Synthesis, characterization, and kinetic study of nanostructured copper-based oxygen carrier supported on silica and zirconia aerogels in the cyclic chemical looping combustion process

Abstract

In this study, copper-based oxygen carriers (OCs) confined in the structure of silica and zirconia aerogels were in situ synthesized by a simple sol–gel method, and the performance of the prepared oxygen carriers was investigated in the chemical looping combustion (CLC) process. The effects of different support types and copper loadings (20–60 wt%) were studied on the physicochemical properties and catalytic behavior of OCs during 15 reduction–oxidation cycles at the temperature of 800 °C. Zirconia-supported oxygen carriers exhibited high reactivity and stability over the cycles. However, the OCs supported on silica showed lower oxygen capacity than the theoretically expected values. This is due to the decomposition of copper oxide (CuO) to Cupric (Cu2O) during the reaction along with the collapse and fuse of mesoporous silica at high calcination and reaction temperatures which leads to a significant loss of oxygen-carrying capacity. The kinetics of reduction/oxidation steps in the CLC process was studied using a modified grain model considering grain size distribution in the OC particles based on their pore size distribution profile and “pore to sphere” factor. The synthesized oxygen carriers were characterized by Brunauer-Emmet-Teller (BET), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX).