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Porous Inorganic Nanoarchitectures for Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Qingmin Ji, Jiao Sun, Shenmin Zhu
Heterogeneous catalysis involves systems in which catalyst and reactants form separate physical phases. Most of typical heterogeneous catalysts are inorganic solids such as metals, oxides, sulfides, and metal salts. The most common examples of heterogeneous catalysis in industry are involved the reactions of gases over the surface of solid catalysts. The catalytic reactions include the catalytic oxidation of volatile organic compounds (VOCs), preferential oxidation of CO, synthesis of ammonia, oxidation of HCl, partial oxidation of CH4 and cracking of gas oil. The reactions proceed basically through several steps: Gaseous reactants are transferred on the surface of catalysts.The reactants are adsorbed.The gas molecules are interacted with atoms or ions on the surface of the catalysts.Products are detached from the surface.
Feedstock Preparation
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Catalytic oxidation is a chemical conversion process that is used predominantly for destruction of volatile organic compounds and carbon monoxide. These systems operate in a temperature regime in the order of 205°C–595°C (400°F–1,100°F) in the presence of a catalyst—in the absence of the catalyst, the system would require a higher operating temperature. The catalysts used are typically a combination of noble metals deposited on a ceramic base in a variety of configurations (e.g., honeycomb-shaped) to enhance good surface contact. Catalytic systems are usually classified on the basis of bed types such as fixed bed (or packed bed) and fluid bed (fluidized bed). These systems generally have very high destruction efficiencies for most volatile organic compounds, resulting in the formation of carbon dioxide, water, and varying amounts of hydrogen chloride (from halogenated hydrocarbon derivatives). The presence in emissions of chemicals such as heavy metals, phosphorus, sulfur, chlorine, and most halogens in the incoming air stream act as poison to the system and can foul up the catalyst. Thermal oxidation systems, without the use of catalysts, also involve chemical conversion (more correctly, chemical destruction) and operate at temperatures in excess of 815°C (1,500°F), or 220°C–610°C (395°F–1,100°F) higher than catalytic systems.
Design of Soil Vapor Extraction Systems
Published in Jimmy H.C. Wong, Chin Hong Lim, Greg L. Nolen, Design of Remediation Systems, 2020
Jimmy H.C. Wong, Chin Hong Lim, Greg L. Nolen
Catalytic oxidation is essentially a flameless combustion process that deploys a catalyst to accelerate the oxidation process. Catalysts are precious metals that are coated on an inert structure. The main operating differences between a catalytic oxidizer and a thermal oxidizer are the influent hydrocarbon concentrations and the operating temperature. In both cases, the catalytic oxidizer operates at lower numbers. Hydrocarbon concentrations are typically limited to below 25% of the LEL (approximately 3000 ppmv). The operating temperature is usually kept in the 700 to 1000°F range. Typically, 650°F is the minimum inlet operating temperature to the catalytic cell and 1200°F is the maximum outlet temperature exiting the catalytic cell.
Effect of preparation method on the catalytic performance of formaldehyde oxidation over octahedral Fe3O4 microcrystals supported Pt catalysts
Published in Journal of Dispersion Science and Technology, 2020
Weiyi Cui, Ling Liu, Jiajun Yang, Naidi Tan
It is well known that Pt-based catalysts are extraordinarily active catalysts for many catalytic oxidation reactions. Previous works have reported that Pt-based catalysts have excellent catalytic performance for HCHO oxidation by selection of suitable support materials and preparation strategies.[17,27,28] The different preparation methods can cause differences in the physicochemical properties of the catalysts, which may further result in unexpected changes in some factors such as surface-active oxygen species, synergism between active components and the support, chemical/oxidation state and low temperature reducibility of the catalysts.[6,7] Therefore, developing an appropriate preparation method to fabricate superior catalytic activity of supported Pt catalysts for HCHO oxidation is an efficient approach.
Sol-gel enhanced mesoporous Cu-Ce-Zr catalyst for toluene oxidation
Published in Combustion Science and Technology, 2018
Running Kang, Xiaolin Wei, Huixin Li, Feng Bin, Ruozhu Zhao, Qinglan Hao, Baojuan Dou
Catalytic oxidation is emerging as an environmentally friendly technique for the degradation of VOCs (Tang et al., 2015a, Wang et al., 2015a). Typical catalysts employed for VOC oxidation are multi-component metal oxides, since they have a lower cost than noble metal catalysts, although the former exhibit activity at moderate temperature (Li et al., 2016, Lu et al., 2015). It is well known that the structure–activity relationship of metal oxides is determined by traditional preparation methods, such as co-precipitation, impregnation, and hydrothermal synthesis, but unfortunately, such bulk-phase catalysts, which are obtained with small pore size, always limit the enhancement of their activity (Hu et al., 2009). By contrast, the sol-gel method can be successfully employed to synthesize metal oxides with relatively broad pore size distributions and large pore volumes. In this case, the unique mesoporous structure is highly beneficial for the migration and diffusion of reactant molecules during reaction. Previously, a Mn-Ce composite oxide with a mesoporous structure, prepared by the sol-gel method, was successfully applied to benzene oxidation. Although the low-temperature reducibility, broad pore size distribution and rich adsorbed surface oxygen species greatly contribute to the activity toward benzene oxidation, the stability is still unsatisfactory, as the activity decreases from 100% to 92% after 12 h at 275°C (Tang et al., 2015b).
Novel Vanadia/meso-Co3O4 catalysts for the conversion of benzene–toluene–xylene to environmental friendly components via catalytic oxidation
Published in Environmental Technology, 2023
E. Shamma, S. Said, M. Riad, S. Mikhail
Currently, catalytic oxidation is regarded as the most effective and economical pathways to transform volatile organic compound into CO2, H2O, or other harmless compounds with high removal efficiency and low energy consumption. The key issue for catalytic oxidation is to develop a low-cost and high-efficiency catalyst with satisfactory stability [8]. Cobalt oxides as transition metal oxides catalysts have demonstrated efficiency for volatile organic compounds destruction due to its spinel structure, controllable morphology and the capability of performing reversible redox transitions (between Co3+ and Co2+). [9]. They have comparable activities to noble metals and supported noble metals catalysts making them a cheaper substitute [10].