Keane MA, Jacobs G, Patterson PM. Ni/SiO2 promoted growth of carbon nanofibers from chlorobenzene: Characterization of the active metal sites.
J Colloid Interface Sci 2006;
302:576-88. [PMID:
16860817 DOI:
10.1016/j.jcis.2006.06.057]
[Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2006] [Revised: 06/16/2006] [Accepted: 06/29/2006] [Indexed: 11/26/2022]
Abstract
The temporal changes to supported Ni sites during the growth of graphitic carbon nanofibers (GCNs) via the decomposition of chlorobenzene over Ni/SiO2 at 873 K have been investigated. The reaction of chlorobenzene with hydrogen also generated benzene, via catalytic hydrodechlorination, as the principal competing reaction. Reaction selectivity was found to be time dependent with a switch from a preferential hydrodechlorination to a predominant decomposition that generated an increasingly more structured carbon product over prolonged time-on-stream. These findings are discussed in terms of Cl/catalyst interaction(s) leading to metal site restructuring, the latter manifest in a sintering and faceting of the Ni metal particles. The pressure exerted on the metal/support interface due to fiber formation was of sufficient magnitude to extract the Ni particle from the support; the occurrence of an entrapped Ni particle at the fiber tip is a feature common to the majority of GCNs with the incorporation of Ni fragments along the length of the GCN. Metal site restructuring has been probed by temperature-programmed reduction of the passivated samples, H2 chemisorption/temperature-programmed desorption (TPD) and XANES/EXAFS analyses. This restructuring serves to enhance destructive chemisorption and/or facilitate carbon diffusion to generate the resultant GCN. The nature of the carbonaceous product has been characterized by a combination of TEM-EDX, SEM, XRD and temperature-programmed oxidation (TPO).
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