Xiangguang Yang

Comparative study of Nickel-based perovskite-like mixed oxide catalysts for direct decomposition of NO

The mixed oxides LaNiO3, La0.1Sr0.9NiO3, La2NiO4 and LaSrNiO4 were prepared and used as catalysts for the direct decomposition of NO. The catalysts were characterized by means of XRD, XPS, O-2-TPD, NO-TPD and chemical analysis. By comparing the physico-chemical properties and catalytic activity for NO decomposition, a conclusion could be drawn as follows. The direct decomposition of NO over perovskite and related mixed oxide catalysts follows a redox mechanism. The lower valent metal ions Ni2+ and disordered oxygen vacancies seem to be the active sites in the redox process. The oxygen vacancy plays an important role favorable for the adsorption and activation of NO molecules on one hand and on the other hand for increasing the mobility of lattice oxygen which is beneficial to the reproduction of active sites. The presence of oxygen vacancies is one of the indispensable factors to give the mixed oxides a steady activity for NO decomposition.

Immobilization of the heteropoly acid (HPA) H4SiW12O40 (SiW12) on mesoporous molecular sieves (HMS and MCM-41) and their catalytic behavior

Supported catalysts, consisting of SiW12 immobilized on hexagonal mesoporous silica (HMS) and its aluminum-substituted derivative (MCM-41) with different loadings and calcination temperatures, have been prepared and characterized by X-ray diffraction, FT-IR and NH3-temperature programmed desorption. It is shown that SiW12 retains the Keggin structure on the mesoporous molecular sieves and no HPA crystal phase is developed, even at SiW12 loadings as high as 50 wt%. In the esterification of acetic acid byn-butanol, supported catalysts exhibit a higher catalytic activity and stability and held some promise of practical application. In addition, experimental results indicate that the loaded amount of SiW12 and the calcination temperatures have a significant influence on the catalytic activity, and the existence of aluminum has also an effect on the properties of supported catalysts.

Vapor phase esterification catalyzed by immobilized dodecatungstosilicic acid (SiW12) on activated carbon

The vapor phase esterification of acetic acid with ethanol and n-butanol catalyzed by SiW12 supported on activated carbon was studied in a flow fixed-bed reactor in the range of 358 to 433 K. The effects of the reaction temperature, liquid hourly space velocity (LHSV) as well as the molar ratio on the catalytic activity have been investigated. The kinetic studies showed that the rate of esterification was dependent on the partial pressures of the reactants and the addition of argon, an inert diluent in the system when the total pressure was kept at 1 atm. Also the alcohol structure has a profound effect on not only the rate of esterification, but also on the mechanism of esterification changing from a dual site mechanism for ethanol to a single site mechanism for n-butanol.

Superior catalytic performance of Ce1−xBixO2−δ solid solution and Au/Ce1−xBixO2−δ for 5-hydroxymethylfurfural conversion in alkaline aqueous solution

Porous Bi-doped ceria (Ce1−xBixO2−δ solid solution) was prepared by the easy citrate method and then used as a supporting material for Au nanoparticles (NPs) obtained by deposition–precipitation. In the presence of O2, Ce1−xBixO2−δ (0.08 ≤ x ≤ 0.5) efficiently catalyzed the conversion of 5-hydroxymethylfurfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HFCA) and 2,5-bishydroxymethylfuran (BHMF) in alkaline aqueous solution without degradation of HMF. The excellent catalytic activity was attributed to the oxygen activation and hydride transfer enhanced by Bi doping and the large amount of oxygen vacancies. After Au NPs were supported on Ce1−xBixO2−δ (x ≤ 0.2), the presence of Auδ+ facilitated the activation of the C–H bond in the hydroxymethyl group and then the production of 2,5-furandicarboxylic acid (FDCA) as an end product, inhibiting the generation of BHMF.

Hydrothermal Method Prepared Ce-P-O Catalyst for the Selective Catalytic Reduction of NO with NH3 in a Broad Temperature Range

Selective catalytic reduction of NOx with ammonia (NH3-SCR) is a widely used process for the abatement of NOx from flue gases and exhaust gases of diesel trucks. The well-known commercial catalysts used for this process are V2O5-WO3/TiO2 or V2O5-MoO3/TiO2 which function within a relatively narrow temperature window of 300–400 8C. As the temperature rises above 400 8C, V-based catalysts exhibit a rapid decrease in activity and selectivity in the reduction of NOx due to the oxidation of SO2 into SO3. [2] Furthermore, the emissions of toxic vanadium lead to health problems. In addition, deactivation by poisoning is another problem because flue gases contain metal oxides (e.g. , K2O) that deactivate V-based catalysts. Therefore, alternative NH3-SCR catalysts with only nontoxic components and stable under harsh operating conditions are required. Low-temperature SCR catalysts, such as amorphous MnOx, [5] Fe–Mn–Ox, [6] MnOx–CeO2, [7] Mn/TiO2, [8] are urgently needed for the abatement of NOx from flue gases to avoid reheating of the gas and thus decrease the capital cost. In the medium temperature range, Fe-based catalysts, such as Fe2O3– WO3/ZrO2, [9] and crystallite iron titanate, exhibit excellent SCR activity. However, these catalysts regularly have problems with low N2 selectivity, H2O and SO2 deactivation, and especially the loss of activity at high temperature and high space velocity. For the high temperature range, some zeolite catalysts, such as Fe-ZSM-5 reported by Long et al. and Carja et al. , have shown highly catalytic performance in the range of 400– 500 8C. However, their applications are greatly restricted by poor hydrothermal stability of the zeolite support. A comprehensive overview of the NH3-SCR reaction mechanism shows that both surface acidity and redox property are necessary for the NH3-SCR reaction. Herein, several metal phosphate catalysts containing different multivalent ions, (M–P–O; M = Cu , Fe + , Mn + , Ce), were prepared. The most promising catalyst, Ce-P-O, is emphasized herein due to its high deNOx activity. The results showed that Ce-P-O(h), prepared by a hydrothermal method (see the Supporting Information), is a novel and efficient catalyst for NH3-SCR with NO conversions above 90 % within the range of 200–550 8C. For comparison, the Ce-P-O catalyst was also prepared by a coprecipitation method and denoted as Ce-P-O(c). Figure 1 shows the comparison of deNOx activities of Ce-P-O catalysts as a function of reaction temperature. Ce-P-O catalysts prepared by hydrothermal and coprecipitation methods exhibited different deNOx performance in low temperatures

