Ethanol is an attractive renewable feedstock offering a sustainable alternative for large-scale industrial applications. ZnO catalysts show intrinsically high catalytic activity in the steam reforming of ethanol (57.9 % at 400 °C) which can be enhanced by doping with various oxides. This study focuses on Al-doped ZnO due to its well-established and reproducible synthesis. Al-doped ZnO catalysts were synthesized by co-precipitation of hydroxycarbonates following Mockenhaupt et al. [B. Mockenhaupt, J. K. Wied, S. Mangelsen, U. Schürmann, L. Kienle, J. Schmedt Auf der Günne, M. Behrens, Dalton Trans., 2023, 52, 5321]. GC data were collected every 30 min with a dual GC system (TCD and FID) to quantify hydrocarbons, oxygenates, and permanent gases.
The steam reforming of ethanol over ZnO produces a variety of products depending on the reaction temperature and Al content with acetaldehyde, acetone, and CO2 being the main products. By-products include ethylene, ethyl acetate, methane, and propylene. At 400 °C, ethanol conversion reaches approximately 60 % with minor deactivation of 2-5 % observed after 8 h TOS. The carbon-based selectivity shifts favorably towards acetaldehyde formation with higher Al doping of ZnO. The formation of high-value chemicals such as acetone appears to be strongly influenced by the structure of the catalyst. Acetaldehyde is converted to acetic acid / ethylacetate which further reacts via oxidative ketonization to acetone [J. F. Goebel, F. Belitz, D. S. Prendes, Y. Haver, P. Diehl, M. Muhler, L. J. Gooßen, ChemSusChem, 2024, 17, e202400094]. A higher Al content in ZnO increases the specific surface area, but hinders these consecutive reactions of acetaldehyde.