Conditions for the Joint Conversion of CO₂ and Syngas in the Direct Synthesis of Light Olefins Using In₂O₃–ZrO₂/SAPO-34 Catalyst

Abstract

The conditions for promoting the joint conversion of CO₂ and syngas in the direct synthesis of light olefins have been studied. In addition, given the relevance for the viability of the process, the stability of the In₂O₃-ZrO₂/SAPO-34 (InZr/S34) catalyst has also been pursued. The CO+CO₂ (CO _<i>x</i> ) hydrogenation experimental runs were conducted in a packed bed isothermal reactor under the following conditions: 375-425 °C; 20-40 bar; space time, 1.25-20 g_catalyst h mol_C ^-1; H₂/(CO _<i>x</i> ) ratio in the feed, 1-3; CO₂/(CO _<i>x</i> ) ratio in the feed, 0.5; time on stream (TOS), up to 24 h. Analyzing the reaction indices (CO₂ and CO _<i>x</i> conversions, yield and selectivity of olefins and paraffins, and stability), the following have been established as suitable conditions: 400 °C, 30 bar, 5-10 g_cat h mol_C ^-1, CO₂/CO _<i>x</i> = 0.5, and H₂/CO _<i>x</i> = 3. Under these conditions, the catalyst is stable (after an initial period of deactivation by coke), and olefin yield and selectivity surpass 4 and 70%, respectively, with light paraffins as byproducts. Produced olefin yields follow propylene > ethylene > butenes. The conditions of the process (low pressure and low H₂/CO _<i>x</i> ratio) may facilitate the integration of sustainable H₂ production with PEM electrolyzers and the covalorization of CO₂ and syngas obtained from biomass.