Atomically dispersed Co(II) cations coordinated to nitrogen in a carbon matrix (Co-N-C) catalyze oxidative dehydrogenation of benzyl alcohol in water with a specific activity approaching that of supported Pt nanoparticles. Whereas Cu(II) cations in N-doped carbon also catalyze the reaction, they are about an order of magnitude less active compared with Co(II) cations. Results from X-ray absorption spectroscopy suggest that oxygen is also bound to N-coordinated Co(II) sites but that it can be partially removed by H 2 treatments at 523−750 K. The N-coordinated Co(II) sites remained cationic in H 2 up to 750 K, and these stable sites were demonstrated to be active for propane dehydrogenation. In situ characterization of Cu(II) in N-doped carbon revealed that reduction of the metal in H 2 started at about 473 K, indicating a much lower thermal stability of Cu(II) in H 2 relative to Co(II). The demonstrated high catalytic activity and thermal stability of Co-N-C in reducing environments suggests that this material may have broad utility in a variety of catalytic transformations.

Copper-exchanged zeolites are promising catalysts for the direct methane-to-methanol reaction, but the design of improved catalysts has been hampered by limited understanding of the active site structures. Here, we show that the identity of the co-cation (H vs Na) in Cu-MOR and Cu-ZSM-5 catalysts significantly affects Cu speciation and the resulting reactivity of the catalysts in the cyclic methane-to-methanol reaction. The combination of reactivity results with spectroscopy and density functional theory (DFT) calculations suggests that the prevailing active site structure depends on the identity of the co-cation. The H-form of the catalysts contains a high concentration of mono-μ-oxo dicopper­(II) species, which are selective for methanol formation, whereas the presence of Na appears to shift the Cu distribution toward species with greater oxygen content (attributed to μ-1,2-peroxo dicopper­(II) species), which promote overoxidation of methane to carbon oxides. Results from DFT calculations indicate that Cu preferentially forms mono-μ-oxo dicopper­(II) species in the 8MR side pockets of MOR, whereas the μ-1,2-peroxo dicopper­(II) species is favored in the 12MR main channels of MOR for some Al pair configurations. Competition between Na and Cu for ion exchange sites in the 8MR side pockets results in displacement of some Cu into the 12MR main channels, thus affecting Cu speciation and catalyst selectivity. These findings suggest that the choice of co-cation can be used to control active site structure in transition-metal ion-exchanged zeolites.