Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2-x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen vacancies are generated as a consequence of electron donation from metal copper atoms to CeO2 acceptor and the subsequent reverse spillover of oxygen induced by electron transfer in well controlled nanoheterojunction. The anchored oxygen vacancies play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interfaces, thus leading to an excellent preferential CO oxidation performance. This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces.

This work reports on the preparation of a noble-metal-free and highly active catalyst that proved to be an efficient and green reductant with renewable capacity. Nitridation of a silent Ta1.1O1.05 substrate led to the formation of a series of TaOxNy hollow nanocrystals that exhibited outstanding activity toward catalytic reduction of nitrobenzenes under ambient conditions. ESR and XPS results indicated that defective nitrogen species and oxygen vacancies at the surfaces of the TaOxNy nanocrystals may play synergetic roles in the reduction of nitrobenzenes. The underlying mechanism is completely different from those previously reported for metallic nanoparticles. This work may provide new possibilities for the development of novel defect-meditated catalytic systems and offer a strategy for tuning any catalysts from silent to highly reactive by carefully tailoring the chemical composition and surface defect chemistry.

This work addresses the chemical nature of the catalytic activity of X-ray "pure" CoO nanocrystals. All samples were prepared by a solvothermal reaction route. X-ray diffraction indicates the formation of CoO in a cubic rock-salt structure, while infrared spectra and magnetic measurements demonstrate the coexistence of CoO and Co 3O 4. Therefore, X-ray "pure" CoO nanocrystals are a unique composite structure with a CoO core surrounded by an extremely thin Co 3O 4 surface layer, which is likely a consequence of the surface passivation of CoO nanocrystals from the air oxidation at room temperature. The CoO core shows a particle size of 22 or 280 nm, depending on the types of the precursors used. This composite nanostructure was initiated as a catalytic additive to promote the thermal decomposition of ammonium perchlorate (AP). Our preliminary investigations indicate that the maximum decomposition temperature of AP is significantly reduced in the presence of CoO/Co 3O 4 composite nanocrystals and that the maximum decomposition peak shifts toward lower temperatures as the loading amount of the composite nanocrystals increases. These findings are different from the literature reports when using many nanoscale oxide additives. Finally, the decomposition heat for the low-temperature decomposition stages of AP was calculated and correlated to the chemical nature of the CoO/Co 3O 4 composite nanostructures.

No abstract

Nanomaterials are widely used as redox-type reaction catalysts, while reactant adsorption and O2 activation are hardly to be promoted simultaneously, restricting their applications in many important catalytic fields such as preferential CO oxidation (CO-PROX) in H2-rich stream. In this work, an interface-enhanced Co3O4–CuCoO2 nanomesh was initially synthesized by a hydrothermal process using aluminum powder as a sacrificial agent. This nanomesh is systematically characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption, X-ray photoelectron spectroscopy, UV–vis absorption spectroscopy, Raman spectroscopy, X-ray absorption near-edge spectroscopy, hydrogen temperature-programmed reduction, and oxygen temperature-programmed desorption. It is demonstrated that the nanomesh possesses high-density nanopores, enabling a large number of CO adsorption sites exposed to the surface. Meanwhile, electron transfer from O2– to Co3+/Co2+ and the weakened bonding strength of Co–O bond at surfaces promoted the oxygen activation and redox ability of Co3O4. When tested as a catalyst for CO-PROX, this nanomesh with an optimized pore structure and a surface electronic structure, exhibits a strikingly high catalytic oxidation activity at low temperatures as well as a broader operation temperature window (i.e., CO conversion >99.0%, 100–200 °C) in the CO selective oxidation reaction. The present finding should be highly useful in promoting the quest for better CO-PROX catalysts, a hot topic for proton exchange membrane fuel cells and automotive vehicles.

No abstract

No abstract

Photocatalytic pathways are proved crucial for the sustainable production of chemicals and fuels required for a pollution‐free planet. Electron–hole recombination is a critical problem that has, so far, limited the efficiency of the most promising photocatalytic materials. Here, the efficacy of the 0D N doped carbon quantum dots (N‐CQDs) is demonstrated in accelerating the charge separation and transfer and thereby boosting the activity of a narrow‐bandgap SnS2 photocatalytic system. N‐CQDs are in situ loaded onto SnS2 nanosheets in forming N‐CQDs/SnS2 composite via an electrostatic interaction under hydrothermal conditions. Cr(VI) photoreduction rate of N‐CQDs/SnS2 is highly enhanced by engineering the loading contents of N‐CQDs, in which the optimal N‐CQDs/SnS2 with 40 mol% N‐CQDs exhibits a remarkable Cr(VI) photoreduction rate of 0.148 min−1, about 5‐time and 148‐time higher than that of SnS2 and N‐CQDs, respectively. Examining the photoexcited charges via zeta potential, X‐ray photoelectron spectroscopy (XPS), surface photovoltage, and electrochemical impedance spectra indicate that the improved Cr(VI) photodegradation rate is linked to the strong electrostatic attraction between N‐CQDs and SnS2 nanosheets in composite, which favors efficient carrier utilization. To further boost the carrier utilization, 4‐nitrophenol is introduced in this photocatalytic system and the efficiency of Cr(VI) photoreduction is further promoted.