Effect of gold loading on ceria-zirconia support in total oxidation of VOCs

Promoted catalytic performance of Ag-Mn bimetal catalysts synthesized through reduction route

VOCs can exert great harm to both human and environment, and catalytic oxidation is believed to be an effective technique to eliminate these pollutants. In this paper, Ag-Mn bimetal catalysts with 10 wt.% of silver were synthesized using doping, impregnation, and reduction methods respectively, and then they were applied to the catalytic oxidation of benzene. Through series of characterizations it showed that the loading of silver using reduction method significantly resulted in improved physico-chemical properties of manganese oxides, such as larger surface area and pore volume, higher proportion of surface Mn3+ and Mn4+, stronger reducibility and more active of surface oxygen species, which were all beneficial to its catalytic activity. As a result, the Ag-Mn catalysts synthesized by reduction method showed a lower T90 value (equals to the temperature at which 90% of initial benzene was removed) of 203°C. Besides, both the used and fresh Ag-Mn catalysts synthesized by reduction method showed preferable stability in this research.

Nickel-Copper Oxide Catalysts Deposited on Stainless Steel Meshes by Plasma Jet Sputtering: Comparison with Granular Analogues and Synergistic Effect in VOC Oxidation

A novel method for the preparation of Ni-Cu oxide catalysts—deposition on stainless steel meshes using hollow cathode plasma jet sputtering—was studied. This method allows the preparation of thin oxide films. Consequently, the whole volume of the active phase is readily accessible for the reactants and can be employed in the catalytic reaction due to the negligible effect of internal diffusion. As a result, the activity of our sputtered catalyst was seven times higher in ethanol oxidation and 61 times higher in toluene oxidation than that of the corresponding granular catalyst. Moreover, due to stainless steel meshes used as a catalyst support, the pressure drop across the catalyst bed was lower. Finally, the catalytic activity of the sputtered Ni-Cu oxide catalyst with Ni:Cu molar ratio of 1:1 in ethanol oxidation was 1.7 times higher than that of the commercial EnviCat® VOC-1544 catalyst, while the amount of the active phase in the catalyst bed was 139 times lower. The outstanding performance of the Ni0.5Cu0.5 catalyst was ascribed to the synergistic effect between the copper and nickel components.

Hydrothermal deposition as a novel method for the preparation of Co-Mn mixed oxide catalysts supported on stainless steel meshes: application to VOC oxidation

The aim of this work was to develop a novel method for the preparation of structured Co-Mn mixed oxide catalysts: deposition on stainless steel meshes by hydrothermal synthesis. The use of meshes enabled the deposition of a thin layer of the active phase, which significantly suppressed the influence of internal diffusion. Consequently, the prepared catalysts exhibited from 48 to 114 times higher catalytic activity in ethanol oxidation than the commercial pelleted Co-Mn-Al catalyst. Moreover, we have shown that their catalytic activity correlated with the proportion of surface oxygen vacancies determined by XPS. Finally, the outstanding activity of the catalyst with Co:Mn ratio of 0.5 was ascribed to the mutual effect of high number of oxygen vacancies and exceptional redox properties.

Modification of Cobalt Oxide Electrochemically Deposited on Stainless Steel Meshes with Co-Mn Thin Films Prepared by Magnetron Sputtering: Effect of Preparation Method and Application to Ethanol Oxidation

Magnetron sputtering is an advantageous method for preparing catalysts supported on stainless steel meshes. Such catalysts are particularly suitable for processes carried out at high space velocities. One of these is the catalytic total oxidation of volatile organic compounds (VOC), economically feasible and environmentally friendly method of VOC abatement. The reactive radio frequency (RF) magnetron sputtering of Mn and Co + Mn mixtures in an oxidation Ar + O2 atmosphere was applied to form additional thin oxide coatings on cobalt oxide layers prepared by electrochemical deposition and heating on stainless steel meshes. Time of the RF magnetron sputtering was changed to obtain MnOx and CoMnOx coatings of various thickness (0.1–0.3 µm). The properties of the supported CoOx-MnOx and CoOx-CoMnOx catalysts were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), Fourier-transform infrared (FTIR) and Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The catalytic activity was investigated in the deep oxidation of ethanol, which was employed as a model VOC. According to the specific activities (amount of ethanol converted per unit mass of metal oxides per hour), the performance of CoOx-MnOx catalysts was higher than that of CoOx-CoMnOx ones. The catalysts with the smallest layer thickness (0.1 µm) showed the highest catalytic activity. Compared to the commercial pelletized Co-Mn-Al mixed oxide catalyst, the sputtered catalysts exhibited considerably higher (23–87 times) catalytic activity despite the more than 360–570 times lower content of the Co and Mn active components in the catalytic bed.

