Strong metal–support interaction (SMSI) has been regarded as one of the most important concepts in heterogeneous catalysis, which has been almost exclusively discussed in metal/oxide catalysts. Here, we show that gold/molybdenum carbide (Au/MoC x ) catalysts feature highly dispersed Au overlayers, strong interfacial charge transfer between metal and support, and excellent activity in the low-temperature water–gas shift reaction (LT-WGSR), demonstrating the active SMSI state. Subsequent oxidation treatment results in strong aggregation of Au nanoparticles, weak interfacial electronic interaction, and poor LT-WGSR activity. The two interface states can be transformed into each other by alternative carbonization and oxidation treatments. This work reveals the active SMSI effect in metal/carbide catalysts induced by carbonization, which opens a new territory for this important concept.

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) Ir1/TiO2 (38%, at 87% conversion) and Mo1/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(η5-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 (Ir1) and Mo single atoms (Mo1) on TiO2. Density functional theory studies reveal that Ir1 sites effect H2 activation while Mo1 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.