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"Metal catalysts"
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Simple Thermocatalytic Oxidation Degradation of VOCs
Volatile organic compounds (VOCs) are a class of pollutants with many sources and harm humans and the environment. The application of noble metal catalysts and metal oxide catalysts in thermal catalytic oxidation degradation of VOCs was reviewed in this paper. Furthermore, the challenges of degradation of VOCs by thermal catalytic oxidation are listed and the prospects are put forward.Graphic Abstract
Journal Article
Current Progress on Methods and Technologies for Catalytic Methane Activation at Low Temperatures
Methane (CH4) is an attractive energy source and important greenhouse gas. Therefore, from the economic and environmental point of view, scientists are working hard to activate and convert CH4 into various products or less harmful gas at low‐temperature. Although the inert nature of CH bonds requires high dissociation energy at high temperatures, the efforts of researchers have demonstrated the feasibility of catalysts to activate CH4 at low temperatures. In this review, the efficient catalysts designed to reduce the CH4 oxidation temperature and improve conversion efficiencies are described. First, noble metals and transition metal‐based catalysts are summarized for activating CH4 in temperatures ranging from 50 to 500 °C. After that, the partial oxidation of CH4 at relatively low temperatures, including thermocatalysis in the liquid phase, photocatalysis, electrocatalysis, and nonthermal plasma technologies, is briefly discussed. Finally, the challenges and perspectives are presented to provide a systematic guideline for designing and synthesizing the highly efficient catalysts in the complete/partial oxidation of CH4 at low temperatures. This review summarizes the current methods and technologies for the catalytic oxidation of CH4 at low temperatures. It focuses on the noble metals and transition metal‐based catalysts that activate CH4 in temperatures ranging from 50 to 500 °C. Then, it briefly discusses the partial oxidation of CH4 at relatively low temperatures through thermocatalysis, photocatalysis, electrocatalysis, and nonthermal plasma technologies.
Journal Article
A review of the catalysts used in the reduction of NO by CO for gas purification
The reduction of NO by the CO produced by incomplete combustion in the flue gas can remove CO and NO simultaneously and economically. However, there are some problems and challenges in the industrial application which limit the application of this process. In this work, noble metal catalysts and transition metal catalysts used in the reduction of NO by CO in recent years are systematically reviewed, emphasizing the research progress on Ir-based catalysts and Cu-based catalysts with prospective applications. The effects of catalyst support, additives, pretreatment methods, and physicochemical properties of catalysts on catalytic activity are summarized. In addition, the effects of atmosphere conditions on the catalytic activity are discussed. Several kinds of reaction mechanisms are proposed for noble metal catalysts and transition metal catalysts. Ir-based catalysts have an excellent activity for NO reduction by CO in the presence of O
2
. Cu-based bimetallic catalysts show better catalytic performance in the absence of O
2
, in that the adsorption and dissociation of NO can occur on both oxygen vacancies and metal sites. Finally, the potential problems existing in the application of the reduction of NO by CO in industrial flue gas are analyzed and some promising solutions are put forward through this review.
Journal Article
“Traditional” Sol-Gel Chemistry as a Powerful Tool for the Preparation of Supported Metal and Metal Oxide Catalysts
The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, sol-gel chemistry gathers plenty of fascinating strategies to prepare materials from solution state precursors. Low temperature chemistry, reproducibility, and high surface to volume ratios of obtained products are features that add merit to this technology. The development of different and fascinating procedure was fostered by the availability of new molecular precursors, chelating agents and templates, with the great advantage of tailoring the physico-chemical properties of the materials through the manipulation of the synthesis conditions. The aim of this review is to present an overview of the “traditional” sol-gel synthesis of tailored and multifunctional inorganic materials and their application in the main domain of heterogeneous catalysis. One of the main achievements is to stress the versatility of sol-gel preparation by highlighting its advantage over other preparation methods through some specific examples of the synthesis of catalysts.
Journal Article
Chromium‐Induced High Covalent Co–O Bonds for Efficient Anodic Catalysts in PEM Electrolyzer
The proton exchange membrane water electrolyzer (PEMWE), crucial for green hydrogen production, is challenged by the scarcity and high cost of iridium‐based materials. Cobalt oxides, as ideal electrocatalysts for oxygen evolution reaction (OER), have not been extensively applied in PEMWE, due to extremely high voltage and poor stability at large current density, caused by complicated structural variations of cobalt compounds during the OER process. Thus, the authors sought to introduce chromium into a cobalt spinel (Co3O4) catalyst to regulate the electronic structure of cobalt, exhibiting a higher oxidation state and increased Co–O covalency with a stable structure. In‐depth operando characterizations and theoretical calculations revealed that the activated Co–O covalency and adaptable redox behavior are crucial for facilitating its OER activity. Both turnover frequency and mass activity of Cr‐doped Co3O4 (CoCr) at 1.67 V (vs RHE) increased by over eight times than those of as‐synthesized Co3O4. The obtained CoCr catalyst achieved 1500 mA cm−2 at 2.17 V and exhibited notable durability over extended operation periods – over 100 h at 500 mA cm−2 and 500 h at 100 mA cm−2, demonstrating promising application in the PEMWE industry. This research reports a promising non‐precious metal anodic electrocatalyst for a proton exchange membrane water electrolyzer (PEMWE). Owing to high covalent Co–O bonds induced by Cr, the CoCr electrocatalyst exhibits notable durability over extended operation periods, over 100 h at 500 mA cm−2 and 500 h at 100 mA cm−2, demonstrating considerable application potential in PEMWE devices.
