单层V2O5 / TiO2催化剂上乙醇选择性氧化的氧化还原机理,Journal of Catalysis

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单层V2O5 / TiO2催化剂上乙醇选择性氧化的氧化还原机理
Journal of Catalysis ( IF 6.5 ) Pub Date : 2016-03-16 14:32:20
Vasily V. Kaichev, Yuriy A. Chesalov, Andrey A. Saraev, Alexander Yu. Klyushin, Axel Knop-Gericke, Tamara V. Andrushkevich, Valerii I. Bukhtiyarov

使用傅里叶变换红外光谱和近环境X射线光电子能谱（XPS）在100至_200的温度范围内原位研究了在单层V ₂ O ₅ / TiO ₂催化剂上乙醇选择性氧化为乙醛和乙酸的过程。到300°C。数据通过程序升温反应光谱和动力学测量得到补充。发现在大气压下在低温下乙醛是形成的主要产物，其选择性几乎为100％。在较高温度下，反应向乙酸转移，在200°C下，其选择性达到60％。高于250°C，会选择性氧化成CO和CO ₂成为主导反应。红外光谱表明，在100℃反应期间，催化剂表面上乙醇，乙醇化物和乙醛的非解离吸附分子位于催化剂表面，而在较高温度下，该表面主要被乙酸盐类所覆盖。根据XPS数据，钛阳离子保持在Ti ⁴⁺状态，而V ⁵⁺阳离子在反应条件下发生可逆还原。提出的数据符合这样的假设，即乙醇通过氧化钒催化剂通过涉及表面晶格氧物种的氧化还原机理在氧化还原V ⁿ ⁺位发生选择性氧化。单层V ₂ O上乙醇氧化的反应方案建议使用₅ / TiO ₂催化剂。

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Redox mechanism for selective oxidation of ethanol over monolayer V2O5/TiO2 catalysts

The selective oxidation of ethanol to acetaldehyde and acetic acid over a monolayer V₂O₅/TiO₂ catalyst has been studied in situ using Fourier transform infrared spectroscopy and near-ambient-pressure X-ray photoelectron spectroscopy (XPS) at temperatures ranging from 100 to 300°C. The data were complemented with temperature-programmed reaction spectroscopy and kinetic measurements. It was found that under atmospheric pressure at low temperatures acetaldehyde is the major product formed with the selectivity of almost 100%. At higher temperatures, the reaction shifts toward acetic acid, and at 200°C, its selectivity reaches 60%. Above 250°C, unselective oxidation to CO and CO₂ becomes the dominant reaction. Infrared spectroscopy indicated that during the reaction at 100°C, nondissociatively adsorbed molecules of ethanol, ethoxide species, and adsorbed acetaldehyde are on the catalyst surface, while at higher temperatures the surface is mainly covered with acetate species. According to the XPS data, titanium cations remain in the Ti⁴⁺ state, whereas V⁵⁺ cations undergo reversible reduction under reaction conditions. The presented data agree with the assumption that the selective oxidation of ethanol over vanadium oxide catalysts occurs at the redox V ⁿ ⁺ sites via a redox mechanism involving the surface lattice oxygen species. A reaction scheme for the oxidation of ethanol over monolayer V₂O₅/TiO₂ catalysts is suggested.

更新日期：2016-03-17

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