Noble-Metal-Based Catalytic Oxidation Technology Trends for Volatile Organic Compound (VOC) Removal

Volatile organic compounds (VOCs) are toxic and are considered the most important sources for the formation of photochemical smog, secondary organic aerosols (SOAs), and ozone. These can also greatly affect the environment and human health. For this reason, VOCs are removed by applying various technologies or reused after recovery. Catalytic oxidation for VOCs removal is widely applied in the industry and is regarded as an efficient and economical method compared to other VOCs removal technologies. Currently, a large amount of VOCs are generated in industries with solvent-based processes, and the ratio of aromatic compounds is high. This paper covers recent catalytic developments in VOC combustion over noble-metal-based catalysts. In addition, this report introduces recent trends in the development of the catalytic mechanisms of VOC combustion and the deactivation of catalysts, such as coke formation, poisoning, sintering, and catalyst regeneration. Since VOC oxidation by noble metal catalysts depends on the support of and mixing catalysts, an appropriate catalyst should be used according to reaction characteristics. Moreover, noble metal catalysts are used together with non-noble metals and play a role in the activity of other catalysts. Therefore, further elucidation of their function and catalytic mechanism in VOC removal is required.

Atomically dispersed Co-N-C electrocatalysts synthesized by a low-speed ball milling method for proton exchange membrane fuel cells

Atomically dispersed cobalt-nitrogen-carbon (Co-N-C) catalysts have appeared as the potential substitutes to the costly noble-metal catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). After...

A Novel Pd-P Nano-Alloy Supported on Functionalized Silica for Catalytic Aerobic Oxidation of Benzyl Alcohol

Catalytic aerobic oxidation of benzyl alcohol (BnOH) to benzaldehyde (PhCHO) over supported noble metal catalysts has grabbed the attention of researchers due to the critical role of PhCHO in numerous industrial syntheses. In the present study, a novel catalyst, Pd-P alloy supported on aminopropyl-functionalized mesoporous silica (NH2-SiO2), was prepared through in situ reduction and characterized by BET-BJH analysis, SEM, TEM, XRD, FTIR, TG-DTA, and XPS. Chemical properties and catalytic performance of Pd-P/NH2-SiO2 were compared with those of Pd0 nanoparticles (NPs) deposited on the same support. Over Pd-P/NH2-SiO2, the BnOH conversion to PhCHO was much higher than over Pd0/NH2-SiO2, and significantly influenced by the nature of solvent, reaching 57% in toluene at 111 °C, with 63% selectivity. Using pure oxygen as an oxidant in the same conditions, the BnOH conversion increased up to 78%, with 66% selectivity. The role of phosphorous in improving the activity may consist of the strong interaction with Pd that favours metal dispersion and lowers Pd electron density.

Smart Designs of Mo Based Electrocatalysts for Hydrogen Evolution Reaction

As a sustainable and clean energy source, hydrogen can be generated by electrolytic water splitting (i.e., a hydrogen evolution reaction, HER). Compared with conventional noble metal catalysts (e.g., Pt), Mo based materials have been deemed as a promising alternative, with a relatively low cost and comparable catalytic performances. In this review, we demonstrate a comprehensive summary of various Mo based materials, such as MoO2, MoS2 and Mo2C. Moreover, state of the art designs of the catalyst structures are presented, to improve the activity and stability for hydrogen evolution, including Mo based carbon composites, heteroatom doping and heterostructure construction. The structure–performance relationships relating to the number of active sites, electron/ion conductivity, H/H2O binding and activation energy, as well as hydrophilicity, are discussed in depth. Finally, conclusive remarks and future works are proposed.

Divergent functionalization of aldehydes photocatalyzed by neutral eosin Y with sulfone reagents

While aldehydes represent a classic class of electrophilic synthons, the corresponding acyl radicals are inherently nucleophilic, which exhibits umpolung reactivity. Generation of acyl radicals typically requires noble metal catalysts or excess oxidants to be added. Herein, we report a convenient and green approach to access acyl radicals, capitalizing on neutral eosin Y-enabled hydrogen atom transfer (HAT) photocatalysis with aldehydes. The generated acyl radicals underwent SOMOphilic substitutions with various functionalized sulfones (X–SO2R’) to deliver value-added acyl products. The merger of eosin Y photocatalysis and sulfone-based SOMOphiles provides a versatile platform for a wide array of aldehydic C–H functionalizations, including fluoromethylthiolation, arylthiolation, alkynylation, alkenylation and azidation. The present protocol features green characteristics, such as being free of metals, harmful oxidants and additives; step-economic; redox-neutral; and amenable to scale-up assisted by continuous-flow technology.

Dual-functional cobalt catalyst enables electrocatalytic allylic C–H alkylation

Transition metal-catalyzed allylic substitution reactions of pre-activated allylation agents with nucleophiles are extensively studied synthetic methods that have enjoyed widespread applications in organic synthesis. The direct alkylation of allylic C–H bonds with nucleophiles, which minimizes pre-functionalization and converts inexpensive, abundantly available materials to value-added alkenyl-substituted products, remains challenging. Current methods generally involve C–H activation, require the use of noble-metal catalysts and stoichiometric chemical oxidants, and often show limited scope. Here we report an electrocatalytic allylic C–H alkylation reaction with carbon nucleophiles employing an easily available cobalt-salen complex as the molecular catalyst. These C(sp3)–H/C(sp3)–H cross-coupling reactions proceed through H2 evolution and require no external chemical oxidants. Importantly, the mild conditions and radical mechanism ensure excellent functional group tolerance and substrate compatibility with both linear and branched terminal alkenes. The synthetic utility of the electrochemical method is highlighted by its scalability (up to 200 mmol scale) and its successful application in the late-stage functionalization of complex structures.