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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.

Au supported on γ-Al2O3 prepared by deposition–precipitation (DP) using urea is found to be a highly active catalyst for the total oxidation of HCHO at room temperature under humid air, without the need for a reducible oxide as support. In-situ DRIFTS studies suggested that the surface hydroxyl groups played a key role in the partial oxidation of HCHO into the formate intermediates, which can be further oxidized into CO2 and H2O with participation of nano-Au. This study challenges the traditional idea of supporting noble metals on reducible oxides for HCHO oxidation at room temperature.

Three-dimensional (3D) ordered cubic mesoporous Co–Mn oxide (denoted as CoMn-HT) was fabricated using a KIT-6-templating strategy and was tested in a “storage–oxidation” cycling process for the removal of formaldehyde. The formation of a 3D ordered mesoporous structure was confirmed by low-angle XRD, nitrogen adsorption–desorption data, and TEM micrographs. The CoMn-HT catalyst showed promising properties in both the storage and regeneration phases, and remained active in highly humid air (RH = 90%) and at high GHSV (160,000 h − 1 ). The excellent catalytic performance of CoMn-HT was associated with its large surface area and 3D ordered mesoporous structure.

Two kinds of Au/CeO2, prepared by deposition–precipitation (DP) using urea (U) or NaOH (N) as precipitants were investigated as catalysts for HCHO oxidation. H2-TPR and XPS techniques were used to characterize the Au/CeO2 samples. Due to the generation of increased amounts of active surface oxygen species resulting from the strong Au–CeO2 interaction, the Au/CeO2 (DPU) catalyst showed higher activity than the DPN catalyst, achieving 100% conversion of HCHO into CO2 and H2O at room temperature, even in the presence of water and at high GHSV (143,000 h−1); moreover, the conversion was stable for at least 60 h. The reaction mechanism and the rate limiting steps for HCHO oxidation over the Au/CeO2 catalysts were identified by means of in situ DRIFTS studies. The influence of oxygen and water on the formation and consumption of the formate reaction intermediates was also investigated. Results suggest that Au/CeO2 (DPU) is a promising catalyst for HCHO removal under real world conditions.

Catalytic removal of indoor HCHO was proposed to proceed in a “storage-oxidation” cycling process. Two kinds of supported silver catalysts, namely Ag/HZSM-5 and Ag–MnO x –CeO 2, were investigated as catalysts for this cycling process. Due to the highly dispersed silver clusters formed and its good redox properties, the Ag–MnO x –CeO 2 catalyst showed better HCHO oxidation properties in both the storage phase (HCHO partial oxidation to HCOO − at room temperature) and oxidation-regeneration phase (total oxidation of the formates into CO 2 and H 2 O at elevated temperatures). The presence of H 2 O (RH = 50%, 25 °C) was found to enhance the HCHO storage capacity for Ag–MnO x –CeO 2 catalyst, while competitive adsorption of HCHO with H 2 O was observed over Ag/HZ catalyst. The results of DRIFTS indicate that the partial oxidation of HCHO into HCOO − is accelerated by the presence of H 2 O over the Ag–MnO x –CeO 2 catalyst. In addition, the catalyst saturated with HCHO can be in situ regenerated without production of secondary pollutants and can be used repeatly. It is suggested that this is a promising approach for indoor HCHO elimination.