Promotional Effects of Cesium Promoter on Higher Alcohol Synthesis from Syngas over Cesium-Promoted Cu/ZnO/Al2O3 Catalysts

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• 作者：Jie Sun ; Qiuxia Cai ; Yan Wan ; Shaolong Wan ; Li Wang ; Jingdong Lin ; Donghai Mei ; Yong Wang
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：September 2, 2016
• 年：2016
• 卷：6
• 期：9
• 页码：5771-5785
• 全文大小：848K
• 年卷期：0
• ISSN：2155-5435

文摘

The promotional effects of a cesium promoter on higher alcohol (C₂₊OH) synthesis from syngas over Cs₂O-Cu/ZnO/Al₂O₃ catalysts were investigated using a combined experimental and density functional theory (DFT) calculation method. In the presence of a cesium promoter, the C₂₊OH productivity increases from 77.1 to 157.3 g kg_cat^–1 h^–1 at 583 K due to the enhancement of the initial C–C bond formation. A detailed analysis of chain growth probabilities (CGPs) confirms that initial C–C bond formation is the rate-determining step in the temperature range of 543–583 K. Addition of a cesium promoter significantly increases the productivities of 2-methyl-1-propanol, while the CGP values (C₃* to 2-methyl-C₃*) are almost unaffected. With the assistance of a cesium promoter, the CGPs of the initial C–C bond formation step (C₁* to C₂*) increase from 0.13 to 0.25 at 583 K. DFT calculations indicate that the initial C–C bond formation during syngas synthesis over the ZnCu(211) model surface is mainly due to the HCO + HCO coupling. In the presence of Cs₂O, the stabilities of key intermediates such as HCO and H₂CO are enhanced, which facilitates both HCO + HCO and HCO + H₂CO coupling steps with lower activation barriers. In addition, Bader charge analysis suggests that the presence of cesium ions could facilitate nucleophilic coupling between HCO and H₂CO for the initial C–C bond formation.