Zi Gao

Application of zeolite-filled pervaporation membrane

Composite hydrophilic membranes, consisting of KA, NaA, CaA, and NaX zeolites and polyvinylalcohol polymer were prepared. The pervaporation and separation characteristics of different alcohol-water systems through these membranes were investigated at temperatures ranging from 20 to 50 °C. Distinct improvement on molecular transport and the molecular sieving effect of the zeolites have been observed. Pervaporation-aided catalytic esterification of acetic acid with ethanol and salicylic acid with methanol have been carried out in a membrane reactor, leading to a considerable increase in conversion and a reduction in reaction time as a result of continuous removal of water-through the membrane. Acetone-water separation by pervaporation on KA- and CaA-filled polyvinylalcohol membrane has been studied as well, which gives even better separation results than that of the ethanol-water system. Application of the zeolite-filled pervaporation membrane to the methanol-acetone condensation reaction also promotes the reaction.

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.

Zeolitization of diatomite to prepare hierarchical porous zeolite materials through a vapor-phase transport process

In this study, we report a new, simple approach to the preparation of hierarchical structured zeolites through transforming the diatomaceous silica into zeolite by a vapor-phase transport (VPT) method. The morphology and macro-porosity of the diatomite are well preserved even in the samples with zeolite content higher than 50%. The products possess high mechanical strength and hydrothermal stability, and are thus promising for application in catalysis, adsorption and separation. The influence of the zeolite structures, the amount of adsorbed seeds, and the VPT treatment time and temperature on the crystallinity of the resulting materials are discussed. Powder XRD, SEM, TEM, IR and N2 adsorption–desorption measurements are employed to monitor the VPT treatment process.

Fabrication of hollow zeolite microcapsules with tailored shapes and functionalized interiors

Abstract Hollow zeolite microcapsules with spherical and various non-spherical shapes were fabricated through a novel strategy involving the crystallization of mesoporous silica (MS) particles. This conversion process was achieved by vapor phase transport treatment of MS particles which were pre-seeded by nanozeolite via the electrostatic assembly technique. The capsule shell was composed of closed packed zeolite crystals growing from the initial seeds by consuming the silica “nutrition” in the internal MS cores. The effects of seed size and seed type on the transformation of MS particles were investigated in detail. More importantly, guest species (e.g. Fe 2 O 3 and Ag nanoparticles) which had been incorporated in the mesopores of the MS particles could be spontaneously encapsulated inside the generated capsules during the MS consumption process, thus, hollow zeolite capsules with functionalized interiors could be easily fabricated.

New catalyst of SO 4 2− /Al2O3–ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H2 and at high temperature in the presence of H2 was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence of H2 significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al2O3 keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH3 adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction.

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.

Regular HZSM-5 microboxes prepared via a mild alkaline treatment

HZSM-5 zeolite microboxes with a thin intact shell and large hollow core have been synthesized by a mild alkaline treatment of ZSM-5 single-crystals with Na2CO3 solution. The obtained product was characterized by means of N2 adsorption, XRD, FT-IR, TEM, and temperature-programmed desorption of ammonia. The morphology and architecture of the small zeolite microboxes are exceptionally uniform and regular. On the other hand, the intrinsic crystalline properties in the alkaline treated zeolite are well preserved. Furthermore, the zeolite microbox catalyst exhibits higher activity than the parent HZSM-5 by facilitating the diffusion of molecules.

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.

New solid superacid catalysts for n-butane isomerization: γ-Al2O3 or SiO2 supported sulfated zirconia

Solid superacid catalysts SO42−/ZrO2 (SZ) supported on γ-Al2O3 and SiO2 (named SZ/Al2O3 and SZ/SiO2, respectively) were prepared by an impregnation method. Their catalytic behaviors of for n-butane isomerization at low temperature in steady state system and at high temperature in flow system were studied. Large improvements of catalytic activities were observed on the SZ/Al2O3 catalysts. In the flow system, the steady activity of the most active sample, 60% SZ/Al2O3, is 2.5 times more active than that of the bulk SZ. However, the activities of the SZ/SiO2 catalysts are lower than that of bulk SZ. The texture properties of the catalysts were studied by the methods of XRD and the adsorption of N2. Experimental results of sulfur content analysis and IR of adsorbed pyridine show that the acid strength and amount of strong acid sites on 60% SZ/Al2O3 sample are higher than those on bulk SZ, while the amount of acid sites is lower on 60% SZ/SiO2. The different activities for the SZ/Al2O3 catalysts and the SZ/SiO2 catalysts are due to the differences of superacidity.

Novel Fe-based complex oxide catalysts for hydroxylation of phenol

Novel catalysts for the hydroxylation of phenol, Fe–Si–O, Fe–Mg–O and Fe–Mg–Si–O complex oxides, have been synthesized by a coprecipitation method. X‐ray diffraction studies show that MgFe2O4 crystallites with spinel structure are formed in Fe–Mg–Si–O and Fe–Mg–O complex oxides and the crystallite size of the metal oxide or complex oxide is reduced after addition of Si. In the hydroxylation of phenol with hydrogen peroxide, Fe‐based complex oxides exhibit high activities after a short induction period. The phenol conversion is improved when silicon is introduced into the Fe‐based complex oxides, and formation of MgFe2O4 crystals with spinel structure in the catalysts increases the diphenol selectivity. The addition of a little acetic acid to the reaction liquid can shorten the induction period effectively. Under the same reaction conditions, phenol conversion and diphenol selectivity over the Fe–Mg–Si–O catalyst are close to those over TS‐1, and furthermore, the reaction time is more than ten times shorter as compared to TS‐1. The reaction mechanism of the hydroxylation of phenol on the catalysts has been studied, and a free‐radical mechanism initiated by the formation of phenoxy free radicals is suggested.