Three-dimensionally ordered macroporous Au/CeO2–Co3O4 catalysts with mesoporous walls for enhanced CO preferential oxidation in H2-rich gases

Ordered porous nitrogen-vacancy carbon nitride for efficient visible-light hydrogen evolution

Photocatalytic H₂ evolution is a promising technology which could be instrumental in producing clean hydrogen energy. In regard to the photocatalyst, its band structure, morphology and light utilization have a significant influence on the H₂ evolution rate and stability. Herein, a three-dimensional ordered macroporous nitrogen-vacancy carbon nitride (3DOM V-CN) photocatalyst was developed by combining vacancies with 3DOM structure for visible-light photocatalytic H₂ evolution. This strategy preserved the structural properties of 3DOM to improve the light utilization and the specific surface area of the photocatalysts. Moreover, constructing suitable vacancies could trap electrons to facilitate the separation of photogenerated carriers, and extend the light absorption region of the photocatalysts by adjusting band structure, thus improving photocatalytic activity. Compared with CN (0.3 mmol h^-1 g^-1), 3DOM V-CN demonstrated a superior photocatalytic H₂ evolution rate of 2.3 mmol h^-1 g^-1 (λ ≥ 420 nm) while possessing excellent stability. This work provides an effective and low-cost strategy for the design of the photocatalysts with high activity and stability by simultaneously tuning the band structure and morphology.

The preparation of ultrastable Al3+ doped CeO2 supported Au catalysts: Strong metal-support interaction for superior catalytic activity towards CO oxidation

The classical strong metal-support interaction (SMSI) plays a key role in improving thermal stability for supported Au catalysts. However, it always decreases the catalytic activity because of the encapsulation of Au species by support. Herein, we demonstrate that Al³⁺ is a functional additive which could effectively improve both catalytic activity and sintering resistant property for H₂ pretreated Al³⁺ doped CeO₂ supported Au (AuCeAl) catalyst at high temperature. The physical characterization and in-situ DRIFTS results provide insight that more oxygen vacancies generated by Al³⁺ doping could be as preferential adsorption sites for CO molecules when the encapsulation of Au species occurred, which is certificated by an accelerated formation of bicarbonate species. In the meantime, smaller Au nanoparticles with higher dispersion (2.8 nm, 85.63%) is achieved in AuCeAl catalysts, compared with that in CeO₂ supported Au (AuCe) catalysts (5.1 nm, 36.17%). Additionally, the as-prepared AuCeAl catalysts also have superior catalytic performance even after calcination at 800 °C in air.

Complete Benzene Oxidation over Mono and Bimetallic Pd—Au Catalysts on Alumina-Supported Y-Doped Ceria

The protection of environment and human health stimulates intensive research for abatement of volatile organic compounds (VOCs) in the atmosphere. Complete catalytic oxidation is an efficient, environmentally friendly and economically feasible method for elimination of VOCs. This study aims to design high performing and cost-effective catalytic formulations by exploration of appropriate and economically viable supports. Alumina-supported ceria (30 wt.%) and Y2O3 (1 wt.%)-doped ceria were prepared by mechanical mixing and were used as support of mono Au (2 wt.%) and Pd (1 wt.%) and bimetallic Pd-Au catalysts. The characterization by textural measurements, X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), EPR (electron paramagnetic resonance) and temperature-programmed reduction (TPR) was carried out in order to clarify the relationship between catalyst composition, textural, structural and surface properties, reducibility and catalytic performance for complete benzene oxidation. Among all studied catalysts, Pd-based catalysts exhibited the best combustion activity. In particular, monometallic Pd on alumina supported Y-doped ceria attained 100% of complete benzene conversion at 180 °C. These catalytic materials have potential to meet stringent emission regulations in an economical and effective way.

Recent advances in synergistic effect promoted catalysts for preferential oxidation of carbon monoxide

We reviewed recent advances in catalysts for PROX with emphasis on synergistic effects that contribute to enhanced catalytic performance.

Novel core-shell nanocomposites based on TiO2 -covered magnetic Co3 O4 for biomedical applications

Magnetic Co₃ O₄ nanoparticles (NPs) have great potential for applications in biomedicine, as contrast enhancement agents for magnetic resonance imaging, or for drug delivery. Although these NPs are so attractive, their potential toxicity raises serious questions about decreasing cellular viability. In this context, Co₃ O₄ NPs were prepared via sol-gel method and encapsulated with a layer of TiO₂ , a biocompatible oxide, and subjected to structural, magnetic and toxicity characterization. X-ray diffractograms of the samples demonstrate the successful synthesis of the spinel and Raman spectroscopy confirms the coating of the Co₃ O₄ spinel with TiO₂ . The Co₃ O₄ cores showed a very intense superparamagnetic character; however, this behavior is strongly suppressed when the material is covered with TiO₂ . According to the neutral red uptake assay, the coating of the cores with TiO₂ significantly decreases the cytotoxic character of the Co₃ O₄ particles and, as it can be observed with the zeta (ξ) potential measurements, they form a stable colloidal dispersion at cytoplasmic pH. The effect of the thermal treatment enhances the biocompatibility even further, with no statistically significant effect on cell viability even at the highest analyzed concentration. The proposed pathway presents a successful sol-gel method for the preparation of Co₃ O₄ @TiO₂ core-shell nanoparticles. This work opens up possibilities for future application of these materials not only for magnetic resonance imaging but also in catalysis and hyperthermia.

