Photocatalytic methanol decomposition: The role of common semiconductor materials in the product formation pathway

Methanol, as a hydrogen carrier, offers high hydrogen content and production advantages while significantly reducing the storage and transportation costs of hydrogen energy. This study aims to investigate the distribution differences and pathways of gas–liquid products during methanol decomposition catalyzed by four photocatalysts (CdS, ZnIn 2 S 4 , g-C 3 N 4 and TiO 2 ) surface-loaded with precious metal Pt. The results demonstrate that the order of hydrogen production amounts is as follows: TiO 2 -Pt > g-C 3 N 4 -Pt > ZnIn 2 S 4 -Pt > CdS-Pt, with TiO 2 -Pt achieving 67.6 mmol/g within 6 h. In addition to hydrogen gas, various gas products such as CH 4 , CO, C 2 H 4 and C 2 H 6 are also generated in each catalytic system. The distribution of these gas products closely correlates with the catalyst type used. Metal sulfide systems tend to produce CO alongside hydrogen generation, while the carbon-containing products include unsaturated olefin C 2 H 4 in addition to C 2 H 6 , without the formation of MF (methyl formate). Conversely, g-C 3 N 4 -Pt and TiO 2 -Pt systems primarily yield CH 4 as a carbon-containing gas product while exclusively containing C 2 H 6 and have the capability to synthesize MF. The reaction pathways for methanol decomposition in each system were deduced through in-situ infrared analysis and verified by DFT theoretical calculations, elucidating the potential correlation between catalyst types and product profiles. Different catalysts exhibit distinct adsorption capacities towards vary intermediate species during catalysis process, leading to their accumulation or continuous conversion on the catalyst surface, thereby resulting in diverse product yields at distinct stages. These findings provide valuable insights for designing photocatalytic methanol cracking processes aiming at high-purity H 2 generation or improving selectivity towards target products.