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Although manganese oxide (MnO2) exhibits excellent activity in various oxidation reactions, especially for volatile organic compound oxidation, the origin of the catalytic activity remains ambiguou...

Catalytic oxidation of formaldehyde with non-noble metal catalysts is desirable yet still challenging. In this work, we describe a hard template method in combination with an in situ chelating strategy to construct a novel three-dimensionally structured CeO2-based composite which contains CeO2 quantum dots of 1.5–2.5 nm size anchored on nitrogen doped hierarchical porous carbon with both macropores and mesopores. When used as an oxidation catalyst, complete oxidation of formaldehyde could be achieved at a temperature 130 °C lower than that of bulk nano-CeO2 catalyst. The significantly improved catalytic activity could be attributed to the higher amount of oxygen vacancies and enhanced redox properties of CeO2 quantum dots as well as the three-dimensional porous texture.

Au catalysts supported on HZSM-5 and SiO 2 prepared by a deposition–precipitation (DP) method with ammonia as the precipitant were very active for HCHO complete oxidation at room temperature under humid air. The treatment atmosphere exerted significant effects on the catalytic performance. The catalysts treated in H 2 had better Au dispersions and smaller Au particle sizes than those treated in air, which were crucial for high reactivity. Both catalysts deactivated at high GHSV (600,000 ml g −1 h −1 ), due to the growth of Au nanoparticles during the reaction, as well as the accumulation of surface species such as formate intermediates on the catalyst. Our results suggested that small Au particle size and strong metal-support interaction were the key factors for the high activity for HCHO oxidation over Au supported on silica-based materials.

Gold stabilized on reducible oxide (CeO 2 and FeO x ) and irreducible oxide (γ-Al 2 O 3 , SiO 2 , and HZSM-5) were prepared by deposition precipitation method and tested for catalytic oxidation of formaldehyde (HCHO) at room temperature under high GHSV of 600000 ml/(g·s). Au/γ-Al 2 O 3 catalyst showed distinctive catalytic performance, presenting the highest initial HCHO conversion and stability. Correlating the reaction rate with Au particle size, there is a linear relationship, suggesting that the smaller Au particle size with higher dispersion possesses high reactivity for HCHO oxidation. All the catalysts deactivated at high GHSV (600000 ml/(g·s)), but in a quite different rate. Reducible oxide (CeO 2 and FeO x ) could stabilize gold through O linkage and therefore exhibits a better stability for HCHO oxidation reaction. However, the aggregation of gold particles occurred over Au/SiO 2 and Au/HZSM-5 catalysts, which result in the fast deactivation. Therefore, our results suggest that the reducibility of the supports for Au catalysis has no direct influence on the activity, but affects the catalytic stability.

A catalytic process including formaldehyde oxidation and benzene “storage-oxidation” cycling for simultaneously removal of formaldehyde and benzene is proposed, by using HZSM-5 supported PtAg bimetallic catalysts. HZSM-5 with different crystal size supported PtAg bimetallic catalysts were synthesized with the investigation focusing on HCHO oxidation at room temperature, benzene storage capacity at room temperature, and benzene catalytic oxidation at elevated temperature. Crystal size of HZSM-5 zeolite not only influences the dispersion of active metals of PtAg, and therefore influence their catalytic properties for formaldehyde and benzene oxidation, but also has great effects on benzene storage capacity and the thermal stability of the stored benzene, which is directly related to the release of benzene at elevated temperature. The ratio of Pt/Ag has an opposite effect on benzene storage capacity and formaldehyde and benzene oxidation properties. Considering these factors, PtAg (Pt/Ag = 1/1) supported on nanoscale HZSM-5 catalysts were found to be suitable for the proposed cycling process, good carbon balances being obtained for each cycle without the production of secondary pollutants.

The influence of moisture on the activity and stability of Mn0.75Co2.25O4 catalyst for HCHO and CO oxidation was compared and investigated. Totally opposite effects of relative humidity (RH) on the reactions were observed: with increase of RH (0–90%), the activity for HCHO oxidation was enhanced, whereas the activity for CO oxidation was greatly decreased. However, in both cases the catalyst lifetime was prolonged in the presence of moisture (RH = 50%). Such modifications were directly evidenced by correlating in-situ DRIFTS data, TPO results and MS–IRAS studies, which clarified the effects of water on the activity and stability of Mn0.75Co2.25O4 catalyst for HCHO and CO oxidation.

FeO x -supported Au catalysts prepared by co-precipitation (CP) were investigated for catalytic HCHO oxidation. The applied calcination temperature was found to greatly influence both the chemical properties and microstructure of the catalysts. Characterization using XRD, H 2 -TPR and XPS suggested that lower calcination temperature improves the reducibility of the catalysts, and favors the presence of surface hydroxyl groups. Consequently, an Au/FeO x catalyst calcined at 200 °C afforded 100% conversion of HCHO into CO 2 and H 2 O at room temperature and under humid air. In situ DRIFTs studies suggested that the moisture was essential for deep oxidation of the formate intermediates into CO 2 and H 2 O, this being the rate limiting step for catalytic HCHO oxidation.