for ethane dehydrogenation. The AP method can effectively regulate the n-octane dehydrogenation cracking product distribution by adjusting the volatilization time of ZnCl2 vapors to regulate the ratio of LAS/BAS in zeolites. The kinetic analysis was used to correlate the roles of the [ZnOx]2+ site and BAS in the dehydrogenation, hydrogen transfer, and cyclization reactions of n-octane and ethane, respectively. Moreover, the hydroxyl group grafted [ZnOx]2+ sites have better activity and stability for higher temperature dehydrogenation.

中文翻译:


分子筛中不同锌活性位点与 Brønsted 酸对正辛烷脱氢裂解和乙烷脱氢芳构化的协同作用的判别



研究了不同锌活性位点与 Zn-MCM-22 中 Brønsted 酸位点 (BAS) 对 n-辛烷脱氢裂化和乙烷脱氢芳构化的协同效应。含有 ZnO 的 Zn-MCM-22 催化剂是使用液离子接枝通过初期湿浸渍 (IM) 制备的,而含有 [ZnOx] 2+ 的催化剂是使用气体脱氯反应通过原子植会 (AP) 制备的。比较了微孔掺入 [ZnOx] 2+ 和外表面 ZnO 物种的 BAS 对不同分子大小反应物 n-辛烷和乙烷脱氢的协同效应。ZnO 和 BAS 的协同作用可以通过芳构化改善乙烷脱氢,而 [ZnOx] 2+ 作为引入的路易斯酸位点 (LAS) 可以覆盖桥 Si-OH-Al 羟基 BAS 以抑制苯-甲苯-二甲苯 (BTX) 的生成,更有利于乙烷脱氢。AP 法通过调节 ZnCl2 蒸气的挥发时间来调节沸石中 LAS/BAS 的比例,从而有效调节辛烷值脱氢裂解产物的分布。动力学分析用于关联 [ZnOx] 2+ 位点和 BAS 分别在 n-辛烷和乙烷的脱氢、氢转移和环化反应中的作用。此外,羟基接枝的 [ZnOx] 2+ 位点对高温脱氢具有更好的活性和稳定性。
更新日期:2024-12-17
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