Experimental and Theoretical Study for Vapor Phase Aldol Condensation of Methyl Acetate and Formaldehyde over Alkali Metal Oxides Supported on SBA-15

Abstract

Alkali metal oxides supported on SBA-15, M/ SBA-15 (M = Li, Na, K, Rb, and Cs), prepared by the impregnation method were characterized and tested for the aldol condensation of methyl acetate and formaldehyde to methyl acrylate (MA). M/SBA-15 catalysts are active for the formation of MA while the support is inert. The supported alkali metals react with hydroxyl groups on SBA-15 by replacing the H atoms and generate weak and medium basic sites. The latter plays an important role in promoting the reaction. Coke formation results in deactivation of Cs/SBA-15, and the deactivated catalyst can be regenerated by burning off the coke. Two possible reaction pathways for the formation of MA were explored using quantum calculations. The predicated activity for M/SBA-15 is consistent with the experimental observations. A pathway with adsorbed enol molecule as an intermediate was suggested to be predominant for the formation of MA.

Fe-Modified Cs–P/γ-Al2O3 Catalyst for Synthesis of Methyl Methacrylate from Methyl Propionate and Formaldehyde

“…19−22 Alkali metal catalysts supported on silica or SBA-15 were studied for aldol condensation and their catalytic activity is increased as the order of basicity Li < Na < K < Cs. 23,24 A similar study was also conducted by Ai using the cesium based catalysts, which showed higher activity than any other metal-based catalysts. 25,26 Through in-depth investigation of condensation of MP with FA, Ai discovered that acid sites were beneficial to improve the selectivity, whereas the base sites were good for increasing conversion.…”

“…As described before, Cs-based catalysts performed excellent catalytic activity, and P could be used as the good support stabilizer. 23,24 Nevertheless, this optimized catalyst did not perform better in the reaction between MP and FA because of the improper or unbalanced acid−base properties.…”

“…Acid and base catalysts can be applied for the vapor-phase aldol condensation reaction. − The acid catalyst usually derives from acidic oxides, including phosphorus oxides, vanadium oxides, niobium oxides, and zirconium dioxides. , The number and strength of acid sites are important in aldol condensation; therefore, acid properties have been modified through various methods such as optimizing the atomic ratio of metals or introducing promoters. , Ai found that the catalyst acidity and surface area could be enhanced effectively through the proper combination of V–Ti or V–P binary metal oxides, resulting in the improvement of the catalytic performance. , Hu et al reported that the V–P–O/SBA-15 catalyst exhibits extraordinary catalytic performance due to a large number of acid sites . Base catalysts are usually composed of alkali metal oxides or alkaline earth metal oxides. − Alkali metal catalysts supported on silica or SBA-15 were studied for aldol condensation and their catalytic activity is increased as the order of basicity Li < Na < K < Cs. , A similar study was also conducted by Ai using the cesium based catalysts, which showed higher activity than any other metal-based catalysts. , …”

Synthesis of Nano‐Cr/Mn Composite Metal Oxides‐SBA‐15 Material and Its Catalytic Performance in Aerobic Oxidations of Benzyl Alcohols

“…[23][24][25][26] The mesoporous composite metal oxides-SBA-15 materials have high surface area, ordered mesopores, and redox catalytic sites, have attracted extensive research attention as effective and low cost catalysts in heterogeneous catalysis. [27][28][29][30][31] Because of the special structure and their potential catalytic activities they exhibit, these compounds have distinguished themselves as catalysts of profound chemical significance. Therefore, preparing these ordered mesoporous materials and investigating their catalytic performance in organic synthesis has attracted considerable attention.…”

“…However, the chemical inertness of SBA‐15, which is mainly composed of silicon dioxide, greatly limits its application in chemical engineering, especially in heterogeneous catalysis [23–26] . The mesoporous composite metal oxides‐SBA‐15 materials have high surface area, ordered mesopores, and redox catalytic sites, have attracted extensive research attention as effective and low cost catalysts in heterogeneous catalysis [27–31] . Because of the special structure and their potential catalytic activities they exhibit, these compounds have distinguished themselves as catalysts of profound chemical significance.…”