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Abstract Modulating unique microenvironment including both oxidation and metallic states on sub-nanocluster metal catalysts remains challenging, since designing heterogeneous catalysis within controllable oxidation state is necessary for achieving optimum performance. Here we construct stable sub-nano-Co clusters, which shows different microenvironment with the reported sub-nanocluster catalysts and reported Co-based catalysts. The coexistence of both ionic bonds of Co-O and metallic bonds of Co-Co shows features of multiple oxidation and metallic states, which changes the electronic orbital configuration of the individual Co atom in clusters. The specific microenvironment within low oxidation state and high electron density promotes combination of empty and filled host orbitals to yield high electron transfer between metal and propane, which exhibits higher reactivity than the reported Co-based and other non-noble metals catalysts. The desired reactivity offers the possibility for the exploitation of highly efficient non-noble metal catalysts for propane dehydrogenation in industrial applications.

Volatile organic compounds (VOCs) have boiling points ranging from 50 ℃ to 260 ℃ at room temperature. These compounds are emitted from complex sources, including automobile manufacturing, fine chemicals, the pharmaceutical industry, interior decoration, and the plastics industry. VOCs serve as important precursors of secondary organic aerosols and ozone. However, some VOCs discharged into the atmosphere undergo photochemical reactions, resulting in the formation of photochemical smog. This byproduct is irritating, teratogenic, and carcinogenic, causing considerable harm to human health and posing a serious threat to the environment. Among VOCs, aromatic hydrocarbons originate from a wide range of sources relevant to human life. These compounds have been a constant hot spot in the field of VOC removal due to their unique aromatic ring structure, highly toxic effects, and challenging treatment. VOC removal mainly comprises source reduction, process management, and end–to–end treatment. End–to–end treatment methods involve adsorption, photocatalytic, plasma decomposition, membrane separation, and catalytic oxidation. Catalytic oxidation can effectively convert VOCs into carbon dioxide and water at relatively low temperatures, making it one of the most effective methods for VOC treatment. Efficient catalyst development is the key point for catalytic oxidation methods. This review highlights progress in catalyst development for the catalytic oxidation of toluene, focusing on the characteristics of noble-metal catalysts, such as noble-metal species, particle size, alloying systems, and support properties. While transition-metal oxide catalysts are abundant and inexpensive, they exhibit low catalytic performance for toluene oxidation. Therefore, discussions on transition-metal oxide catalysts include synthesis or calcination temperature, atomic substitution (isovalent and heterovalent substitutions), surface modification (noble- and transition-metal doping), and in situ surface treatment (chemical etching and surface modification). Although studies on toluene degradation using spinel- and perovskite-type oxide catalysts and metal-organic framework-based catalysts are limited, a brief summary of their characteristics during catalytic oxidation of toluene is provided, focusing on the relationship between the catalyst microstructure and performance. Furthermore, the kinetic model for the catalytic oxidation of toluene was briefly evaluated, and the corresponding reaction mechanism and kinetics were analyzed. This review aims to contribute to the development of efficient catalysts for the complete or selective oxidation of toluene.

Developing the alternative supported noble metal catalysts with low cost, high catalytic efficiency, and good resistance toward carbon dioxide and water vapor is critically demanded for the oxidative removal of volatile organic compounds (VOCs). In this work, we prepared the mesoporous chromia-supported bimetallic Co and Ni single-atom (Co1Ni1/meso-Cr2O3) and bimetallic Co and Ni nanoparticle (CoNPNiNP/meso-Cr2O3) catalysts adopting the one-pot polyvinyl pyrrolidone (PVP)- and polyvinyl alcohol (PVA)-protecting approaches, respectively. The results indicate that the Co1Ni1/meso-Cr2O3 catalyst exhibited the best catalytic activity for n-hexane (C6H14) combustion (T50% and T90% were 239 and 263 °C at a space velocity of 40,000 mL g−1 h−1; apparent activation energy and specific reaction rate at 260 °C were 54.7 kJ mol−1 and 4.3 × 10−7 mol gcat−1 s−1, respectively), which was associated with its higher (Cr5+ + Cr6+) amount, large n-hexane adsorption capacity, and good lattice oxygen mobility that could enhance the deep oxidation of n-hexane, in which Ni1 was beneficial for the enhancements in surface lattice oxygen mobility and low-temperature reducibility, while Co1 preferred to generate higher contents of the high-valence states of chromium and surface oxygen species as well as adsorption and activation of n-hexane. n-Hexane combustion takes place via the Mars−van Krevelen (MvK) mechanism, and its reaction pathways are as follows: n-hexane → olefins or 3-hexyl hydroperoxide → 3-hexanone, 2-hexanone or 2,5-dimethyltetrahydrofuran → 2-methyloxirane or 2-ethyl-oxetane → acrylic acid → COx → CO2 and H2O.

Chlorinated volatile organic compounds (CVOCs) are persistent pollutants and harmful to the atmosphere, environment, and human health. The catalytic elimination of CVOCs has become a hotspot of interest due to their self-toxicity, the secondary generation of chlorinated by-products, and the Cl poisoning of catalysts. The development of high-performance, highly selective, and anti-poisoning catalysts is a critical issue. Bimetallic catalysts exhibit an improved dechlorination performance, poisoning resistance, and product selectivity through the modulation of geometrical and electronic structures. The present review article gives a brief overview of the recent advancements in the preparation of bimetallic catalysts and their catalytic CVOC elimination activities. In addition, representative case studies are provided to investigate the physicochemical properties, CVOC conversion, COx and inorganic chlorine species selectivities, and by-product control so that the structure–performance relationships of bimetallic catalysts can be established. Furthermore, this review article provides a fundamental understanding of designing bimetallic catalysts with specific active components and the desired physicochemical properties for target reactions. In the end, related perspectives for future work are proposed.

Intermetallic compounds (IMCs) have attracted significant attention in recent years due to their unique properties and potential applications in various fields, particularly in catalysis. This review aims to provide an in-depth understanding of IMCs, including their synthesis methods, structural characteristics, and diverse catalytic applications. The review begins with an introduction to IMCs, highlighting their distinct features and advantages over traditional catalyst materials. It then delves into the synthesis techniques employed to prepare IMCs and explores their structural properties. Subsequently, catalytic applications of the IMCs are introduced, focusing on the key reactions and highlighting their superior catalytic performance compared to conventional catalysts. Future perspectives for, and challenges to, the catalysis of IMCs are then proposed.