Aijun Duan

Three-dimensionally ordered macroporous Ce0.8Zr0.2O2-supported gold nanoparticles: synthesis with controllable size and super-catalytic performance for soot oxidation

A series of catalysts of three-dimensionally ordered macroporous (3DOM) Ce0.8Zr0.2O2-supported gold nanoparticles with controllable sizes were successfully synthesized by the facile method of gas bubbling-assisted membrane reduction (GBMR). All the catalysts possess well-defined 3DOM structures, which consist of interconnected networks of spherical voids, and the Au nanoparticles are well dispersed and supported on the inner wall of the uniform macropore. The relationship between Au particle sizes and the ability to adsorb and activate oxygen was characterized by means of O2-TPD and XPS. The results show that the active oxygen species (O−) and gold ions with oxidation state of Au+ are essential for soot oxidation reaction. 3DOM Au0.04/Ce0.8Zr0.2O2catalyst with Au particle size of 2–3 nm has the strong capability of adsorption and activation of oxygen. Thus, it exhibits super-catalytic activity for diesel soot oxidation, especially at low temperature. The reaction pathways of catalytic soot oxidation in the presence or absence of NO can be outlined as follows: at low temperature ( 250 °C), the catalytic activity is strongly related to the NO gas, because NO2 derived from NO oxidation is used as intermediate to catalyze soot oxidation.

Effect of Ce doping of TiO2 support on NH3-SCR activity over V2O5–WO3/CeO2–TiO2 catalyst

CeO2-TiO2 composite supports with different Ce/Ti molar ratios were prepared by a homogeneous precipitation method, and V2O5-WO3/CeO2-TiO2 catalysts for the selective catalytic reduction (SCR) of NOx with NH3 were prepared by an incipient-wetness impregnation method. These catalysts were characterized by means of BET, XRD, UV-Vis, Raman and XPS techniques. The results showed that the catalytic activity of V2O5-WO3/TiO2 was greatly enhanced by Ce doping (molar ratio of Ce/Ti=1/10) in the TiO2 support. The catalysts that were predominantly anatase TiO2 showed better catalytic performance than the catalysts that were predominantly fluorite CeO2. The Ce additive could enhance the surface adsorbed oxygen and accelerate the SCR reaction. The effects of O2 concentration, ratio of NH3/NO, space velocity and SO2 on the catalytic activity were also investigated. The presence of oxygen played an important role in NO reduction. The optimal ratio of NH3/NO was 1/1 and the catalyst had good resistance to SO2 poisoning.

Design and Synthesis of 3D Ordered Macroporous CeO2‐Supported Pt@CeO2‐δ Core–Shell Nanoparticle Materials for Enhanced Catalytic Activity of Soot Oxidation

The fabrication of multifunctional nanostructure material is emerging as an important fi eld of research in connection with heterogeneous catalytic reaction. [ 1 ] To design and synthesize high performance materials in terms of catalytic activity, understanding the properties affecting catalytic performance is of great importance. [ 2 ] The catalytic oxidation of diesel soot particles, emitted from diesel engines as a typical kind of solid particles, takes place on the three-phase boundary among a solid catalyst, a solid reactant (soot) and gaseous reactants (O 2 ). [ 3 ] So, the catalytic activity for soot oxidation is affected by two factors: the contact effi ciency between soot and catalyst, and the intrinsic activity of material. [ 4 ] Three-dimensionally ordered macroporous (3DOM) materials have become a focus research topic due to their potential applications, such as catalysts, photonic crystals and energetic materials. [ 5 ] It is clear to realize that the size effect of 3DOM structure with big pore size ( > 50 nm) can remarkably improve the contact effi ciency between solid reactant and catalyst. [ 6 ] And the coordinatively unsaturated cation sites in noble-metal/oxide catalysts are essential for their good intrinsic catalytic properties. [ 7 ] For effi ciently catalyzing a deep oxidation reaction, the design of multifunctional nanocatalyst with the high density of active sites on the surface of 3DOM oxides is generally required and it still needs an intensive study. Ce-based oxide-supported Pt nanoparticle catalysts are critical to many important commercial chemical processes with utmost practical importance. [ 8 ] The catalytic performances of model systems with Pt nanoparticles dispersed on a porous or fl at substrate oxide supports often show strong structure and size dependencies duo to so-called “the strong metal–support interactions” (SMSI) occurring at the interface between the active (Pt) phase and the support. [ 9 ] In

