Tonghao Wu

Surface structure and catalytic behavior of silica-supported copper catalysts prepared by impregnation and sol–gel methods

Abstract Supported copper on silica catalysts prepared by sol–gel and impregnation methods were studied in this paper. The surface structures of these catalysts were characterized by various techniques, including BET, XRD, FTIR, XPS, TPR, and ESR. The results showed that the distribution of copper species was in different ways in the catalysts prepared by the two methods. Cu(II) species highly dispersed in the silica matrix for the sol–gel catalyst, while copper oxide clusters are dominant in the CuO-SiO 2 sample prepared by the impregnation method. The catalysts were then used for dehydrogenation of 2-butanol. Obvious differences of catalytic behavior were observed for the catalysts prepared by the two methods. High selectivity (>90%) toward dehydrogenation and high 2-butanol conversion was observed for the impregnated catalyst; however, for the CuO-SiO 2 sol–gel catalyst, very low dehydrogenation selectivity and 2-butanol conversion were obtained. The surface structures of catalysts were closely related to the preparation methods, and the catalytic behaviors were affected subsequently. The copper oxide clusters, which may be reduced to Cu 0 , are responsible for the dehydrogenation reaction. The highly dispersed Cu(II) ions were inactive for catalyze 2-butanol dehydrogenation.

Aromatization of methane in the absence of oxygen over Mo-based catalysts supported on different types of zeolites

The catalytic performance of Mo-based catalysts supported on various zeolites has been studied for methane aromatization in the absence of oxygen in a fixed-bed continuous-flow quartz reactor, and their catalytic properties are correlated with features of zeolite structure. It was found that H-type silica–alumina zeolites, such as ZSM-5, ZSM-8, ZSM-11 and β possessing two-dimensional structure and pore diameter equaling the dynamic diameter of a benzene molecule (about 6 Å) simultaneously, are fine supports for methane activation and aromatization catalysts. Among them, MoO3/H-ZSM-11 has the best activity and stability; for instance, a methane conversion of 8.0% and selectivity higher than 90% was obtained at 973 K. The catalytic performance of MoO3/H-ZSM-8 is somewhat lower than that of MoO3/H-ZSM-5, while activity of MoO3/H-β is lower than that of MoO3/H-ZSM-8. Catalysts supported on H-MCM-41 and H-SAPO-34 exhibit low activity for methane aromatization and those supported on H-MOR, H-X and H-Y give only a little amount of ethylene. Over MoO3/H-SAPO-5 and MoO3/H-SAPO-11 no hydrocarbons were detected.

The function of Cu(II) ions in the Mo/CuH-ZSM-5 catalyst for methane conversion under non-oxidative condition

Non-oxidative aromatization of methane was carried out over Mo/CuH-ZSM-5 and compared with that over Mo/H-ZSM-5. Cu(II) ions act as promoter in this reaction and improve the activity of the Mo/H-ZSM-5 catalyst notably. The effect of Cu species on the chemical state of Mo species and the changes of Cu species itself after reaction were studied by ESR and XPS methods. The introduction of Cu ions by ion-exchange method altered the reduction of Mo species, suppressed the dealumination of ZSM-5 framework and decreased coke formation over the catalyst. The results showed improved catalytic performance of Mo/H-ZSM-5 catalyst. The amount and nature of the coke which were influenced by the introduction of Cu ions were also investigated.

Studies on the decomposition of carbon dioxide into carbon with oxygen-deficient magnetite: I. Preparation, characterization of magnetite, and its activity of decomposing carbon dioxide

The magnetite Fe3O4+delta (0 less than or equal to delta less than or equal to 0.5) of different particle sizes were prepared using wet-heating oxidation method, supercritical fluid dry method and ferrous oxalate and ferric oxalate high-temperature decomposition method, and their structure were characterized by XRD, Mossbauer spectra, IR spectra and STEM. The oxygen-deficient magnetite of Fe3O4+delta (0 < delta < 1) was prepared using H-2 reduction of Fe3O4+delta (0 < delta < 0.5) at 573 K and its properties (lattice constant, magnetism, stability, and reduction ability) were studied ih detail. The activity of decomposing CO2 with oxygen-deficient magnetite of different sizes were compared and the effects of degree of oxygen-deficiency, reaction time, and temperature on the activity of the decomposing CO2 into carbon with oxygen-deficient magnetite were investigated. It is found that oxygen in the CO2 was incorporated in the form of O2- into oxygen-deficient magnetite and CO2 was reduced to carbon, at the same time Fe3O4-delta converted into stoichiometric Fe3O4. The smaller the particle size of magnetite is, the larger the oxygen-deficient degree is, the higher the reaction temperature is, and the higher the activity of decomposing CO2 is

Synthesis, characterization and catalytic activity of cubic Ia3d and hexagonal p6mm mesoporous aluminosilicates with enhanced acidity

