Alcohol dehydration offers a pathway for upgrading biomass-derived short-chain alcohols into alkenes, which are important building blocks in the chemical industry. Bulk oxides with Lewis acid-base pairs, such as TiO2, have been widely used for this process due to their high efficiency and low cost. In this study, we aim to investigate the mechanistic details of alcohol reactions on anatase TiO2catalysts using in-situ titration experiments, as well as kinetic and spectroscopic methods. Our findings show that the reaction of 2-propanol on anatase TiO2 leads to the formation of propene and acetone via parallel dehydration and dehydrogenation pathways. These two reactions occur on acidic sites with distinct acid strengths and binding affinities to 2-propanol and water molecules. The number of acidic sites that catalyze dehydrogenation is approximately one-third smaller than those involved in dehydration on the anatase TiO2 sample tested. Both reaction rates were inhibited by water, when co-fed to the reaction stream, as water competes for acidic sites, particularly at low 2-propanol pressures. Water inhibition persists even at high 2-propanol pressures, where acid sites become saturated with molecularly adsorbed 2-propanol, forming 2-propanol-water dimers. These water effects align with infrared spectra measured as a function of 2-propanol with and without water co-feed. Dehydration rates for 2-propanol were four times higher than for 1-propanol (at 543 K), suggesting the involvement of a carbocation-type transition state in the rate-determining step. These results provide a mechanistic understanding of alcohol dehydration and dehydrogenation pathways on bulk TiO2 catalysts, which could ultimately contribute to more efficient biomass utilization.