One-pot synthesis of core–shell Au@CeO2−δ nanoparticles supported on three-dimensionally ordered macroporous ZrO2 with enhanced catalytic activity and stability for soot combustion

A series of multifunctional catalysts of three-dimensionally ordered macroporous (3DOM) ZrO2-supported core–shell structural Au@CeO2−δ nanoparticles were successfully synthesized by the one-pot method of gas bubbling-assisted membrane reduction–precipitation (GBMR/P). All the catalysts possess a well-defined 3DOM structure with interconnected networks of spherical voids, and the Au@CeO2−δ core–shell nanoparticles with different molar ratios of Au/Ce are well dispersed and supported on the inner wall of the uniform macropore. 3DOM support facilitates the contact efficiency between solid reactant and catalyst, and the Au@CeO2−δ core–shell nanoparticles with strong metal-oxides interaction improve the amount of active oxygen species and the sintering resistance of supported Au nanoparticles due to the optimization of the interface area by formation of the metal-oxides core–shell (MOCS) nanostructure particles. 3DOM Au@CeO2−δ/ZrO2 catalysts exhibit high catalytic activity and stability for diesel soot oxidation. Among the as-prepared catalysts, 3DOM Au@CeO2−δ/ZrO2-2 catalyst with the moderate thickness of CeO2−δ nanolayer shell shows the highest catalytic activity for soot combustion, i.e., its T50 is 364 °C. In summary, 3DOM Au@CeO2−δ/ZrO2 catalysts are excellent systems for catalytic combustion of solid particles or macromolecules, and the design concept and facile synthesis method of 3DOM oxide-supported MOCS nanoparticle catalysts can be extended to other metal/oxide compositions.

Hierarchical Macro-meso-microporous ZSM-5 Zeolite Hollow Fibers With Highly Efficient Catalytic Cracking Capability

Zeolite fibers have attracted growing interest for a range of new applications because of their structural particularity while maintaining the intrinsic performances of the building blocks of zeolites. The fabrication of uniform zeolite fibers with tunable hierarchical porosity and further exploration of their catalytic potential are of great importance. Here, we present a versatile and facile method for the fabrication of hierarchical ZSM-5 zeolite fibers with macro-meso-microporosity by coaxial electrospinning. Due to the synergistic integration of the suitable acidity and the hierarchical porosity, high yield of propylene and excellent anti-coking stability were demonstrated on the as-prepared ZSM-5 hollow fibers in the catalytic cracking reaction of iso-butane. This work may also provide good model catalysts with uniform wall thickness and tunable porosity for studying a series of important catalytic reactions.

3D ordered macroporous TiO2-supported Pt@CdS core–shell nanoparticles: design, synthesis and efficient photocatalytic conversion of CO2 with water to methane

A series of photocatalysts of three-dimensionally ordered macroporous (3DOM) TiO2-supported core–shell structured Pt@CdS nanoparticles were facilely synthesized by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. All the catalysts possess a well-defined 3DOM structure with interconnected networks of spherical voids, and the Pt@CdS core–shell nanoparticles with different molar ratios of Cd/Pt are well dispersed and supported on the inner wall of uniform macropores. The 3DOM structure can enhance the light-harvesting efficiency due to the increase of the distance of the light path by enhancing random light scattering. And the all-solid-state Z-scheme system with a CdS(shell)–Pt(core)–TiO2(support) nanojunction is favourable for the separation of photogenerated electrons and holes because of the vectorial electron transfer of TiO2 → Pt → CdS. 3DOM Pt@CdS/TiO2 catalysts exhibit super photocatalytic performance for CO2 reduction to CH4 under simulated solar irradiation. Among the as-prepared catalysts, the 3DOM Pt@CdS/TiO2-1 catalyst with the moderate thickness of a CdS nanolayer shell shows the highest photocatalytic activity and selectivity for CO2 reduction, e.g., its formation rate of CH4 is 36.8 μmol g−1 h−1 and its selectivity for CH4 production by CO2 reduction is 98.1%. The design and versatile synthetic approach of the all-solid-state Z-scheme system on the surface of 3DOM oxides are expected to throw new light on the fabrication of highly efficient photocatalysts for CO2 reduction to hydrocarbon.

