Heterogeneous photocatalytic decomposition of saturated carboxylic acids on titanium dioxide powder. Decarboxylative route to alkanes

The heterogeneous photocatalytic decomposition of acetic acid/acetate mixtures was studied on n-type Ti02 powder. The influence of solution composition, reaction temperature, light intensity, and semiconductor properties (crystallographic structure, doping) was investigated. For photodecarboxylation in the absence of molecular oxygen, anatase powders proved to be most efficient with increased reactivity due to doping and/or partial coverage of the powder particles with platinum. The products of the photodecomposition of acetic acid on platinized anatase powder were mainly methane and CO2, with small amounts of hydrogen and ethane. Other saturated carboxylic acids (propionic, n-butyric, n-valeric, pivalic, adamantanel-carboxylic acid) were also photocatalytically decarboxylated to the corresponding alkanes. An interpretation based on the photoelectrochemical properties of n-type TiOz, with photooxidation and (dark) reduction reactions occurring on the particles on local cell processes, is proposed.