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Support and additive effects on the state of rhodium catalysts

1989; Science Press; Volume: 55; Issue: 1 Linguagem: Inglês

10.1016/0304-5102(89)80242-1

1873-3131

Leonore Kraus, Mohamed I. Zaki, Helmut Knözinger, B. Tesche,

Mesoporous Materials and Catalysis

Abstract The influence of oxide modifiers ZrOx, TiOx, and NbOx on the state of rhodium supported on SiO2 and Al2O3 has been studied by CO adsorption and IR spectroscopy. Due to large particles, oxidative disruption of Rh particles does not occur on unmodified SiO2. TiOx and NbOx stabilize smaller particle sizes by their Lewis acidity and therefore facilitate particle disruption and Rh+(CO)2 formation. The effect of ZrOx is negligible. Due to initially smaller particles, these additive effects are less pronounced on Al2O3-supported rhodium. Evidence is provided for geometric blocking effects of rhodium metal surface by the reducible modifiers TiOx and NbOx, these effects being reversed in CO atmosphere at elevated temperatures. Also, morphological changes are induced by CO on SiO2-supported rhodium, which seem to be retarded by the modifier oxides.