Conversion of ethanol over transition metal oxide catalysts: Effect of tungsta addition on catalytic behaviour of titania and zirconia

• TiO2 and ZrO2: medium Lewis acidity, activity, selectivity in ethanol conversion.
• WO3 introduces strong Brønsted acid sites on both TiO2 and ZrO2 supports.
• WO3/TiO2 and WO3/ZrO2 are very active and selective to ethylene and diethyl ether.
• WO3/TiO2 performs better than WO3/ZrO2.
• Spent WO3/ZrO2 strongly reduced, spent WO3/TiO2 weakly reduced.

Ethanol dehydration was investigated at atmospheric pressure with 1.43 h−1 WHSV in nitrogen, in the temperature range 423–773 K over titania and zirconia, as such and modified by addition of WO3. As for comparison, data on other WO3-free and WO3-containing catalysts are also discussed: a strong Lewis acid (alumina), a covalent oxide (silica) and a basic material (calcined hydrotalcite). The catalysts were characterized using FT-IR of adsorbed pyridine and of wolframate species, and by UV–vis spectroscopy. The results presented here show that WO3/ZrO2 and WO3/TiO2 are excellent catalysts for ethanol dehydration. Their performances may compete with those of zeolites and alumina for conversion to diethyl ether and to ethylene. The addition of WO3 to both ZrO2 and TiO2 introduces strong Brønsted acid sites that are supposed to represent the active sites in the reaction, but also inhibits the formation of byproducts, i.e. acetaldehyde and higher hydrocarbons. This is attributed to the poisoning of basic sites and of reducible surface Ti and Zr centres, respectively.

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