3D Gold-Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation

A hard template method is used to prepare porous gold-doped cerium and cobalt oxide (Au-Ce_x Co_y ) materials. A series of 3D Au-Ce _x Co_y /graphene aerogel (GA) composites is then fabricated by a facile heating method. The obtained catalysts possess a well-defined structure of ordered arrays of nanotubes and good performance in formaldehyde (HCHO) oxidation. The composition and surface elemental valence states of the catalysts are modulated by the Ce/Co molar ratio. The Au-Ce_x Co_y catalyst and graphene oxide sheets are well compounded within 60 s through a diamine cross-linker to form 3D Au-Ce_x Co_y /GA composites. In addition, the resulting catalyst of 3 wt% Au-Ce₃ Co/GA achieves ≈55% conversion at room temperature and 100% conversion when the reaction temperature is raised at 60 °C. The synergistic effect between CeO₂ and Co₃ O₄ promotes the migration of oxygen species and the activation of Au, which facilitates HCHO oxidation. The method used to prepare the 3D catalyst could be used to produce other catalytic materials with good replication of the template. In addition, these findings provide a simple method for rapid fabrication of catalyst/GA composites. The superior activity and stability of the 3D Au-Ce₃ Co/GA catalyst make it potentially applicable in HCHO removal.

Enhancement of the visible-light photocatalytic activity of CeO2 by chemisorbed oxygen in the selective oxidation of benzyl alcohol

Enriched chemisorbed oxygen on CeO₂ significantly improved the activity of photocatalytic oxidation of benzyl alcohol under visible light.

Rapid microwave-assisted hydrothermal synthesis of CeO2 octahedra with mixed valence states and their catalytic activity for thermal decomposition of ammonium perchlorate

CeO₂ octahedra are prepared rapidly and they exhibit improved catalytic activity due to high concentration of oxygen vacancies and exposed (111) facets.

Au/Co promoted CeO2 catalysts for formaldehyde total oxidation at ambient temperature: role of oxygen vacancies

Cobalt enables formation of additional oxygen vacancies in Au/Co–CeO₂ and significantly boosts the ambient oxidation of formaldehyde.

AuPd/3DOM TiO2 Catalysts: Good Activity and Stability for the Oxidation of Trichloroethylene

Three-dimensionally ordered macroporous (3DOM) TiO2-supported AuPd alloy (xAuyPd/3DOM TiO2 (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials possessed a good-quality 3DOM structure and a surface area of 49–53 m2/g. The noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the surface of 3DOM TiO2. The 0.91Au0.51Pd/3DOM TiO2 sample showed the highest catalytic activity with the temperature at a TCE conversion of 90% being 400 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 0.91Au0.51Pd/3DOM TiO2 sample possessed better catalytic stability and moisture-resistant ability than the supported Au or Pd sample. The partial deactivation induced by H2O introduction of 0.91Au0.51Pd/3DOM TiO2 was reversible, while that induced by CO2 addition was irreversible. No significant influence on TCE conversion was observed after introduction of 100 ppm HCl to the reaction system over 0.91Au0.51Pd/3DOM TiO2. The lowest apparent activation energy (51.7 kJ/mol) was obtained over the 0.91Au0.51Pd/3DOM TiO2 sample. The doping of Au to Pd changed the TCE oxidation pathway, thus reducing formation of perchloroethylene. It is concluded that the high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd NPs and 3DOM TiO2 as well as more amount of strong acid sites were responsible for the good catalytic activity, stability, and water- and HCl-resistant ability of 0.91Au0.51Pd/3DOM TiO2. We believe that 0.91Au0.51Pd/3DOM TiO2 may be a promising catalyst for the oxidative elimination of chlorine-containing volatile organics.

Calcination system-induced nanocasting synthesis of uniform Co3O4 nanoparticles with high surface area and enhanced catalytic performance

Nanoscale Co₃O₄ synthesized by open-system nanocasting with uniform size, high surface area, large pore-distribution and abundant active-sites exhibited improved catalysis.

Variation of redox activity and synergistic effect for improving the preferential oxidation of CO in H2-rich gases in porous Pt/CeO2–Co3O4 catalysts

The porous Pt/CeO₂–Co₃O₄ catalysts show superior catalytic performance for CO preferential oxidation in H₂-rich gases.

Nanogold supported on manganese oxide doped alumina microspheres as a highly active and selective catalyst for CO oxidation in a H2-rich stream

The exceptionally high catalytic activity for CO-PROX reaction is due to the Au–support interaction and the unique reducibility of the support.