Weiming Hua

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.

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.

Excellent photocatalytic degradation activities of ordered mesoporous anatase TiO2-SiO2 nanocomposites to various organic contaminants.

Ordered 2-D hexagonal mesoporous TiO(2)-SiO(2) nanocomposites consisted of anatase TiO(2) nanocrystals and amorphous SiO(2) nanoparticles, with large mesochannels and high specific surface areas, have been extensively and detailedly evaluated using various cationic dyes (methylene blue, safranin O, crystal violet, brilliant green, basic fuchsin and rhodamine-6G), anionic dyes (acid fuchsin, orange II, reactive brilliant red X3B and acid red 1) and microcystin-LR. We use mesoporous 80TiO(2)-20SiO(2)-900 for the degradation of cationic dyes and MC-LR, due to the dominant adsorption of SiOH groups and synergistic role of coupled adsorption and photocatalytic oxidation. For anionic dyes, due to the adsorption results predominantly from TiOH groups, our strategy realizes the enhanced photocatalytic oxidation by strong surface acids and larger available specific surface area. Based on this, we prepared 90TiO(2)-10SiO(2)-700 to degrade them. The results show that our samples exhibit excellent degradation activities to all the contaminants, which are much higher than that of P25 photocatalyst. The dyes are not only decolorized promptly but degraded readily as well. It is strongly indicated that our mesoporous nanocomposites are considerably stable and reusable. These results demonstrate that our mesoporous TiO(2)-SiO(2) nanocomposites present extensive and promising application in the fast and highly efficient degradation of various organic pollutants.

Studies on SO 4 2? promoted mixed oxide superacids

Sulfated binary and trinary oxide solid superacids were prepared and characterized. The incorporation of Cr, Fe, Mn and V into sulfated zirconia increases its superacidity and catalytic activity forn-butane isomerization at 35°C significantly. The catalytic activity of sulfated oxides of Cr-Zr, Fe-Cr-Zr and Fe-V-Zr is 2–3 times greater than that of the well-known sulfated Fe-Mn-Zr oxide. A negative effect was observed in the cases of sulfated Mn-Zr, Sn-Zr, W-Zr and Mo-Zr oxides. The origin of the enhancement in superacidity and activity is discussed in the light of experimental results obtained by XRD, IR and chemical analysis.

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.

Benzoylation of toluene with benzoyl chloride on Al‐promoted sulfated solid superacids

The catalytic performance of Al‐promoted sulfated zirconia and sulfated titania for benzoylation of toluene with benzoyl chloride has been investigated. The incorporation of Al enhances the catalytic activity of the sulfated oxide catalysts prominently owing to an increase in superacidity of the catalysts. Al‐promoted sulfated zirconia catalysts are more active than the analogous sulfated titania catalysts because of their higher superacidity. In particular, SO42-–/3%Al2O3–ZrO2 is a good clean catalyst for the benzoylation reaction, which gives 100% yield of methylbenzophenones after on stream for 12 h at 110 °C.

Catalytic decomposition of CFC-12 over solid acids WO3/MxOy (M = Ti, Sn, Fe)

Abstract Catalytic decomposition of dichlorodifluoromethane (CFC-12) in the presence of water vapor was investigated over a series of pure and WO 3 -promoted metal oxides. Although pure TiO 2 , SnO 2 and Fe 2 O 3 showed less activity for the decomposition of CFC-12, obvious enhancement in activity was actualized by supporting WO 3 on them using Ti(OH) 4 , Sn(OH) 4 and Fe(OH) 3 as support precursors. The decomposition activity depended on the calcination temperature obviously and attained to a maximum as the content of WO 3 reached its utmost dispersion capacity on different supports. The 95% conversion temperature of WTi, WSn and WFe catalysts prepared by optimum conditions were 260°C, 315°C and 345°C, respectively. CO 2 was the main-product and no CO was detected as by-product. The selectivity to by-product CFC-13 on WO 3 -modified metal oxides was much lower than on unmodified metal oxides and it also exhibited a coverage-dependent effect. The catalytic activity of WO 3 /TiO 2 , WO 3 /SnO 2 and WO 3 /Fe 2 O 3 all remained steady for 120 h on stream.

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.