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发表于 2022-2-26 10:51:33
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Extensive studies have demonstrated that the challenge of selective conversion of syngas to light olefins lies in the precise control of C–C coupling and simultaneously the suppression of over-hydrogenation of C═C and methane formation. (1−4) In the past century, most studies on syngas conversion focused on modifying the conventional Fischer–Tropsch to olefins (FTTO) catalysts. (1,3,5) The FTTO process is widely thought to proceed through a surface polymerization mechanism. The distribution of hydrocarbon products follows the Anderson–Schulz–Flory (ASF) model, among which the highest selectivity of C2–C4 hydrocarbons is predicted to be 58%. (1−3) We recently reported an oxide–zeolite (OX–ZEO) catalyst design concept combining partially reduced ZnCrOx and mesoporous SAPO-34 zeolite (denoted as MSAPO, with M representing mesoporous). (2) This composite catalyzes syngas conversion with a high selectivity of 80% for light olefins (C2═–C4═) and 94% for C2–C4 hydrocarbons at ～17% CO conversion. Furthermore, the CH4 selectivity was suppressed to ～2%. Thereafter, more bifunctional catalysts consisting of different oxides and zeolites were reported for direct hydrogenation of CO or CO2 to light olefins with a high selectivity. (4,6−11) Cheng et al. reported a similar process based on a composite of ZnO–ZrO2 mixed oxide and SAPO-34, which gave 10% CO conversion and 70% C2═–C4═ selectivity. (4) The bifunctionality of the composite was unambiguously demonstrated, i.e., metal oxides mainly act for activation of CO and H2 while the C–C coupling occurred within the zeolite pores. The performance can be further enhanced by matching the bifunctionalties in a proper way. For example, by employing shape-selective mordenite zeolite, the selectivities were finely tuned toward ethylene with a selectivity up to 83% among hydrocarbons. (11) However, the activity still needs to be further enhanced to be competitive with conventional processes such as FTTO and methanol-to-olefin (MTO). This will rely on the fundamental understanding of the structure–performance relationship.Extensive studies have demonstrated that the challenge of selective conversion of syngas to light olefins lies in the precise control of C–C coupling and simultaneously the suppression of over-hydrogenation of C═C and methane formation. (1−4) In the past century, most studies on syngas conversion focused on modifying the conventional Fischer–Tropsch to olefins (FTTO) catalysts. (1,3,5) The FTTO process is widely thought to proceed through a surface polymerization mechanism. The distribution of hydrocarbon products follows the Anderson–Schulz–Flory (ASF) model, among which the highest selectivity of C2–C4 hydrocarbons is predicted to be 58%. (1−3) We recently reported an oxide–zeolite (OX–ZEO) catalyst design concept combining partially reduced ZnCrOx and mesoporous SAPO-34 zeolite (denoted as MSAPO, with M representing mesoporous). (2) This composite catalyzes syngas conversion with a high selectivity of 80% for light olefins (C2═–C4═) and 94% for C2–C4 hydrocarbons at ～17% CO conversion. Furthermore, the CH4 selectivity was suppressed to ～2%. Thereafter, more bifunctional catalysts consisting of different oxides and zeolites were reported for direct hydrogenation of CO or CO2 to light olefins with a high selectivity. (4,6−11) Cheng et al. reported a similar process based on a composite of ZnO–ZrO2 mixed oxide and SAPO-34, which gave 10% CO conversion and 70% C2═–C4═ selectivity. (4) The bifunctionality of the composite was unambiguously demonstrated, i.e., metal oxides mainly act for activation of CO and H2 while the C–C coupling occurred within the zeolite pores. The performance can be further enhanced by matching the bifunctionalties in a proper way. For example, by employing shape-selective mordenite zeolite, the selectivities were finely tuned toward ethylene with a selectivity up to 83% among hydrocarbons. (11) However, the activity still needs to be further enhanced to be competitive with conventional processes such as FTTO and methanol-to-olefin (MTO). This will rely on the fundamental understanding of the structure–performance relationship.Extensive studies have demonstrated that the challenge of selective conversion of syngas to light olefins lies in the precise control of C–C coupling and simultaneously the suppression of over-hydrogenation of C═C and methane formation. (1−4) In the past century, most studies on syngas conversion focused on modifying the conventional Fischer–Tropsch to olefins (FTTO) catalysts. (1,3,5) The FTTO process is widely thought to proceed through a surface polymerization mechanism. The distribution of hydrocarbon products follows the Anderson–Schulz–Flory (ASF) model, among which the highest selectivity of C2–C4 hydrocarbons is predicted to be 58%. (1−3) We recently reported an oxide–zeolite (OX–ZEO) catalyst design concept combining partially reduced ZnCrOx and mesoporous SAPO-34 zeolite (denoted as MSAPO, with M representing mesoporous). (2) This composite catalyzes syngas conversion with a high selectivity of 80% for light olefins (C2═–C4═) and 94% for C2–C4 hydrocarbons at ～17% CO conversion. Furthermore, the CH4 selectivity was suppressed to ～2%. Thereafter, more bifunctional catalysts consisting of different oxides and zeolites were reported for direct hydrogenation of CO or CO2 to light olefins with a high selectivity. (4,6−11) Cheng et al. reported a similar process based on a composite of ZnO–ZrO2 mixed oxide and SAPO-34, which gave 10% CO conversion and 70% C2═–C4═ selectivity. (4) The bifunctionality of the composite was unambiguously demonstrated, i.e., metal oxides mainly act for activation of CO and H2 while the C–C coupling occurred within the zeolite pores. The performance can be further enhanced by matching the bifunctionalties in a proper way. For example, by employing shape-selective mordenite zeolite, the selectivities were finely tuned toward ethylene with a selectivity up to 83% among hydrocarbons. (11) However, the activity still needs to be further enhanced to be competitive with conventional processes such as FTTO and methanol-to-olefin (MTO). This will rely on the fundamental understanding of the structure–performance relationship. |
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楼主: 佛爷
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