一國 伸之

Taking the advantage of excellent applicability for multi-component fine particles, new types of supported metal catalysts, Ru/Al2O3and Ru/TiO2were prepared by a spray reaction method. The structure and characteristics were studied by SEM, TEM, XRD and EXAFS. The high performance catalytic behaviors were clarified in the hydrogenation of CO2and the hydrocracking of ethane comparing with those by an impregnation and a hybrid method.

The novel host-guest catalysts, in which a chiral rhodium complex was intercalated into structural tuning guests modified smectites, were synthesized, and drastic change in catalysis was observed depending on the orientation of guest molecules.

Spray reaction (spr) method was applied to prepare Co/Al2O3 catalysts and Ni/Al2O3 catalysts and clarified synergetic effects between metal and mixed-oxide, and between metal oxide and mixed-oxide playing important roles for catalysis; NO-CO reaction on spr Co/Al2O3 and CO hydrogenation on spr Ni/Al2O3. The various applicability of the catalyst design by using spr was discussed.

Hectorite(HT)-supported Rh complex catalysts were prepared by the intercalation of [Rh(P*-P*)(COD)](+) (P*-P*=(S)-BINAP and (S)-(R)-BPPFA, COD=cyclooctadiene) into sodium hectorites (NaHT) in acetonitrile/H2O. The basal spacing of each modified clay was 2.94 nm (BINAP) and 2.72 nm (BPPFA), respectively. Asymmetric hydrogenation of alpha,beta-unsaturated carboxylic acid esters containing ester groups of various chain lengths was studied on these modified hectorites. The dependence of selectivity on employed solvents and bulkiness of the ester groups suggested that the interaction between substrates and the active sites increased in the interlayer space, thus enhancing the asymmetric selectivity.

Surface structures of SiO2-supported niobium catalysts prepared by use of a Nb-monomer complex, a Nb-dimer complex, Nb pentaethoxides and Nb pentachlorides as precursors have been determined by means of EXAFS and XANES. These different Nb structures on SiO2 have been characterized by ethanol dehydrogenation as a test reaction. In contrast to the case of Mo catalysts, the activity and selectivity of the Nb catalysts dramatically depended on the structure of the reaction sites at an atomic scale. Dynamic structural changes of the Nb sites are presented and local structural changes at the interface between the supported Nb atom and the SiO2 surface are proposed to explain the role of support in catalysis.

New Nb dimers on a SiO2 surface prepared by using [Nb(eta5-C5H5)H-mu-(eta5, eta1-C5H4)]2 were found to have an oxygen-bridged dimeric structure(Nb-O(surface)=0.193 nm; Nb--Si=0.328 nm; Nb--Nb=0.303 nm) by EXAFS. The attached Nb dimers were active for ethanol dehydration in contrast to the dehydrogenation ability of the Nb monomer catalyst. The regulation of the catalysis from dehydrogenation to dehydration, or equivalently from basic property to acidic property, was achieved by the nucleation of one Nb atom to two Nb atoms in active structures. The inverse isotope effect for ethene formation through the late-transition state of reaction was observed. The rate constant for ethene formation reduced by the second ethanol adsorption on the adjacent Nb site. It was also found that the selectivity of ethanol reaction was affected by the separation of Nb-Nb on SiO2.