Yinghong Yue

Gas-phase photo-oxidation of organic compounds over nanosized TiO2 photocatalysts by various preparations

Gas-phase photocatalytic oxidation of hexane over nanosized TiO2 catalysts with different specific surface area, particle size and crystal phase at ambient temperature was studied and compared with Degussa P25. The photo-oxidation products are CO2 and H2O, and the activity is dominantly dependent on the surface area of the catalysts, although the faster electron–hole recombination in smaller TiO2 particles exerts to a certain extent a negative effect on the photocatalytic process. No significant difference in the activity has been observed between pure anatase and rutile catalysts with comparable specific surface area and particle size. Sulfation of anatase TiO2 catalysts improves their activity and stability efficiently. The complete oxidation of methanol and benzene to CO2 and H2O can also be achieved on the sulfated nanosized anatase photocatalysts successfully, and the catalysts are rather stable after reaching the steady state.

Chromium oxide supported on mesoporous SBA-15 as propane dehydrogenation and oxidative dehydrogenation catalysts

The catalytic activity and selectivity of Cr2O3 supported on mesoporous SBA-15 for non-oxidative and oxidative dehydrogenation of propane by O2 and CO2 have been studied and compared with those of Cr2O3/ZrO2 and Cr2O3/γ-Al2O3 catalysts. Cr2O3/SBA-15 and Cr2O3/ZrO2/SBA-15 are more selective to propene and more resistant to coking in comparison with Cr2O3/ZrO2 and Cr2O3/γ-Al2O3 for non-oxidative dehydrogenation of propane. In oxidative dehydrogenation of propane by O2 and CO2, Cr2O3/SBA-15 also displays better activity, selectivity and stability than the other two supported catalysts. The propane conversion and propene yield on Cr2O3/SBA-15 catalyst for oxidative dehydrogenation of propane by CO2 at 823 K reach 24.2 and 20.3%, respectively. XPS and TG/DTA have been used to characterize the catalysts before and after reaction. The differences in catalytic behavior of various supported Cr2O3 catalysts in the reactions have been discussed on the basis of the characterization results.

Acidity enhancement of SBA mesoporous molecular sieve by modification with SO42−/ZrO2

Abstract The SO 4 2− /ZrO 2 modified SBA mesoporous molecular sieves were prepared and characterized by XRD, N 2 adsorption, TG/DTG/DTA and IR pyridine chemisorption. The acidity of the molecular sieve was greatly enhanced after modification, and IR pyridine chemisorption results revealed that Lewis acidity was dominant in these samples. The catalytic activities of the modified molecular sieves towards strong and medium strong acid catalyzed reactions were lower than those of bulk SO 4 2− /ZrO 2 , but higher than those of Al-containing SBA molecular sieve from direct synthesis, whereas the activities of all these catalysts for weak acid catalyzed reaction were close to each other.

Disordered mesoporous KIT-1 as a support for hydrodesulfurization catalysts

MoO3 and NiO were supported on KIT-1, a new disordered mesoporous molecular sieve. MoO3 is homogeneously dispersed as a monolayer on the support, whereas NiO tends to form small crystallites in the mesoporous channels. KIT-1 supported MoO3 and/or NiO catalysts exhibit higher catalytic activities for thiophene hydrodesulfurization than similar MCM-41 and NaY zeolite supported catalysts, because the three-dimensional disordered network of short channels in KIT-1 reduces the risk of blockage in the catalysts and facilitates the transport of reactant and product molecules.

Nanosized anatase TiO2 as precursor for preparation of sulfated titania catalysts

Abstract Nanosized anatase TiO 2 has been prepared by a sol–gel hydrothermal process. The effect of water:alkoxide molar ratio, hydrothermal aging temperature and aging time on the properties of the nanocrystalline anatase TiO 2 was investigated in detail. The specific surface area, sulfur content and surface acidity of sulfated titania catalysts prepared by sulfation of sol–gel hydrothermal derived nanocrystalline TiO 2 were greater than those of the analogous catalyst prepared from ordinary amorphous titania hydrate. The former catalysts displayed higher catalytic activities in isopropanol dehydration, cumene cracking and n -pentane conversion reactions. The influence of the crystalline state and crystalline grain of titania precursors on the properties of sulfated titania catalysts was studied and discussed.

