Synergistic Effects for Enhanced Catalysis in a Dual Single-Atom Catalyst

Synergistic effects have been discussed extensively in bimetallic heterogeneous catalysis, but it remains unclear how the effects function at the atomic scale. Here, we report a dual single-atom catalyst (DSAC) Ir1Mo1/TiO2 displaying much greater catalytic chemoselectivity (>96%, at 100% conversion) than comparable single-atom catalysts (SACs) Ir-1/TiO2 (38%, at 87% conversion) and Mo-1/TiO2 (no activity) for the hydrogenation of 4-nitrostyrene (4-NS) to 4-vinylaniline (4-VA). Activation of the TiO2-supported bimetallic carbonyl cluster Ir2Mo2(CO)(10)(eta(5)-C5H5) (2) in an Ar atmosphere affords the DSAC Ir1Mo1/TiO2. Characterization of the dual single-atom structure confirms that it consists of well-dispersed Ir single atoms (Ir-1) and Mo single atoms (Mo-1) on TiO2. Density functional theory studies reveal that Ir-1 sites effect H-2 activation while Mo-1 sites are responsible for 4-NS adsorption, with synergistic cooperation between the two sets of single atoms contributing to the better catalytic performance for the hydrogenation of 4-NS. This work provides a deep understanding of synergistic effects in dual single-atom catalysis.