Photocatalytic oxidation of methanol to formaldehyde on bismuth-based semiconductors

Methanol is widely applied in photocatalysis as a scavenger of holes, and is also studied as a model system for heterogeneous photocatalysis for the production of formaldehyde. Compared to commercial processes for formaldehyde production via thermal catalytic methanol oxidation, photocatalytic oxidation of methanol to formaldehyde may be more promising when considering the following aspects: 1) lower reaction temperature and pressure (generally operated at room temperature and ambient pressure); 2) lower cost of the energy source (such as solar light) and 3) easy-to-design reactive system. Photocatalytic methanol oxidation was carried out using four different bismuth-based semiconductors (BBS), Bi₂WO₆, Bi₂MoO₆, BiOBr and BiVO₄, under varying system temperature (5-50 °C), bubbling speed (0.1-1.0 LPM), catalyst dosage (0.2-2.0 g/L), and initial methanol concentration (12.5-250 mM). It was found that the formaldehyde formation rate for all photocatalysts increased as a function of each of these system parameters. Of these four BBS, it was found that Bi₂WO₆ had the highest formaldehyde formation rate (0.081 mM/h). This work provides a new approach to produce formaldehyde using photocatalysis, and future work has also been proposed.