Decisive Influence of SAPO-34 Zeolite on Light Olefin Selectivity in Methanol-Meditated CO₂ Hydrogenation over Metal Oxide-Zeolite Catalysts

Methanol-mediated CO2 selective hydrogenation to light olefins (LO) over bifunctional catalysts containing metal oxide and zeolite components is an attractive sustainable chemical process. The main challenges of this process include achieving high LO selectivity and low selectivity to light paraffins and CO. Herein, we analyze the selectivity-conversion correlations over metal oxide-zeolite bifunctional catalysts and elucidate the functions of each catalyst component. A series of catalytic systems based on oxides of Zn, In, Mn, Cr, or Ga and different SAPO-34 zeolites were synthesized and evaluated at different CO2 conversion levels. It was uncovered that the selectivity to LO within hydrocarbon fractions ultimately depended on the zeolite component and decreased as a function of the hydrocarbon yield. The metal oxide catalyst component was responsible for the CO2 conversion, overall hydrocarbon, and CO selectivities. The SAPO-34 morphology and acidity were identified as major descriptors of the CO-free LO selectivity in the CO2 hydrogenation over bifunctional metal oxide-zeolite catalysts.