Chenxi Feng,Junyang Liu,Kai Zhao,Lei Wang,Zengxi Li,Guoliang Zhang,Chunshan Li
Methyl methacrylate (MMA) synthesis via aldol condensation of methyl propionate with formaldehyde over Cs-based supported catalysts is intensively investigated, while the effect of their pore structures on catalytic performance still lacks in-depth understanding. Herein, series of Cs-Zr/SiO 2 catalysts with different pore structures were prepared for this aldol condensation. The physicochemical characteristics of as-prepared Cs-Zr/SiO 2 catalysts were characterized using physical N 2 adsorption–desorption isotherms and CO 2 -/NH 3 -TPD. In addition, the impact of pore structure on mass transfer, adsorption, and desorption of reactants and products was studied through in situ DRIFTS. The results show that the acid and base site densities elevated with the increasing pore volume. The mass transfer of reactants and products could be promoted with increasing pore size, while their adsorption energies exhibited a volcanic trend. As a result, the Cs-Zr/SiO 2 catalysts having average pore diameter of 12-18 nm and acid-base balance was considered as the optimal candidate for MMA production.
Qi Li,Senlin Deng,Junyang Liu,Tingting Yan,Jinguo Hao,Gang Wang,Guoliang Zhang,Jie Li,Chunshan Li
The dispersion of active sites plays an imperative role in the promotion of catalytic performance on methyl acrylate synthesis via direct vaporous aldol condensation. Herein, a novel PEG-assisted impregnation method was proposed to synthesize Cs/Zr-SiO 2 catalyst with high dispersion of acid and base sites. A series of characterization techniques including NMR, TEM, physical N 2 adsorption isotherms, XRD, XPS, NH 3 -/CO 2 -TPD, and Py-IR were used to investigate the physico-chemical properties of these prepared catalyst series. The introduction of PEG improved the specific surface area, dispersion of active sites, and density of acid and base sites, resulting in superior catalytic performance of Cs/PEG@Zr-SiO 2 by comparison with that of Cs/SiO 2 and Cs/Zr-SiO 2 . The kinetic experiments revealed that the activation energy of aldol condensation was 80.8 kJ/mol over the Cs/PEG@Zr-SiO 2 catalyst. The deactivation behavior derived from carbon deposition was discovered, and the spent catalyst could be regenerated by simple thermal treatment.
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