Acid gas valorization through a carbonyl sulfide (COS) intermediate over Na-containing FAU and LTA zeolites

A promising route for the valorization of acid gas (CO₂ and H₂S) components involves their simultaneous transformation into carbon monoxide and sulfur, through carbonyl sulfide (COS) intermediate. In this work, we systematically explore the catalytic performance of 13X and 4 A for COS formation under varying conditions of temperature, acid gas partial pressure, and zeolite hydration state. H 2 S, CO 2 , and COS breakthrough experiments at 45 °C reveal that the capacities of all three molecules are higher for 13X than for 4 A. Thermal gravimetry on hydrated zeolites specifies water contents of 13.1 and 12.0 mmol/g for 13X and 4 A, respectively. COS yield is highest at 100 °C, showing temperature dependence in the case of 13X; in contrast, 4 A retains more than 70% of its maximum activity over an extended range of temperatures. An increase in acid gas partial pressure from 0.2 to 0.8 bar gradually increases the total COS in 13X, whereas the activity of 4 A remains constant. Likewise, COS formation increases with decreasing zeolite hydration; threshold-dependent in 13X but progressive and relatively less pronounced in 4 A. Both zeolites, independent of conditions, undergo a decline in COS formation over time due to the water-induced inhibition of active sites, attributed to poisoning. While activity in 4 A decays rapidly, 13X exhibits a more gradual decay, corresponding to the inhibitory effect of the produced water being less pronounced in 13X than in 4 A. This reduces competitive adsorption on active sites and mitigates site blockage in 13X, which in turn preserves catalytic performance over time, indicating that 13X is more sensitive to changing conditions than 4 A. An optimum operating window identified for the two materials can help reduce the energy required for the industrial conversion of acid gas and subsequent catalyst regeneration. This corresponds to reaction at 120 °C and 250 °C and the regeneration at 250 °C and 300 °C for 13X and 4 A, respectively. • Acid gas valorization via carbonyl sulfide (COS) intermediate was explored • |Conversion of CO 2 and H 2 S to COS was studied over zeolites 13X and 4 A • Various temperatures, acid gas partial pressures & zeolite water contents were investigated • 13X activity decays slowly over time and 4 A shows faster decay • Optimal operating window: 13X (120/250 °C) and 4 A (250/300 °C) for reaction/regeneration