Highly Active Catalytic CO₂ Hydrogenation to Lower Olefins via Spinel ZnGaO_x Combined with SAPO‐34

Abstract

A key primary method for creating a carbon cycle and carbon neutrality is the catalytic hydrogenation of CO 2 into high value-added chemicals or fuels. In this work, ZnGaO x oxides were prepared by parallel co-precipitation and physically mixed with SAPO-34 molecular sieves prepared by hydrothermal synthesis to produce ZnGaO x /SAPO-34 bifunctional catalysts, which were evaluated for the catalytic synthesis of lower olefins (C 2 = À C 4 = ) from carbon dioxide hydrogenation. It was demonstrated that the reaction process requires oxygen defect activation, synergistic hydrogenation, and CO 2 alkaline adsorption of ZnGaO x . The spinel structure of ZnGaO x has more abundant oxygen defects and alkaline adsorption sites than the ZnGaO x solid solution, which effectively enhances the catalytic performance. The CO 2 conversion was 28.52%, the selectivity of C 2 = À C 4 = in hydrocarbons reached 70.01%, and the single-pass yield of C 2 = À C 4 = was 10.95% at 370 °C, 3.0 MPa, and 4800 mL/g cat /h.

CO2 Conversion into Light Olefins Using an InCeZrOX/H-ZSM-5-Si Bifunctional Catalyst

“…This shows that the activation and conversion of CO 2 is mainly controlled by the In 0.9 Ce 1 Zr 4 O X oxide. 32 As the In 0.9 Ce 1 Zr 4 O X /H-ZSM-5-Si mass ratio decreases, the selectivity of C 2 = −C 4 = first increases and then decreases, reaching a maximum value of 60.3% at 1:1. According to the previous conclusions, the CH 3 OH intermediate is generated on In 0.9 Ce 1 Zr 4 O X from CO 2 .…”

“…When Ga is doped into In 1 Zr 4 O X , the CH 4 selectivity in the CO 2 hydrogenation on In 1 Ga 1 Zr 4 O X /H-ZSM-5 is 96.5% in hydrocarbons, whereas the C 2 –C 4 selectivity and C 5+ selectivity are 3.4 and 1%, respectively. The inactivation of H-ZSM-5 is probably due to the basic sites and migration of Ga. , When In 1 Zn 1 Zr 4 O X /H-ZSM-5 is used to catalyze the CO 2 hydrogenation, C 2 = –C 4 = selectivity in hydrocarbons is only 16.6% and the C 2 0 –C 4 0 selectivity and C 5+ selectivity are 34.9 and 42.8%, respectively. The strong ability of Zn to dissociate H 2 promotes hydrogen transfer, resulting in excessive hydrogenation of C 2 = –C 4 = . , The C 2 = –C 4 = selectivity in hydrocarbons in the CO 2 hydrogenation on In 1 Ce 1 Zr 4 O X /H-ZSM-5 is 37.2%.…”

“…Zeolites play an important role in the performance of bifunctional catalysts. Most of the reported bifunctional catalysts use SAPO-34 as a zeolite component owing to its mild acidity and unique eight-membered channels. , However, SAPO-34 undergoes quick deactivation owing to the inherent diffusion limitation and coke deposition . Furthermore, ZSM-5, which possesses three-dimensional 10-membered ring crossing channels, is widely used in the CH 3 OH conversion to propylene by virtue of its high shape-selective property and long lifetime .…”

Selective Valorization of CO2 towards Valuable Hydrocarbons through Methanol‐mediated Tandem Catalysis

“…[69][70] Numerous reducible mixed-metal oxides such as In 2 O 3 -ZrO 2 , ZnAlO x , ZnZrO x , ZnO-Y 2 O 3 , ZnGa 2 O 4 were further reported to be highly efficient for this route, where the charge imbalances among the metal cations (e. g., Zn 2 + , Zr 4 + , In 3 + ) can facilitate the formation of oxygen vacancies, which enhance both CO 2 activation and the dissociation of H 2 . [6,26,[51][52]62,64,[71][72][73][74][75] An additional advantage of using reducible metal oxides is their ability to suppress CO formation through the stabilization of reaction intermediates. Two mechanisms have been proposed for CH 3 OH synthesis: carboxylate-mediated (*HOCO) and formate-mediated (*HCOO) routes.…”

“…The surface hydroxyls combine to form H 2 O, which desorbs, creating surface oxygen vacancies, while the metal hydride participates in hydrogenation [69–70] . Numerous reducible mixed‐metal oxides such as In 2 O 3 ‐ZrO 2 , ZnAlO x , ZnZrO x , ZnO‐Y 2 O 3 , ZnGa 2 O 4 were further reported to be highly efficient for this route, where the charge imbalances among the metal cations ( e. g ., Zn 2+ , Zr 4+ , In 3+ ) can facilitate the formation of oxygen vacancies, which enhance both CO 2 activation and the dissociation of H 2 [6,26,51–52,62,64,71–75] …”