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Characteristic features of Pt/C catalysts prepared through reductive deposition from an aqueous solution have been investigated. The carbon support was found to act as an effective nucleating agent and to ensure the formation of small and predominantly nonaggregated Pt particles, probably through a preliminary formation of oxide nuclei on the carbon surface. The deposition rates could be high enough to provide the location of Pt nanoparticles near the external surface of the support and outside micropores. The depositions onto bare carbon supports and Pt/C samples presynthesized by using another method proved equally effective, which thus opened a route to various types of metal distribution. With the same metal precursor, reductant, and base (H2PtCl6, NaOOCH, Na2CO3), catalytic properties could be influenced through the support, Pt loading, and deposition conditions. In the oxidation of isopropyl alcohol as a model test reaction, alcohol conversion could be as high as 99.7 % and turnover frequencies 80 000 h−1 [H2O, O2, 1 bar (100 kPa), 30 °C].

Metal clusters with sizes below 1 nm attract great scientific interest, but the main information on their properties still comes from quantum mechanics modeling and costly physical methods of limited availability. We have studied ultradispersed Pt/γ-AlO samples with temperature-programmed desorption (TPD) and complementary adsorption/desorption techniques and observed that the H-TPD profile of Pt/γ-AlO is strongly dependent on the pretreatment conditions (0 < P ≤ 1 bar; 200 K ≤ T ≤ 470 K). The results corroborate recent theoretical and spectroscopic studies predicting alterations in the structure of Pt nanoclusters under H-treatment conditions but reveal that the restructuring needs to overcome continuous activation barriers and leads both to an increase in surface coverage and strengthening of the Pt-H bonds. This was interpreted as being a consequence of the strong interaction of Pt clusters with the support. The results extend insights into the behavior of supported metal particles and expand the potential of existing experimental techniques.

Treatments of Pt/γ-AlO with H under harsh conditions have long been known to strongly influence the properties of this important catalytic system, but the true causes of the high-temperature effects still remain unclear. We have performed a more detailed study of this issue, having used H-TPD as a sensitive probe of metal-support interactions. The experimental results are in accordance with previous studies and demonstrate strong changes in adsorption and catalytic properties of Pt/γ-AlO after high-temperature H treatments, as well as the possibility to reverse the changes, completely or in part, through O and HO treatments. Thorough examination has shown that such behaviour is an intrinsic property of Pt/γ-AlO and cannot be attributed to impurities or experimental artifacts. Moreover, there is no abrupt transition to a high-temperature state, but the system undergoes smooth and gradual changes upon increasing the H-treatment temperature (T), with the changes being already apparent at a T of ∼ 300 °C. The results suggest that hydrogen can generate oxygen vacancies on the surface of the support in close vicinity to the Pt particles, and the system appears under equilibrium to be kinetically driven by temperature and thermodynamically driven by the P/P ratio or local concentration of surface hydroxyls near Pt particles. The generated vacancies change the properties of contacting particles, and the changes are most pronounced for sub-nanometric Pt clusters and single atoms. Implications of the phenomena for the synthesis, study, and use of Pt/γ-AlO and its related nanosystems are discussed.