Through a two-step crystallization procedure, an ordered mesoporous aluminosilicate with cubic Ia3d structure denoted as MB48 has been synthesized from the assembly of preformed zeolite beta precursors, utilizing cetyltrimethylammonium bromide (CTAB) as a template. By adjusting the alkalinity during the second crystallization step, an ordered mesoporous aluminosilicate with hexagonal p6mm structure named as MB41 has also been prepared. MB48 and MB41 were characterized with PXRD, FTIR, 27Al-MAS NMR, N2 adsorption–desorption and NH3-TPD techniques, etc. Experiments show that both MB48 and MB41 are pure mesoporous phases, containing the secondary structural units of zeolite beta. Compared with conventional mesoporous aluminosilicates, MB48 and MB41 have enhanced acidity and show higher catalytic activity in the cracking of cumene and the phenol alkylation with tert-butanol.

Reduction of carbon dioxide into carbon by the active wustite and the mechanism of the reaction

Normal wustite (Fe0.94O) was prepared by rapidly decomposing ferrous oxalate in vacuum at 923 K. Normal wustite, which was kept in a He atmosphere at 573 K for 10 min, undergoes eutectoid decomposition into active wustite (Fe0.98O) and stoichiometric magnetite. Compared with normal wustite, active wustite is more unstable and it is active for decomposing carbon dioxide. Carbon dioxide (1.013 x 10(5) Pa) was almost completely reduced into carbon by active wustite at 573 K, which was associated with the transformation of active wustite into stoichiometric magnetite. The oxygen in CO2 is considered to be transferred to the surface of wustite in the form of O2- ions and then these ions react with excess iron ions from the inside of the oxide to form the spinel structure. In order to maintain the electrical neutrality of the oxide, active wustite releases electrons, which will move to the surface and be donated to the carbon in CO2; therefore the carbon is reduced. The reduction of CO2 into carbon is undergone via two steps: CO2 --> CO --> C, the former step, CO2 --> CO, is the control step of the reaction speed and CO is the intermediate of this reaction, because the speed of CO conversion is faster than that of CO2 when CO was produced in the process of the reaction. During the reaction, the partial pressure of CO2 decreased gradually with increasing reaction time and finally the reaction system became a vacuum. Elevating reaction temperature, the speed of CO2 decomposition increased and the content of CO produced in the reaction process decreased

Preparation, Characterization And Catalytic Properties OF α -Fe2O3/SiO2 Catalyst in Phenol Hydroxylation with Hydrogen Peroxide

Abstract7KH .H2 O3 /SiO2 catalyst was synthesized by simple impregnation. The catalyst was characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Mössbauer spectroscopy. The results showed that the size RI .H2 O3 particles on silica was very small. This kind of catalyst exhibited very good catalytic performance in phenol hydroxylation by H2 O2 to dihydroxy-benzene.

Effect of Au loading, H2O and CO concentration on the stability of Au/ZnO catalysts for room-temperature CO oxidation

Au/ZnO catalysts prepared by co-precipitation method with different Au:Zn atomic ratios have been studied for room-temperature CO oxidation in the presence/absence of water in the feed stream. The catalysts exhibited excellent catalytic activity and stability compared with pure ZnO. Furthermore, it was found that the lifetime of Au/ZnO catalysts was improved significantly by increasing CO concentration but decreased by addition of H2O in the feed stream. The deactivation may be related to the sintering of metallic gold and the accumulation of carbonate-like species in the catalyst.

Synthesis of mesoporous titanium phosphate with high surface area using long-chain alkylamine

A mesoporous titanium phosphate with high surface area was synthesized in an alcoholic system containing a small quantity of water using n-octodecylamine as structure-directing agent. The stability and structure order of the product treated by postsynthetic treatment can be improved remarkably after removal of the structure-directing agent by acidified ethanol extraction. The mesoporous product calcinated at 500 jC exhibits wormhole-like pore structure and high surface area about 497 m 2 /g.

The role of copper species and Brønsted acidity in CuCl/ZSM-5 catalysts during the selective catalytic reduction of NO by propene

The role of copper species and Bronsted acidity in the selective catalytic reduction (SCR) of NO by propene over CuCl/ZSM-5 catalysts prepared by dispersion method has been investigated. The results of IR and H2-TPR show that the main active species of CuCl/H-ZSM-5 catalyst are isolated copper ions (Cu2+ and Cu+) located in the ion exchange sites of ZSM-5, which formed during the high-temperature solid-state exchange reaction occurred between CuCl and the Bronsted acid sites of H-ZSM-5. While the high dispersed CuCl on the surface of ZSM-5 is inactive for this reaction. Some direct evidences indicate that the initial Bronsted acidity of the starting zeolite is useful to produce active copper ions species during the preparation process of catalysts. However, it is not necessary for the SCR of NO over Cu-ZSM-5 catalysts.