Optimizing oxygen uncoupling performance and stability of novel MgO/TiO2 supported CuO oxygen carrier: Effect of impregnation steps and ZrO2 addition

Abstract

In our ongoing campaign, we are attempting to address the inferior stability of CuO oxygen carrier because it has exceptional reactivity in the chemical looping field ascribed to its oxygen uncoupling feature. In our previous work, impregnation method employed to synthesize CuO on novel double supports with strong anti-sintering (MgO) and high-crushing strength (TiO2) materials. Outstanding reactivity and sintering resistance were reported over 10 TGA cycles, while TiO2 recorded a weak XRD peak and Cu2MgO3 formed. This study has investigated impregnating Cu precursor on TiO2, followed by impregnating Mg precursor, for further modifications. The effect of partial replacement of MgO by ZrO2 was also investigated. The stability has been investigated over 21 cycles in a batch fluidized bed and materials characterized by XRD, XRF, SEM-EDS, and XPS techniques. Strong interaction between MgO and TiO2 has been identified, producing undesired MgTiO3 and MgTi2O5; however, impregnating Cu over TiO2 first significantly inhibited this phenomenon; recorded better stability. Replacement of MgO by ZrO2 also remarkably reduced MgO-TiO2 interaction and showed the highest XRD peak of desired (TiO2) rutile. SEM proved high sintering resistance for all samples throughout cycling, with slight grain growth. A sample with two impregnation steps and ZrO2 addition reported the best overall stability and the highest oxygen vacancies (XPS). Cu2MgO3 was detected in all samples, more clearly after cycles; however, it did not detect by XRD of reduced samples, suggesting it dissociates in inert condition and eventually did not reduces oxygen uncoupling capacity.