Hydrogen production via sulfur-based thermochemical cycles: Part 1: Synthesis and evaluation of metal oxide-based candidate catalyst powders for the sulfuric acid decomposition step

The present work concerns the synthesis of various single and mixed oxide materials and their study as catalysts for the sulfuric acid dissociation reaction via which the production of SO2 and O2 is achieved. This is the most energy intensive step of sulfur-based thermochemical cycles for the production of hydrogen. Commercial (i.e. FeO, Fe3O4, Fe2O3, CuO, Cr2O3, γ-Al2O3, Pt/γ-Al2O3) and in-house binary and ternary compositions of the Cu–Fe–Al system as well as Fe–Cr mixed oxide materials prepared by the Solution Combustion Synthesis (SCS) technique were comparatively tested. The materials were studied in powder form, in a fixed bed reactor at 850 °C and ambient pressure. The feedstock was concentrated liquid sulfuric acid (95–98% wt) and all tests were performed at a Liquid Hourly Space Velocity-LHSV of 50–52 h−1. It was found that systems of both in-house synthesized mixed oxide families (Cu–Fe–Al and Fe–Cr) with proper composition could achieve SO3 conversions comparable to that of the reference Pt/γ-Al2O3 system, being at the same time much less expensive. The results, in combination with characterization results of fresh and spent catalysts are employed to identify possible mechanisms of the reaction and streamline the synthesis of more efficient catalytic systems.