Promotion of surface oxygen vacancies on the light olefins synthesis from catalytic CO2 hydrogenation over Fe-K/ZrO2 catalysts

The performance of K and Fe loaded ZrO2 species (Fe-K/ZrO2) for CO2 hydrogenation was relevant to the concentration of oxygen vacancies due to the differences of ZrO2 crystal phases. The K and Fe were deposited on the surface of monoclinic zirconia (m-ZrO2) and tetragonal zirconia (t-ZrO2) with the Fe loading of 0-20 wt% and the K loading of 1 wt% by impregnation methods. The ZrO2 served as both a support and a co-catalyst for CO2 hydrogenation, exhibiting 40.54% CO2 conversion and 14.98% light olefins selectivity over the 10Fe-1K/m-ZrO2 with 10 wt% Fe and 1 wt% K, at 2.0 MPa and 340 degrees C. Such CO2 conversion were almost 200% higher than that of 10Fe-1K/t-ZrO2. The better activity of 10Fe-1K/m-ZrO2 is mainly attributed to the higher concentration of oxygen vacancies on the surface of m-ZrO2 after the reduction in H-2/N-2. However, covering the surface of m-ZrO2, excess surface Fe species lowered the concentration of surface oxygen vacancies for reduced 10Fe-1K/t-ZrO2, which inhibited the catalytic performance of ZrO2 for CO2 conversion. These investigations may propel the utilization of Zr-based catalysts on CO2 hydrogenation to various value-added chemicals. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.