Hanfeng Lu

Mesoporous MnCeOx solid solutions for low temperature and selective oxidation of hydrocarbons

The development of noble-metal-free heterogeneous catalysts that can realize the aerobic oxidation of C–H bonds at low temperature is a profound challenge in the catalysis community. Here we report the synthesis of a mesoporous Mn0.5Ce0.5Ox solid solution that is highly active for the selective oxidation of hydrocarbons under mild conditions (100–120 °C). Notably, the catalytic performance achieved in the oxidation of cyclohexane to cyclohexanone/cyclohexanol (100 °C, conversion: 17.7%) is superior to those by the state-of-art commercial catalysts (140–160 °C, conversion: 3-5%). The high activity can be attributed to the formation of a Mn0.5Ce0.5Ox solid solution with an ultrahigh manganese doping concentration in the CeO2 cubic fluorite lattice, leading to maximum active surface oxygens for the activation of C–H bonds and highly reducible Mn4+ ions for the rapid migration of oxygen vacancies from the bulk to the surface.

Constructing Hierarchical Interfaces: TiO2-Supported PtFe–FeOx Nanowires for Room Temperature CO Oxidation

In this communication, we report a facile approach to constructing catalytic active hierarchical interfaces in one-dimensional (1D) nanostructure, exemplified by the synthesis of TiO2-supported PtFe-FeO(x) nanowires (NWs). The hierarchical interface, constituting atomic level interactions between PtFe and FeO(x) within each NW and the interactions between NWs and support (TiO2), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeO(x) and TiO2 participate in the initial CO oxidation, facilitating the reaction through a redox pathway. Moreover, the intact 1D structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe-FeO(x)/TiO2 catalyst exhibits no activity decay. Our results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis.

Cu–Mn–Ce ternary mixed-oxide catalysts for catalytic combustion of toluene

Cu-Mn, Cu-Mn-Ce, and Cu-Ce mixed-oxide catalysts were prepared by a citric acid sol-gel method and then characterized by XRD, BET, H2-TPR and XPS analyses. Their catalytic properties were investigated in the toluene combustion reaction. Results showed that the Cu-Mn-Ce ternary mixed-oxide catalyst with 1:2:4 mole ratios had the highest catalytic activity, and 99% toluene conversion was achieved at temperatures below 220°C. In the Cu-Mn-Ce catalyst, a portion of Cu and Mn species entered into the CeO2 fluorite lattice, which led to the formation of a ceria-based solid solution. Excess Cu and Mn oxides existed on the surface of the ceria-based solid solution. The coexistence of Cu-Mn mixed oxides and the ceria-based solid solution resulted in a better synergetic interaction than the Cu-Mn and Cu-Ce catalysts, which promoted catalyst reducibility, increased oxygen mobility, and enhanced the formation of abundant active oxygen species.

High thermal stability of ceria-based mixed oxide catalysts supported on ZrO2 for toluene combustion

Cu–Mn–Ce mixed oxide catalysts (CMCs) supported on ZrO2 were prepared by an impregnation method. Their catalytic activity was evaluated by a model reaction, that of toluene combustion. 5% CMC/ZrO2 catalysts show a very high activity and thermal stability, and 90% of toluene conversion could be obtained at temperatures below 260 °C, even with the catalyst being annealed at 900 °C. A new phase of Zr0.88Ce0.12O2 in the interface was formed by the interaction between ZrO2 and CMC on the catalyst with low loading. Zr0.88Ce0.12O2 serves as the actual carrier of the active phase, and can significantly improve the thermal stability of the catalyst.

Novel hydrophobic PDVB/R-SiO2 for adsorption of volatile organic compounds from highly humid gas stream.

A novel organic-inorganic hydrophobic polydivinylbenzene-silica adsorbent (PDVB/R-SiO2) was successfully prepared by introducing a specific amount of divinylbenzene and solvent (i.e., tetrahydrofuran) to SiO2pores and initiating polymerization under solvothermal conditions. New smaller structures and surface areas were formed in the SiO2 pores. The PDVB/R-SiO2-0.5 samples exhibited a bimodal pore size distribution with both SiO2 micropores/mesopores (0.5-2.0 nm) and mesopores (2.0-5.0 nm). The surface areas increased from 116 m(2)/g (SiO2) to 246 m(2)/g. The breakthrough curves of toluene adsorption indicated that the amount adsorbed on PDVB/R-SiO2-0.5 was 12 times higher than that on SiO2. The highly humid environment exhibited no effect on adsorption because the surface of PDVB was functionalized. The adsorbed toluene was easily desorbed in hot N2 stream at 100 °C. After 10 adsorption-desorption cycles, PDVB/R-SiO2-0.5 continued exhibiting excellent adsorption, indicating superior structural and regeneration abilities.

