Supported base metal catalysts for the preferential oxidation of carbon monoxide in the presence of excess hydrogen (PROX)
Résumé
Supported base metal catalysts were tested for the preferential oxidn. of CO (CO PROX). Studied catalysts covered a range of oxide-supported transition metals (Co, Cr, Cu, Ni, Zn) with very different acid, base, and redox properties (MgO, La2O3, SiO2-Al2O3, CeO2, Ce0.63Zr0.37O2). The effect of metal loading (Cu), support properties (acidity, basicity, redox, surface area), and reaction conditions (temp., feed compn.) on catalyst activity and selectivity was evaluated. Activity of CeO2- and CeO2/ZrO2-supported Cu catalysts was comparable to the performance of noble metal samples classically used for the PROX reaction. Also, Cu-CeO2 catalysts exhibited a practically const. high selectivity towards CO oxidn. at 50-150↓. Due to the strong synergetic effect between Cu and CeO2, only a small amt. of Cu (0.3 wt. percent) was necessary to achieve an active catalyst. Best catalytic performance was obtained for samples contg. 1-3 wt. percent Cu. The presence of small Cu particles in close interaction with the CeO2 support was responsible for enhanced activity. Except for H oxidn., no parallel reactions (CO or CO2 methanation reactions, coking, RWGS) were detected over these catalysts. Classically, an increase of O2 excess led to increased CO conversion with a simultaneous loss of selectivity toward CO2. The presence of CO2 in the feed neg. affected catalytic activity. This effect was attributed to CO2 adsorption on Cu sites, probably as CO.