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

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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.