Youzhu Yuan

Highly Active CNT-Promoted Cu–ZnO–Al2O3 Catalyst for Methanol Synthesis from H2/CO/CO2

With types of in-house-synthesized multi-walled carbon nanotubes (CNTs) and the nitrates of the corresponding metallic components, highly active CNT-promoted Cu–ZnO–Al2O3 catalysts, symbolized as CuiZnjAlk-x%CNTs, were prepared by the co-precipitation method. Their catalytic performance for methanol synthesis from H2/CO/CO2 was studied and compared with the corresponding CNT-free co-precipitated catalyst, CuiZnjAlk. It was shown experimentally that appropriate incorporation of a minor amount of the CNTs into the CuiZnjAlk could significantly increase the catalyst activity for methanol synthesis. Under the reaction conditions of 493 K, 5.0 MPa, H2/CO/CO2/N2 = 62/30/5/3 (v/v), GHSV = 8000 h-1, the observed CO conversion and methanol formation rate over a co-precipitated catalyst of Cu6Zn3Al1-12.5%CNTs reached 36.8% and 0.291 μmol CH3OH s-1 (m2-surf. Cu)-1, which was about 44 and 25% higher than those (25.5% and 0.233 μmol CH3OH s-1 (m2-surf. Cu)-1) over the corresponding CNT-free co-precipitated catalyst, Cu6Zn3Al1. Addition of a minor amount (10–15 wt%) of the CNTs to the Cu6Zn3Al1 catalyst was found to considerably increase specific surface area, especially Cu surface area of the catalyst. H2-TPD measurements revealed that the CNTs and the pre-reduced CNT-promoted catalyst systems could reversibly adsorb and store a considerably greater amount of hydrogen under atmospheric pressure at temperatures ranging from room temperature to ∼573 K. This unique feature would be beneficial for generating microenvironments with higher stationary-state concentration of active hydrogen adspecies on the surface of the functioning catalyst, especially at the interphasial active sites since the highly conductive CNTs might promote hydrogen spillover from the Cu sites to the Cu/Zn interphasial active sites, and thus be favorable for increasing the rate of the CO hydrogenation reactions. Alternatively, the operation temperature for methanol synthesis over the CNT-promoted catalysts can be 15–20 degrees lower than that over the corresponding CNT-free contrast system. This would contribute considerably to an increase in equilibrium CO conversion and CH3OH yield. The results of the present work indicated that the CNTs could serve as an excellent promoter.

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.

Remarkable enhancement of Cu catalyst activity in hydrogenation of dimethyl oxalate to ethylene glycol using gold

The performance of an SBA-15-supported Cu catalyst for hydrogenation of dimethyl oxalate to ethylene glycol is markedly promoted with Au. A key genesis of the high activity of the catalyst is ascribed to the formation of Cu–Au alloy nanoparticles which stabilize the active species and retard their agglomeration during the hydrogenation process.

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.

Aqueous Biphasic Hydroformylation of Higher Olefins Catalyzed by Rhodium Complexes with Amphiphilic Ligands of Sulfonated Triphenylphosphine Analog

The catalytic performances of rhodium complexes with three new amphiphilic phosphine ligands, bis-(3-sodium sulfonatophenyl)-(4-tert-butylphenyl)-phosphine (3), phenyl-(3-sodium sulfonatophenyl)-(4-tert-butyl-phenyl)-phosphine (4) and bis-(4-tert-butylphenyl)-(3-sodium sulfonatophenyl) phosphine (5), in hydroformylation of 1-hexene, 1-octene and 1-dodecene have been studied. The steric attributes of free ligands are investigated by Tolmans cone angle method through geometric optimizations. The results reveal that the new phosphines are surface-active as the typical surfactants and the corresponding rhodium complexes show significant enhancements in the reaction rate and higher selectivities toward the normal aldehydes in comparison with those obtained by triphenylphosphine trisulfonate (TPPTS)- and triphenylphosphine disulfonate (TPPDS) rhodium complexes under identical conditions.

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.

