Dealuminated H−Y Zeolites:  Influence of the Number and Type of Acid Sites on the Catalytic Activity for Isopropanol Dehydration

The effect of the number and type of acid sites of H−Y catalysts dealuminated by different techniques on the dehydration of 2-propanol has been studied in this work. The increase in the number of acid sites generally increases the activity for the formation of both main products, propene and diisopropyl ether. The presence of different types of extraframework phases generated by steaming or treatment by SiCl4 or by (NH4)2SiF6 treatment affects the activity and selectivity in different ways. The yield of propene is always higher than that of ether but shows a minimum at 95 °C in the catalysts with few acid sites and Si−Al amorphous phases formed by dealumination with SiCl4. Highly crystalline catalysts with relatively high acidity (parent or dealuminated by (NH4)2SiF6 or steaming/EDTA) give propene yields higher than ether's only at temperatures higher than 95 °C. The presence of extraframework Al generated by relatively low-temperature steaming reduces the catalyst activity for both products. A statistical analysis of the turnover frequency at different temperatures showed that all acid sites of the crystalline zeolitic phase participate in the formation of both products, while the catalytic sites of the amorphous phase formed by SiCl4 contribute at relatively low temperatures with propene as the main product. A common compensation effect for the formation of both products exists for all the tested crystalline dealuminated H−Y catalysts.