Intercalation compounds of α-zirconium hydrogen phosphate with Rh3+ ions and Rh3+-diamine complexes. Part II. Their behaviour towards CO, CO2 and H2 and their use in the CO catalytic oxidation
✍ Scribed by P. Giannoccaro; A.La Ginestra; M.A. Massucci; C. Ferragina; G. Mattogno
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 924 KB
- Volume
- 111
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
The reactivity of Rh3+ ions and Rh3+ -diamine CI-ZI(HPOJ~ . H,O complexes intercalated in a-zirconium hydrogen phosphate towards small molecules (CO, 0,, H2) was studied. The compounds only containing Rh3+ ions, of composition ZrH,Rh,(PO,)z .4H,O (X = 2 -3y; 0 < y I 0.66) react with CO at atmospheric pressure and temperatures ranging from 80 to lOO"C, and undergo selective reduction of Rh3+ to Rh' +. The resulting materials containing Rh'+ are reoxidized to Rh3+ by molecular dioxygen under the same pressure and temperature conditions. The simultaneous action of a CO/O, mixture determines the catalytic oxidation of the CO to CO, and the system acts as a stable catalyst of this reaction. At higher temperatures, the reduction of Rh3+ IS no longer selective and in these conditions Rho is formed, which escapes from the support and causes its deactivation. Similar behaviour is found in systems containing Rh3+-diamine complexes, which react with CO at temperatures higher than 120°C and undergo an irreversible reduction of Rh3+ to Rho. The reaction with H, (70 < T< 100°C) also causes a non selective reduction of the Rh3+ to Rh'+ and Rho. The progress over time of the catalytic activity of some compounds with different contents of Rh3+ in converting CO to CO, has shown not only that these materials maintain a constant catalytic activity, indicating the stability of the systems to the loss of metal during working cycles, but also that Rh3+ Rh3+ in solution.
supported in these matrixes is more active and selective in this type of reaction than