Khi-Rui Tsai

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.

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.

Development of coking-resistant Ni-based catalyst for partial oxidation and CO2-reforming of methane to syngas

Abstract Addition of small amount of trivalent-metal oxides, Cr 2 O 3 and La 2 O 3 , to a Ni Mg O (Ni/Mg=1/1, mol/mol) catalyst for partial oxidation of methane (POM) and CO 2 -reforming of methane (MCR) reactions has been found to improve the performance of the catalyst for coking-resistance. The POM operation at 1053 K for 50 h, or the MCR operation at 1100 K for 6 h, did not leave any detectable amount of carbon deposit on the surface of the catalyst. Studies of XRD, XPS, and H 2 -TPR spectroscopies showed that the doping of small amounts of Cr 3+ and La 3+ to the Ni Mg O system led to the formation of a host-dopant-type Ni Mg Cr La O solid solution, with a considerable number of Schottky defects in the form of cationic vacancies. An increase in the degree of disorder in the solid solution due to Cr 2 O 3 and La 2 O 3 dissolved in Ni x Mg 1− x O lattice would be expected to enhance the mobility of the lattice oxygen anions. This would be in favor of speeding up the reaction between the carbon-containing species and reactive oxygen species via migration of the lattice O 2− so as to inhibit the deposition of carbon on the surface of the catalyst. On the other hand, part of the Schottky defects in the form of cationic vacancies may diffuse to the surface, where Ni + -species can be well accommodated and stabilized, thus, forming a rich-in-Ni (with mixed valence states) surface layer. As a result, the proportion of the reducible Ni-species was pronouncedly increased, but the temperature for their reduction was considerably raised, so that the surface Ni-species were maintained with higher possibility in positive valence states under POM and MCR reaction conditions. This would, to some extent, lead to the reduction of the rate of deep dehydrogenation of methane to carbon, therefore tending to reduce, if not avoid, coking caused by an excess of carbon on the surface.

SYNTHESES AND STRUCTURES OF THE POTASSIUM-AMMONIUM DIOXOCITRATOVANADATE(V) AND SODIUM OXOCITRATOVANADATE(IV) DIMERS

Abstract The two dimers potassium-ammonium dioxocitratovanadate (V), K2(NH4)4[VO2(cit)]2·6H2O (1) and sodium oxocitratovanadate (IV), Na4[VO(cit)]2·6H2O (2) have been prepared by the reactions of citric acid and metavanadate in neutral solution. Complex 1 crystallizes in the triclinic space group P 1 with unit cell parameters: α = 8.894(1), b = 9.783(1), c = 9.930(2) A , σ = 70.00(1), β = 88.09(1), γ = 68.42(1)°, V = 750.8 A 3 , Z = 1, R = 0.035 for 2622 observed reflections. The dimeric anion contains a centrosymmetric planar four-member V2O2 ring with the bridging hydroxyl oxygens. The citrate ion is coordinated via oxygen atoms of the hydroxyl and α-carboxylato groups, and the two acetato branches are not coordinated to vanadium. The principal V-O dimensions are: V-O(hydroxy), 1.961(2), 2.005(2) A; V-O(σ-carboxy), 1.981(3) A. Complex 2 crystallizes in the monoclinic space group P21/n with unit cell parameters: a = 10.120(2), b = 10.822(4), c = 11.934(4) A , β = 111.57(2)°, V = 1215.4 A 3 , Z = 2, R = 0.035 for 2255 observed reflections. The dimer contains a similar planar V2O2 ring with bridging hydroxyl oxygens. The tetradentate citrato ligands coordinate via hydroxyl and α-carboxylato oxygens to one vanadium, and via two acetato branches to the two vanadiums in the dimer. The principal V-O dimensions are: V-O(hydroxy), 1.971(2), 2.206(2) A; V-O (α-carboxy), 2.038(2) A: V-O(β-carboxy), 2.017(2), 2.032(2) A. The coordination number of the vanadium ions in complex 1 and complex 2 is therefore five and six, respectively.

SYNTHESES, STRUCTURES AND SPECTROSCOPIC PROPERTIES OF NICKEL(II) CITRATO COMPLEXES, (NH4)2[Ni(Hcit)(H2O)2]2-2H2O AND (NH4)4[Ni(Hcit)2]-2H2O

