Mechanisms of Simultaneous Hydrogen Production and Formaldehyde Oxidation in H2O and D2O over Platinized TiO2

The simultaneous photocatalytic degradation of formaldehyde and hydrogen evolution on platinized TiO 2 have been investigated employing different H 2 O/D 2 O mixtures under oxygen-free conditions using quadrupole mass spectrometery (QMS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The main reaction products obtained from the photocatalytic oxidation of 20% formaldehyde were hydrogen and carbon dioxide. The ratio of evolved H 2 to CO 2 was to 2/1. The HD gas yield was found to be dependent on the solvent and was maximized in a H 2 O/D 2 O mixture (20%/80%). The study of the solvent isotope effect on the degradation of formaldehyde indicates that the mineralization rate of formaldehyde (CO 2 ) decreases considerably when the concentration of D 2 O is increased. On the basis of the ATR-FTIR data, the formaldehyde in D 2 O is gradually converted to deuterated formic acid during UV irradiation, which was confirmed by different band shifting. An additional FTIR band at 2050 cm –1 assigned to CO was detected and was found to increase during UV irradiation due to the adsorption of molecular CO on Pt/TiO 2 . The results of these investigations showed that the molecular hydrogen is mainly produced by the reduction of two protons originating from water and formaldehyde. A detailed mechanism for the simultaneous hydrogen production and formaldehyde oxidation in D 2 O is also presented.