ИСТИНА

The nature of Ni anchoring on nanodiamond (ND) surface in the catalysts prepared by impregnation of detonation ND with NiNO3 water solution was investigated using EXAFS, TPR and catalytic studies. On the base of IR and zeta-potential measurements as well as the literature data, the presence of various oxygen-containing groups on the ND surface was confirmed. TPR investigation demonstrated staged NiO reduction in NiO/ND catalytic precursor, which was explained in terms of two type of Ni bonding with ND surface, through physical sorption by van der Waals interaction (weakly bonded Ni) and through chemical interaction with surface functional groups (strongly bonded Ni). Indeed, both Ni_Ni and Ni_O_C scattering paths were found in Ni/ND catalysts using wavelet transform of EXAFS data on the base of Morley function. In situ experiment demonstrated that the ratio between two forms depends on the temperature of NiO/ND reduction with H2. This hypothesis was confirmed by preparation of the samples containing mainly weakly bonded Ni (by removal of surface functional groups using annealing in Ar at 900 Ni-O-CC) or mainly strongly bonded Ni (by calcination of the NiO/ND precursor in air at 300C). These samples demonstrated drastic difference in styrene formation selectivity during hydrogenation of phenylacetylene: weakly bonded Ni gives mainly ethylbenzene, while strongly bonded Ni through Ni-O-C bond provides mainly styrene formation.