Ethylene epoxidation on Ag catalysts supported on non-porous, microporous and mesoporous silicates

The ethylene epoxidation activity of Ag catalysts supported on non-porous SiO2, microporous silicalite zeolite and mesoporous MCM-41 and HMS silicates was investigated in the present study in comparison to conventional low surface area alpha-A1(2)O(3) based catalysts. The MCM-41 and HMS based catalysts exhibited similar ethylene conversion activity and ethylene oxide (EO) selectivity with the SiO2 and alpha-Al2O3 based catalysts at relatively lower temperatures (up to similar to 230 degrees C, whereas their activity and selectivity decreased significantly at higher temperatures (>= 300 degrees C. The silicalite based catalyst was highly active for a wide temperature range, similar to the SiO2 and alpha-Al2O3 based catalysts, but it was the less selective amongst all catalysts tested. High loadings of Ag particles (up to ca. 40 wt.%) with medium crystallites size (similar to 20-55 nm) could be achieved on the mesoporous materials resulting in very active epoxidation catalysts. The HMS-type silicate with the 3D network of wormhole-like framework mesopores (with average diameter of similar to 3.5 nm), in combination with a high-textural (interparticle) porosity, appeared to be the most promising mesoporous support. (C) 2007 Elsevier B.V. All rights reserved.