Si-Modified Cs/Al₂O₃ for Aldol Condensation of Methyl Acetate with Formaldehyde to Methyl Acrylate by Chemical Liquid Deposition

Abstract

SiO2-modified γ-Al2O3 by chemical liquid deposition (CLD) was developed as a catalyst support for use in the aldol condensation of methyl acetate with formaldehyde to produce methyl acrylate. Cs/Al2O3 and Cs/Si–Al2O3 catalysts synthesized by incipient-wetness impregnation were characterized, and catalytic performance was evaluated. A correlation between structural features and acid–base properties has been established, and the effect of SiO2 deposition was investigated. The amount of strong acid sites was reduced, and the Brønsted acid sites were introduced onto the surface of Al2O3 with the deposition of SiO2. Moreover, interaction of Cs with the Brønsted acid sites generates the surface Si–O–Cs species which served to enhance selectivity to methyl acrylate. Conversion of methyl acetate was increased due to the formation of new basic sites following Cs incorporation. An excess of SiO2 and Cs hampered decomposition of the cesium nitrate, resulting in strong acid site formation and lower product yield. A 10Cs/1.2Si–Al2O3 composition has been established as optimal with a 4.8 times higher product yield in comparison with 10Cs/Al2O3. Lower activity in the case of the 10Cs/1.2Si–Al2O3 catalyst can be associated with carbon deposition during the reaction; activity can be regenerated after heat treatment at 400 °C.

Effect of Carbon Modification on Properties of NiMo/γ-Al2O3 and Its Catalytic Performance in the Hydrogenation of Methyl Acrylate

“…The first weight loss (50–90 °C) corresponds to the desorption of physically adsorbed water in the catalyst. There is a significant weight loss in the temperature range of 290–570 °C, which is related to the combustion of coke. , It was noted that the coke content increased gradually with sucrose addition. For the SA x Ni 10 Mo 10 /γ-Al 2 O 3 catalysts after calcined at 450 °C, as shown in Figure b, it was noted that mass loss at 290–570 °C increased obviously when sucrose addition was above 0.6, indicating more carbon deposition in the catalysts.…”

Preparation of Methyl Acrylate through Catalytic Aldol Condensation over Cs/TS-1 Catalysts

“…21−23 Previous research studies have reported that the Si−O−Cs active sites through the interaction of Cs + with Si−OH groups were proposed as active centers to promote the dispersion of Cs species and catalytic performance. 2,10,23 Ghosh et al also discovered that the Cs + single sites located within channels of β zeolite through ion exchange showed highly efficient catalytic activity for the self-and cross-aldol condensation and that the active centers were proposed to be monovalent Cs + single sites. 24 Supported Cs catalysts are expected as promising candidates; however, active centers of aldol condensation still need in-depth investigation.…”

“…As versatile resin monomers, methyl acrylate (MA) and acrylic acid (AA) are widely used for the production of polymers, rubbers, adhesives, and plastics. − Currently, nearly most of the MA is manufactured industrially from hydrolysis of acrylonitrile and oxidation of propylene (Scheme ). , The hydrolysis of the acrylonitrile process relies on excessive toxic hydrogen cyanide with large amounts of sulfuric acids as raw materials, leading to environmental pollution as well as a large amount of the low-valuable NH 4 HSO 4 , which has been gradually replaced by the two-step oxidation of propylene.…”

“…For the optimized catalyst of 20% VPO-TiO 2 , the acetic acid conversion and (AA+MA) selectivity achieved 29–31 and 85%, respectively . Noteworthily, VPO catalysts are involved more than surface acid–base-catalyzed aldol condensation, which is also applied to the complex oxidation–reduction because of the complicated crystalline phase and structure, resulting in the formation of byproducts and rapid deactivation of catalysts. ,− Many studies on aldol condensation of MA with FA have been conducted over Cs catalysts supported on Al 2 O 3 , SiO 2 , and SBA-15 via simple impregnation methods with excellent catalytic performance. − Previous research studies have reported that the Si–O–Cs active sites through the interaction of Cs + with Si–OH groups were proposed as active centers to promote the dispersion of Cs species and catalytic performance. ,, Ghosh et al also discovered that the Cs + single sites located within channels of β zeolite through ion exchange showed highly efficient catalytic activity for the self- and cross-aldol condensation and that the active centers were proposed to be monovalent Cs + single sites . Supported Cs catalysts are expected as promising candidates; however, active centers of aldol condensation still need in-depth investigation.…”

Acid Promoter-Modified Cs/Al2O3 Catalyst for Methyl Methacrylate Production by Aldol Condensation of Methyl Propionate with Formaldehyde

“…However, it is noticeable that the above catalysts have merely a single function of either a Lewis acidic or alkaline catalyst for aldol condensation, which usually renders it difficult to achieve high yields of the target products, as well. In contrast to conventional single-functional catalysts, polymetallic catalysts with multifunction have recently garnered considerable interest in the context of typical aldol condensation. − In 2022, Yan et al reported a CuMgAlO layered double oxide catalyst and applied it in the preparation of crotonaldehyde by aldol condensation. The selectivity of crotonaldehyde was increased to 80.4% after doping with Cu, which is much higher than that catalyzed by the primary MgAlO oxide.…”