Supported Molybdenum Oxides for the Aldol Condensation Reaction of Acetaldehyde
Supported Molybdenum Oxides for the Aldol Condensation Reaction of Acetaldehyde
复制标题
DOI：
10.1016/j.jcat.2022.03.002
复制
发表时间：
2022-03
影响因子：
7.3
通讯作者：
M. Rasmussen;Sean Najmi;Giada Innocenti;A. Medford;Carsten Sievers;J. Will Medlin
中科院分区：
文献类型：
--
作者：
M. Rasmussen;Sean Najmi;Giada Innocenti;A. Medford;Carsten Sievers;J. Will Medlin
（反）醛醇缩合反应是生物质衍生化合物升级为燃料和有价值的特种化学品的重要化学转化。在本研究中，我们发现负载型氧化钼（MoOx）催化剂在稳态反应器条件下对乙醛醛缩合为巴豆醛具有活性和选择性。通过对吸附吡啶的透射电子显微镜（TEM）、紫外-可见（UV-VIS）漫反射光谱、傅里叶变换红外（FTIR）光谱以及稳态反应器测试，我们确定了高度分散的mooxa与γ- al2o3载体有很强的相互作用，从而在低重量负载下产生最佳的催化剂性能。相反，负载在sio2上的MoOxparticles与载体的相互作用较弱，导致Mo负载与醛醇缩聚活性之间呈单调关系。Lewis酸位点密度和强度是预测所有样品中醛醇缩合活性的重要参数。弱酸位点的浓度与醛缩活性的相关性很差，很可能是因为这些位点太弱，无法激活乙醛进行反应。中酸和强酸位点与醇缩合活性均有良好的相关性。x射线吸收近边结构（XANES）和乙醛程序升温解吸（TPD）结果表明，部分还原的moox对醛醇缩合更有活性，但还原或氧化环境下的预处理对稳态催化活性没有显著影响。通过程序升温氧化（TPO）和热重分析（TGA）对废催化剂样品的表征表明，在反应过程中，具有高密度强酸位点的催化剂倾向于在表面形成更多的碳质沉积物。
The (retro-)aldol condensation reaction is an important chemical transformation in the upgrading of biomass-derived compounds into fuels and valuable specialty chemicals. In this study, we found that supported molybdenum oxide (MoOx) catalysts were active and selective for the aldol condensation of acetaldehyde to crotonaldehyde under steady-state reactor conditions. Through a combination of transmission electron microscopy (TEM), ultraviolet–visible (UV–VIS) diffuse reflectance spectroscopy, Fourier transform infrared (FTIR) spectroscopy of adsorbed pyridine, and steady-state reactor testing, we determined that highly dispersed MoOxhas a strong interaction with a γ-Al2O3support resulting in optimal catalyst performance at low weight loadings. In contrast, MoOxparticles supported on SiO2have a weaker interaction with the support, resulting in a monotonic relationship between Mo loading and aldol condensation activity. The Lewis acid site density and strength are important parameters for predicting aldol condensation activity across all samples. The concentration of weak acid sites had a poor correlation with aldol condensation activity, most likely because these sites are too weak to activate acetaldehyde for the reaction. Medium and strong acid sites both had good correlations to aldol condensation activity. Results from X-ray absorption near edge structure (XANES) and acetaldehyde temperature programmed desorption (TPD) indicated that partially reduced MoOxwas more active for aldol condensation, but pretreatment in reducing or oxidizing environments had no significant effect on steady-state catalytic activity. Characterization of spent catalyst samples through temperature programmed oxidation (TPO) and thermogravimetric analysis (TGA) revealed that catalysts with high densities of strong acid sites tended to form more carbonaceous deposits on the surface over the course of the reaction.