The reduction of Fe-bearing copper slag for its use as a catalyst in carbon oxide hydrogenation to methane. A contribution to sustainable catalysis

Abstract

Reduction of Fe-phases in a slag from the copper smelting process is studied for its use as a catalyst in methanation of carbon oxide (CO). This material contains 36.4 wt% Fe and the main Fe-phases in its fresh and reduced forms were identified and quantified. Chemical analysis and X-ray diffraction (XRD) for crystalline phase detection and determination of Fe dispersion were carried out. Reducibility of Fe-oxides was studied by thermal programmed reduction (TPR) under H-2 at 650 and 800 degrees C using 0.5 and 2 h soak time. In the fresh slag, iron was found to be in the form of Fe3O4 (17.4 wt%) and fayalite, Fe2SiO4 (43.4 wt%). The composition was experimentally determined and verified by stoichiometric balances and thermogravimetric analysis (TGA). Upon reduction at 800 degrees C and 2 h soak time, 87 % of the Fe-phases were reduced, leaving an activated catalyst with a 35.2 % Fe-0, which is the active phase for CO hydrogenation to methane. An expression was derived to determine the Fe-0 concentration in the reduced slag based on the composition of the fresh slag and its reduction degree. The catalytic activity of the reduced slag during CO hydrogenation was evaluated in a fixed bed differential reactor. The selectivity to methane, at 300 degrees C, was 87 %, thus confirming its catalytic activity for the selected reaction.