Role of Zr loading into In2O3 catalysts for the direct conversion of CO2/CO mixtures into light olefins

Abstract

The effect of the ZrO2 content on the performance (activity, selectivity, stability) of In2O3-ZrO2 catalyst has been studied on the hydrogenation of CO2/CO mixtures. This effect is a key feature for the viability of using In2O3-ZrO2/SAPO-34 tandem catalysts for the direct conversion of CO2 and syngas into olefins via oxygenates as intermediates. The interest of co-feeding syngas together with CO2 resides in jointly valorizing syngas derived from biomass or wastes (via gasification) and supplying the required H-2. The experiments of methanol synthesis and direct synthesis of olefins, with In2O3-ZrO2 and In2O3-ZrO2/SAPO-34 catalysts, respectively, have been carried out under the appropriate conditions for the direct olefins synthesis (400 ?, 30 bar, H-2/COX ratio = 3) in an isothermal fixed bed reactor at low space time values (kinetic conditions) to evaluate the behavior and deactivation of the catalysts. The Zr/In ratio of 1/2 favors the conversion of CO2 and COX, attaining good oxygenates selectivity, and prevents the sintering attributable to the over-reduction of the In2O3 (more significant for syngas feeds). The improvement is more remarkable in the direct olefins synthesis, where the thermodynamic equilibrium of methanol formation is displaced, and methanation suppressed (in a greater extent for feeds with high CO content). With the In2O3-ZrO2/SAPO-34 tandem catalysts, the conversion of COx almost 5 folds respect oxygenates synthesis with In2O3-ZrO2 catalyst, meaning the yield of the target products boosts from ~0.5% of oxygenates to > 3% of olefins (selectivity > 70%) for mixtures of CO2/COX of 0.5, where an optimum performance has been obtained.