Yinyan Huang

Preparation and catalytic testing of mesoporous sulfated zirconium dioxide with partially tetragonal wall structure

Methods were explored to synthesize sulfated mesoporous zirconia with crystalline pore walls of tetragonal crystal structure. The material has been characterized by small and large angle X-ray diffraction, nitrogen physisorption, transmission electron microscopy (TEM) and catalytic tests using n-butane isomerization to iso-butane and alkylation of 1-naphthol with 4-tert-butylstyrene as probe reactions. It has been found that sulfate deposition is crucial for the transformation of a mesoporous precursor with amorphous pore walls into a material with crystalline pore walls maintaining the mesoporous morphology with narrow pore size distributions. TEM shows no ordered stacking of the pores. As a catalyst for acid catalyzed reactions of large molecules, mesoporous sulfated zirconia is superior to microporous sulfated zirconia.

On the mechanism of catalytic hydrogenation of nitriles to amines over supported metal catalysts

Hydrogenation of nitriles over NaY-supported transition metal catalysts has been studied in the liquid phase in an autoclave and in the gas phase in a microflow reactor. The results show that all reaction steps converting nitriles to primary, secondary and tertiary amines and unsaturated compounds take place on the catalysts surface. At low temperature the selectivity to a particular amine is controlled by the nature of metal: tertiary amines are preferentially formed over Pt/NaY, secondary amines over Pd/NaY, and primary amines over Ru/NaY. With butyronitrile, the selectivity to the primary amine over a variety of metals shows the same selectivity pattern for gas phase and liquid phase hydrogenation, it decreases in the order of Ru, Rh, Ni, Pd, Pt. Clearly, no liquid phase is required for the formation of the higher amines. In the liquid phase hydrogenation of butyronitrile over PdNi/NaY in the presence of pentylamine, small amounts of the enamines: N-butenyl-dibutylamine, N-butenyl-N-butyl-pentylamine, and N-butenyl-dipentylamine have been identified by GC-MS. Higher concentrations of an enamine are found in the liquid phase hydrogenation of benzylcyanide in the presence of diethylamine over Co/Al2O3 catalyst. The concentration of the enamine, N-(2-phenylvinyl)-diethylamine, passes through a maximum with reaction time. Amine addition to the reaction mixture lowers the hydrogenation rate of either nitrile and promotes primary amine formation.

Metal/overlayer and encaged carbonyl cluster catalysis

Abstract Two classes of metal catalyzed reactions are described to which the classical Langmuir–Hinshelwood or Eley–Rideal mechanisms do not apply. In one class the metal is partially covered with an overlayer, for instance a hydrocarbonaceous deposit. Hydrogen transfer from this layer to adsorbed intermediates is followed by migration of H atoms from the metal surface to the overlayer. When unsaturated molecules are fed with an excess of D2, this situation results in the initial formation of hydrogenation products with a much lower D/H ratio than the feed. If the overlayer contains asymmetric sites, molecules with prochiral C atoms are hydrogenated to a product with significant enantiomeric excess, i.e. the product carries the geometric imprint of overlayer groups. A second class of modified metal catalysts contains transition metal clusters in zeolite cavities. At high partial pressure of CO they are transformed to carbonyl clusters characterized by distinctive IR spectra. The transformation from metal-to-metal carbonyl clusters induces dramatic changes in activity and selectivity for catalytic reactions such as CO hydrogenation or olefin hydroformylation. With Rh/NaY the hydrogenation of CO can be directed towards preferential formation of acetic acid.

The effect of catalyst pore structure on liquid phase catalysis: Hydrogenation of stearonitrile over ruthenium supported on mesoporous sulfated zirconia

Abstract Ruthenium supported on mesoporous sulfated zirconia was tested as a catalyst for the liquid phase hydrogenation of stearonitrile, >n-C17H35CN, and compared with Ru, supported on either microporous sulfated zirconia or the zeolite HY. The mesoporous catalyst is significantly more active than the microporous catalyst; the zeolite supported catalyst is inactive under the same conditions. The results illustrate the effect of pore size on the reaction rate for large molecules. Both mesoporous and microporous catalysts show good stability and a high selectivity towards formation of primary amine. The reaction order in hydrogen is positive with both catalysts; the apparent reaction order in nitrile is negative with the mesoporous catalyst but positive with the microporous catalyst. The activation energy of the reaction is about 90 kJ/mol. TPR data show that under the conditions chosen for pretreatment no SO4 reduction takes place; at higher temperature the sulfur is reduced from S6+ to S2−.

Catalytic hydrogenation of nitriles to prim., sec. and tert. amines over supported mono- and bimetallic catalysts

Abstract The selectivity of nitrile hydrogenation to prim., sec. and tert. amines is dominantly controlled by the transition metal, similar selectivities are observed in gas phase flow and liquid phase batch runs. All amines are formed during one residence at the catalyst surface. Isotopic labeling in acetonitrile hydrogenation and co-hydrogenation of acetonitrile and butyronitrile show that the hydrogen atoms in the amine groups of the product are not provided by H ads at the metal surface, but by the methyl group of other acetonitrile molecules. It is concluded that N-bonded surface complexes are likely intermediates for the formation of prim., sec. and tert. amines