Roles of ethanol and Si–OH in the aldol condensation of ethyl acetate over a Cs/SBA-15 catalyst,Reaction Chemistry & Engineering

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Roles of ethanol and Si–OH in the aldol condensation of ethyl acetate over a Cs/SBA-15 catalyst
Reaction Chemistry & Engineering ( IF 3.4 ) Pub Date : 2021-3-25 , DOI: 10.1039/d1re00020a
Xiang Tian _{1,

2,

3,

4} , Hengshui Tian _{1,

2,

3,

4}

Affiliation

Alkali and alkaline earth metal-supported mesoporous SBA-15 catalysts via impregnation were characterized and tested in the vapor phase aldol condensation of ethyl acetate and formaldehyde in ethanol to synthesize ethyl acrylate (EA) and acrylic acid (AA). Ethanol dehydrogenation exerts a negative effect on the main reaction, and Lewis acid sites donated by either gust or support prefer forming acetaldehyde to compete for formaldehyde with the main aldol condensation. Combined with the good dispersion of active sites and acceptable diffusion conditions, the pairs of weak acidity and weak-medium basicity enable 5Cs/SBA-15 to achieve the highest yield of 63% for acrylic products based on formaldehyde. Aliphatics are confirmed as the main compositions of coke depositions to lead the deactivation of cesium-modified catalysts whose activity could be regenerated completely by calcination. According to experimental and DFT results, Si–OH assisting Si–O–Cs plays the role of accelerating the enol structure formation by decreasing the activation barrier, and performs the necessary favor for the cleavage of ethanol hydroxyl by reducing the electronegativity of ethanol oxygen. The predominant pathway for producing AA is also confirmed through EA hydrolysis, and the relatively strong adsorption energy of EA should account for the high AA/EA molar ratio.

中文翻译：

乙醇和Si-OH在乙酸乙酯在Cs / SBA-15催化剂上的醛醇缩合中的作用

碱金属和碱土金属负载的介孔SBA-15催化剂通过在乙酸乙酯和甲醛在乙醇中的汽相醇醛缩合反应中，表征了其浸渍性能，合成了丙烯酸乙酯（EA）和丙烯酸（AA）。乙醇脱氢对主要反应产生不利影响，阵风或载体提供的路易斯酸位点更倾向于形成乙醛，与主要的醛醇缩合竞争甲醛。结合活性位的良好分散性和可接受的扩散条件，弱酸度和弱中性碱对使5Cs / SBA-15可以实现基于甲醛的丙烯酸类产品的最高收率63％。脂肪族化合物已被证实是焦炭沉积的主要成分，可导致铯改性催化剂失活，而铯改性催化剂的活性可通过煅烧完全再生。根据实验和DFT结果，Si-OH辅助Si-O-Cs通过降低活化能垒来促进烯醇结构形成，并通过降低乙醇氧的电负性来裂解乙醇羟基。EA水解也证实了生产AA的主要途径，而EA相对较强的吸附能应能说明高的AA / EA摩尔比。

更新日期：2021-04-09

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