Hydrogen production via sulfur-based thermochemical cycles: Part 2: Performance evaluation of Fe 2O 3-based catalysts for the sulfuric acid decomposition step

Abstract

The sulfuric acid dissociation reaction, via which the production of SO 2 and O 2 is achieved, is the most energy intensive step of the so-called sulfur-based thermochemical cycles for the production of hydrogen. Efforts are focused on the feasibility and effectiveness of performing this reaction with the aid of a high-temperature energy/heat source like the sun. Such coupling can be achieved either directly in a solar reactor by concentrated solar radiation, or indirectly by means of a heat-exchanger/decomposer reactor using a suitable heat transfer fluid. Since a very limited amount of work regarding the potential formulations and sizing of such suitable reactors has been performed so far, the present work addresses further steps necessary for the efficient design, manufacture and operation of such reactors for sulfuric acid decomposition. In this respect, parametric studies on the SO 3 decomposition with iron(III) oxide-based catalysts were performed investigating the effect of temperature, pressure and space velocity on SO 3 conversion. Based on these results, an empirical kinetic law suitable for the reactor design was developed. In parallel, siliconised silicon carbide honeycombs coated with iron(III) oxide were prepared and tested in structured laboratory-scale reactors to evaluate their durability (i.e. activity vs. time) during SO 3 decomposition, with the result of satisfactory and stable performance for up to 100 h of operation. The results in combination with characterization results of “aged” materials can provide valuable input for the design of prototype reactors for sulfuric acid decomposition.