Direct addition of acetic acid to ethylene to form ethyl acetate in the presence of H4SiW12O40/SiO2

The direct addition of acetic acid to ethylene to form ethyl acetate over H4SiW12O40/SiO2 using SiO2 with various surface areas and mesopore sizes was studied. H4SiW12O40/SiO2 was superior in activity to conventional solid acids including H3PO4/SiO2, Nafion-SiO2, WO3-ZrO2, and unsupported H4SiW12O40. While the selectivity for ethyl acetate was more than 98% regardless of the catalyst, the activities were significantly different. Maximum activity was obtained when SiO2 having a high surface area and moderate pore size (ave. 6 nm) was utilized. The temperature-programmed desorption of benzonitrile technique and XRD both confirmed that this catalyst had a large amount of acid sites located on the outermost surface due to the high dispersion of H4SiW12O40. In contrast, H4SiW12O40/SiO2, with SiO2 of very small mesopores (3 nm) showed a very low activity, despite having the largest amount of acid sites located on the outermost surfaces. On this catalyst, diffusion of the reactant and product were slow due to the very small-sized mesopores. This limited diffusion rate results in its low activity.