Abstract
The use of CO2 in reforming methane to produce the industrial feedstock syngas is an economically and environmentally attractive reaction. An alumina-supported nickel catalyst active for this reaction additionally forms filamentous carbon. The catalyst is investigated by inelastic neutron scattering as well as elemental analysis, temperature-programmed oxidation, temperature-programmed hydrogenation, X-ray diffraction, transmission electron microscopy and Raman scattering. Isotopic substitution experiments, using 13CO2 for 12CO2, show the oxidant to contribute to the carbon retention evident with this sample. At steady-state operation, a carbon mass balance of 95% is observed. A kinetic scheme is proposed to account for the trends observed.
Highlights
Syngas (CO + H2) is a vital feedstock for chemical manufacturing industries,[1] with the steam reforming of methane being a well established production route, eqn (1).[2]
Supported nickel catalysts are often utilised for both steam and dry methane reforming reactions,[7] with the latter reaction in particular being plagued by rapid deactivation issues compared to noble metals (e.g. Pt, Pd), as characterised by excessive carbon retention by the heterogeneous catalyst.[8,9,10]
Post-reaction, the inelastic neutron scattering (INS) sample was characterized by a combination of elemental analysis, temperature-programmed oxidation, X-ray diffraction, transmission electron microscopy and Raman scattering
Summary
Syngas (CO + H2) is a vital feedstock for chemical manufacturing industries,[1] with the steam reforming of methane being a well established production route, eqn (1).[2]. The dry reforming reaction has strong environmental credentials and yields a product mixture suited to up-stream processes such as the Fischer–Tropsch synthesis of relatively high molecular weight hydrocarbons.[5,6] Supported nickel catalysts are often utilised for both steam and dry methane reforming reactions,[7] with the latter reaction in particular being plagued by rapid deactivation issues compared to noble metals (e.g. Pt, Pd), as characterised by excessive carbon retention by the heterogeneous catalyst.[8,9,10] The topic of Against this background, it is desirable to secure a better understanding of the processes that lead to diminished activity with increasing time-on-stream for representative dry reforming catalysts. That work showed both an alumina-supported nickel catalyst and a gold-modified variant to be highly efficient at cycling hydrogen.[13] Further, the determination of C : H ratios for the retained overlayers associated with these catalysts led to a proposed reaction scheme that accounted for a reduction in syngas selectivity which pivoted on the fate of adsorbed carbon atoms at the nickel surface. Carbon retention was attributed to an enhanced rate of polymerisation (eqn (3)) relative to the rate of oxidation of the adsorbed carbon atoms:[13] n C (ad) A Cn(s)
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