物理化学学报 >> 1991, Vol. 7 >> Issue (06): 681-687.doi: 10.3866/PKU.WHXB19910609

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合成气转化为乙醇的反应机理

汪海有; 刘金波; 傅锦坤; 蔡启瑞   

  1. 厦门大学化学系，物理化学研究所，厦门 361005
  • 收稿日期:1990-07-02 修回日期:1991-03-22 发布日期:1991-12-15
  • 通讯作者: 汪海有

The Mechanism of Syngas Conversion to Ethanol

Wang Hai-You; Liu Jin-Bo; Fu Jin-Kun; Cai Qi-Rui   

  1. Department of Chemistry and Institute of Physical Chemistry, Xiamen University, Xiamen 361005
  • Received:1990-07-02 Revised:1991-03-22 Published:1991-12-15
  • Contact: Wang Hai-You

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摘要： 本文在助剂型Rh催化剂上采用了以CH_2OD、D_2~(18)O为捕获剂的原位化学捕获反应, 以及以D_2~(18)O为重氧源试剂的原位氧同位素交换反应, 对合成气转化为乙醇的反应机理进行了研究。在原位捕获反应中检测到CH_2DCOOCH_3、CH_3COOCH_3和CH_2DCOOD、CH_3COOD的生成, 表明合成乙醇反应过程中存在中间体乙烯酮和乙酰基, 当CH_3OD/H_2比值足够大时主要捕获到CH_2DCOOCH_3, 说明乙酰基主要由乙烯酮的部分氢化反应生成。原位氧同位素交换反应检测到含~(18)O的乙醇、乙醛、乙酸的生成, 表明乙烯酮等C_2-含氧化合物前驱怵与重氧水发生了氧同位素交换反应。籍此, 无须如Katzer等人那样假设乙烯酮互变异构为位能较商的环氧乙烯而后进行氧同位素交换, 就可以得到Katzer等人在~(13)C~(16)O/~(13)C~(18)O+H_2反应中观察到的产物乙醇的同位素组成结果。本文的实验结果进一步说明我们提出的“CO缔合—卡宾—乙烯酮—乙酰基—乙醇(醛)”机理是合理的。

关键词: 助剂型Rh催化剂, 乙醇, 合成气转化, 原为化学捕获反应技术

Abstract: The mechanism of syngas conversion to ethanol over promoted Rhodium catalyst has been studied by in-situ chemical trapping reaction technique with CH_3OD as trapping agent. After trapping reaction, the products CH_3COOCH_3 and CH_2DCOOCH_3 were identified, which indicated the existence of ketene and acetyl intermediates in the ethanol synthesis reaction. With high CH_3OD/H_2 ratio in the feed (e.g., 18/5), more than 50% of CH_2DCOOCH_3 in total AcOMe was obtained, showing the acetyl intermediate is mainly derived from the tetene by further hydrogenation.
In order to further study ethanol formation mechanism in-situ chemical trapping reaction and isotopic exchange reaction of oxygen with D_2~(18)O as trapping and isotopic exchange agent was conducted. As for trapping reaction with D_2~(18)O, after trapping reaction and scanvenging with methanol in N_2 stream four kinds of methyl acetate, i.e., CH_2H(D)COOCH_3, CH_2H(D)C~(18)OOCH_3 were detected, again proving the existence of ketene and acetyl intermediates. As for isotopec exchange reaction of oxygen with D_2~(18)O, after this reaction and scanvenging with methanol in N_2 stream compounds including CH_3CH_2~(18)OH, CH_3CH~(18)O, and CH_2H(D)C~(18)OOCH_3 were formed, in which exchange of oxygen between D_2~(18)O and the ~(16)O-containing precursors of ethanol such as ketene, acetyl, and adsorbed acetaldehyde. Based on the mode of isotopic exchange of ketene with water produced in the syngas reaction, the isotopic distribution of ethanol in Tabeuchi and Katzer's experiment conducted with ~(13)C~(16)O/~(12)C~(18)O-H_2 could also be obtained by statistic calculation without the hypothesis proposed by Takeuchi and Katzer.
These results support the ketene mechanism, "CO-metalloxycarbene-carbene-ketene-acetyl-ethanol; (acetaldehyde)", proposed by us previously.

Key words: Promoted rbodium catalyst, Ethanol, Syngas conversion, In-situ chemical trapping reaction technique