Haiqiang Lin

Robust and Recyclable Nonprecious Bimetallic Nanoparticles on Carbon Nanotubes for the Hydrogenation and Hydrogenolysis of 5‐Hydroxymethylfurfural

Selective hydrogenation and hydrogenolysis of 5‐hydroxymethylfurfural were performed with carbon nanotube‐supported bimetallic NiFe (NiFe/CNT) catalysts. The combination of Ni and Fe in an appropriate atomic ratio of Ni/Fe (2.0) significantly increased the selectivity to 2,5‐furandimethanol or 2,5‐dimethylfuran depending on the reaction temperature. The selectivities to 2,5‐furandimethanol and 2,5‐dimethylfuran were as high as 96.1 % at 383 K and 91.3 % at 473 K, respectively. The characterization results confirmed that bimetallic particles with sizes less than 7 nm were formed on the catalyst. Several key molecules related to 5‐hydroxymethylfurfural transformation were used to investigate the product distribution and reaction pathway. The results indicated that the formation of NiFe alloy species is beneficial to the selective cleavage of the CO bond. Recycling experiments showed that the catalyst can be easily separated with a magnet and reused several times without significant loss of activity.

Effects of acidity and immiscibility of lactam-based Brønsted-acidic ionic liquids on their catalytic performance for esterification

Several lactam-based Bronsted-acidic ionic liquids with different acidities were synthesized and applied to the esterification of carboxylic acids with alcohols. High conversion and perfect selectivity were obtained under mild conditions. Among the ionic liquids investigated, those having a methyl sulfonate anion (which has weaker acidity than those with a tetrafluoroborate anion) afforded the highest activity for esterification. The results indicated that the acidity and immiscibility of Bronsted-acidic ionic liquids has a synergistic effect on their esterification performance. Furthermore, after removal of water under vacuum, such ionic liquids could be reused several times without substantial loss of activity.

Efficient synthesis of poly(oxymethylene) dimethyl ethers over PVP-stabilized heteropolyacids through self-assembly

A series of polyvinylpyrrolidone-stabilized heteropolyacids (PVP-HPAs) are generated by self-assembly of HPAs and PVP in methanol. The PVP-HPAs are then employed as catalysts for the synthesis of poly(oxymethylene) dimethyl ethers (DMMn, n⩾1) by the methanolysis of trioxane. The results suggest that the acidity of PVP-HPAs is tunable by changing the ratio of PVP and HPAs, which is a key factor for the selectivity of the DMMn product. By optimizing the composition and reaction conditions, two types of PVP-HPA, PVP-phosphotungstic acid (PVP-HPW) in a PVP/HPW ratio of 1/4:1 and PVP-silicotungstic acid (PVP-HSiW) in a PVP/HSiW ratio of 1/4:3/4, respectively afford 52.4% and 50.3% yields of DMM2–5. The optimized catalysts are reusable for a minimum of 10 times without a significant drop in performance.

PVP-stabilized heteropolyacids as reusable self-assembling catalysts for alcoholysis of cellulosic saccharides

Polyvinylpyrrolidone-stabilized heteropolyacids (PVP–HPAs) are synthesized by self-assembling in alcohol. The structure of PVP–HPAs is determined by various characteristic techniques. HPAs can protonate PVP to form polymeric cations. In turn, the protonated PVP interacts strongly with the heteropolyanion by forming an ionic liquid (IL)-like structure. The self-assembling separation and recyclability characteristics are related to the PVPs IL-like structure. The catalyzing performance of PVP–HPAs varies with the species of HPA and the content of PVP. The optimized PVP–H4SiW12O40·5H2O (HSiW) (1/5:3/4) gives more than 60% conversion of cellulose and complete conversion of highly selective cellobiose into butylglucosides. The optimized PVP–HSiW is separated directly by centrifugation and retains the activity without any post-treatment during recycling. The deactivation of PVP–HPAs is related to the loss of the catalyst during recycling. The functional mechanism of the IL-like structure is explored in this control experiment.

Enhanced performance of lipase-catalyzed kinetic resolution of secondary alcohols in monoether-functionalized ionic liquids.

Several cationic monoether-functionalized ionic liquids (MEF-ILs) with different substituents were synthesized and used as media for kinetic resolution of secondary alcohols catalyzed by several lipases. The results indicate that Novozym 435 (an immobilized Candida antarctica Lipase B) had higher efficiency compared to other lipases in deracemization. The alkyl substituents at the 2- and 3-positions in the imidazolium ring of MEF-ILs were found to contribute to the increased enantioselectivity and enhancement of the reaction rate, respectively, while the higher stereo-hindrance of ether bonds decreased the activity. An enantioselectivity higher than 99% with 50% conversion of rac-1-phenylethanol was achieved using the catalyst system comprised of Novozym 435 and the MEF-IL 1-(3-ethoxypropyl)-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide. The catalytic system could be separated and reused without considerable activity loss. MEF-ILs can be a new class of enzyme-benign media suitable for lipase-catalyzed kinetic resolution of secondary alcohols.

Influence of calcination temperature on the primary products of methane partial oxidation to synthesis gas over Rh/Al2O3 catalyst

The reaction pathway of methane partial oxidation to synthesis gas over Rh/Al2O3 calcined at 600 and 900 °C was studied by using the in situ time-resolved FTIR spectroscopy to follow the primary reaction products over the catalysts. The results of TPR and XPS characterizations suggest that the difference in the reaction mechanism of methane partial oxidation to synthesis gas over the two catalysts can be related to the difference in the reducibility of the supported Rh species, which may affect the concentration of O2− species on the surface of the catalysts under the reaction conditions.

Mechanistic studies of methane partial oxidation to synthesis gas over SiO2-supported rhodium catalyst

The mechanism of partial oxidation of methane (POM) to syngas over Rh/SiO 2 catalyst was investigated by means of TPSR, chemical-trapping reaction with CH 3 I as trapping agent, XPS, 1 H NMR and TR-FTIR. It is proposed that a pyrolysis oxidation mechanism was involved in the POM reaction over Rh/SiO 2 catalyst, in which CH x (x=1∼3) and CH x O (x=1 and/or 2) was intermediate carbon species and oxygen-containing intermediate, respectively.

Novel method of preparing zeolite membranes from colloidal zeolite NaY

Publisher Summary NaY zeolite membrane with little defects was prepared on modified support using colloidal zeolite. The results of permeation test indicate that the permselectivity of a series of gases were significantly higher than those of Knudsen that should be interpreted by the transport mechanism of molecular sieving and/or activation diffusion. It is expected that the possibility to develop a kind of Y zeolite composite membrane enclosed catalytic reactor be explored that may be used in some dehydrogenation reactions, although the permeablities seem to be relatively low. To obtain a perfect zeolite membrane, i.e., ultra thin and defect-free, several aspect of the preparing process should be improved, for example, a more proper drying procedure, a dust-free atmosphere and a support with low resistance and suitable pore size should be involved.