High-Loading Single-Atom Ru Catalysts Anchored on N-Doped Graphdiyne/γ-Graphyne Quantum Dots for Selective Hydrodehalogenation and Hydrodearomatization

Selective hydrodehalogenation and hydrodearomatization of toxic chlorophenols into value-added chemicals represents a grand challenge for their efficient reutilization. For this purpose, single-atom catalysts (SACs) could be a strategy with relatively high catalytic selectivity and atom utilization but suffer from the catalytic limitation caused by low metal loading densities. Graphdiyne and γ-graphyne are considered promising substrates of SACs with excellent catalytic properties. Additionally, their quantum dots with nanometer size are expected to supply numerous surface anchoring sites and large atom spacing to confine metal cations to synthesize high-loading SACs. Here we report a synthesis approach for high-loading Ru SACs anchored on graphdiyne/γ-graphyne quantum dots (GDQD-Ru/GNQD-Ru), which exhibit remarkably higher turnover frequency (TOF) and selectivity (>99%) of hydrodehalogenation and hydrodearomatization of chlorophenols than graphdiyne/γ-graphyne nanosheet-based Ru SACs and nanoparticles. There is no significant selectivity decrease in chlorophenol transformation by GDQD-Ru/GNQD-Ru observed in 5 catalyst reuse cycles. GDQD-Ru/GNQD-Ru contribute to nearly exclusive hydrodehalogenation and hydrodearomatization without altering any other bonds in chlorophenols. Experimental results and theoretical calculations reveal that GDQD-Ru is more prone to lower energies of rate-limiting steps in H2-driven chlorophenol transformation than GNQD-Ru. The results confirm that graphdiyne/γ-graphyne quantum dots play crucial roles in facilitating the metal atom loading of SACs. Ru loadings are 27.6 and 16.0 wt % in GDQD-Ru/GNQD-Ru, approximately 7-fold and 4-fold higher than reported Ru SACs, respectively. This study provides mechanistic insights toward the roles of high-loading Ru SACs on sp- and sp2-hybridized carbonaceous substrates in selective hydrodehalogenation and hydrodearomatization.