Surface Acidity Effect of Alumina in a Catalytic 1-Phenylethanol Dehydration Reaction under Excess Water

In the propylene oxide and styrene coproduction (PO/SM) process, styrene is produced by the catalytic dehydration of 1-phenylethanol in the presence of alumina. In addition to hydrocarbon flow, direct steam is supplied to the reactor to regulate the thermal regime and reduce the rate of side reactions and the rate of catalyst deactivation. In this work, the contribution of acid sites of different natures and strengths to the activity of catalysts based on alumina in the dehydration of 1-phenylethanol, which occurs in the presence of excess water in the temperature range of 230-300°C, was assessed. A series of catalysts were prepared using the impregnation method from aqueous solutions of sodium carbonate, ammonium molybdate, ammonium metavanadate and ammonium tungstate. The acidity of the catalysts was studied using low-temperature adsorption of carbon monoxide. The dehydration reaction is not associated with Brønsted acid sites present on the surface of alumina (frequency range of CO absorption bands νCO = 2155-2165 cm–1). In the presence of Lewis acid sites of varying strength on the surface of the catalyst (νCO = 2238–2240, 2203–2210, and 2189–2195 cm–1) in the temperature range up to ~250°С, the contribution to the integral dehydration of the weakest Lewis acid sites (νCO = 2189–2195 cm–1) did not exceed 20%. All transition metals increase the concentration of Lewis acid sites (νCO = 2238–2240, 2203–2210 cm–1), which leads to an increase in the dehydration activity of catalysts toward 1-phenylethanol.