Synthesis and characterization of AlMCM-41 molecular sieves

Abstract The synthesis of AlMCM-41 molecular sieves with Si/Al ratios 14–32 is reported. Intermittent pH adjustments during synthesis may improve the long-range order of the mesopores. N 2 adsorption and 27 Al MAS NMR experiments reveal that all the AlMCM-41 samples contain a small amount of aluminum-rich extra-framework species both inside and outside the mesoporous channels after calcination. The proton exchanged AlMCM-41 catalysts are weak-medium acidic, and are catalytically active for isopropanol dehydration at moderate temperature and for cumene cracking at high temperature.

MSU-S mesoporous materials: An efficient catalyst for isomerization of α-pinene

MSU-S((BEA)) and MSU-S((Y)) mesoporous molecular sieves with different Si/Al ratios were prepared and characterized by XRD, XRF, N(2) adsorption, (27)Al MAS NMR, NH(3)-TPD and 2,6-di-tert-butyl-pyridine adsorption. Their catalytic behavior for the liquid phase isomerization of alpha-pinene has been investigated and compared with conventional zeolites and mesoporous molecular sieves. The activity correlates well with the amount of the accessible acid sites on the catalyst surface. MSU-S((BEA)) with Si/Al ratio of 67 has the highest activity in comparison to others. Ninty-seven percent conversion of alpha-pinene and 91% yield for main products like camphene, limonene, tricylene and terpinolene can be obtained at 70 degrees C. The catalyst is stable and reusable, and the product yield is only reduced by 10% after four runs, which is probably caused by the slow dealumination in the framework wall during the reaction.

Effect of modifiers on the activity of a Cr2O3/Al2O3 catalyst in the dehydrogenation of ethylbenzene with CO2

Chromium oxide supported on alumina was modified with various transition metal oxides by an incipient wetness method. The effect of modifiers on the activity of 20% Cr2O3/Al2O3 catalyst in the dehydrogenation of EB with CO2 was investigated. The activity is enhanced for ceria and vanadia modified supported chromium oxide catalysts, whereas the activity is decreased for catalysts modified with cobalt, manganese, molybdenum and zinc oxides. Carbon monoxide was detected in the course of the reaction, suggesting that carbon dioxide, which is one of the most important greenhouse gases, could be utilized as a mild oxidant in the oxidative dehydrogenation of ethylbenzene to styrene over unmodified and modified Cr2O3/Al2O3 catalysts.

Oxidative dehydrogenation of ethane with CO2 over Cr supported on submicron ZSM-5 zeolite

Abstract A series of submicron ZSM-5-supported chromium oxide catalysts were prepared and characterized by XRD, N2 adsorption, 27Al MAS NMR, SEM, XPS, laser Raman spectroscopy and diffuse reflectance UV-Vis spectroscopy. The catalytic performance of these materials during ethane dehydrogenation in the presence of CO2 was investigated. The catalysts exhibited both high activity and stability, with an ethane conversion of ∼65% and ethylene yield of ∼49% without any obvious deactivation following 50 h. Characterization results show that the excellent catalytic performance results from the high degree of dispersion of CrOx species on the submicron ZSM-5 surface. Both a high Si/Al ratio and the use of the Na-form of the ZSM-5 support were found to favor CrOx dispersion. The promotional effect of CO2 on the dehydrogenation reaction was quite evident and can be attributed to the reverse water-gas shift reaction.

Support effect in hydrogenation of methyl benzoate over supported manganese oxide catalysts

Abstract Manganese oxide supported on MgO, γ-Al 2 O 3 , SiO 2 , ZrO 2 , TiO 2 and SiO 2 -Al 2 O 3 catalysts were prepared. The effect of support on their catalytic behavior for hydrogenation of methyl benzoate to benzaldehyde was studied. The formation of toluene is suppressed on the supported catalysts due to the dilution of oxygen vacancies on the catalyst surface. The benzaldehyde yield of the supported catalysts follows the trend Mn/γ-Al 2 O 3 >Mn/TiO 2 >Mn/ZrO 2 >Mn/SiO 2 -Al 2 O 3 >Mn/SiO 2 >Mn/MgO. XRD measurements show that the Mn nitrate precursor is essentially transformed to highly dispersed MnO 2 on the supports at calcination and subsequently to MnO under reaction conditions with an exception of Mn/MgO. TPR and XPS analyses suggest that a strong interaction between manganese oxide and the γ-Al 2 O 3 support plays a positive role in the hydrogenation reaction.