Huilin Wan

Chemical synthesis of lactic acid from cellulose catalysed by lead(II) ions in water

The direct transformation of cellulose, which is the main component of lignocellulosic biomass, into building-block chemicals is the key to establishing biomass-based sustainable chemical processes. Only limited successes have been achieved for such transformations under mild conditions. Here we report the simple and efficient chemocatalytic conversion of cellulose in water in the presence of dilute lead(II) ions, into lactic acid, which is a high-value chemical used for the production of fine chemicals and biodegradable plastics. The lactic acid yield from microcrystalline cellulose and several lignocellulose-based raw biomasses is >60% at 463 K. Both theoretical and experimental studies suggest that lead(II) in combination with water catalyses a series of cascading steps for lactic acid formation, including the isomerization of glucose formed via the hydrolysis of cellulose into fructose, the selective cleavage of the C3-C4 bond of fructose to trioses and the selective conversion of trioses into lactic acid.

Oxidative dehydrogenation of propane over a series of low-temperature rare earth orthovanadate catalysts prepared by the nitrate method

A series of high‐purity rare earth orthovanadates were prepared by the nitrate method and found to be effective low‐temperature catalysts for the oxydehydrogenation of propane at 320°C, at which no reactions occurred over the catalysts reported in the literature, and, thus, may be of practical significance. The catalytic performances of LnVO4 (Ln = Y, Ce–Yb) at 500°C were much better than those of rare earth orthovanadate catalysts and also slightly exceeded that of magnesium orthovanadate Mg3(VO4)2 reported in the literature. LnVO4 (Ln = Y, Ce–Yb) materials were tetragonal active phases which could stabilize the existence of active sites for the oxydehydrogenation of propane. Some catalysts with a certain amount of LnVO3 reduced from LnVO4 (Ln = Ho–Yb) under reaction atmosphere exhibited better redox properties and catalytic performances possibly due to the existence of biphasic catalytic synergy. LaVO4 was a monoclinic unstable active phase, although its bulk structure did not change after reaction. The remarkable deactivation of the LaVO4 catalyst was probably due to that LaVO4 could not stabilize the existence of surface active sites.

Characterizations and catalytic properties of Cr-MCM-41 prepared by direct hydrothermal synthesis and template-ion exchange

Abstract Cr-MCM-41 prepared by direct hydrothermal synthesis (DHT) and template-ion exchange (TIE) has been characterized by X-ray diffraction (XRD), N 2 adsorption (77 K), diffuse reflectance UV–vis, X-ray absorption (XANES and EXAFS), and UV-Raman spectroscopic measurements. It is suggested that monochromate species mainly exist on the Cr-MCM-41 by the DHT method while several types of chromate species including both monochromates and polychromates coexist on that by the TIE method. The two kinds of samples exhibit similar catalytic property in the dehydrogenation of propane with carbon dioxide. The selectivity to propylene is higher than 90% and the presence of carbon dioxide enhances propane conversion. The chromate species on both types of samples are reduced to aggregated Cr(III) with octahedral coordination during the dehydrogenation reactions. On the other hand, the selectivity to formaldehyde in the partial oxidation of methane with oxygen is remarkably higher over the sample by the DHT method than that by the TIE method. The structure of the chromate species is kept during the oxidation of methane, and the high dispersion of monochromate species probably accounts for the higher selectivity over the sample by the DHT method.

Enhanced photodegradation activity of methyl orange over Z-scheme type MoO3–g-C3N4 composite under visible light irradiation

