INTERCALATION COMPOUNDS OF ALPHA-ZIRCONIUM HYDROGEN PHOSPHATE WITH RH3-DIAMINE COMPLEXES .2. THEIR BEHAVIOR TOWARDS CO, CO2 AND H-2 AND THEIR USE IN THE CO CATALYTIC-OXIDATION( IONS AND RH3+)

The reactivity of Rh3+ ions and Rh3+-diamine alpha-Zr(HPO4)(2) . H2O c omplexes intercalated in alpha-zirconium hydrogen phosphate towards sm all molecules (CO, O-2, H-2) was studied. The compounds only containin g Rh3+ ions, of composition ZrHxRhy(PO4)(2) . H2O (x = 2 - 3 y; 0 < y less than or equal to 0.66) react with CO at atmospheric pressure and temperatures ranging from 80 to 100 degrees C, and undergo selective r eduction of Rh3+ to Rh1+. The resulting materials containing Rh1+ are reoxidized to Rh3+ by molecular dioxygen under the same pressure and t emperature conditions, The simultaneous action of a CO/O, mixture dete rmines the catalytic oxidation of the CO to CO2 and the system acts as a stable catalyst of this reaction, At higher temperatures, the reduc tion of Rh3+ is no longer selective and in these conditions Rh-0 is fo rmed, which escapes from the support and causes its deactivation. Simi lar behaviour is found in systems containing Rh3+-diamine complexes, w hich react with CO at temperatures higher than 120 degrees C and under go an irreversible reduction of Rh3+ to Rh-0. The reaction with H-2 (7 0 < T < 100 degrees C) also causes a non selective reduction of the Rh 3+ to Rh1+ and Rh-0. The progress over time of the catalytic activity of some compounds with different contents of Rh3+ in converting CO to CO2 has shown not only that these materials maintain a constant cataly tic activity, indicating the stability of the systems to the loss of m etal during working cycles, but also that Rh3+ supported in these matr ixes is more active and selective in this type of reaction than Rh3+ i n solution.