Denitrification technology and its catalysts have received widespread attention in the industry due to the acceleration of industrialization and environmental pollution issues. The selection of various denitrification technologies and catalysts on the market has also brought broad application prospects. This article reviews the advantages and disadvantages, mechanism of action, and application prospects of denitrification technologies and catalysts, and proposes the future challenges of denitrification technologies and catalysts in actual production.

Abstract

With the acceleration of industrialization and the increasing prominence of environmental pollution problems, the emission of nitrogen oxides (NO_x) in the atmosphere has become a global concern. These emissions are not only hazardous to human health, but also one of the main factors leading to acid rain, photochemical smog and global climate change. Therefore, the development and implementation of efficient denitrification technologies are an important issue for environmental protection. The present review focuses on the research progress of the denitrification technology in the recent years, including the traditional denitrification methods and common technologies. At the same time, the advantages, limitations and application prospects of each method are analyzed. The mechanisms, influencing factors, advantages and disadvantages of the denitrification catalysts are also discussed. In addition, the future research trends and potential challenges of denitrification technology are discussed. It is expected that this review will provide useful references for promoting the development and application of denitrification technology, which may help researchers to choose high-performance and cost-effective methods.

The catalytic performance of Mo₂C MXene for reverse water gas shift (RGWS) reaction is computationally assessed on an holistic fashion, unveiling the reaction mechanism and its thermodynamics through density functional theory (DFT) calculations on suitable models, and gaining information about kinetics, and dynamics aspects by means of mean-field microkinetic modelling (MKM), and kinetic Monte Carlo (kMC) simulations.

Abstract

Pristine Mo₂C MXene has been proposed as an heterogeneous catalysis of the reverse water gas shift (RWGS) reaction. The present computational study aims at understanding its catalytic performance and reaction mechanisms tackling its thermodynamics, kinetics, and surface dynamic effects, combining Gibbs free energy profiles gained by density functional theory (DFT), mean-field kinetics by microkinetic modeling, and rare-event steps by kinetic Monte Carlo (kMC). The RWGS endergonicity goes for the use of high temperatures and reactants partial pressures to make the reaction exergonic. Gibbs free energy profiles show a preference for redox mechanism, whereas microkinetic simulations favor a low-temperature preference of formate mechanism. The kMC reveals simultaneous operating redox and formate pathways, where surface coverage disfavors redox favoring the formate pathway. A peak performance is found at 700 K, in line with reported experiments, where the formation of surface O₂* is found to be key, acting as a reservoir for O* adatoms while freeing surface sites upon O₂* formation. Even though high turnover frequencies are predicted, the system could benefit from swing operando conditions, alternating CO production steps with H₂ reduction regeneration steps, and/or ways to reduce the surface O₂* and so to have more active catalytic sites.

Several strategies to improve the Ag/CaTiO₃ (Ag/CTO) photocatalysts for selective photocatalytic CO₂ reduction with water to form CO are shortly reviewed, such as fabrication of well–structured fine crystal photocatalysts with moderate size, modification of Ag NPs cocatalyst with size control or additives, enhancement of surface CO₂ adsorption, development of dual cocatalyst, and improvement of photoabsorption.

Abstract

The rapid increase of carbon dioxide (CO₂) in the atmosphere has sparked a global enthusiasm for carbon recycling. Photocatalytic CO₂ reduction with water into carbon–containing products has attracted much attention since it can convert solar energy to the chemical potential of the products and CO₂ to valuable compounds at the same time. One of the main products in the photocatalytic reaction system is carbon monoxide (CO), a useful compound for the one-carbon chemistry and related ones. The current shortage of this system is the low production efficiency, demanding us to improve the activity of the photocatalyst. In this perspective article, by taking a calcium titanate (CaTiO₃, CTO) photocatalyst with silver cocatalyst (Ag/CTO) and so on as examples that can promote the selective photocatalytic CO₂ reduction with water, we shortly review some strategies to improve the photocatalytic activity such as fabrication of well–structured crystal photocatalysts, development of the surface property and cocatalyst, improvement of surface CO₂ adsorption, and improvement of photoabsorption. These concepts will be widely applied and contribute to further development of photocatalytic systems.

Utilizing MgAl₂O₄ as a support for Mn-doped K₂WO₄ catalysts to maintain high surface area under the harsh reaction conditions of OCM, to get high CH₄ conversion rata, compared with commonly used SiO₂ support.

Abstract

The oxidative coupling of methane (OCM) provides a direct route to transform methane into higher value products. The alkali metal tungstate catalysts have demonstrated high selectivity towards C₂ products, ethane (C₂H₆) and ethylene (C₂H₄). However, the severe sintering of the SiO₂ support limits the reaction rate requiring active site densification to compete with unselective gas phase combustion reaction especially at high pressure operations. This work studies alkaline earth metal oxides as supports for K₂WO₄ catalysts to maintain comparatively high surface area under OCM conditions. Among Mg, Ca, and Sr aluminates, the K₂WO₄/MgAl₂O₄ catalyst exhibited the highest C₂ yields. To achieve high C₂ product selectivity, a relatively large loading of K₂WO₄ (20 wt %) was required likely to cover the unselective surface sites of MgAl₂O₄ support. The catalyst further showed high levels of stability when utilized at high pressures (0.9 MPa) for over 60 h, without any change in product selectivity. The Mn/K₂WO₄/MgAl₂O₄ showed multifold higher CH₄ conversion rate, compared with the SiO₂ counterpart. The findings showcase the potential of the MgAl₂O₄ support as a viable candidate for alkali metal tungstate catalysts for OCM, which introduces high density of active components in given volume in the reactor, which induces high contribution of the catalyst relative to the pure gas phase oxidation.