Novel Z-scheme type MoO3–g-C3N4 composites photocatalysts were prepared with a simple mixing–calcination method, and evaluated for their photodegradation activities of methyl orange (MO). The optimized MoO3–g-C3N4 photocatalyst shows a good activity with a kinetic constant of 0.0177 min−1, 10.4 times higher than that of g-C3N4. Controlling various factors (MoO3–g-C3N4 amount, initial MO concentration, and pH value of MO solution) can lead to the enhancement of the photocatalytic activity of the composite. Only MoO3 and g-C3N4 are detected with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) spectra. N2 adsorption and UV-vis diffuse reflectance spectroscopy (DRS) results suggest that the addition of MoO3 slightly affects the specific surface area and the photoabsorption performance. The transmission electron microscopy (TEM) image of MoO3–g-C3N4 indicates a close contact between MoO3 and g-C3N4, which is beneficial to interparticle electron transfer. The high photocatalytic activity of MoO3–g-C3N4 is mainly attributed to the synergetic effect of MoO3 and g-C3N4 in electron–hole pair separation via the charge migration between the two semiconductors. The charge transfer follows direct Z-scheme mechanism, which is proven by the reactive species trapping experiment and the ˙OH-trapping photoluminescence spectra.

New chiral catalysts for reduction of ketones

The condensation of o-(diphenylphosphino)benzaldehyde and various chiral diamine gives a series of diimino-diphosphine tetradentate ligands, which are reduced with excess NaBH4 in refluxing ethanol to afford the corresponding diaminodiphosphine ligands in good yield. The reactivity of these ligands toward trans-RuCl2(DMSO)4 and [Rh(COD)Cl]2 had been investigated and a number of chiral Ru(II) and Rh(I) complexes with the PNNP-type ligands were synthesized and characterized by microanalysis and IR, NMR spectroscopic methods. The chiral Ru(II) and Rh(I) complexes have proved to be excellent catalyst precursors for the asymmetric transfer hydrogenation of aromatic ketones, leading to optically active alcohols in up to 97% ee.

Preparation of supported gold catalysts from gold complexes and their catalytic activities for CO oxidation

A phosphine-stabilized mononuclear gold complex Au(PPh3)(NO3) (1) and a phosphine-stabilized gold cluster [Aug(PPh3)8](NO3)3 (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as α-Fe2O3, TiO2, and SiO2 were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h2/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. α-Fe2O3 and TiO2 were much more efficient supports than SiO2 for the gold particles which were characterized by XRD and EXAFS.

New chiral cationic rhodium–aminophosphine complexes for asymmetric transfer hydrogenation of aromatic ketones

The new chiral ligands (S,S)-N,N′-bis[o-(diphenylphosphino)benzylidene]1,2-diiminocyclohexane, [(S,S)-1] and (S,S)-N,N′-bis[o-diphenylphosphino]benzyl-1,2-diaminocyclohexane, [(S,S)-2] have been prepared. The interaction of [(S,S)-1] and [(S,S)-2] with [Rh(COD)Cl]2 afforded the corresponding cationic rhodium complexes [(S,S)-3][X] and [(S,S)-4][X] (X=PF6−, BF4− or ClO4−), respectively. [(S,S)-1], [(S,S)-2], [(S,S)-3][X] and [(S,S)-4][X] have been fully characterized by elemental analyses and spectroscopic methods. These chiral cationic rhodium complexes serve as catalytst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in 2-propanol and [(S,S)-4][PF6] acts as an excellent catalyst in the reduction of m-chloroacetophenone, giving the corresponding optical alcohols in 99% yield and up to 94% ee.

Mechanistic study of partial oxidation of methane to synthesis gas over supported rhodium and ruthenium catalysts using in situ time-resolved FTIR spectroscopy.

Abstract In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH 4 /O 2 /He (2/1/45) gas mixture with adsorbed CO species over SiO 2 and γ-Al 2 O 3 supported Rh and Ru catalysts at 500–600°C. It was found that CO is the primary product for the reaction of CH 4 /O 2 /He (2/1/45) gas mixture over H 2 reduced and working state Rh/SiO 2 catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO 2 catalyst. CO 2 is the primary product for the reaction of CH 4 /O 2 /He (2/1/45) gas mixture over Ru/γ-Al 2 O 3 and Ru/SiO 2 catalysts. The dominant reaction pathway of CO formation over Ru/γ-Al 2 O 3 and Ru/SiO 2 catalysts is via the reforming reactions of CH 4 with CO 2 and H 2 O. The effect of space velocity on the partial oxidation of methane over SiO 2 and γ-Al 2 O 3 supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO 2 formation during the partial oxidation of methane to synthesis gas over Rh/SiO 2 and Ru/γ-Al 2 O 3 catalysts.

