Onion-Like Graphene Carbon Nanospheres as Stable Catalysts for Carbon Monoxide and Methane Chlorination

Article abstract of DOI:10.1002/cctc.201500662

Thermal treatment induces a modification in the nanostructure of carbon nanospheres that generates ordered hemi-fullerene-type graphene shells arranged in a concentric onion-type structure. The catalytic reactivity of these structures is studied in comparison with that of the parent carbon material. The change in the surface reactivity induced by the transformation of the nanostructure, characterized by TEM, XRD, X-ray photoelectron spectroscopy (XPS), Raman, and porosity measurements, is investigated by multipulses of Cl₂ in inert gas or in the presence of CH₄ or CO. The strained C-C bonds (sp²-type) in the hemi-fullerene-type graphene shells induce unusually strong, but reversible, chemisorption of Cl₂ in molecular form. The active species in CH₄ and CO chlorination is probably in the radical-like form. Highly strained C-C bonds in the parent carbon materials react irreversibly with Cl₂, inhibiting further reaction with CO. In addition, the higher presence of sp³-type defect sites promotes the formation of HCl with deactivation of the reactive C-C sites. The nano-ordering of the hemi-fullerene-type graphene thus reduces the presence of defects and transforms strained C-C bonds, resulting in irreversible chemisorption of Cl₂ to catalytic sites able to perform selective chlorination. Tidy up the carbon! CO and CH₄ chlorination over hemi-fullerene-type graphene is described. The surface nano-ordering, induced by thermal treatment, transforms strained C-C bond sites resulting in irreversible Cl₂ chemisorption to catalytic sites that are able to selectively chlorinate CO and CH₄.