Catalytic low-temperature combustion of dichloromethane over V–Ni/TiO2 catalyst

Vanadium–nickel mixed oxides supported on TiO2 (anatase) were prepared by wet impregnation using ammonium metavanadate and nickel nitrate aqueous solution. The performance of as-prepared samples in catalytic dichloromethane (DCM) combustion was investigated, and their physicochemical properties were characterized in detail by X-ray diffraction, N2 physisorption, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, and Raman spectroscopy analyses. Results showed DCM combustion activity over V–Ni/TiO2 catalyst was superior to that of V2O5/TiO2 and NiO/TiO2 catalysts. DCM could be completely converted into CO2, HCl, and a little amount of CO over Ni–V/TiO2 catalyst at 350 °C, the toxic by-products, such as CH3Cl, aldehydes and phosgene could not be observed by online IR spectroscopy. The high catalytic activity, selectivity, and stability of V–Ni/TiO2 catalyst could be due to the good oxidative dehydrogenation ability (ODH), the good reducibility of active oxygen species, and suitable strength of Lewis acidic sites upon introduction of nickel oxide.

Propene and CO oxidation on Pt/Ce-Zr-SO 4 2- diesel oxidation catalysts: Effect of sulfate on activity and stability

Abstract Platinum/cerium-zirconium-sulfate (Pt/Ce-Zr-SO 4 2– ) catalysts were prepared by wetness impregnation. Catalytic activities were evaluated from the combustion of propene and CO. Sulfate (SO 4 2– ) addition improved the catalytic activity significantly. When using Pt/Ce-Zr-SO 4 2– with 10 wt% SO 4 2– , the temperature for 90% conversion of propene and CO decreased by 75 °C compared with Pt/Ce-Zr. The conversion exceeded 95% at 240 °C even after 0.02% sulfur dioxide poisoning for 20 h. Temperature-programmed desorption of CO and X-ray photoelectron spectroscopy analyses revealed an improvement in Pt dispersion onto the Ce-Zr-SO 4 2– support, and the increased number of Pt particles built up more Pt &+ -(SO 4 2– ) &– couples, which resulted in excellent activity. The increased total acidity and new Bronsted acid sites on the surface provided the Pt/Ce-Zr-SO 4 2– with good sulfur resistance.

Preparation of metallic monolithic Pt/FeCrAl fiber catalyst by suspension spraying for VOCs combustion

We report a facile and general strategy for the preparation of metallic monolithic catalysts. Our strategy involved subjecting the surfaces of FeCrAl fibers to thermal treatment and the spraying of Pt nanoparticles suspension liquid. The catalyst exhibited high catalytic activity and good stability in the combustion of volatile organic compounds to CO2 and H2O at mild temperature. The exceptional activity of the catalyst can be attributed to the well-adhered alumina coating that formed on the surfaces of the FeCrAl fibers after thermal treatment and the highly dispersed Pt nanoparticles on the surface of the alumina coating.

Design structure for CePr mixed oxide catalysts in soot combustion

Four CePr mixed oxides with different structures were designed and synthesized using a solid-phase grinding method: a uniform solid solution of Ce and Pr (CePr-NN), Pr6O11-coated CeO2 (CePr-NO), CeO2-coated Pr6O11 (CePr-ON), and particle packing of CeO2 and Pr6O11 (CePr-OO) were obtained, and characterized by XRD, H2-TPR, TEM and TG. The results show that CePr-NN exhibits the best low temperature catalytic activity among the CePr catalysts. CeO2 is the major active phase on the surface of the CePr catalysts, and the use of Pr6O11 as the framework maintains the thermal stability of the CePr composite oxide. Moreover, both the oxygen storage capacity and mobility of the active oxygen of the catalyst were improved with the incorporation of Pr into CeO2, resulting in a higher combustion rate. The “molten state” which appeared during the preparation when nitrate was used as the precursor, plays a significant role in the migration of Ce and Pr, and is the premise of forming different structures of solid solution or coating structure.

Morphology-dependent properties of CeO2 nano-catalysts on CH2Cl2 oxidation

Four types of CeO2 nanoparticles with different morphologies (nanorods, nanocubes, nanopolyhedra, and bulk CeO2 nanoparticles) were synthesized and used in dichloromethane (DCM) oxidation. Their detailed physicochemical properties were investigated by X-ray diffraction, N2 physisorption, H2 temperature-programmed reduction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Results indicated that DCM oxidation over CeO2 nanoparticles has significant morphology-dependent effects. CeO2 nanorods showed the best activity among all the investigated samples (T90 is only 323 °C). The main products were CO2 and HCl, although trace amounts of CHCl3, CCl4, CO, and Cl2 could be detected. The high performance of CeO2 nanorods in DCM oxidation may be related to the abundant surface defects, increased amount of adsorbed active oxygen species, and good reducibility of the catalyst.