Catalytic performance, structure, surface properties and active oxygen species of the fluoride-containing rare earth (alkaline earth)-based catalysts for the oxidative coupling of methane and oxidative dehydrogenation of light alkanes

Abstract The fluoride-containing catalysts, mostly of the rare earth (alkaline earth)-based system, demonstrate good catalytic performances for the oxidative coupling of methane and oxidative dehydrogenation of ethane, propane as well as iso-butane. The results of structural analysis of the catalysts for oxidative coupling of methane show that the promoting effects of the fluoride in the catalysts may be principally related to the phase–phase interaction between fluoride and oxide. Compared to the corresponding alkaline earth oxide promoted rare earth oxide catalyst system, an alkaline earth fluoride-promoted rare earth oxide catalyst system is less basic and will therefore be favorable to reduce CO2 inhibition in the reaction of methane oxidative coupling. However, there is no simple correlation between the acidity/basicity of a methane oxidative coupling catalyst and its catalytic performance. In the experiments of in situ spectroscopic characterizations carried out at the temperature from 650°C to 800°C, O−2 species was detected over five fluoride-containing rare earth (alkaline earth)-based catalysts for methane oxidative coupling reaction, and the reactions between O−2 species and CH4 to form C2H4 and the corresponding side-products were observed using in situ IR over four catalysts, which suggest that O−2 is probably the active oxygen species for the methane oxidative coupling reaction over the corresponding catalysts.

Synthesis and characterization of iron(2+) and ruthenium(2+) diimino-, diamino- and diamido-diphosphine complexes. X-ray crystal structure of trans-RuCl2(P2N2C2H4) ∗d CHCl3

Abstract The interaction of Ru(OAc)2(Ph3P)2 with one equivalent of N,N′-bis[o-(diphenylphosphino)benzylidene]ethylenediamine (P2N2C2) in refluxing dichloromethane gave trans-Ru(OAc)2(P2N2C2) ∗d 2H2O (I) in moderate yield (63%) ; in refluxing-toluene, it gave a red solid which upon recrystallization in CHCl3 gave trans-RuCl2(P2N2C2) ∗d 2H2O (II) in good yield (92%). Compound II could also be prepared in good yield (85%) via the interaction of RuCl2(DMSO)4 with one equivalent of P2N2C2 in refluxing toluene. The interaction of RuCl2(DMSO)4 with one equivalent of N,N′-bis[o-(diphenylphosphino)benzylidene]-1,3-diaminopropane (P2N2C3), N,N′-bis[o-d(diphenylphosphineo)benzyl]ethylendiamine (P2N2C2H4) and N,N′-bis[o-(diphenylphosphino)benzamido]ethane (P2N2C2-amide) in refluxing toluene gave trans-RuCl2(P2N2C3) (III), trans-RuCl2(P2N2C2H4) (IV) and trans-RuCl2(P2N2C2-amide) (V) in good yield, respectively. The interaction of Fe(ClO4)2 ∗d 6H2O with one equivalent of P2N2C2 and P2N2C2H4 in refluxing acetonitrile gave trans-[Fe(P2N2C2(CH3CN)2](ClO4)2 (VI) and trans-[Fe(P2N2C2H4)(CH3CN)2](ClO4)2 (VII), respectively. Interaction of FeCl2 ∗d 4H2O with one equivalent of N,N′-bis[o-(diphenylphosphino)benzylidene]-1,6-diaminohexane (P2N2C6) in refluxing gave trans-FeCl2(P2N2C6) (VIII). Complexes I–VIII have been fully characterized by analytical and spectroscopic methods. The structure of IV has been established by an X-ray diffraction study. Compound II could be reduced to compound IV with NaBH4 in ethanol and oxidized to V with aqueous H2O2 acetonitrile. Catalytic studies showed that both II and IV were effected catalysts for the hydrogenation of acrylic acid to propionic acid.