Decarbonylation of group six metal carbonyl M(CO)(6) (M = Cr, Mo, W) encaged in FAU zeolites: basicity of framework oxygen

Thermal decarbonylation of group six hexacarbonylmetal (0) M(CO)(6) (M = Cr , Mo, NV) encapsulated in zeolite X or Y was studied by using a temperature programmed decomposition (TPDE) technique. M(CO)(6) is decomposed to M-met al in vacuo in two steps via thermally stable subcarbonyl intermediate spec ies, M(CO)(3). The decomposition temperature of M(CO)(6) decreases with dec reasing O 1s binding energy of the host zeolite, whereas that of M(CO)(3) t o M-metal increases. The decomposition temperature Of M(CO)6 encaged in zeo lite increases in the order Mo(CO)(6) much less than Cr(CO)(6) similar to W (CO)(6). In contrast, the thermal stability of M(CO)(3) anchored in zeolite increases in the order, Cr(CO)(3) much less than Mo(CO)(3) similar to W(CO )(3). The decomposition rate of M(CO)(6) was measured by IR. In conformity with the TPDE results, the decomposition rate of M(CO)(6) increases as the basic strength of the zeolite increases. The rate increases in the order Cr (CO)(6) < W(CO)(6) much less than Mo(CO)(6). These results are discussed in terms of the first dissociation energy of the M-CO bond of M(CO)(6) and co ordination of the zeolite framework oxygens to the M(CO)(3) moiety. (C) 200 1 Elsevier Science B.V. All rights reserved.