Crowded supported metal atoms on catalytically active supports may compromise intrinsic activity: A case study of dual-site Pt/a-MoC catalysts

Increasing the surface population of supported catalytic sites, assuming these sites are stable, is considered a straightforward approach to improving the overall catalytic performance. We report an exception represented by the Pt/a-MoC catalysts featuring atomically dispersed Pt. The Pt/a-MoC catalysts display very high activity for the reverse water gas shift reaction with near 100% CO selectivity for CO2:H-2 ratios from 0.25 to 4 and from 250 to 400 ?. Despite the excellent performance, the intrinsic activity per Pt-centric catalytic center declines as the Pt loading increases from 0.1 to 1.0 wt%. With the dispersed Pt evolving from isolated atoms to fully exposed ensembles, the shrinking inter-Pt-atom space impedes CO2 activation at the critical Pt-Mo interfaces, where the Pt shall temporarily take the -O intermediates. The Pt, even as atomically dispersed without noticeable sintering, is underutilized in such a crowded state. This caution for high-loading catalyst design is translational to other systems where the direct catalytic roles of the supports are crucial.