Acta Phys. -Chim. Sin. ›› 1991, Vol. 7 ›› Issue (06): 681-687.doi: 10.3866/PKU.WHXB19910609

• ARTICLE • Previous Articles     Next Articles

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

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