ACTIVITY AND STRUCTURAL-CHANGES OF ALUMINA-SUPPORTED CUO AND CUCR2O4 CATALYSTS DURING CARBON-MONOXIDE OXIDATION IN THE PRESENCE OF WATER

The deactivation effect of water on carbon monoxide oxidation over CuO/Al2O3 and CuCr2O4/Al2O3 catalysts has been examined. This deactivation effect, more marked for the former than for the latter catalyst, was a reversible process. Samples of the catalyst used in the reaction with and without water, or fresh samples pretreated in situ in environments similar to those of reaction, were characterized by scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). According to the SEM-EDX results, water addition modified the copper distribution, increasing the aggregation of copper species. XPS revealed that water addition also causes changes in the nature of the surface copper, the active Cu0 and Cu+ are oxidized to Cu2+ species. In the CuCr2O4/Al2O3 catalyst, chromium ions diminish the aggregation of active copper into oxide particles when water is present.