Effect of Water and Alkali Modifications on ETS-10 for the Cycloaddition of CO2 to Propylene Oxide
Sodium oxide (NaO x ) impregnated Engelhard Titanosilicate-10 (ETS-10) molecular sieve catalysts were prepared to enhance the basicity associated with ETS-10 and subsequently investigated for the cycloaddition of carbon dioxide to propylene oxide to produce propylene carbonate. For dry NaO x -modifi...
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Published in | The journal of physical chemistry. B Vol. 109; no. 6; pp. 2315 - 2320 |
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Main Author | |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
17.02.2005
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Online Access | Get full text |
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Summary: | Sodium oxide (NaO x ) impregnated Engelhard Titanosilicate-10 (ETS-10) molecular sieve catalysts were prepared to enhance the basicity associated with ETS-10 and subsequently investigated for the cycloaddition of carbon dioxide to propylene oxide to produce propylene carbonate. For dry NaO x -modified ETS-10 catalysts that contained no adsorbed water, a maximum yield of propylene carbonate was achieved at a loading of 2.0 excess NaO x species per unit cell. However, the greatest enhancements in the rate of reaction were observed when small amounts of water were adsorbed onto the unmodified ETS-10 catalyst immediately prior to reaction. Surface-bound water appears to enhance the surface Bronsted acidity of the unmodified ETS-10 catalyst via the formation of surface −OH groups at lower water loadings, producing a surface of better-tuned acid−base bifunctional characteristics for the cycloaddition reaction. At levels of hydration greater than 12.5% by mass, the yield of propylene carbonate was further enhanced, but at a smaller rate than that observed at lower rehydration levels, which is more indicative of an enhanced transport effect. Adsorption microcalorimetry of carbon dioxide indicated that, at loadings less than 2.0 NaO x per unit cell, the total uptake of the CO2 adsorption sites required for the reaction were less than in the parent ETS-10 material. However, at higher levels of NaO x occlusion, where the total uptake and strength of the adsorption sites exceeded those observed for the as-received ETS-10 material, the cycloaddition activity of this catalyst suffered due to the reduced pore volume and surface area. It appears that precise tuning of both the surface acidity and basicity is crucial in creating an effective acid−base bifunctional ETS-10 catalyst for the cycloaddition reaction investigated. |
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Bibliography: | ark:/67375/TPS-9R7ZVGZD-8 Part of the special issue “Michel Boudart Festschrift”. istex:0841291E7FAA5ACA8FEC16286ADE06E54EE6394C ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1520-6106 1520-5207 |
DOI: | 10.1021/jp048870g |