Direct methanol production from mixed methane/H2O/N2O feedstocks over Cu–Fe/Al2O3 catalysts

Abstract

Bimetallic Cu/Fe-based catalysts were prepared through a novel hydrothermal (HT) method, structurally examined, and catalytically employed for the oxidation of methane to methanol. The highest CH4 conversion rate, CH3OH selectivity, and productivity were obtained over HT Cu–Fe/Al2O3. To compare the activity of the latter, bi-/monometallic Cu/Fe were also fabricated through support wet impregnation or co-precipitation (CP). These were characterised using chemisorption, reducibility, physisorption, diffraction and microscopy. N2 analysis showed that Cu or Fe species might be occupying pores, but was not incorporated into γ-Al2O3 structure. For Cu–Fe/Al2O3, interfacial copper nanoparticles acted as hydrogen activation sites, facilitating the reduction of Fe3O4 at lower measured temperatures. A high CH3OH synthesis yield was observed at 300 °C for HT Cu–Fe/Al2O3, 350 °C for CP Cu–Fe/Al2O3, while Cu/Al2O3 or Fe/Al2O3 demonstrated the optimum at 400 °C, which was in a correlation with the reducible material nature of Cu/Fe. The present catalysis process resulted from metal atom dispersion because of isolated Cu/Fe. The predominant direct chemosynthesis of alcohol (1228 µmolCH3OH gcat.–1h−1) was determined when N2O or a mixture of H2O/N2O was applied as the oxidant over Cu–Fe/Al2O3 substance, produced via developed HT experimental steps. Comparatively, though, active Cu/Fe, dispersed on alumina surface layer, were more selective for the production of CH3OH under N2O atmosphere. The formation of CH3OH by oxidizing CH4 followed an elementary redox mechanism, while reactivity, intermediate mechanistic pathways and the distribution of products depended on the oxidant molecule type in reactions involved.