Wangcheng Zhan

A novel Ce/AlPO-5 catalyst for solvent-free liquid phase oxidation of cyclohexane by oxygen

Cerium-containing AlPO-5 with an AFI structure has been prepared by hydrothermal synthesis in the presence of HF, and characterized by XRD, XPS, SEM, N2 adsorption/desorption, solid state 27Al, 31P MAS NMR and TG-DTA techniques. The results show that all the samples have good crystallinity, high dispersity of Ce and high surface area, and Ce(III) replaces the position of Al(III) and enters the framework of AlPO-5. Ce/AlPO-5 is a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the condition of 0.5 MPa O2 and 413 K for 4 h, the conversion of cyclohexane is 13%, the total selectivity of cyclohexanol and cyclohaxnone is above 92%. In addition, the Ce/AlPO-5 catalyst is very stable in the cyclohexane oxidation system.

Current status and perspectives of rare earth catalytic materials and catalysis

Abstract Rare earth elements possess 4f orbitals without full electron occupancy and lanthanide contraction. This characteristic results in their unique catalytic performance when they are used as active components or as catalyst supports. Research into and the development of rare earth catalytic materials will significantly promote the high-efficiency utilization of abundant rare earth elements, such as lanthanum and cerium. Currently, rare earth catalytic materials play an important role in such areas as the petroleum chemical industry, the catalytic combustion of fossil fuels, automotive emissions control, the purification of industrial waste air, and solid solution fuel cells. In this paper, we review the application of and recent research progress that has been made on rare earth catalytic materials, including relative theoretical research. The effects of rare earth elements on the structure, activity, and stability of the catalysts of interest are described.

Preparation of high oxygen storage capacity and thermally stable ceria–zirconia solid solution

Ceria–zirconia solid solution is a very important material in three-way catalysts for automotive emission control. High oxygen storage capacity (OSC) and thermally stable Ce0.5Zr0.5O2 was prepared by a modified complexing–coprecipitation (CC) method, and its surface area reached 44 m2 g−1 after calcination at 1100 °C for 6 h. Based on the characterizations of its structural and physicochemical properties, it was found that Ce0.5Zr0.5O2 prepared by the CC method existed as the t′′-phase with rich oxygen defects and surface Ce3+ and has a larger BET surface area, uniform particle and pore sizes, and excellent bulk oxygen migration and redox abilities than samples prepared by other methods. After being calcined at 1100 °C for 6 h, its surface area, OSC (and OSCC, oxygen storage capacity complete) and catalytic activity for the oxidation of CO were still the best among three Ce0.5Zr0.5O2 solid solutions prepared by three methods whether it was used as the catalyst or as a support for a Pd catalyst, reflecting its good thermostability, although its particle and pore sizes were somewhat increased. This complexing–coprecipitation method can be used to prepare other high surface area and thermally stable inorganic materials.

Synthesis of cerium-doped MCM-48 molecular sieves and its catalytic performance for selective oxidation of cyclohexane

Cerium-doped MCM-48 molecular sieves were synthesized hydrothermally and characterized by X-ray diffraction, nitrogen adsorption, transmission electron microscope, FT-IR spectroscopy, UV-visible spectroscopy, and Raman spectroscopy. The results showed that all the samples held the structure of MCM-48, and Ce could enter the framework of MCM-48. However, when Ce/Si molar ratio in the samples was high (0.04 or 0.059), there were CeO2 crystallites as secondary phase in the extraframework of MCM-48. Ce-doped MCM-48 was a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the conditions of 0.5 MPa O2 and 413 K for 5 h, the conversion of cyclohexane was 8.1% over Ce-MCM-48-0.02, the total selectivity of cyclohexanol and cyclohaxnone was 98.7%. With an increase of Ce content, the conversion of cyclohexane and the selectivity to cyclohexanol decreased somewhat, but the selectivity to cyclohexanone increased.

Surfactant-Assisted Stabilization of Au Colloids on Solids for Heterogeneous Catalysis

The stabilization of surfactant-assisted synthesized colloidal noble metal nanoparticles (NPs, such as Au NPs) on solids is a promising strategy for preparing supported nanocatalysts for heterogeneous catalysis because of their uniform particle sizes, controllable shapes, and tunable compositions. However, surfactant removal to obtain clean surfaces for catalysis through traditional approaches (such as solvent extraction and thermal decomposition) can easily induce the sintering of NPs, greatly hampering their use in synthesis of novel catalysts. Such unwanted surfactants have now been utilized to stabilize NPs on solids by a simple yet efficient thermal annealing strategy. After being annealed in N2 flow, the surface-bound surfactants are carbonized in situ as sacrificial architectures that form a conformal coating on NPs and assist in creating an enhanced metal-support interaction between NPs and substrate, thus slowing down the Ostwald ripening process during post-oxidative calcination to remove surface covers.

Synthesis of mesoporous CeO2-MnOx binary oxides and their catalytic performances for CO oxidation

Abstract Mesoporous CeO 2 -MnO x binary oxides with different Mn/Ce molar ratios were prepared by hydrothermal synthesis and characterized by scanning electron microscopy (SEM), N 2 sorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and H 2 temperature-programmed reduction (H 2 -TPR). The characterization results indicated that the CeO 2 -MnO x catalysts exhibited flower-like microspheres with high specific surface areas, and partial Mn cations could be incorporated into CeO 2 lattice to form solid solution. The CeO 2 -MnO x catalysts showed better catalytic activity for CO oxidation than that prepared by the coprecipitation method. Furthermore, the CeO 2 -MnO x catalyst with Mn/Ce molar ratio of 1 in the synthesis gel (Ce-Mn-1) exhibited the best catalytic activity, over which the conversion of CO could achieve 90% at 135 °C. This was ascribed to presence of more Mn species with higher oxidation state on the surface and the better reducibility over the Ce-Mn-1 catalyst than other CeO 2 -MnO x catalysts.

