(650a) Direct CO2 Hydrogenation to Light Olefins over a Tandem Catalyst Composed of YSZ-Supported in2O3 and SAPO-34

Light olefins (C₂⁼–C₄⁼) are key building blocks of polymers, solvents and drugs, and production of light olefins with CO₂ as a feedstock is of interest for sustainable activation of greenhouse gas. Direct synthesis of light olefins from CO₂ is feasible through a methanol intermediate generated on the In- or Cu-based catalysts followed by the methanol to olefins (MTO) reaction on molecular sieves such as SAPO-34 and ZSM-5. The proposed route can be accomplished by tandem catalysts, in which metal oxides and molecular sieves are combined in a single reactor. This direct and single-step process can promote shifting of the reaction equilibrium to the right, leading to a high light olefins selectivity. The novel tandem catalysts need to be developed to maintain a high light olefins production while minimizing the undesired reverse water-gas shift (RWGS) reaction.

In this work, we have prepared a tandem catalyst composed of YSZ (yttria-stabilized zirconia)-supported In₂O₃ and SAPO-34 for direct CO₂ hydrogenation to light olefins. Our results show that the light olefins selectivity for the In₂O₃/ZrO₂//SAPO-34 decreases from 9.7% to 4.2%, while CO selectivity increases up to 91.8% during 45 h of reaction. However, the developed In₂O₃/YSZ//SAPO-34 tandem catalyst presents steady light olefins selectivity of 11.9% producing a C₂⁼–C₄⁼ yield of 0.997 mmol h^−1 g^−1 throughout the reaction. The stable performance of the YSZ-supported catalyst can be explained by higher oxygen vacancy concentration and stronger metal–support interaction compared to the regular ZrO₂-supported In₂O₃. YSZ-supported In₂O₃ can prevent In species from hydroxylation and overreduction, stabilizing the active sites. However, In₂O₃ supported on ZrO₂ presents a decline in light olefins production with time, because water produced in RWGS can facilitate indium hydroxide formation at the reaction temperature of 693 K.