A photonic crystal-based CdS–Au–WO3 heterostructure for efficient visible-light photocatalytic hydrogen and oxygen evolution

A photonic crystal-based CdS–Au–WO3 heterostructure was constructed on WO3 photonic crystal segments. Highly efficient visible-light-driven hydrogen and oxygen evolution are demonstrated relative to those of single-, two-component and unstructured systems due to good light harvesting of photonic crystals and efficient electron transfer of this heterostructure.

Synthesis of hierarchically porous silicas with mesophase transformations in a four-component microemulsion-type system and the catalytic performance for dibenzothiophene hydrodesulfurization

Hierarchical porous materials especially the silica-based ones are undergoing rapid development due to potential applications in the fields of catalysis, adsorption, separation, and biomedical processes. Although various synthesis methods involving emulsions, colloids, and surfactants have been reported, synthesis of hierarchical porous silicas (HPS) with complex mesophase transformations by using a four-component microemulsion (surfactant/cosurfactant/oil/water) templating approach is still challenging. Herein, we have successfully synthesized porous silica materials by introducing n-butanol (Bu) as the cosurfactant and 1,3,5-trimethylbenzene (TMB) as the oil component in a four-component P123–n-butanol–1,3,5-trimethylbenzene–water system. By simply increasing the molar ratio of Bu to TMB continuously while keeping a fixed mass of TMB in the mean time, mesophase transformations, progressing from mesocellular foam (MCF) via a vesicle-like structure to an ordered 2D hexagonal structure (SBA-15), can be observed. Moreover, an opposite phase transformation process was also proved by gradually increasing the molar ratio of TMB to Bu by maintaining a certain value for the Bu content in the initial system. All the mixed phase silica materials including hexagonal–vesicle, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type show hierarchically porous structures. The mechanism for the mesophase transformation was proposed and a micelle/microemulsion method with bimodal templates was put forward to form hierarchical porous silicas with a mixed phase of the MCF–disordered-SBA-15-type structure. Furthermore, a series of Al-containing mesoporous silicas with different structures (hexagonal, vesicle, MCF, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type) were used as catalyst supports for dibenzothiophene hydrodesulfurization. The NiMo/Al-hierarchical porous silica catalyst with pore structures of MCF–disordered-SBA-15-type displayed the best hydrodesulfurization performance among all the studied catalysts.

The encapsulation of CdS in carbon nanotubes for stable and efficient photocatalysis

A CdS encapsulated carbon nanotube (CNT) photocatalyst was prepared by a liquid-chemistry method. Through filling of CNTs with CdS, the aggregation of CdS was prevented efficiently by the good confinement effect of CNTs, and the photocatalytic performance of CdS was enhanced by 2.5 times via synergistic integration of the confinement effect of CNTs and heterojunction between CNTs and CdS. The photostability of CdS encapsulated in and attached on CNTs was investigated systematically through methylene blue photocatalytic degradation, X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-atomic emission spectroscopy. The results indicate that the photocorrosion of CdS is successfully suppressed when it is encapsulated in the CNTs. The mechanism analysis suggests that spatial synergy of the CdS and powerful adsorptivity of CNTs are the primary causes for photocorrosion inhibition. Our efforts propose a new scheme to remarkably promote both the photostability and photocatalytic activity of photocorrosion-susceptible photocatalysts.

Dehydrogenation of propane over PtSnAl/SBA-15 catalysts: Al addition effect and coke formation analysis

A series of PtSnAl/SBA-15 catalysts were prepared by incipient-wetness impregnation and their catalytic performance was tested for propane dehydrogenation. The catalysts were characterized by XRF, XRD, BET, TEM, UV-vis DRS, NH3-TPD, O2-TPO, 27Al MAS-NMR, XPS and in situ Raman analyses. The addition of aluminum enhances the interaction of the Sn support and consequently stabilizes the oxidation state of Sn during the propane dehydrogenation reaction. The acid centers formed by aluminum addition show close contact with metal centers (Pt), which favors the synergistic effect of the bifunctional active centers. High catalytic performance over PtSnAl0.2/SBA-15 was obtained, and one-pass propane conversion and propene selectivity are 55.9% and 98.5%, respectively. Moreover, the in situ Raman results indicated the faster coke formation rate of PtSnAl0.4/SBA-15 than that of PtSnAl0.2/SBA-15, which may be accelerated by strong acid sites by excess aluminum addition.