Relationship between Pd Facets and Surface Active Sites in Photocatalysis via NMR Molecular Probes

Although facets play an important role in catalysis, the relationship between facets and the active site has rarely been reported. Herein, Pd-loaded C3N4 photocatalysts with different exposed metal Pd facets were synthesized by controlling the flow-rate of the precursor. The influence of facets on active site in photocatalytic methanol reforming was monitored through an nuclear magnetic resonance molecular probe. The catalyst prepared at a low flow rate (Pd–C3N4-7.5) exhibited both Pd(111) and (100) facets, whereas that prepared at a high flow rate (Pd–C3N4-150) predominantly had Pd(100) facets. Furthermore, different crystal facets exhibited different active-site locations. The oxidation sites were dispersed over the entire surface (Pd, C3N4 surface, and Pd/C3N4 interface) of the catalysts with only Pd(100) facets. In contrast, they were mainly located on the metal Pd(111) surface and the Pd/C3N4 interface for catalysts with both Pd(111) and (100) facets. We believe this study would improve our understanding of the relationship between facet and active site.