Cobalt–carbon nanocomposite catalysts of gas-phase hydrodechlorination of chlorobenzene

Abstract

The catalytic efficiency of three different cobalt–carbon composites has been compared in the gas-phase hydrodechlorination (HDC) of chlorobenzene (CB) in a flow type fixed bed reactor. The Co@C composite was synthesized by evaporation of overheated liquid drop of Co in the flow of an argon–butene mixture; the Co/C composite – by pyrolysis of sawdust impregnated with Co(NO3)2 water solution, and the Co/CNT composite – by the impregnation of carbon nanotubes with Co(NO3)2 water solution. Different oxidation states of cobalt were observed in the studied composites according to XPS, TPR, and in situ vibrating sample magnetometry results: predominantly Co0 in Co@C, CoO in Co/C, and Co3O4 in Co/CNT. TPR showed the possibility of the reduction of Co3O4 to CoO and even to Co0 under conditions of HDC and established the temperatures of these transitions. TEM revealed that Co0 nanoparticles in the Co@C composite are encapsulated by the thin carbon shell, CoO nanoparticles in Co/C are immersed in the carbon matrix, and Co3O4 nanoparticles in Co/CNT are located both on the surface and inside the channels of CNTs. All the composites demonstrated activity in HDC of CB. The efficiency of not only Co0 but CoO in the CB HDC was shown. The CB conversion at 150–250 °C for Co/C and Co/CNT composites, containing predominantly cobalt oxides, was higher than that for Co@C one, containing Co0 nanoparticles coated with the thin carbon shell. The Co/C composite with the lowest Co content (1.3 wt.%) was more effective in HDC than Co/CNT (14.6 wt.% of Co) and Co@C (79 wt.% of Co) ones. High CB conversion for the Co@C composite at 350 °C resulted from the catalytic action of the graphene shell of Co particles, activated by subsurface Co0.