Abstract. Liquid multiphase systems (MPS) have gained attention in recent years due to their versatility for catalytic processes. This review article presents a critical discussion of the most recent advances on the utilization of MPS in both homogeneous and heterogeneous metal-catalyzed reactions. Pros and cons of some exemplificative multiphase configurations are highlighted and compared to conventional methods in single liquid solvents. The application of MPS for the implementation of strategies for the upgrading of biobased molecules is also examined with emphasis on process intensification and sustainability including the catalyst/products separation and the in-situ recycle and reuse of the metal catalysts. These aspects are analyzed with a view on expanding MPS applications and whenever possible, explore scaleup opportunities.

Over the past few decades, a significant amount of research effort has focused on investigating the active site requirements and reaction mechanisms for partial methane oxidation (PMO) to methanol over copper-exchanged zeolites during stoichiometric and stepwise chemical looping routes. More recently, research efforts have expanded to include investigating the PMO reaction in a continuous catalytic regime, primarily focusing on determining the influence of catalyst composition on Cu speciation and structure and, in turn, on PMO rate and selectivity. The structures of candidate Cu active sites are commonly studied using a combination of ex situ and in situ spectroscopic approaches. In this perspective, we critically examine the prior literature on catalytic PMO over Cu-zeolites to identify key knowledge gaps that remain in our understanding as motivation for future research efforts. We identify opportunities for future research to address these gaps by adapting analogous interrogation techniques that have been successfully used to elucidate the active site requirements and mechanistic details of another catalytic redox reaction cycle on Cu-zeolites, the selective catalytic reduction (SCR) of nitrogen oxides (NOx).

Carbon dots (CDs) have attracted much attention in the field of electrocatalysis due to their many advantages. These reactions are of great significance for energy conversion and storage, as well as environmental remediation. In this review, we summarize the latest achievements in the electrochemical applications of CDs and their composites, with a focus on environmentally relevant electrocatalysis. We present some representative examples of CDs-based electrocatalysts for different reactions and analyze the catalytic mechanisms and the factors that affect the electrocatalytic performance. Furthermore, we conclude with some challenging issues and future perspectives of this emerging material. This review aims to help readers better understand the application of CDs in the field of electrocatalysis, reveal the reasons that affect electrocatalytic performance, and guide further constructing more efficient, stable, and green electrocatalysts.

Molybdenum triazolylidene complexes displayed excellent catalytic activity in the synthesis of a wide variety of quinolines through acceptorless dehydrogenative coupling reactions.

Abstract

The first molybdenum triazolylidene complexes catalyzing the atom-economical synthesis of quinolines through acceptorless dehydrogenative coupling of alcohols is reported. A new family of Mo(0) complexes bearing chelating bis-1,2,3-triazolylidene, pyridyl-1,2,3-triazolylidene, and bis-triazole ligands have been prepared and applied as catalysts for the synthesis of quinolines. Interestingly, Mo complexes bearing bis-1,2,3-triazolylidene ligands with alkyl groups (Et, n-Bu) displayed superior catalytic activities than those containing aryl substituents on the triazolylidene rings. Control experiments corroborated that the catalytic reaction involves the dehydrogenation pathway.

carbon nanotubes (CNTs) have been demonstrated to have far-reaching applications in modifying electrodes, and electrocatalysts due to their high surface area and high mobility for charge carriers. Present study shows a catalyst constructed from covalent modification of CNTs with B₄C for electrochemical nitrogen reduction. The formation of new C−B−O covalent bonds was verified by a series of characterizations.

Abstract

Electrochemical reduction of N₂ to NH₃ provides an alternative to the Haber-Bosch process for sustainable NH₃ production driven by renewable electricity. Here, we reported carbon nanotubes (CNTs) covalently modified with boron carbide (B₄C) as a nonmetallic catalyst for efficient electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The structure of the catalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), elemental mapping, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The catalyst held a superior selectivity for NRR with high Faraday efficiency of 78.2 % accompanying with NH₃ yield rate of 14.0 μg mg⁻¹ _cat. h⁻¹ under the condition of 0.1 M Na₂SO₄ and −0.6 V vs. RHE. Electrochemical experiments including cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization curves were performed to explain the best electrochemical properties of B₄C/CNTs among the samples. This work demonstrates that the strategy of covalent modification plays an important role to improve the selectivity of electrochemical NRR catalyst, thus allowing the reactions to proceed more efficiently.

The remediation of polluted water is a major concern for public health and the environment. Catalytic removal of model organic and inorganic pollutants in water using carbon catalysts has shown promising results. In the present work, stereolithographically 3D-printed bio-based carbon monoliths with different textural and surface chemistry properties were used as catalysts for oxalic acid oxidation and catalyst supports for bromate reduction in continuous systems. A significant synergistic effect between ozone or dihydrogen and carbon catalyst was evidenced by mineralization of 14-25 % of oxalic acid or reduction of 15-45 % of bromates in the steady state, respectively. The best results were achieved with samples with the highest mesoporous surface area or, in the case of lower surface area, with samples having the strongest basic character. As materials with great potential, optimizing the textural properties of architected carbon monoliths will enable them to compete with other macro-structured carbon catalysts.