Ke Tang

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.

The promoting influence of nickel species in the controllable synthesis and catalytic properties of nickel–ceria catalysts

In this paper, a series of well-dispersed nickel–ceria catalysts with high surface area were successfully fabricated using a simple solvothermal approach and characterized by XRD, TEM, EDS, N2-sorption, Raman and TPR techniques. The results show that the amount of nickel species can have an impact on the morphology of the nickel–ceria catalysts, i.e. the hollow structure, particle size and porous structures. The prepared nickel–ceria samples (with the atomic ratio Ni:Ce (At% (Ni/Ce)) at approximately 6.58%) exhibit high catalytic performance in carbon monoxide (CO) oxidation with 100% conversion at 200 °C. The XRD, Raman, XPS and H2-TPR data confirm that the nickel species are the main promoting factor in the catalysis, including the doped nickel species, highly dispersed free NiO and the interfacial Ni–[O]–Ce structures. Further, the as-prepared nickel–ceria catalysts show high stability in the catalysis.

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.

Facile synthesis of Mn-doped Fe2O3 nanostructures: enhanced CO catalytic performance induced by manganese doping

In this paper, a facile solvothermal method has been employed to synthesize monodispersed Mn-doped Fe2O3 with shuttle-like nanostructure. The structure of the samples was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscope (SEM). Manganese species doped into the Fe2O3 lattice were then confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The doping of Mn ions led to the formation of the shuttle-like structure and increase of the surface area compared to pure Fe2O3. PVP also played an important role in the formation of the shuttle-like structure. The mechanism for the growth of Mn-doped Fe2O3 was proposed as the recrystallization of metastable precursors (RMP) route. H2-TPR measurement revealed better reduction behavior of the Mn-doped Fe2O3. Finally, the as-prepared Mn-doped Fe2O3 exhibited excellent catalytic performance and cycling stability towards CO oxidation.

Solvothermal synthesis of 1D nanostructured Mn2O3: effect of Ni2+ and Co2+ substitution on the catalytic activity of nanowires

In this paper, cation modified one dimensional Mn2O3 nanowires were synthesized via a solvothermal synthesis and calcination free from the template-assisted method. The samples were characterized in detail by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS). XRD results revealed the homogeneity of Ni–Mn–O/Co–Mn–O solid solutions. By introducing the two different cations the Mn2O3 nanowires can be freely manipulated. The H2-TPR measurement showed the enhanced reduction behaviors of the doped manganese oxide (Mn2O3) samples. The presence of Ni2+ and Co2+ produced lattice defects and promoted the production of oxygen vacancies, which explained the results that Ni2+/Co2+ doped Mn2O3 showed higher catalytic activity than the pure sample.

Solvent extraction of palladium(II) with newly synthesized asymmetric branched alkyl sulfoxides from hydrochloric acid

A group of new asymmetric branched alkyl sulfoxides was synthesized and applied in palladium(II) extraction for the first time. According to the experimental data, the concentration of hydrochloric acid in aqueous phase greatly influenced Pd(II) extraction, which could be interpreted by different mechanisms (ligand substitution mechanism at low acidity and ion association mechanism at high acidity). In regard to structure effect, the steric hindrance of branched alkyl showed remarkable influence on the extraction performance of sulfoxides. On the basis of thermodynamic analysis, it was demonstrated that higher temperature exerted positive influence on the Pd(II) extraction reaction. As for the separation of Pd(II) and Pt(IV), low concentration of hydrochloric acid was considered to be appropriate for highly effective separation. Furthermore, ammonia solution was proven to be an efficient stripping agent for palladium recovery from organic phase.

Influence of Chitosan on the Microstructured Au/CeO2 Catalyst: An Enhanced Catalytic Performance for CO Oxidation

In this work, a facile solvothermal method with the assistance of chitosan (CS) has been developed to prepare well-dispersed ceria core–shell nanospheres. The effects of CS on the growth mechanism and the catalytic performance of CeO2 and Au/CeO2 nanocomposites for CO oxidation are investigated in detail. CS leads to the formation of core–shell nanospheres as soft template, changing the exposed lattice planes, and reducing Ce4+ to Ce3+ as reducing agent, resulting in the increasing of the oxygen vacancy, following the co-existence of Au3+ and Au0, which leads to the improvement of the catalytic activity for CO oxidation. As a result, the synthesized Au/CeO2 nanospheres with the assistance of CS exhibit a higher catalytic activity in CO oxidation than Au/CeO2 like-cube.Graphical Abstract

The effect of copper species in copper-ceria catalysts: structure evolution and enhanced performance in CO oxidation

In this paper, copper doped ceria porous nanospheres were synthesized using carbon nanospheres as a hard template via a homogenous precipitation method at low temperature. The results showed that the copper-doped ceria has undergone a morphology transformation from the initial double-shell spheres to hollow spheres as the copper doping concentration increased from 0 to 7.5%mol. Notably, the Cu/Ce + Cu atomic ratio in the final products was approximately five times the initial design ratio, which confirmed an efficient utilization of copper in this system. Furthermore, the copper-ceria catalysts exhibited enhanced catalytic performance towards CO conversion when compared with pure ceria catalysts (e.g., for the optimal catalysts, the complete conversion temperature was 160 °C, for the pure catalysts, complete conversion temperature was 300 °C). Through the analysis of the catalysts structure, we proved that the superior catalytic performance was derived from a combination of CuOx clusters and copper ions in the Cu–[Ox]–Ce bulk phase.

Insight Investigation of Active Palladium Surface Sites in Palladium-Ceria Catalysts for NO + CO Reaction

The palladium species in ceria-based catalysts have a significant influence on their catalytic performance. In this work, the structure evolution of palladium species induced by various calcination rate was investigated and then these calcined catalysts were applied to NO + CO catalytic reaction. Systematic investigations by various measurements demonstrate that the calcination rate and catalytic process play crucial roles on the formation ways of palladium species and identify the forms of active palladium surface sites for NO + CO reaction. Results indicate that the calcination process resulted in the formation of three types of palladium components: PdO interacted with ceria supports (PdO x/Pd-O-Ce cluster), PdO nanoparticles on the surface, and Pd2+ ions incorporated into the subsurface lattice (Pd-O-Ce solid solution). It is also proven that the state and distribution of palladium components are dependent on the calcination rate: rapid calcination rate is beneficial for the generation of PdO species (PdO x/Pd-O-Ce and PdO), while slow calcination rate makes contribution to the formation of Pd-O-Ce. Furthermore, the subsequent catalytic process could induce the decomposition of PdO x/Pd-O-Ce and formation of more fractions of active Pd species in PdO oxide phase. On the basis of the catalytic performances, we found the superior catalytic properties are detected for catalysts containing 0.5% Pd (0.5% is corresponding to the palladium content in molar ratio) with fast calcination rate. This is due to the synergistic effect of active Pd in PdO decomposed form PdO x/Pd-O-Ce in the catalytic process and the palladium ions in Pd-O-Ce solid solution.