Selective CO oxidation in the presence of hydrogen: fast parallel screening and mechanistic studies on ceria-based catalysts

An accelerated investigation of various ceria-supported platinum catalysts by means of parallel synthesis and testing reactors is reported. The aim is to discover new catalysts for purifying hydrogen for fuel cells and other applications by studying three reactions: selective CO oxidation in the absence and in the presence of hydrogen (SelO x), water–gas shift (WGS), and reverse water–gas shift (RWGS). A set of catalysts is prepared by impregnating platinum on various doped ceria supports. These catalysts display, despite their nearly identical X-ray crystal structures, diverse redox/acidic/basic properties and different selectivities in the three test reactions. The best SelO x catalysts are also the most active for WGS/RWGS equilibration. In contrast to the conventional two-stage approach of discovery screening followed by lead optimization, we demonstrate that it is possible to extract valuable mechanistic information directly from the discovery stage. Specifically, we elucidate the elementary steps coupling the SelO x and WGS processes and gain insight as to the combined effects of hydrogen presence and cation doping on the CO oxidation reaction.