Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)2.

The organometallics chemical vapour deposition (OM-CVD) technique, using Rh(acac)(CO)(2) as a precursor, was employed for the preparation of heterogeneous Rh catalysts supported on low surface area refractory oxides (alpha-Al2O3, ZrO2, MgO and La2O3). Prepared systems were tested in the methane catalytic partial oxidation (CH4-CPO) reaction in a fixed bed reactor and compared to a reference catalyst prepared from impregnation of Rh4(CO)12. Catalysts supported on Al2O3, ZrO2 and MgO show better or comparable performances with respect to the reference system. Complete decomposition of Rh precursor during formation of the metal phase under reductive conditions was investigated by TPRD and confirmed by infrared and mass spectrometry data. Supported Rh phase was characterized by CO and H-2 chemisorption, CO-DRIFT spectroscopy and HRTEM microscopy in fresh and aged selected samples. Rh(I) isolated sites and Rh(0) metal particles were found on fresh catalysts: after ageing an extensive reconstruction occurs mainly consisting in a sintering of Rh isolate sites to metal particles but without large increase in mean particles size. Catalytic performances and Rh species balance were found to be dependent on the support material.