Mixed Ni-Co sub-stoichiometric spinels as catalytic precursors for dry reforming of methane

Abstract

Eight mixed Ni-Co spinels with (Ni+Co)/Al molar ratios between 0.05 and 0.50 were synthesised by co-precipitation to serve as precursors for bimetallic Ni-Co catalysts for the dry reforming of methane reaction. Both calcined and reduced samples were examined by BET measurements, X-Ray diffraction, Raman spectroscopy, XPS spectroscopy, STEM/HAADF, STEM/EDS elemental mapping, temperature-programmed reduction with H₂, temperature-programmed surface reaction with CH₄, temperature-programmed desorption of CO₂, thermogravimetric analysis and TEM, and their catalytic activity was studied for the dry reforming of methane at 650 °C at 80 L g⁻¹ h⁻¹. All the precursors synthesised with (Ni+Co)/Al molar ratios below 0.25 presented a high degree of spinel formation without the presence of segregated oxides. On the other hand, all the reduced catalysts presented a comparable structure, with crystallites of sizes between 20 and 30 nm composed of a homogeneous Ni-Co alloy, with the absence of isolated metals. The catalyst based on the spinelic precursor with a (Ni+Co)/Al molar ratio of 0.15 resulted the most active and selective towards H₂ formation, achieving CH₄ conversion values of 93 % after 24 h of time on stream and yielding a syngas with a H₂/CO molar ratio of 1.1. Despite significant formation of carbonaceous deposits, this optimum sample was still able to operate efficiently for 200 h.