In this study, relationships between preparation conditions, structure, and activity of Pt-containing TiO₂ photocatalysts in photoinduced reforming of glycerol for H₂ production were explored. Commercial Aerolyst^® TiO₂ (P25) and homemade TiO₂ prepared by precipitation-aging method were used as semiconductors. Pt co-catalysts were prepared by incipient wetness impregnation from aqueous solution of Pt(NH₃)₄(NO₃)₂ and activated by calcination, high temperature hydrogen, or nitrogen treatments. The chemico-physical and structural properties were evaluated by XRD, ¹H MAS NMR, ESR, XPS, TG-MS and TEM. The highest H₂ evolution rate was observed over P25 based samples and the H₂ treatment resulted in more active samples than the other co-catalyst formation methods. In all calcined samples, reduction of Pt occurred during the photocatalytic reaction. Platinum was more easily reducible in all of the P25 supported samples compared to those obtained from the more water-retentive homemade TiO₂. This result was related to the negative effect of the adsorbed water content of the homemade TiO₂ on Pt reduction and on particle growth during co-catalyst formation.

An aerial humidity-induced solid-phase hydrolytic transformation of the [Zn(NH₃)₄]MoO₄@2H₂O (compound 1 @2H₂O) with the formation of [(NH₄)_xH_(1−x)Zn(OH)(MoO₄)]_n (x = 0.92–0.94) coordination polymer (formally NH₄Zn(OH)MoO₄, compound 2) is described. Based on the isostructural relationship, the powder XRD indicates that the crystal lattice of compound 1@2H₂O contains a hydrogen-bonded network of tetraamminezinc (2+) and molybdate (2−) ions, and there are cavities (O₄N₄(μ-H₁₂) cube) occupied by the two water molecules, which stabilize the crystal structure. Several observations indicate that the water molecules have no fixed positions in the lattice voids; instead, the cavity provides a neighborhood similar to those in clathrates. The @ symbol in the notation is intended to emphasize that the H₂O in this compound is enclathrated rather than being water of crystallization. Yet, signs of temperature-dependent dynamic interactions with the wall of the cages can be detected, and 1@2H₂O easily releases its water content even on standing and yields compound 2. Surprisingly, hydrolysis products of 1 were observed even in the absence of aerial humidity, which suggests a unique solid-phase quasi-intramolecular hydrolysis. A mechanism involving successive substitution of the ammonia ligands by water molecules and ammonia release is proposed. An ESR study of the Cu-doped compound 2 (2#dotCu) showed that this complex consists of two different Cu²⁺(Zn²⁺) environments in the polymeric structure. Thermal decomposition of compounds 1 and 2 results in ZnMoO₄ with similar specific surface area and morphology. The ZnMoO₄ samples prepared from compounds 1 and 2 and compound 2 in itself are active photocatalysts in the degradation of Congo Red dye. IR, Raman, and UV studies on compounds 1@2H₂O and 2 are discussed in detail.

The influence of the semiconductor microstructure on the photocatalytic behavior of Pt-PtO_x/TiO₂ catalysts was studied by comparing the methanol-reforming performance of systems based on commercial P25 or TiO₂ from sol–gel synthesis calcined at different temperatures. The Pt co-catalyst was deposited by incipient wetness and formed either by calcination or high-temperature H₂ treatment. Structural features of the photocatalysts were established by X-ray powder diffraction (XRD), electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), optical absorption, Raman spectroscopy and TEM measurements. In situ reduction of Pt during the photocatalytic reaction was generally observed. The P25-based samples showed the best H₂ production, while the activity of all sol–gel-based samples was similar in spite of the varying microstructures resulting from the different preparation conditions. Accordingly, the sol–gel-based TiO₂ has a fundamental structural feature interfering with its photocatalytic performance, which could not be improved by annealing in the 400–500 °C range even by scarifying specific surface area at higher temperatures.