Journal
ACS CATALYSIS
Volume 10, Issue 15, Pages 8303-8314Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.0c01579
Keywords
syngas; carbon dioxide; hydrogenation; lower olefins; bifunctional catalyst; spinel-structured metal oxide; oxygen vacancy; zeolite
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Funding
- National Key Research and Development Program of the Ministry of Science and Technology of China [2017YFB0602201]
- National Natural Science Foundation of China [91945301, 91545203, 21972116, 21673188, 21872112]
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Transformation of syngas (H-2/CO) and hydrogenation of CO2 into lower olefins are attractive routes for chemical utilization of various carbon resources and CO2, but both suffer from limited product selectivity. Tandem catalysis that integrates the activation of CO or CO2 to an intermediate and the subsequent controllable C-C bond formation to form lower olefins offers a promising approach. Here, we report the hydrogenation of both CO and CO2 over bifunctional catalysts composed of a spinel binary metal oxide and SAPO-34. ZnAl2O4/SAPO-34 and ZnGa2O4/SAPO-34 are found to be highly selective for the synthesis of lower olefins from both CO and CO2. Our studies reveal that the oxygen vacancy site on metal oxides plays a pivotal role in the adsorption and activation of CO or CO2, while the -Zn-O- domain accounts for H-2 activation. We demonstrate that methanol and dimethyl ether formed on metal oxide are the reaction intermediates, which are subsequently converted to lower olefins by the Bronsted acid sites in zeolite. The hydrogenation of CO and CO(2 )on metal oxide surfaces proceeds via the same formate and methoxide species. We elucidate that the water-gas shift reaction on oxide surfaces is responsible for CO2 formation during syngas conversion. The cofeeding of CO2 in syngas offers a useful strategy to inhibit CO2 formation.
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