Abstract Dimeric ammonium diaquocitratonickelate (II) dihydrate (NH4)2[Ni(Hcit)(H,O)2]2 -2H2O, 1, and its sodium and potassium salts, as well as ammonium dicitratonickelate (II) dihydrate (NH4)4[Ni(Hcit)2] ·2H2O, 2, (H4cit = citric acid) have been synthesized and characterized by spectroscopic methods. The crystal structures of 1 and 2 were determined by X-ray methods. Compound 1 is triclinic. space group Pl with a = 6.4071(7), b = 9.4710(7), c = 9.6904(5) A, α = 105.064(5), β = 91.992(7). γ = 89.334(8)°, V = 567.5(1) A Z = 1, R = 0.037 for 1714 observed reflections. The structure consists of centrosymmetric dimers, [Ni(Hcit)(H2O)2]2 2- The principal Ni[sbnd]O dimensions are Ni[sbnd]O(hydroxy), 2.074(2)A, Ni[sbnd]O(α-carboxy), 2.020(3)A, Ni[sbnd]O(β-carboxy), 2.031(2). 2.037(2)A, Ni[sbnd]O(water), 2.065(2), 2.072(3)A. Compound 2 crystallizes in the monocliruc space group P 21/a with a = 9.361(1), b= 13.496(1), c = 9.4238(7)A, (3= 115.475(6)°, V= 1074.9(3)A;. Z= 2, R = 0.052 for 1507 observed reflections. ...

Molybdenum(VI) complex with citric acid: synthesis and structural characterization of 1:1 ratio citrato molybdate K2Na4[(MoO2)2(cit)2]·5H2O

Abstract Sodium potassium citrato molybdate K 2 Na 4 [(MoO 2 ) 2 O(cit) 2 ]·5H 2 O has been prepared by the reaction of potassium trihydrogen citrate and sodium molybdate. Analysis of the crystal structure reveals that the anion of the complex contains a bent (MoO 2 )O(MoO 2 ) core with an MoOMo angle 142°. Each molybdenum has a distorted octahedral coordination and citrato ligands are tridentate to the two molybdenum atoms via the deprotonated hydroxy-, α- and β-carboxyl groups. Principal dimensions are: [MoO(t)] av , 1.706(4); [MoO(b)] av , 1.899(3); [MoO(hydroxy)] av , 1.944(3); [Mo Oα-carboxyl)] av , 2.207(3), and [MoO(β-carboxyl)] av , 2.264(3) A. The IR, 1 H and 13 C NMR spectra are in agreement with this structure.

Asymmetric transfer hydrogenation of prochiral ketones catalyzed by chiral ruthenium complexes with aminophosphine ligands

Abstract The condensation of ( S )-propane-1,2-diamine with two equivalents of o -(diphenylphosphino)benzaldehyde gives ( S )- N , N ′-bis[ o -(diphenylphosphino)benzylidene]propane-1,2-diamine [( S )- 1 ] ligand. The reduction of ( S )- 1 with excess NaBH 4 is carried out in refluxing ethanol to afford corresponding ( S )- N , N ′-bis[ o -(diphenylphosphino)benzyl]propane-1,2-diamine [( S )- 2 ]. The interaction of trans -RuCl 2 (DMSO) 4 with one equivalent of ( S )- 1 or ( S )- 2 in refluxing toluene gives ( S )- 3 or ( S )- 4 in good yield, respectively. ( S )- 1 , ( S )- 2 , ( S )- 3 and ( S )- 4 have been fully characterized by analytical and spectroscopic methods. The structure of ( R )- 3 has been also established by an X-ray diffraction study. Catalytic studies showed that ( S )- 4 as an excellent catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with 90% yield and up to 91% enantiomeric excess.

Influence of trivalent metal ions on the surface structure of a copper-based catalyst for methanol synthesis

Abstract The method of doping trivalent metal ions into a copper-based catalyst for methanol synthesis is effective in modifying the surface structure of the catalyst. The promotion effect and its relation to catalytic activity for hydrogenation of CO to methanol after doping with trivalent metal ions such as Al 3+ , Sc 3+ , and Cr 3+ into Cu–ZnO have been investigated by XRD, ESR, XPS, TPR, and the evaluation of catalytic activity. The results show that doping trivalent metal ions into ZnO assists in the formation of monovalent cationic defects on the surface of ZnO. These monovalent cationic defects both enrich and stabilize monovalent copper on the surface of copper-based catalysts for methanol synthesis during reduction and reaction. They increase catalytic activity for methanol synthesis and extend the life of catalysts.

METHANE OXIDATIVE COUPLING OVER FLUORO-OXIDE CATALYSTS

LaF3 modified ZrO2, CeO2 and ThO2 catalysts for the oxidative coupling of methane indicate that ZrO2/LaF3, CeO2/LaF3 and ThO2/LaF3 catalysts have high activity and high selectivity at low temperature. In the temperature region 480–650 °C, the methane conversion is 24.38–30.8% and the C2= selectivity is 40–55.38%. The characterization of oxygen species on the catalysts indicates that, because of the modification of LaF3 to ZrO2, CeO2 and ThO2, it is favourable for the activation of O2.