Chemical looping tar reforming using La/Sr/Fe-containing mixed oxides supported on ZrO2

Abstract

Biomass gasification gas contains condensable hydrocarbons usually referred to as “tars”. The use of chemical-looping reforming (CLR) has been proposed as a downstream technology for tar removal from the hot raw gasification gas. In this work two different ZrO2 support materials impregnated with La, Sr, Fe and mixtures thereof have been investigated as bed material for this proposed CLR process, with benzene and ethylene as tar surrogates. It was found that only combinations of La and Fe yielded significant catalytic activity for benzene conversion that could be further improved by adding Sr. Over this material, the benzene conversion reaction was found to be of first order with respect to benzene, and a simple kinetic model indicates that a high degree of benzene conversion can be obtained at reasonable residence times when the reactor temperature is sufficiently high (T=850°C). It was also observed that this material exhibited some activity for selective catalytic oxidation of benzene, which could further increase the tar conversion when either the bed material provided oxygen to the gas or a small stream of molecular O2 was added to the gasification gas feed. XRD analysis of the used bed materials revealed that a pyrochlore phase and SrZrO3 perovskite were formed during the experiment.