Unveiling the promotion of Bronsted acid sites in Cs dispersion and consequential Si-O-Cs species formation for methyl acrylate synthesis from methyl acetate and formaldehyde over Cs/Beta zeolite catalyst

With the gradual depletion of petroleum resources and overcapacity of coal industry, the one-step synthesis of methyl acrylate (MA) from the coal-based methyl acetate (Ma) and formaldehyde via aldol condensation, regarded as a supplementary route for the petroleum-based propene selective oxidation, receives significant attention in decades. Herein, a series of Cs/Beta zeolite catalysts were developed for this transformative process using incipient wetness impregnation with varied Cs loading amount and SiO2/Al2O3 ratio. The physicochemical properties of both prepared Cs/Beta zeolite catalyst series and Beta zeolite supports were characterized by using FT-IR, ICP, XRF, physical N-2 adsorption-desorption isotherms, NH3-TPD, Py-IR, P-31-MAS NMR, XRD and XPS, in combination with catalytic evaluation experiments. The effects of Bronsted acid sites, SiO2/Al2O3 ratio and Cs loading on the catalytic performance and catalyst deactivation were systematically investigated. The Bronsted acid sites on Beta zeolite support showed promotional effects on the dispersion of loaded Cs species and formation of (Al-O)-Si-O-Cs groups which were crucial to the improvement of catalytic activity and selectivity. However, the excessive Bronsted acid sites on Cs/Beta or Beta zeolite would lead to the heavy side reactions, including the hydrolysis of Ma and dehydration and further aromatization of methanol (MeOH). As a result, the highest formation rate of 7.23 mmol.g(Cat)(-1).h(-1) for MA could be achieved with a relatively high selectivity of 85% on the optimal 17.5Cs/Beta40 catalyst. While the undesired catalytic deactivation behavior resulting from the accumulation of alkyl-substituted single-ring aromatic species in the micropores of catalyst was found during the reaction by employing FT-IR, GC-MS, TGA and UV-vis analysis, which could be easily regenerated by thermal treatment at 400 degrees C and air atmosphere.