ZnO supported on zinc spinel structures enabling the direct conversion of CO2 to olefins when combined with acidic CHA catalysts

Bi-functional oxide-zeotype catalytic systems can convert CO₂ to light olefins, but at low conversions. Knowledge of the active sites for methanol synthesis over the oxide and the synergy with the zeotype at different operating conditions can guide future improvements. Here we investigate catalysts based on H-SAPO-34 combined with either ZnAl₂O₄ or ZnGa₂O_4. We show that the methanol synthesis activity of the metal oxide is dependent on the Zn-content; the activity increases dramatically when Zn content exceeds the stoichiometric level, Zn/(Zn + M) > 0.33 for M = Al or Ga. This creates supported surface ZnO domains, which selectively produce methanol and DME. Combining either of the Zn-spinel catalysts with H-SAPO-34 showed a light olefin selectivity > 70 carbon mol% among the hydrocarbon products, but at a low CO₂ to hydrocarbon conversion of ∼3 %. Co-feeding CO increased the CO₂ to hydrocarbon conversion significantly without affecting the olefin selectivity.