Mingshi Li

Effect of structural properties on catalytic performance in citral selective hydrogenation over carbon–titania composite supported Pd catalyst

A novel C/TiO2 composite supported palladium catalyst (Pd/C/TiO2) was prepared. The effects of the structural properties on the catalytic performance in citral hydrogenation were estimated from calculations and compared with a commercial activated carbon supported palladium catalyst (Pd/AC). The results showed that although the reaction rate was comparatively low over Pd/C/TiO2, which took approximately 24 h to reach 90% citral conversion, fourfold the time of Pd/AC, the selectivity for citronellal in citral hydrogenation remained high (approximately 85%) at the same citral conversion, while decreasing to 40% over Pd/AC. The comparatively lower reaction rate over Pd/C/TiO2 was attributed to the fewer surface Pd sites (3.94 μmol g−1 per cat) than on Pd/AC (12.2 μmol g−1 per cat). Further calculations discovered similar initial turnover frequency values over the two catalysts (approximately 0.1 s−1), which implied that citral hydrogenation is structure-insensitive over Pd catalysts and that crystallite size effects have little influence on the differences in the kinetics between the two catalysts. The high selectivity for citronellal over Pd/C/TiO2 was due to the negligible internal diffusion limitation inside the catalyst, which was proved by calculating the Weisz–Prater numbers (less than 0.3 of each reactant). In contrast, the pore structures, mainly composed of micro pores, caused serious internal diffusion limitation over Pd/AC, which finally led to the increase of the selectivity to the deeply hydrogenated product, 3,7-dimethyloctanol.

Selective Oxidation of Propylene to Acetone over Supported Vanadia Catalysts

A 10%V2O5/TiO2 catalyst showed a pronounced catalytic activity for the selective oxidation of propylene to acetone and the formation of isopropoxy species from the adsorption of propylene was found to be the rate-limiting step.

Methane Aromatization in the Absence of Oxygen Over Mo/H[B]ZSM-5 Catalysts

The catalytic performance of Mo/H[B]ZSM-5 has been investigated for methane non-oxidative aromatization and compared with that of a Mo/H[Al]ZSM-5 catalyst. It is found that the non-oxidative aromatization of methane proceeds only in the presence of weak acidic sites without the participation of strong acidic sites. Coke is found to be the main cause of the rapid decrease in the activity of Mo/H[B]ZSM-5 catalysts.

Microkinetic analysis for the selective oxidation of propylene to acetone over vanadia/titania

Abstract The reaction mechanisms for the oxidation of isopropanol and propylene to acetone over the 10% V2O5/TiO2 catalyst were modeled according to the results of FTIR, microcalorimetric adsorption and microreactor kinetics. The two reaction mechanisms are closely correlated since isopropanol can be taken as the intermediate for the oxidation of propylene to acetone. The simulations revealed how the reaction conditions affect surface coverages that in turn influence the reaction activities. The abstraction of α-H from the surface isopropoxy groups by the oxidation sites (V5+–O) is the rate-limiting step for the oxidative dehydrogenation of isopropanol to acetone, while the adsorption of propylene on surface Bronsted acid sites (V–OH) to form the surface isopropoxy groups is the rate-limiting step for the selective oxidation of propylene to acetone. Both Bronsted acid sites and oxidation sites (V5+–O) are required for the conversion of propylene to acetone. Thus, one way to promote the rate of propylene adsorption in order to enhance the rate of propylene conversion to acetone may be to increase the strength of the Bronsted acid sites by adding some other acidic materials. The oxygen deficient vanadium sites were found to promote the dissociative adsorption of isopropanol to form the surface isopropoxy groups and the adsorption of water to form the surface Bronsted acid sites (V–OH) needed for the adsorption of propylene.

Synthesis of Carbon Nanofiber-Titania-Cordierite Monolith Composite and its Application as Catalyst Support on Citral Hydrogenation

We reported the synthesis of a promising carbon nanofiber-titania-cordierite monolith composite (C/TiO2/monolith) and its application in citral hydrogenation. The composite was synthesized through two steps: TiO2 coating on the surface of the monolith with sol-gel method and the following carbon deposit by methane decomposition. C/TiO2/monolith was subsequently employed to prepare its supported palladium catalyst, Pd/C/TiO2/monolith and its catalytic performance was evaluated in selective hydrogenation of citral. Results revealed that 2.0 wt% tetrabutyl titanate sol in composite synthesis was the best in improving textural properties of C/TiO2/monolith. The optimal composite possessed a BET surface area of 39.4 m2/g and micropore area accounted for only 3.8% of its total BET surface area. It contained about 30 wt% of carbon, which was mainly composed of carbon nanofiber. Pd/C/TiO2/monolith exhibited the high citronellal selectivity (81%) at 90% citral conversion, which was attributed to the decrease of internal diffusion limitation due to its mesoporous structure.

Surface Modification of PEOT/PBT Membrane with Silk Fibroin Anchoring and its Potential Application in Artificial Salivary Gland Construct

We reported the preparation of surface modified poly (ethylene oxide terephthalate) - poly (butylene terephthalate) membrane by the method of silk fibroin anchoring, namely SF/(PEOT/PBT). Its surface properties were characterized by contact angles and XPS and the biocompatibility of the composite membrane was further evaluated by human salivary epithelial cells (HSG cells) growth in vitro. Results revealed that SF/(PEOT/PBT) possessed the low water contact angle (48.0±3.0°) and immobilized a great amount of fibroin (fibroin surface coverage: 26.39 wt%), which attributed to the formation of polar groups such as hydrosulfide group, sulfonic group, carboxyl and carbonyl ones in the process of SO2 plasma treatment. HSG cells growth in vitro indicated that the silk fibroin anchoring could significantly enhance the biocompatibility of PEOT/PBT membrane, which suggested the potential application of fibroin anchoring PEOT/PBT for clinical HSG cells transplantation in the artificial salivary gland construct.