Role of Zr loading into InO catalysts for the direct conversion of CO/CO mixtures into light olefins.

The effect of the ZrO content on the performance (activity, selectivity, stability) of InO-ZrO catalyst has been studied on the hydrogenation of CO/CO mixtures. This effect is a key feature for the viability of using InO-ZrO/SAPO-34 tandem catalysts for the direct conversion of CO and syngas into olefins via oxygenates as intermediates. The interest of co-feeding syngas together with CO resides in jointly valorizing syngas derived from biomass or wastes (via gasification) and supplying the required H. The experiments of methanol synthesis and direct synthesis of olefins, with InO-ZrO and InO-ZrO/SAPO-34 catalysts, respectively, have been carried out under the appropriate conditions for the direct olefins synthesis (400 °C, 30 bar, H/CO 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 CO and CO, attaining good oxygenates selectivity, and prevents the sintering attributable to the over-reduction of the InO (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 InO-ZrO/SAPO-34 tandem catalysts, the conversion of CO almost 5 folds respect oxygenates synthesis with InO-ZrO catalyst, meaning the yield of the target products boosts from ∼0.5% of oxygenates to >3% of olefins (selectivity >70%) for mixtures of CO/CO of 0.5, where an optimum performance has been obtained.