Pretreatment Effects on the Surface Chemistry of Small Oxygenates on Molybdenum Trioxide
Pretreatment Effects on the Surface Chemistry of Small Oxygenates on Molybdenum Trioxide
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DOI：
10.1021/acscatal.0c01992
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发表时间：
2020-08-07
期刊：
影响因子：
12.9
通讯作者：
Sievers, Carsten
中科院分区：
文献类型：
--
作者：
Najmi, Sean;Rasmussen, Mathew;Sievers, Carsten
了解生物质含氧化合物在金属氧化物上的表面反应对于设计生物质的催化剂具有重要意义。这项工作阐明了不同的预处理对三氧化钼（MoO 3）的影响，以了解表面反应性是如何由表面氧化态控制的。催化剂在氧化、惰性和还原环境中预处理。惰性和还原预处理在催化剂表面上产生氧空位，其充当用于吸附含氧分子的活性位点，还原预处理产生更高密度的这些活性位点。将催化剂暴露于醇溶剂如甲醇也导致类似于惰性预处理的部分还原。预处理后，催化剂暴露于乙醇，乙醛，巴豆醛与随后的表征漫反射红外光谱（DRIFTS），程序升温脱附（TPD），X射线吸收近边光谱（XANES），和X射线光电子能谱（XPS）。密度泛函理论（DFT）也被用来确定吸附构型和能量的乙醇，乙醛，巴豆醛。还原表面被证明对羰基具有更强的亲和力，导致乙醛和乙醇到C-4分子的羟醛缩合的更高活性。在氧化性环境中预处理的催化剂对乙醛的化学吸附和反应完全失活。
Understanding surface reactions of biomass-derived oxygenates on metal oxides is important for designing catalysts for valorization of biomass. This work elucidated the effect of different pretreatments on molybdenum trioxide (MoO3) to understand how surface reactivity is controlled by the surface oxidation state. The catalyst was pretreated in oxidative, inert, and reducing environments. The inert and reducing pretreatments created oxygen vacancies on the catalyst surface that acted as active sites for the adsorption of oxygenated molecules, with the reducing pretreatment yielding a higher density of these active sites. Exposing the catalyst to an alcoholic solvent such as methanol also led to a partial reduction similar to the inert pretreatment. After pretreatment, the catalyst was exposed to ethanol, acetaldehyde, and crotonaldehyde with subsequent characterization by diffuse reflectance infrared spectroscopy (DRIFTS), temperature-programmed desorption (TPD), X-ray absorption near edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) was also used to determine adsorption configurations and energies of ethanol, acetaldehyde, and crotonaldehyde. Reduced surfaces were shown to have a stronger affinity for carbonyls, leading to a higher activity for the aldol condensation of acetaldehyde and ethanol to C-4 molecules. Catalysts pretreated in an oxidative environment were completely inactive toward chemisorption and reaction of acetaldehyde.