Vapor phase butanal self-condensation over unsupported and supported alkaline earth metal oxides

• Published in: Journal of catalysis 2012-02, Vol.286, p.248-259
• Main Authors: Shen, Wenqin, Tompsett, Geoffrey A., Xing, Rong, Curtis Conner, W., Huber, George W.
• Format: Article
• Language: English
• Subjects: Acid/base bifunctional catalysts; alkaline earth metals; Alkalinity; Catalysis; catalysts; catalytic activity; Chemistry; CO2 and NH3-TPD; Condensation; esterification; Exact sciences and technology; Gases; General and physical chemistry; Heavy metals; hydrolysis; magnesium oxide; Oxidation; poisoning; Reaction network; silica; Supported alkaline earth metal oxides; temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TPD-DRIFTS; Vapor phase butanal condensation; vapors
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2011.11.009

Vapor phase butanal condensation was studied over well-characterized solid base catalyst MgO, and silica supported MgO, SrO and MgOSrO and MgO/HY in a fixed-bed flow reactor. The silica supported MgO, SrO and MgOSrO and MgO/HY had almost a five times higher activity and a higher stability compared to the unsupported MgO indicating that both acid and base sites are needed to achieve good catalytic performance. The reaction network for butanal vapor phase condensation has been proposed, and the catalyst activation and deactivation mechanisms were studied. [Display omitted] ► Silica supported MgO, SrO and MgOSrO and MgO/HY had almost five times higher activity and higher stability compared to the unsupported MgO at 300°C. ► Acid/base bifunctionality and week surface bonding of butanoic acid are required for the improved catalyst for butanal vapor phase condensation. ► Butanoic acid, a reaction intermediate, was the main cause of supported catalyst deactivation at the low reaction temperature. ► A reaction network for butanal vapor phase condensation has been proposed. Vapor phase butanal condensation was studied over well-characterized MgO, MgO/SiO2, SrO/SiO2, MgOSrO/SiO2 and MgO/HY in a fixed-bed flow reactor. CO2-TPD showed that the base strength and the number of basic sites decreased when the alkaline earth metal oxides were supported on silica. NH3-TPD illustrated that new acid sites were generated when the alkaline metal oxides were supported on silica. The primary product for all catalysts was 2-ethyl-2-hexenal (EHEA) produced by aldol condensation of butanal. Side reactions produced several other products including butanoic acid, heptanone, 2-ethyl-2-hexenol, butanoic acid 2-ethyl-2-hexenol ester and 2,4,-diethyl-2-,4-octandienel by reactions including the Tishchenko cross esterification reactions, double aldol addition, ester hydrolysis, ketonization, cyclization and dehydration. As compared to the unsupported MgO, the silica supported MgO, SrO and MgOSrO and MgO/HY exhibited an almost five times higher activity, a higher stability and an improved selectivity. This indicates that both acid and base sites are needed to achieve good catalytic performance for gas phase aldol condensation reactions. Catalyst activation and deactivation mechanisms were studied by butanal-TPD-DRIFTS and butanoic acid TPD-TGA. At temperatures below 300°C, all catalysts deactivated due to poisoning by the butanoic acid, which was produced as a by-product. The weak bonding of