At present, the selective oxidation of toluene to benzyl alcohol, benzaldehyde, benz oic acid and benzyl benzoate is an environmental unfriendly process . The problems of thermal oxidation of toluene are low toluene conversion and high pollution emission. Therefore, solvent free selective oxidation of toluene to benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate over Pt/TiO 2 catalysts using O 2 under mild condition is significant . Pt/TiO 2 and Pt/B TiO 2 (reduced TiO 2 catalysis with different Pt dispersion were synthesized by electrostatic adsorption and impregnation methods. The size distribution , the chemical valence of Pt and the surf ace properties of TiO 2 were characterized. The effects of material properties on the thermal and photothermal selective oxidation of toluene were studied. The catalytic active sites of Pt/TiO 2 and the reaction mechanism for thermal and photothermal selecti ve oxidation of toluene under different reaction conditions were proposed
(1)We synthesize single Pt atom s (SA) SA), subnanometric Pt clusters (NC) and Pt nanoparticle s (NP) supported on TiO 2 or reduced TiO 2 catalysts by electrostatic adsorption method . The products of C H oxidation of toluene are benzyl alcohol,benzaldehyde, benzoic acid and benzyl benzoate . T he selectivity to thermal oxidation of primary C H bond of toluene over Pt/TiO 2 catalysts is less than 50%. It is found that O 2 molecule activated on the single Pt atom catalysts are more likely to oxidize toluene to generate CO 2 and hydrocarbon, which leads to a decrease in the selectivity of the C H bond oxidation products. T he selectivity of photothermal oxidation of C H bond products is close to 100 which is attributed to O 2 activation occured on TiO 2 The active oxygen species generated on TiO 2 facilitate the C H bond oxidation of toluene. First, t he selective oxidation of toluene to produce benzyl alcohol , then benzyl alcohol is further oxidized to benz aldehyde next benzaldehyde is oxidized to benzoic acid B enzyl alcohol and benzoic acid are polymerized to form benzyl benzoate.Because the selective oxidations of toluene do not go on after a period of time, the yield of benzyl alcohol decreases with the reaction time increases. Because benzyl alcohol can be oxidized to benzoic acid after the selective oxidation of toluene stopping, t he yield of benzoic acid increases with the reaction time increases .
(2)Subnanometric Pt clusters (NC) and Pt nanoparticle s (NP) supported on TiO2 or reduced TiO 2 catalysts were synthesized by impregnation method. The metal support interaction was found to affect the catalytic performance of selective oxidation of toluene. For the Pt/TiO 2 catalysts calcinated at 2 00 º C , the interaction between Pt and TiO 2 is weak. O xygen molecules activated on free Pt nanoparticles can oxidiz e toluene to form CO 2 and hydrocarbon . T hus, t he selectivity to photothermal oxidation of C H bond of toluene is only 41% 41%. When there exist a strong interaction between Pt and TiO 2 , the C H bonds of toluene is activated and oxidized on the surface of TiO 2 to form C H bond oxidation products (benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate). The selectivity of C H bond oxidation products is close to 100%.
(3)The abatement of HCHO and CO at room temperature by catalytic oxidation over metal oxides can be achieved. However, the catalytic performance of metal oxides is influenced by H 2 O vapor in the reaction air and the mechanism o f H 2 O role is still debated. In this paper, the effect of H 2 O on the catalytic performance of a MCo 2 O 4 (M = Mn, Ce and Cu) catalyst for HCHO and CO oxidation at room temperature was investigated. For both HCHO oxidation and CO oxidation, all the MCo 2 O 4 cat alysts in humid air are less active than in dry air except for HCHO oxidation catalyzed by CuCo 2 O 4 catalyst. The CuCo 2 O 4 is inactive for HCHO oxidation in dry air, but active for HCHO oxidation in humid air. The associatively adsorbed H 2 O on MCo 2 O 4 contrib uted to the active HOH sites for HCHO oxidation.Formate species are intermediates of HCHO oxidation. However, if formate cannot be further transferred into CO 2 , the formate adsorbed on active sites will result in catalyst deactivation. In humid air, hydro gen bonded OH and free OH generated and covered active sites accelerated the catalyst deactivation in HCHO oxidation. The CO was oxidized by the active oxygen species but not included OH species. Thus, the H 2 O adsorbed on oxygen vacancies blocked the generation of active oxygen species, which resulted in MCo 2 O 4 deactivation for CO oxidation in humid air. This work provide a fundamental understanding of the key role of H 2 O in the HCHO and CO oxidation at room temperature, which is helpful for the design of high activity and long lifetime catalyst used in dry or humid conditions.
Solvent free oxidation of toluene to pr oduce benzyl alcohol, benzaldehyde,benzoic acid and benzyl benzoate over Pt/TiO 2 catalysts with oxygen meets the requirements of clean er p roduction. Th is research proposed the thermal and photothermal catalytic active sites and reaction mechanism of selective oxidation of toluene over Pt/TiO 2 catalysts, which is helpful for pereparation of material with good catalytic performance in the gree n selective oxidation of toluene.