Aerobic oxidation of 5-hydroxymethylfurfural (HMF) effectively catalyzed by a Ce0.8Bi0.2O2−δ supported Pt catalyst at room temperature

The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) was efficiently catalyzed when Pt nanoparticles (NPs) were supported onto a Ce0.8Bi0.2O2−δ solid solution. 98% yield of FDCA was achieved within 30 min at room temperature and the catalyst was reused five times without much loss of FDCA selectivity. It is the first report on the oxidation of HMF, an alcohol and an aldehyde, effectively catalyzed by a ceria-based material supported Pt catalyst. The individual properties of the Pt NPs and the ceria-based support were retained and not affected after their combination. The superior oxygen activation ability of the Bi-doped ceria thoroughly changed the performance of the ceria supported Pt catalyst. Pt NPs were responsible for the formation of the Pt–alkoxide intermediate, followed by β-H elimination with the help of hydroxide ions. Bi-containing ceria accelerated the oxygen reduction process because of the presence of a large amount of oxygen vacancies and the cleavage of the peroxide intermediate promoted by bismuth. These specific functions were well incorporated during the catalytic oxidation cycle, leading to the generation of the highly efficient Pt/Ce0.8Bi0.2O2−δ catalyst for HMF oxidation at room temperature.

The role of redox property of La2−x(Sr,Th)xCuO4±λ playing in the reaction of NO decomposition and NO reduction by CO

Two systems of mixed oxides, La2-xSrxCuO4 +/- lambda (0.0 less than or equal to x less than or equal to 1.0) and La(2-x)Tn(x)CuO(4 +/-) (lambda) (0.0 less than or equal to x less than or equal to 0.4), with K2NiF4 structure were prepared. The average valence of Cu ions and oxygen nonstoichiometry (lambda) were determined by means of chemical analysis. Meanwhile, the adsorption and activation of nitrogen monoxide (NO) and the mixture of NO + CO over the mixed oxide catalysts were studied by means of mass spectrometry temperature-programmed desorption (MS-TPD). The catalytic behaviors in the reactions of direct decomposition of NO and its reduction by CO were investigated, and were discussed in relation with average valence of Cu ions, A and the activation and adsorption of reactant molecules. It has been proposed that both reactions proceed by the redox mechanism, in which the oxygen vacancies and the lower-valent Cu ions play important roles in the individual step of the redox cycle. Oxygen vacancy is more significant for NO decomposition than for NO + CO reaction. For the NO + CO reaction, the stronger implication of the lower-valent Cu ions or oxygen vacancy depends on reaction temperature and the catalytic systems (Sr- or Th-substituted)

A novel PdNi/Al2O3 catalyst prepared by galvanic deposition for low temperature methane combustion

Galvanic deposition method was used to prepare the Pd/Ni-Al2O3-GD catalyst for the combustion of methane under lean conditions. The new catalyst and compared catalysts (Pd/Al2O3-IW, Pd-Ni/Al2O3-IW, Pd/Ni-Al2O3-IW) prepared by incipient wetness impregnation were characterized by N2-physisorption, XRD and TEM to clarify particle size and size distribution of palladium species. Combined O2-TPD and XPS results with the catalytic data, it shows that the surface palladium species with low valence exhibits better combustion performance due to their stronger interaction with support. The results indicate that the galvanic deposition method is an effective route to prepare efficient catalyst for methane combustion, and it also provides useful information for improving the present commercial catalyst.

Superconductor mixed oxides La2–xSrxCuO4 ±λ for catalytic hydroxylation of phenol in the liquid–solid phase

Superconductor mixed oxides are often used as catalysts at high temperature in gas–solid phase oxidations and considered not suitable for lower temperature reactions in the liquid–solid phase; here the catalysis of La2–xSrxCuO4 ±λ(x= 0, 0.1, 0.7, 1) mixed oxides in phenol hydroxylation at lower temperatures are studied, and we find that the value of x has a significant effect on catalytic activity: the lower its value, the higher the catalytic activity; a mechanism is proposed to explain the experimental phenomena.

A Novel Ce-P-O Catalyst for the Selective Catalytic Reduction of NO with NH3

A novel Ce-P-O catalyst for the selective catalytic reduction of NO with NH3 was synthesized. The Ce-P-O catalyst was calcined at 500 °C and showed higher deNOx activity (NO conversion > 90%) with the temperature range of 300–550 °C and at GHSV = 20 000 h−1. The NO conversion was not significantly affected by the presence of H2O and SO2. By comparison with the commercial V-W-Ti catalyst, the Ce-P-O catalyst exhibited better resistance to deactivation due to K2O poisoning.