A series of TiO₂ photocatalysts loaded with various metals (Pt, Pd, Ni, and Cu) were prepared by using the wet impregnation method. Their physicochemical properties were studied by using XRD, BET, TPR-H₂, FTIR and TPD-NH₃/CO₂ techniques. The photocatalytic activity of samples was investigated in the gas-phase reduction of carbon dioxide under continuous flow operation mode. Among all investigated catalysts, the Pt and Ni were the most active in terms of the formation rate of methanol. In general, the photocatalytic activity of modified TiO₂ decreased with increasing metal loading and reaction time. The reversible deactivation of photocatalysts was associated with the covering of TiO₂ surface by the reaction products.

Ethanol steam reforming was studied over Ni supported catalysts. The effects of support (Al₂O₃, Al₂O₃–ZnO, and Al₂O₃–CeO₂), metal loading, catalyst activation method, and steam-to-ethanol molar feed ratio were investigated. The properties of catalysts were studied by N₂ physisorption, TPD-CO₂, X-ray diffraction, and temperature programmed reduction. After activity tests, the catalysts were analyzed by TOC analysis. The catalytic activity measurements showed that the addition either of ZnO SSor CeO₂ to alumina enhances both ethanol conversion and promotes selectivity towards hydrogen formation. The same effects were observed for catalysts with higher metal loadings. High process temperature and high water-to-ethanol ratio were found to be beneficial for hydrogen production. An extended catalyst stability tests showed no loss of activity over 50 h on reaction stream. The TOC analysis of spent catalysts revealed only insignificant amounts of carbon deposit.

The photocatalytic activity of TiO₂ depends on numerous factors, such as the chemical potential of electrons, charge transport properties, band-gap energy, and concentration of surface-active sites. A lot of research has been dedicated to determining the properties that have the most significant influence on the photocatalytic activity of semiconductors. Here, we demonstrated that the activity of TiO₂ in the gas-phase reduction of CO₂ is governed mainly by the desorption rate of the reaction intermediates and final products. This indicates that the specific surface area of TiO₂ and binding strength of reaction intermediates and products are the main factors affecting the photocatalytic activity of TiO₂ in the investigated process. Additionally, it was shown that rutile exhibits higher photocatalytic activity than anatase/rutile mixtures mainly due to its high efficiency in the visible portion of the electromagnetic spectrum.