The results of selective oxidation of CH3OH and CH3SH to produce formaldehyde are presented and the effect of the reaction conditions on the CH2O yield is evaluated. The yield of formaldehyde was evaluated by thermodynamic calculations by using the HSC Chemistry (R) and Aspen Plus (R) simulation programmes. Oxidation of CH3OH and CH3SH was investigated by calculating the system equilibrium composition. Based on the modelling results, the yield of formaldehyde was almost zero with all the reactants present, i.e. the CH3OH, CH3SH and CH3OH + CH3SH mixture, which was also supported by the experiments. Catalytic experiments were performed over TiO2,V2O5/SiO2 and V2O5/(SiO2 + 10% TiO2) catalysts to evaluate the effect of feed concentration, reaction temperature and catalyst loading on the formaldehyde yield. Both CH3OH and CH3SH were oxidized separately and as mixtures. The V2O5/(SiO2 + 10% TiO2) catalyst was the most active catalyst in formaldehyde production. At optimal reaction conditions, 88% yield of CH2O was achieved at 413 degrees C in a feed mixture of 1000 ppm of CH3OH + CH3SH with the space velocity of 94,000 h(-1). The catalysts showed no activity loss when tested for 6 h. (C) 2011 Elsevier B.V. All rights reserved.