Platinum nanoparticles supported on N-doped carbon nanotubes for the selective oxidation of glycerol to glyceric acid in a base-free aqueous solution

Selective oxidation of glycerol was carried out over Pt catalysts supported on nitrogen-doped carbon nanotubes (Pt/N-CNTs) with molecular oxygen under atmospheric pressure in base-free aqueous solution. The N-CNTs were readily synthesized through a catalyst-free approach of annealing the mixture of CNTs and melamine. Results of X-ray diffraction, nitrogen absorption, and Raman spectroscopy confirmed that the tubular structure of CNTs was intact during annealing. Analyses of transmission electron microscopy, X-ray photon spectroscopy, and temperature-programmed desorption indicated that the surface of the CNTs was successfully functionalized with nitrogen atoms, which changed the electronic structure and surface basicity of the N-CNTs. Pt/N-CNTs out-performed Pt/CNTs for glycerol oxidation in terms of glycerol conversion and glyceric acid selectivity. Pt/N-CNTs showed highly stable catalytic performance during consecutive recycles when the used catalyst was reduced in a H2 atmosphere.

Aqueous phosphine-Rh complexes supported on non-porous fumed-silica nanoparticles for higher olefin hydroformylation

Non-porous fumed-silica nanoparticles were used as supports for the first time to immobilize water-soluble complex HRh(CO)(P(m-C6H4SO3Na)3 (1) [P(m-C6H4SO3Na)3, i.e. trisodium salt of tri-( m-sulfophenyl)-phosphine, TPPTS] to obtain supported aqueous-phase catalysts (SAPC) (fumed-SiO2-SAPC) for hydroformylation of 1-hexene. The experimental results proved that the structure of support and the support hydration were the determining factors contributing to the hydroformylation performance. The fumed-SiO2-SAPC where the water-soluble rhodium complexes were well dispersed onto the external surface of the silica nanoparticles presented a higher hydroformylation performance over a relatively wider range of support hydration as compared to the SAPC with conventional porous granular-SiO2 support (porous SiO2-SAPC). A positive effect on the reaction performance was observed from the particle size and surface area of the fumed-silica nanoparticles. The hydroformylation performance with fumed-SiO2-SAPC was promoted by an addition of basic alkali metal salts such as Na2CO3 ,K 2CO3, and NaH2PO4, which depressed the oxidation of ligand TPPTS to OTPPTS [OTPPTS, i.e. trisodium salt of tri-(m-sulfophenyl)-phosphine oxide, OP(m-C6H4SO3Na)3] as evidenced by 31 P NMR observation.

Study of the supported K2MoO4 catalyst for methanethiol synthesis by one step from high H2S-containing syngas

ESR and XPS are used to study the Mo-based catalysts MoO3/K2CO3/SiO2 and K2MoO4/SiO2 prepared with two kinds of precursors, (NH4)6Mo7O24⋅4H2O and K2MoO4. The catalytic properties of the catalysts for methanethiol synthesis from high H2S-containing syngas are explored. The activity assay shows that the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of “oxo-Mo(V)” (g=1.93), “thio-Mo(V)” (g=1.98) and S (g=2.01 or 2.04) can be detected. In the catalyst MoO3/SiO2 modified with K2CO3, as increasing amounts of K2CO3 are added, the content of “oxo-Mo(V)” increases, but “thio-Mo(V)” decreases. The XPS characterization indicates that Mo has mixed valence states of Mo4+, Mo5+ and Mo6+, and that S includes three kinds of species: S2− (161.5 eV), [S–S]2− (162.5 eV) and S6+ (168.5 eV). Adding K2CO3 promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo2S and “oxo-M(V)”, and the derivation of [S–S]2− and S2− species from S is promoted simultaneously. The methanethiol synthesis is favored if the mole ratio of (Mo6+ + Mo5+)/Mo4+ ≤ 0.8 and S2−/[S–S]2− is kept at a value of about 1.

Lipases are soluble and active in glycerol carbonate as a novel biosolvent

Glycerol carbonate was synthesized as biosolvent for the development of soluble enzymatic system. The effects of various reaction parameters on activity and stability of lipases were investigated using the transesterification of ethyl butyrate with n-butanol as a model reaction. Enzymatic activity in glycerol carbonate was compared with that in water and in conventional organic solvents with different ionizing and dissociating abilities. The pK(a) value of trichloroacetic acid and transesterification activities of Candida antarctica lipase B and Candida rugosa lipase in glycerol carbonate are similar to those in water, indicating that ionizing and dissociating powers are capable of satisfactorily predicting the biocompatibility of organic solvents for soluble enzymatic systems.