METHANE HYDROGENATION AND CONFIRMATION OF CHX INTERMEDIATE SPECIES ONNAY ENCAPSULATED COBALT CLUSTERS AND CO SIO2 CATALYSTS - EXAFS, FTIR,UV CHARACTERIZATION AND CATALYTIC PERFORMANCES/
Gc. Shen et M. Ichikawa, METHANE HYDROGENATION AND CONFIRMATION OF CHX INTERMEDIATE SPECIES ONNAY ENCAPSULATED COBALT CLUSTERS AND CO SIO2 CATALYSTS - EXAFS, FTIR,UV CHARACTERIZATION AND CATALYTIC PERFORMANCES/, Journal of the Chemical Society. Faraday transactions, 93(6), 1997, pp. 1185-1193
Citations number
52
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The adsorption of Co-2(CO)(8) onto dehydrated NaY powder under an N-2
atmosphere predominantly yielded supported Co-4(CO)(12). The molecular
cobalt carbonyl clusters and their decarbonylated products have been
structurally characterized by in situ IR, extended X-ray absorption fi
ne structure (EXAFS) and diffuse reflectance spectroscopies. The TR sp
ectrum assigned to the species Co-4(CO)(12)/NaY is shifted significant
ly from that observed for externally supported analogues on NaY and fo
r this cluster in solution, which indicates that the cobalt carbonyl c
lusters occurring on the NaY are similar to those occurring in weakly
basic solution. EXAFS coordination numbers (N) show that the successiv
ely decarbonylated samples maintain small cluster sizes, which depend
on the temperature-programmed oxidation of the precursor. Methane hydr
ogenation was carried out on intrazeolitic cobalt clusters using a two
-step process. It showed a relatively higher activity and selectivity
to C2+ hydrocarbons in comparison with Co/SiO2 catalysts. On the basis
of IR (v(C-H) 2960, 2880 cm(-1) and delta(C-H) 1520, 1393 cm(-1)) spe
ctroscopy, mass spectrometry and reaction studies, one can conclude th
at CHx (x = 0, 1 or 2) surface carbonaceous species were generated by
CH4 dissociation on the activated cobalt catalyst; the CH2 species was
quite reactive, and propagated higher hydrocarbons.