Gold and Ceria as Catalysts for VOC Abatement: A Review

Due to its excellent oxygen storage capacity, ceria is a well-known oxidation catalyst. However, its performance in the oxidation of volatile organic compounds can be improved by the introduction of gold. Depending on the type of VOC to be oxidized, the surface of gold nanoparticles and the gold/ceria interface may contribute to enhanced activity and/or selectivity. Choosing a proper preparation method is crucial to obtain optimal gold particle size. Deposition–precipitation was found to be more suitable than coprecipitation or impregnation. For industrial applications, monolithic catalysts are needed to minimize the pressure drop in the reactor and reduce mass and heat transfer limitations. In addition to the approach used with powder catalysts, the method employed to introduce gold in/on the washcoat has to be considered.

Geometric and electronic modification of the active Fe3+ sites of α-Fe2O3 for highly efficient toluene combustion

In the present study, catalytically inactive or low-active Ti⁴⁺ (d⁰) or Zn²⁺ (d¹⁰) ions were doped to α-Fe₂O₃ to tune the geometric and electronic engineering for Fe active center. X-ray absorption near edge structure (XANES) and Powder X-ray diffraction (XRD) analyses coupled with density functional theory (DFT) calculation show that the added of Ti⁴⁺ could occupy the interstitial octahedral or tetrahedral sites, resulting in surface Fe²⁺ species are oxidized to octahedrally coordinated Fe³⁺. As a result, more oxygen vacancies are generated, which improve the catalytic performance for toluene combustion. On the other hand, Fe²⁺ was substituted by Zn²⁺ ion could result in the partial destruction of hematite crystal structure, forming an additional phase of ZnFe₂O₄, and meanwhile part of Zn²⁺ ions replace the octahedrally coordinated Fe³⁺ sites, and therefore significantly decreasing the toluene catalytic performance. Moreover, our studies demonstrate that the combustions of toluene over Fe-based catalysts involve both the MvK and L-H mechanisms.

Bimetallic Catalysts for Volatile Organic Compound Oxidation

In recent years, the impending necessity to improve the quality of outdoor and indoor air has produced a constant increase of investigations in the methodologies to remove and/or to decrease the emission of volatile organic compounds (VOCs). Among the various strategies for VOC elimination, catalytic oxidation and recently photocatalytic oxidation are regarded as some of the most promising technologies for VOC total oxidation from urban and industrial waste streams. This work is focused on bimetallic supported catalysts, investigating systematically the progress and developments in the design of these materials. In particular, we highlight their advantages compared to those of their monometallic counterparts in terms of catalytic performance and physicochemical properties (catalytic stability and reusability). The formation of a synergistic effect between the two metals is the key feature of these particular catalysts. This review examines the state-of-the-art of a peculiar sector (the bimetallic systems) belonging to a wide area (i.e., the several catalysts used for VOC removal) with the aim to contribute to further increase the knowledge of the catalytic materials for VOC removal, stressing the promising potential applications of the bimetallic catalysts in the air purification.

Structured cobalt oxide catalysts for VOC abatement: the effect of preparation method

Magnetron sputtering was employed for the deposition of cobalt oxide thin films on stainless steel meshes. Catalysts prepared by sputtering in inert and oxidation atmosphere were compared with those obtained by electrochemical deposition and hydrothermal synthesis. Systematic characterization using X-ray diffraction, scanning electron microscopy, N₂ physisorption, infrared spectroscopy, Raman spectroscopy, and temperature-programmed reduction by hydrogen allowed detailed monitoring of their physicochemical properties. Ethanol gas-phase oxidation was employed as a model reaction to reveal the catalytic performance of the catalysts. It was shown that the catalyst prepared by magnetron sputtering in oxidation atmosphere exhibited the best mechanical stability among all studied catalysts. Moreover, its catalytic activity was 18 times higher than that of pelletized commercial cobalt oxide.