Hydrogen from synthetic biogas by catalyzed MDR and SIP: Screening of catalyst and iron oxide mixtures

Abstract

Hydrogen production plus purification has been studied by the joint use of methane dry reforming (MDR) and the reduction–oxidation of iron oxides (Steam-Iron Process or SIP) within the same reactor. The raw material studied has been an equimolar mixture of CH4 and CO2 simulating the composition of a biogas exempt of any other contaminant. The study has been mainly carried out by thermogravimetry, using mixtures of a catalyst and a doped iron oxide both synthesized in laboratory. The catalyst has been based in a nickel aluminate with nickel oxide in excess above its stoichiometric composition. The iron oxide indirectly “stores” the hydrogen produced by MDR by becoming into its metallic state during the reduction step. This hydrogen is released later on during the oxidation step of the metal with steam. On this way, dry reforming reaction is displaced towards products (H2 and CO) which are consumed “on site” by the oxide. This cyclic process has demonstrated that the key issue to achieve the goal of hydrogen purity enough to be consumed in a PEMFC, is producing a metallic iron with low coke deposition and an acceptable inert role. The nature of the coke and the way in which it is deposited, have also been studied in this work.