Continuous Photocatalytic Steam Reforming of Methanol in the Gas Phase Over Pt/Srtio3

For a defossilized energy system, CH3OH is currently discussed as hydrogen carrier. The chemically stored hydrogen can be released by aqueous photocatalytic methanol reforming under mild reaction conditions. Most studies explore photocatalytic methanol reforming in the liquid phase using batch reactors, whereas a scalable process requires continuous operation and easy product separation. Here, we study the gas-phase methanol photoreforming at 100 °C in a continuously operated flat-plate flow reactor illuminated by an LED array (λmax = 368 nm) using Pt-modified SrTiO3. Quantitative online analysis of the gas-phase products combined with diffuse reflectance infrared Fourier transform spectroscopy to study surface adsorbates reveal that formyl species are key intermediates with formaldehyde being the main valuable by-product. We propose a reaction mechanism consisting of the photooxidation of adsorbed methoxy species to formyl species followed by three parallel reactions in which formyl species are further converted to CO2 and H2 via formate, to CO and H2, and to methyl formate by reaction with methoxy species. We also show that the product selectivity to carbon-based products does not depend on the Pt loading, whereas the overall methanol conversion strongly depends on the Pt loading. Using optimized SrTiO3 photocatalysts with a Pt loading of 0.1 wt% resulted in a methanol conversion of more than 12 % using a gas hourly space velocity of 10 L g-1 h-1. Only a minor performance loss of the optimized photocatalyst was observed during extended operation, demonstrating that photocatalytic methanol reforming in the gas phase is preferred for the future scalable release of H2 from methanol, especially in smaller decentralized plants operating under intermittent conditions.