Jingcai Zhang

The Effect of Exposed Facets of Ceria to the Nickel Species in Nickel-Ceria Catalysts and Their Performance in a NO + CO Reaction.

CeO2 rods with {110} facets and cubes with {100} facets were utilized as catalyst supports to probe the effect of crystallographic facets on the nickel species and the structure-dependent catalytic performance. Various analysis methods (ex and in situ XRD, TEM, Raman, XPS, TPR, TPD) were used to investigate the structural forms of the catalysts, and these results indicated that the deposition of nickel species resulted in the formation of two main active types of the catalyst components: NiO strongly or weakly interacted with the surface and Ni-Ce-O solid solution. Notably, the states and distribution ratio of nickel species were related to the shape of CeO2. It was found that CeO2 rods had more active sites to coordinate with nickel species to form a strong interaction with NiO on the surface and a more stable construction when compared to cubes. Furthermore, the nickel-ceria catalysts with rod shape were more active towards NO oxidation with complete conversion below 191 °C, but for cube shape, complete conversion occurred above 229 °C (e.g., for nickel loading of ∼5%, the complete conversion temperature was 154 °C for the rod shape and 229 °C for the cube shape). On the basis of the analysis of the catalysts structure, the superior catalytic activity was due to a combination of surface structures of NiO (mainly strongly interacting with the surface) and nickel ions Ni(2+) in the Ni-Ce-O bulk phase.

Mesoporous CeO2 nanoparticles assembled by hollow nanostructures: formation mechanism and enhanced catalytic properties

In this paper, novel hierarchically mesoporous CeO2 nanoparticles assembled by hollow nanocones were prepared through a facile solvothermal strategy using Ce(HCOO)3 as the precursor. X-Ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and thermal gravimetric analysis (TGA) were utilized to characterize the products and research the formation mechanism. The whole synthesis process involves two steps: formation of Ce(HCOO)3 nanoparticles constructed with nanocones at room temperature in an alkaline environment and oxidation induced phase transformation from Ce(HCOO)3 to CeO2 with formation of hollow nanocones assembled by nanocrystals in a solvothermal process at 150 °C. The as-prepared mesoporous CeO2 nanoparticles with an average diameter of 500 nm displayed a high surface area of 147.6 m2 g−1 using N2 adsorption and desorption measurement. The H2-TPR test showed its great reduction behavior in a low temperature zone. By comparing the T100 temperature of CO conversion with a commercial sample (above 350 °C) and other reported samples (above 300 °C) in the literature, the mesoporous CeO2 nanoparticles (270 °C) presented an excellent catalytic activity for CO oxidation.

Designed synthesis and formation mechanism of CeO2 hollow nanospheres and their facile functionalization with Au nanoparticles

In this work, a facile one-step solvothermal method with the assistance of hydrochloric acid has been developed to prepare well-dispersed CeO2 hollow nanospheres with high surface areas. The effects of hydrochloric acid on the growth mechanism and the size distribution are investigated in detail. It is found that the hydrogen ions expedite the nucleation rate of the CeO2 nuclei in the nucleation course, while the chloride ions accelerate the Ostwald ripening in the acidic environment. Both the hydrogen ion (H+) and the chloride ion (Cl−) are confirmed to play a key role in the formation of hollow morphology. Based on our experiments, a HCl-assisted oxidation–nucleation with an Ostwald ripening process mechanism was proposed. Furthermore, Au nanoparticles with a size of 2.5–6 nm were uniformly deposited on the surface of the ceria support by a simplified reduction process with sodium borohydride (NaBH4). The synthesized Au/CeO2 nanospheres exhibit a higher catalytic activity in CO oxidation than pure ceria nanospheres due to the existence of different Au species (metallic Au0 and positively charged Auδ+) and the strengthened interfacial interactions between the Au NPs and the ceria support.

Construction of Ce(OH)4 nanostructures from 1D to 3D by a mechanical force-driven method

A simple protocol has been reported here to successfully perform a controllable conversion between Ce(OH)4 nanorods [Ce(OH)4-NR] and Ce(OH)4 nanoflowers [Ce(OH)4-NF] based on a prolonged mechanical force-driven stirring process. Results show that the Ce(OH)4 nanostructures undergo a morphology transformation from the initial nanorods to irregular nanoflowers, then to nanoflowers emanating from one center only, by varying the stirring time before solvothermal reaction. The detailed study confirmed that the mechanical force significantly improved the mass transport of the solution and drove the seeds of Ce(OH)4-NR [seeds-NR] to generate the seeds of Ce(OH)4-NF [seeds-NF]. The final CeO2 products (CeO2 nanorods [CeO2-NR] and CeO2 nanoflowers [CeO2-NF]) that inherited the original morphology were obtained by annealing Ce(OH)4-NR and Ce(OH)4-NF, respectively. To further optimize the performance of the final products, Au/CeO2-NR and Au/CeO2-NF were synthesized by a simple oxidation–reduction process, which led to increased surface areas and promising potential in CO oxidation.

Hierarchical polymorphic MnCO3 series induced by cobalt doping via a one-pot hydrothermal route for CO catalytic oxidation

In this study, a series of cobalt-doped MnCO3 hierarchical microstructures with different morphologies were synthesized by tuning a single variable (the dopant content) via a one-step, mild solvothermal synthesis in a N,N-dimethylformamide (DMF) solution system. Structure evolution of the polymorphic MnCO3 took place with the morphology obviously transforming from an initial flower-microstructure to fan-like, then to hedgehog-like hemispheres and finally to flake-spheres as the Co2+ theoretical content (Co/(Co + Mn)) increased from 0 to 20% in the solvothermal process. Cobalt ion modulated reaction-limited aggregation (RLA) is proposed in the growth mechanism. The mechanism of Co2+-induced acceleration and full growth is further investigated. The Co2+ doped manganese carbonate displays wonderful catalytic performance towards CO oxidation.