Synthesis of lathanum or La-B doped KIT-6 mesoporous materials and their application in the catalytic oxidation of styrene

Abstract La-doped and La-B-doped KIT-6 mesoporous materials were prepared by direct hydrothermal synthesis with pH-adjusting method and characterized by X-ray diffractometer (XRD), nitrogen sorption, FT-IR, UV-Vis, X-ray photoelectron spectroscopy (XPS) and ICP-AES. The catalytic performance for the oxidation of styrene by hydrogen peroxide, tert-butyl hydroperoxide or oxygen was investigated. The results showed that the introduction of heteroatoms did not destroy the mesostructure of KIT-6 with cubic Ia 3 d space group. La or B cations were incorporated into the framework of KIT-6 and the coexistence of B could hinder the dispersion or incorporation of La into the framework. La 3+ species in the framework of La-KIT-6 promoted the catalytic performance of La-KIT-6 catalyst for the oxidation of styrene. H 2 O 2 is the better oxidant for the oxidation of styrene than tert-butyl hydroperoxide and oxygen, in which the styrene conversion of 20.6% and the selectivity to benzaldehyde of 74.6% were achieved over La-KIT-6-0.02.

Synthesis of Ln-doped MCM-41 mesoporous materials and their catalytic performance in oxidation of styrene

Abstract Using cetyl-trimethyl-ammonium bromide (CTMAB) as the template agent and tetraethylorthosilicate (TEOS) as the silica source, the MCM-41 mesoporous materials were synthesized with La or Ce incorporated in the framework under hydrothermal conditions. The structure and the state of La or Ce were investigated through the analyses of XRD, nitrogen adsorption-desorption, FT-IR, and UV-Vis. XRD and N 2 adsorption-desorption results showed that Ln-MCM-41 exhibited the loss of the lattice ordering of the MCM-41 construct, and larger unit cell parameter and pore diameter than pure silica MCM-41. The FT-IR and UV-Vis results indicated the presence of isolated terra-coordinated La or Ce ions in the framework and other Ln species dispersed highly on the Ln-MCM-41 surface simultaneously. Furthermore, their catalytic behaviors in the oxidation of styrene were studied using H 2 O 2 as the oxidant. The La-MCM-41 catalysts exhibited high reactivity and the reactivity increased with the increase of the La content in the La-MCM-41 samples. On the contrary, Ce-MCM-41 catalysts showed low reactivity in the oxidation of styrene and the conversion of styrene decreased with the increase of the Ce content in the Ce-MCM-41 samples.

Selective catalytic oxidation of ammonia over MnOx–TiO2 mixed oxides

The selective catalytic oxidation of ammonia to nitrogen (NH3–SCO) was investigated over MnOx–TiO2. The physicochemical properties of MnOx–TiO2 were characterized by XRD, O2-TPD, NH3-TPD, H2-TPR and XPS, and the reaction mechanism was studied by in situ DRIFTS. The addition of Mn into TiO2 accelerated the support phase transformation and the formation of Mn–O–Ti bonds. MnOx(0.25)–TiO2 showed the best performance in NH3–SCO, for which complete conversion of NH3 was obtained at 200 °C with the temperature window (180–300 °C) for N2 yield > 80%. The formation of Mn–O–Ti provided abundant oxygen vacancies which promoted the adsorption and dissociation of molecular oxygen to form active oxygen species. The finely dispersed MnOx species on the support favored NH3 adsorption. N2O was produced over the whole temperature range while NOx was produced only at high temperatures (>250 °C). N2O was formed from the combination of two HNO species at low temperatures, whereas it was formed from NH3 and nitrate/nitrite species reaction at high temperatures.

A highly effective Ni-modified MnOx catalyst for total oxidation of propane: the promotional role of nickel oxide

Nickel promoted manganese oxide (MnNiOx) was prepared by the co-precipitation method and used as a catalyst for propane deep oxidation. The results show that the doping of Ni can effectively improve the catalytic performance of MnOx for propane total oxidation, and when Ni/Mn is 0.2, the MnNi0.2Ox catalyst exhibits the highest catalytic activity, for instance, the reaction temperature of 90% propane conversion (T90) was only ∼240 °C, and it demonstrates good thermal stability in the operation at temperatures alternating between 220 °C and 350 °C. It was found that an Mn–Ni–O solid solution can be formed by adding a moderate Ni amount into MnOx, resulting in changes in catalytically active sites by the synergetic interaction of Mn–Ni, such as a higher surface concentration of Mn4+ and oxygen vacancies, higher oxygen mobility and better reducibility. And the outstanding catalytic property of MnNi0.2Ox can be also related to its high surface area. Furthermore, the in situ DRIFT technique was used to investigate the reaction process of propane oxidation over the MnOx and MnNi0.2Ox catalysts, and the results suggest that the reaction mechanism is hardly changed after Ni doping in MnOx.