Journal Article
Analysis of the Influencing Factors of the Efficient Degradation of Waste Polyurethane and Its Scheme Optimization
This work proposes an efficient catalytic recovery and utilization method for waste polyurethane foam. This method uses ethylene glycol (EG) and propylene glycol (PPG) as two-component alcohololytic agents for the alcoholysis of waste polyurethane foams. For the preparation of recycled polyethers, the conditions of different catalytic degradation systems were catalyzed by duplex metal catalysts (DMC) and alkali metal catalysts, and a synergy with both was also used. The experimental method was adopted with the blank control group and was set up for comparative analysis. The effect of the catalysts on the recycling of waste polyurethane foam was investigated. The catalytic degradation of DMC and the alkali metal catalysts alone, as well as the synergistic effect of the two catalysts, was explored. The findings revealed that the NaOH and DMC synergistic catalytic system was the best, and that the system activity was high under a two-component catalyst synergistic degradation. When the amount of NaOH added in the degradation system was 0.25%, the amount of DMC added was 0.04%, the reaction time was 2.5 h, and the reaction temperature was 160 °C, the waste polyurethane foam was completely alcoholized, and the prepared regenerated polyurethane foam had high compressive strength and good thermal stability. The efficient catalytic recycling method of waste polyurethane foam proposed in this paper has certain guiding and reference values for the practical production of solid-waste-recycled polyurethane.
Journal Article
An Updated Comprehensive Literature Review of Phenol Hydrogenation Studies
Cyclohexanone is an important industrial intermediate to produce nylons. The main industrial routes for cyclohexanone manufacture used cyclohexane and phenol as feedstock. The selective hydrogenation of phenol to cyclohexanone comprises one-step and two-step processes. This review presents a detailed analysis of the research findings available in the open literature for phenol hydrogenation to produce cyclohexanone and cyclohexanol and covers the research conducted during 2014–2020 using conventional and modern catalysts. This review aims to disseminate the knowledge of the current research conducted for phenol hydrogenation and provide a comprehensive resource for researchers working in this field. This review has included and discussed both methods of thermocatalytic and electrocatalytic hydrogenation of phenol. Most of the studies have used carbon or carbon–nitrogen supported catalysts loaded with Pd. The carbon and carbon–nitrogen materials were derived from different sources including polymers, activated carbon, and MOF. Oxygen treatment was found to produce highly active and stable catalysts. The high performance was found associated with the high surface area of the catalyst and uniformly dispersed metal nanoparticles. The acidic conditions exhibited an increase in catalyst performance. Alkali-promoted precious metal-loaded catalysts performed better than un-promoted catalysts.Graphic Abstract
Journal Article
Research Progress of Non-Noble Metal Catalysts for Carbon Dioxide Methanation
The extensive utilization of fossil fuels has led to a rapid increase in atmospheric CO2 concentration, resulting in various environmental issues. To reduce reliance on fossil fuels and mitigate CO2 emissions, it is important to explore alternative methods of utilizing CO2 and H2 as raw materials to obtain high-value-added chemicals or fuels. One such method is CO2 methanation, which converts CO2 and H2 into methane (CH4), a valuable fuel and raw material for other chemicals. However, CO2 methanation faces challenges in terms of kinetics and thermodynamics. The reaction rate, CO2 conversion, and CH4 yield need to be improved to make the process more efficient. To overcome these challenges, the development of suitable catalysts is essential. Non-noble metal catalysts have gained significant attention due to their high catalytic activity and relatively low cost. In this paper, the thermodynamics and kinetics of the CO2 methanation reaction are discussed. The focus is primarily on reviewing Ni-based, Co-based, and other commonly used catalysts such as Fe-based. The effects of catalyst supports, preparation methods, and promoters on the catalytic performance of the methanation reaction are highlighted. Additionally, the paper summarizes the impact of reaction conditions such as temperature, pressure, space velocity, and H2/CO2 ratio on the catalyst performance. The mechanism of CO2 methanation is also summarized to provide a comprehensive understanding of the process. The objective of this paper is to deepen the understanding of non-noble metal catalysts in CO2 methanation reactions and provide insights for improving catalyst performance. By addressing the limitations of CO2 methanation and exploring the factors influencing catalyst effectiveness, researchers can develop more efficient and cost-effective catalysts for this reaction.
Journal Article
A Review of Noble Metal Catalysts for Catalytic Removal of VOCs
Volatile organic compounds (VOCs) are important precursors for the formation of secondary pollutants, such as fine particulate matter (PM) and ozone (O3), which will lead to severe atmospheric environmental problems to restrict the sustainable development of the social economy. Catalytic oxidation is a safe, eco-friendly, and simple method for eliminating VOCs, which can be converted into CO2 and H2O without the generation of other harmful substances. The fabrication and development of catalysts are very crucial to enhance the catalytic oxidation efficiency of the removal of VOCs. The noble metal catalyst is one of the commonly used catalysts for the catalytic oxidation of VOCs because of the high reaction activity, good stability, poisoning-resistant ability, and easy regeneration. In this review, the research progress of noble metal (Pt, Pd, Au, Ag, and Ir) catalysts for the removal of VOCs in recent years was summarized with the discussion of the influence factors in the preparation process on the catalytic performance. The reaction mechanisms of the removal of VOCs over the corresponding noble metal catalysts were also briefly discussed.
Journal Article