Effects of the potassium incorporation in Fe–Ce–Zr based catalysts and activation condition in CO2 hydrogenation to C2/C3 olefins at atmospheric pressure

Abstract

Fe–Ce–Zr-based catalysts (FCZ) were promoted with potassium and evaluated in the CO2 hydrogenation reaction, carried out at atmospheric pressure, to produce light olefins, as ethene and propene. The FCZ catalyst was prepared using the coprecipitation technique, followed by a hydrothermal step. Potassium was added to the catalyst considering four nominal weight contents (0.5, 1, 2, and 4% wt) through wet impregnation. They were characterized using the following techniques: XRF, XRD, XPS, TPR-H2, TPD-H2, TPD-CO2, and in situ DRIFTS along the CO2 desorption and CO2 hydrogenation reaction. Selectivity towards ethene and propene reached the highest values with catalysts containing 1% and 2% wt of K. With this last one, the selectivity towards CO was around 95%, as potassium promotes the reverse water-gas shift reaction. Nonetheless, with this catalyst, the selectivity towards CH4, on a CO-free basis, was lower than 40%, and the olefins’ concentration in the C2–C3 range was superior to 90%, which can facilitate the light olefins separation in downstream processes. The catalysts were also in situ activated using the same feed flow, i.e., H2 and CO2 simultaneous flow, with the H2: CO2 ratio of 3:1, at 550 °C, for 1 h. CO2 conversion showed opposite trends for the case of H2 and H2+CO2 activation. With the former condition, the CO2 conversion increased with the incorporation of potassium, and it decreased for the second case. As the capability of the H2 adsorption diminished with the potassium incorporation to the catalysts, there was not enough hydrogen available to react with the CO2. Hence, for the activation using H2+CO2 flow, CO2 conversion diminished with potassium incorporation.