Effects of Acid Sites and Formaldehyde Decomposition on the Catalyst Lifetime for Methanol-to-Olefins over Ca-Modified HZSM-5

IF 11.3 1区化学 Q1 CHEMISTRY, PHYSICAL ACS Catalysis Pub Date : 2024-09-10 DOI:10.1021/acscatal.4c0284210.1021/acscatal.4c02842

Jinsong Luo, Tianci Xiao, Wu Wen, Jun Bao, Chengyuan Liu* and Yang Pan*,

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Abstract

The pursuit for higher light olefin selectivity and extended catalyst lifetime has been a hot topic in the methanol-to-olefins (MTO) process. The incorporation of Ca in HZSM-5 (Ca-modified HZSM-5) could exhibit outstanding catalytic stability and high C3+ olefins yield. In this work, synchrotron radiation photoionization mass spectrometry was applied to study the lifetime enhancement mechanism of Ca-modified HZSM-5. It is interesting to note that the mechanism differs in the cases of different Ca-loading. Under low Ca-loading, the main reason for lifetime enhancement is the modification of acid sites, which limited hydrogen transfer reactions and subsequent coking process. While higher Ca-loading would introduce CaO species over HZSM-5, which showed prominent activity for HCHO elimination. The decomposition of HCHO would suppress the HCHO-mediated aromatic formation pathway during the MTO process, therefore alleviating the coking process. Moreover, the elimination mechanism of HCHO over CaO was investigated using in situ IR measurements. This study provides some additional insights into the role of acid sites and CaO during the Ca-modified HZSM-5 catalyzed MTO process.

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酸性位点和甲醛分解对 Ca 改性 HZSM-5 上甲醇制烯烃催化剂寿命的影响

追求更高的轻质烯烃选择性和延长催化剂寿命一直是甲醇制烯烃（MTO）工艺的热门话题。在 HZSM-5 中加入 Ca（Ca 改性 HZSM-5）可表现出卓越的催化稳定性和高 C3+ 烯烃产率。本研究采用同步辐射光离子化质谱法研究了钙改性 HZSM-5 的寿命增强机制。值得注意的是，在不同的 Ca 负载情况下，机理有所不同。在低 Ca 加载条件下，寿命增强的主要原因是酸性位点的改性，这限制了氢转移反应和随后的结焦过程。而较高的 Ca 负载会在 HZSM-5 上引入 CaO 物种，从而显示出突出的 HCHO 消除活性。HCHO 的分解会抑制 MTO 过程中 HCHO 介导的芳烃形成途径，从而减轻结焦过程。此外，还利用原位红外测量法研究了 HCHO 在 CaO 上的消除机理。这项研究为了解钙改性 HZSM-5 催化 MTO 过程中酸性位点和 CaO 的作用提供了一些新的见解。

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来源期刊

ACS Catalysis CHEMISTRY, PHYSICAL-

CiteScore

20.80

自引率

6.20%

发文量

1253

审稿时长

1.5 months

期刊介绍： ACS Catalysis is an esteemed journal that publishes original research in the fields of heterogeneous catalysis, molecular catalysis, and biocatalysis. It offers broad coverage across diverse areas such as life sciences, organometallics and synthesis, photochemistry and electrochemistry, drug discovery and synthesis, materials science, environmental protection, polymer discovery and synthesis, and energy and fuels. The scope of the journal is to showcase innovative work in various aspects of catalysis. This includes new reactions and novel synthetic approaches utilizing known catalysts, the discovery or modification of new catalysts, elucidation of catalytic mechanisms through cutting-edge investigations, practical enhancements of existing processes, as well as conceptual advances in the field. Contributions to ACS Catalysis can encompass both experimental and theoretical research focused on catalytic molecules, macromolecules, and materials that exhibit catalytic turnover.