Reversible, carbon dioxide mediated chemical hydrogen storage was first demonstrated using a heterogeneous Pd catalyst supported on mesoporous graphitic carbon nitride (Pd/mpg-C 3 N 4 ). The Pd nanoparticles were found to be uniformly dispersed onto mpg-C 3 N 4 with an average size of 1.7 nm without any agglomeration and further exhibit superior activity for the dehydrogenation of formic acid with a turnover frequency of 144 h À1 even in the absence of external bases at room temperature. Initial DFT studies suggest that basic sites located at the mpg-C 3 N 4 support play synergetic roles in stabilizing reduced Pd nanoparticles without any surfactant as well as in initiating H 2 -release by deprotonation of formic acid, and these potential interactions were further confirmed by X-ray absorption near edge structure (XANES). Along with dehydrogenation, Pd/mpg-C 3 N 4 also proves to catalyze the regeneration of formic acid via CO 2 hydrogenation. The governing factors of CO 2 hydrogenation are further elucidated to increase the quantity of the desired formic acid with high selectivity.

We present the role of Pd ensembles in the selective direct synthesis of H2O2 from H2 and O2 on a PdAu alloy surface based on periodic density functional theory calculations. Our calculations demonstrate that H2O2 formation is strongly affected by the spatial arrangement of Pd and Au surface atoms. In particular, Pd monomers surrounded by less active Au atoms that suppress O−O bond scission are primarily responsible for the significantly enhanced selectivity toward H2O2 formation on PdAu alloys compared to that on the monometallic Pd and Au counterparts.

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