Investigating the Support Effect for Catalytic Elimination of Methyl Mercaptan: Role of Hydroxyl Groups over Cr-based Ca
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Investigating the Support Effect for Catalytic Elimination of Methyl Mercaptan: Role of Hydroxyl Groups over Cr‑based Catalysts Yutong Zhao1 · Dedong He2 · Dingkai Chen1 · Jichang Lu1 · Jie Yu1 · Jiangping Liu1 · Xiaohua Cao1 · Caiyun Han1 · Yongming Luo1 Received: 2 February 2020 / Accepted: 10 March 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The support effect for HZSM-5 and Al2O3-supported chromium (Cr) catalysts on the catalytic decomposition of methyl mercaptan (CH3SH) is investigated. Characterization results reveal that the distribution, reducibility, oxidation states and coordination environment of chromium species mightily depend on the nature of support. Al2O3 support is covered by surface hydroxyl groups, thus conducing to the formation of monochromatic Cr(VI) species with tetrahedral coordination, which remarkably increases the reducibility and dispersion of chromium species. In contrast, plenty of inactive α-Cr2O3 particles are formed on the surface of Cr/HZSM-5 catalyst due to the lack of adequate hydroxyl sites. Furthermore, a positive correlation is established between the content of active Cr(VI) species and the number of surface hydroxyl groups over Cr/Al2O3 catalysts. Reactivity data suggest that the addition of chromium species can observably enhance the conversion of CH3SH for both two supports. More importantly, 5% Cr/Al2O3 catalyst features the superior catalytic performance at 400 °C (100% conversion). The promoting effect can be attributed to the high-content hydroxyl groups on A l2O3, which are proven to stabilize monochromatic Cr(VI) species. This result also provides evidence for the active sites of CH3SH decomposition reaction. Graphic Abstract
Keywords Sulfur-containing VOC · CH3SH elimination · Support effect · Active sites · Hydroxyl groups · Cr doping Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03178-z) contains supplementary material, which is available to authorized users. * Dedong He [email protected] * Yongming Luo [email protected] Extended author information available on the last page of the article
1 Introduction Recently, environmental pollution from VOCs (volatile organic compounds) has become an important issue, which has gained sustained attention in the field of environmental protection [1]. As typical sulfur-containing VOCs, methyl mercaptan (CH3SH) with subtle olfactory threshold and
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high levels of toxicity generally forms in the processes of petroleum refining and environmental pollution control activities [2, 3]. Great trials have been dedicated to exploiting efficient routes for eliminating C H3SH. Among these methods, catalytic conversion has been extensively investigated in the past years because of many advantages such as high degradation efficiency and less harmful compounds formation [4]. The process of CH3SH catalytic conversion (M2TH) can be described as the equation: CH3SH ⇌ CH3SCH3 + H2S → CH4 + H2S. D
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