Ethanol dehydration over WO3/TiO2 catalysts using titania derived from sol-gel and solvothermal methods with palladium modification

Abstract

In this research, the characteristics and catalytic activity of WO3/TiO2 prepared by sol-gel and solvothermal and their metal modified were investigated. The research was divided into two parts. In the first part, the catalyst performance of WO3/TiO2 catalysts using titania derived from sol-gel and solvothermal methods over ethanol dehydration reaction was examined. The results showed that the different preparation methods essentially altered the physicochemical properties of TiO2 supports. It revealed that the titania derived from solvothermal method denoted as TiO2-SV exhibited higher surface area and pore volume, and larger amounts acid sites than the one obtained from sol-gel method (TiO2-SG). As a result, the different characteristics of support catalyst seemingly influenced the catalytic properties of WO3/TiO2 catalysts. It showed that the highest ethanol conversion (ca. 88%) at 400oC was achieved by the WO3/TiO2-SV catalysts due to its high acidity. Furthermore, WO3/TiO2-SV catalyst is promising to convert ethanol into ethylene and diethyl ether, having the highest ethylene yield of ca. 77% at 400°C and highest diethyl ether yield of ca. 26% at 250°C. These can be attributed to proper pore structure, acidity and distribution of tungsten. In the second part, the Pd modification and supporting effect of WO3/TiO2 catalysts on catalytic ethanol dehydration to ethylene and diethyl ether were investigated. The catalyst characterization and activity examination results indicated that the different sequence during impregnation influenced the physicochemical properties and catalyst activity. The Pd incorporated into catalysts enhanced the ethanol conversion depending on the sequence of impregnation. The diethyl ether is the main product at low temperature, whereas ethylene is the main product at high temperature. At low temperature (ca. 200 to 300oC), the Pd incorporated over W/TiO2 catalyst resulted in an increasing of diethyl ether yield. It is worth noting that the ethanol conversion increased by palladium modification, while diethyl ether selectivity did not change. This can be attributed to the higher amount of weak acids sites present after Pd modification into catalyst. Among the catalysts, the PdW/TiO2 catalyst (co-impregnation) accomplished the highest diethyl ether yield of 41.4% at 300oC. At high temperature (ca. 350 to 400oC), the W/Pd/TiO2 catalyst (with sequential impregnation of Pd on TiO2 followed by W) achieved the highest ethylene yield of 68.1% at 400oC. Thus, the modification of Pd onto W/TiO2 upon different sequence of Pd and W impregnation improved diethyl ether and ethylene yield in catalytic ethanol dehydration.