Spectroscopic identification of adsorbed intermediates derived from the CO + H{sub 2}O reaction on zeolite-encapsulated gold catalysts
Identification of reaction intermediates in the water-gas shift reaction (WGSR: H{sub 2}O + CO {yields} H{sub 2} + CO{sub 2}) on Au{sup n+} (1 {le} n < 3) incorporated into NaY, Na-mordenite, and Na-ZSM-5 zeolites has been studied by means of in situ FT-IR spectroscopy. Exposure of Au{sup n+}/zeolites to a gas mixture consisting of CO + H{sub 2}O at 323 K produced IR carbonyl spectra characterized by Au{sup +}-CO at 2,192 cm{sup {minus}1} and Au{sup 0}-CO at 2,128 cm{sup {minus}1}. On Au{sup n+}/NaY, a unidentate formate species (1,710, 1,620, and 1,340 cm{sup {minus}1}) is produced as a surface intermediate, which was very readily removed upon evacuation at 323 K. The reduction of the catalyst by H{sub 2} at 423 K prior to the admission of the reacting gas mixture caused inhibition of formate species formation. This result suggests that Au{sup +} is the dominant species on which the reaction took place. Au{sup +}/Na-mordenite displayed unidentate formate and organic carbonate species (1,936 and 1,850 cm{sup {minus}1}). On the other hand, Au{sup +}/Na-ZSM-5 resulted in the formation of different carbonate-like species (1,936, 1,850, 1,730, and 1,400 cm{sup {minus}1}) as well as the rapid appearance of deformation vibrations of adsorbed water molecules at 1,630 cm{sup {minus}1} that built up very quickly compared to that in the Au{sup +}/Na-mordenite sample. These results were consistent with the catalytic activity data that showed the highest formation rates of CO{sub 2} on Au{sup +}/NaY compared to those on Au{sup +}/Na-mordenite and Au{sup +}/Na-ZSM-5 catalysts.
- Research Organization:
- Benha Univ. (EG)
- OSTI ID:
- 20075571
- Journal Information:
- Journal of Colloid and Interface Science, Vol. 224, Issue 2; Other Information: PBD: 15 Apr 2000; ISSN 0021-9797
- Country of Publication:
- United States
- Language:
- English
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