PNNL

Abstract

Oxide-supported Pt-group single atoms and clusters in the subnanometer size regime maximize the metal utilization and have shown extraordinary catalytic properties for many reactions including selective hydrogenation. Establishing relations between the metal nuclearity, electronic and catalytic properties is crucial to help design more efficient catalysts. Here, we varied the nuclearity of Pt supported on TiO2 from single atoms to subnanometer clusters to larger nanoparticles to develop such relations for acetylene hydrogenation. We show that in contrast to the low selectivity on large Pt nanoparticles, in the subnanometer size regime Pt exhibits remarkably high selectivity to ethylene. Through a combination of x-ray photoelectron spectroscopy and calorimetry, we demonstrate that the origin of high selectivity is decreased electron density on Pt and destabilization of C2H4 as the Pt nuclearity decreases. However, as the Pt nuclearity decreased, the activity for H2 activation and acetylene hydrogenation decreased, indicating a trade-off between activity and selectivity. The results show that while new properties emerge in the subnanometer regime, Pt supported on TiO2 appears to be bound by similar scaling and Brønsted-Evans-Polanyi relationships as on metal surfaces.