Showing papers by "Zi Gao published in 2005"

Gas-phase photo-oxidations of organic compounds over different forms of zirconia

Abstract: Nanosized zirconia powders with different phase structure and specific surface area were prepared by various methods and were used as catalysts for gas-phase photocatalytic oxidations of methanol and hexane. The phase structure of the samples was analyzed by X-ray diffraction and Raman spectroscopy. The photocatalytic activity of the amorphous zirconia synthesized in this experiment is much higher than that of the crystalline samples. The activity of hexane oxidation on ZrO 2 -0-110 reaches 25.6%, which is even higher than that of Degussa P25 (17.3%). Thermal gravimetric studies show that the high activity is due to the abundant surface hydroxyl groups on the catalysts. Sulfation of zirconia samples induces a decrease in the amount of surface hydroxyl groups and has a negative influence on the activity of the zirconia photocatalysts. The results of a 100 h test show that the activity of the synthesized amorphous zirconia catalyst is very stable.

Alkylation of hydroquinone with tert-butanol over AlSBA-15 mesoporous molecular sieves

Abstract: A series of AlSBA-15 catalysts with different pore size and different Si/Al ratio were prepared and characterized by N2 adsorption and NH3-temperature programmed desorption (NH3-TPD) methods. Their catalytic behaviors for the alkylation of hydroquinone with tert-butanol were studied and compared with that of HZSM-5, HY, HAlMCM-41. It is found that the catalytic activity correlates well with the amount of medium-strong acid sites on the surface of the catalysts, and the selectivity towards 2-tert-Butylhydroquinone has some connection with the pore size of the catalysts. The reusability of the catalyst depends on its hydrothermal stability, which needs to be improved for the AlSBA-15 catalysts.

New catalysts for dichlorodifluoromethane hydrolysis: Mesostructured titanium and aluminum phosphates

Abstract: Catalytic decomposition of CCl2F2 in the presence of water vapor and air was investigated over mesoporous titanium and aluminum phosphates. They are much more active than the ordinary titanium and aluminum phosphates. Comparison between two mesoporous catalysts shows that mesoporous aluminum phosphate is slightly more active than mesoporous titanium phosphate, but the latter catalyst exhibits higher stability than the former one during the reaction. The results based on NH3-TPD and IR show that the activity of the catalysts is correlated with their surface acidity and hydroxyl groups.

In situ 13 C MAS NMR Study on the Mechanism of Butane Isomerization Over Catalysts with Different Acid Strength

Abstract: Reaction mechanism of skeletal isomerization of n-butane over sulfated zirconia (SZ), Cs25H05PW12O40 (Cs25) and H-form mordenite (H-MOR) catalysts was studied using 13C MAS NMR with 13C-labeled n-butane The isomerization of n-butane over SZ type catalysts proceeds predominantly via a monomolecular mechanism below 333 K and gradually changes to a bimolecular alkylation-β-scission mechanism as the reaction temperature is increased to 423 K Iron promoter in SZ catalyst facilitates the bimolecular process The n-butane isomerization over Cs25 also proceeds mainly via a monomolecular mechanism below 373 K The bimolecular mechanism becomes significant as the reaction temperature is increased to 423 K On both SZ and Cs25 catalysts hydrogen inhibits the isomerization reaction, in particular the bimolecular process In contrast, the n-butane isomerization over H-MOR with relatively moderate acid strength proceeds mainly via a bimolecular mechanism at 473 K The kinetics of n-butane isomerization on SZ below 333 K and Cs25 below 373 K are well represented by the Langmuir–Hinshelwood equation for a reversible first order surface reaction, further supporting that a monomolecular mechanism proceeds primarily on SZ and Cs25 catalysts at early reaction stage All results suggest that the stronger the acidity of the catalyst the lower the reaction temperature of n-butane isomerization and the more contribution of the monomolecular mechanism The overall mechanism of 1−13C-n-butane reaction on SZ, Cs25 and H-MOR catalysts including 13C scrambling and butane isomerization is proposed

Delamination and aromatic amine intercalation of layered aluminophosphate with [Al3P4O16]3- stoichiometry.

Abstract: The delamination and intercalation of a layered microporous aluminophosphate, [Al3P4O16]3−⋅3[CH3(CH2)NH3]+ (AlP), with aromatic amine have been carried out and were followed by XRD and SEM measurements. The basicity of the amine plays an important role in this process, as do the dielectric constant of the solution and the amount of amine added. A saturated benzylamine (p K a of 9.34) intercalate of the aluminophosphate are obtained in solutions with dielectric constant of 50–70 and an amine concentration of 10 mmol/g AlP, while no aniline (p K a of 4.60) intercalates are formed under similar conditions. The remarkable effect of basicity of the amine can be explained by a metathetical balanced reaction model, which was proved by the results of the intercalation processes of 4-methylpiridine (p K a = 6.00 ) and 4-methylimidazole (p K a = 7.55 ).

Hydrogenation of Methyl Benzoate over Mn/Al Catalysts: Comparison among Catalyst Preparation Routes

Abstract: Mn/Al catalysts for hydrogenation of methyl benzoate to benzaldehyde were prepared by different methods. The catalyst prepared from hydrotalcite-like precursor, the mesoporous MSU-γ supported Mn catalyst and the Mn-incorporated MSU-γ catalyst are more active than conventional Mn/γ-Al2O3 catalyst. The reaction temperature for the same yield level can be reduced by 20–60 °C. High specific surface area, high dispersion of manganese oxide species and strong interaction of manganese oxide species with γ-Al2O3 are of benefit to the reaction.