CeO2 with varied morphologies (nanopolyhedra, nanorods, and nanocubes) were synthesized via a hydrothermal method and applied to the catalytic combustion of toluene. The physicochemical properties of all catalysts were characterized by transmission electron microscopy, N2-physisorption, X-ray diffraction, H2-temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The CeO2 nanopolyhedra showed superior catalytic activity compared to CeO2 nanorods and nanocubes. Kinetic studies showed that the catalytic combustion of toluene processed through the Mars–van-Krevelen (MvK) mechanism and the oxidation of the reduced CeO2 surface by molecular oxygen are the rate-determining steps in the low-temperature region. The XPS and H2-TPR results showed that CeO2 with varied morphologies had distinct oxygen distribution, especially surface lattice oxygen. A linear relationship between surface lattice oxygen and catalytic activity was observed, indicating that surface lattice oxygen played an important role in the catalytic activity of toluene combustion. Furthermore, the in situ DRIFTS results provided a full roadmap of catalytic combustion of toluene: toluene first rapidly adsorbed onto the surface of CeO2 to form molecularly adsorbed toluene, which then reacted with the surface hydroxyl groups to generate benzyl species without O2. The benzyl species could be further oxidized to benzyloxy, benzaldehyde, and benzoate species, and finally fully oxidized to CO2 and H2O. All these results indicated that the reactivity of surface lattice oxygen was crucial on the catalytic combustion of toluene, providing a basic understanding for the catalytic combustion of toluene on CeO2 with varied morphologies.

An unprecedented ordered mesoporous carbon material co-doped with nitrogen and iron shows high activity for ORR catalysis in alkaline electrolyte.

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via the overall reaction of H 2 with O 2 , only giving rise to water without pollution. Beyond that, hydrogen fuel cells have also high safety, quick-refueling, fast-charging, power grid compatibility, and high energy conversion efficiency (40-70%) even restricted by polarization in practical conditions, which make them potential for long-range and high-utilization transportation as electric vehicles. [2] The energy conversion efficiency mainly depends on the cathodic oxygen reduction reaction (ORR) due to its naturally complex and sluggish kinetics as compared to the anodic hydrogen oxidation reduction during electron transfer. [3] It is, as such, highly desirable to employ efficient electrocatalysts, capable in alleviating overpotentials of electrocatalytic ORR while also, promoting the slow transformation process. Currently, the expensive platinum (Pt) electrocatalysts still exhibit unparalleled catalytic performance for ORR; [4] however, the scarcity of resources, sluggish ORR kinetics, inferior operational stability, and susceptibility to poisoning of the Pt catalysts result in high cost, which remains to be one of key factors that hamper commercial applications of fuel cells. [1a,5] At this juncture, the replacement of costly Pt-based catalysts with other cost-effective, high-performing and durable nonprecious metal catalysts (NPMCs) for ORR is urgently needed. [6] In pursuit of a diverse class NPMCs, M/N codoped M-N-C (M = Fe, Co, Ni, etc.) especially Fe-N-C catalysts, widely prepared by annealing a compound of carbon carriers, nitrogen-containing precursors and transition metal salts or without carbon supports under inert or reactive gas, attract substantial interest due to comparable activity with that of benchmark Pt/C for ORR in alkaline media. [7] However, their volumetric activity is still far from that of Pt/C. Furthermore, their stability remains poor in acid because of the dissolution of Fe-based species associated with active sites. [4b,8] As such, Fe-N-C catalysts demonstrate low competency for proton exchange membrane fuel cell (PEMFC) application at present. It is greatly challenging but yet, extremely desirable to exploit novel NPMCs having outstanding activity and durability in ORR. Elucidation of the active site nature and pursuit of unprecedented high ORR activity and stability motivates design of unique NPMCs. Recently, transition-metal carbides, such as Fe 3 C, Fuel cells represent the most suitable energy conversion, capable of addressing energy crises and environmental pollution. Recently, as one of nonprecious metal catalysts (NPMCs), the MC@N-C (M = Fe, Co, Ni, Mo, W) catalysts, especially for Fe 3 C encased in carbon layer (denoted as Fe 3 C@N-C) have emerged as promising replacements for costly Pt-based catalysts for oxygen reduction reaction (ORR). This review highlights the synthetic strategies undertaken such as hard template, soft template, and template-free methods for deriving enhancements in electrocatalytic activity and durability. It also provides a comparison on the synth...

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Over the past several years, selective catalytic reduction of NO x with hydrogen (H2-SCR) has been regarded as a promising technology for NO x abatement under lean-burn conditions. In this review, we discuss the recent progress in the development and understanding of H2-SCR catalysts. The various mechanisms that have been proposed in the literature are reviewed first. The influence of the catalyst chemical components (noble metals, supports, promoters, and perovskites) and their roles in H2-SCR are then analyzed. Non-noble metal catalysts and the new strategy of alloying Pt with transition metals (Ni, Fe, Co, and Cu) are of particular interest and discussed. From a practical viewpoint, the effects of exhaust gas composition on H2-SCR is also addressed. Finally, we propose potential opportunities and challenges in the area of H2-SCR.

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