Rational control of pore orientation holds great potential to enhance mass transfer in carbon-supported single-atom catalysts (SACs), thereby increasing single-atom site utilization and catalytic performance; however, this strategy remains underexplored in catalytic hydrogenation reactions. In this paper, cobalt single-atom catalysts supported on oriented porous carbon (Co-SAC/OPC) and cobalt single-atom catalysts supported on non-oriented porous carbon (Co-SAC/NOPC) were synthesized using the hard-template method, and their performance in hydrogenation reactions was systematically investigated using 1-chloro-4-nitrobenzene (p-CNB) hydrogenation as a model reaction. Results from experiments (diffusion, substrate size-dependent conversion, and recycling) and finite-element analysis show that oriented pores facilitate p-CNB diffusion more effectively than non-oriented pores. This faster transfer enhances the accessibility and utilization of single-atom cobalt sites, resulting in significantly improved hydrogenation performance of Co-SAC/OPC. This work establishes a general strategy for enhancing the performance of carbon-supported single-atom catalysts in hydrogenation catalysis and related reactions.

Carbon-supported single-atom catalysts were found to suffer reversible deactivation in catalytic hydrogenation, but the mechanism is still unclear. Herein, nitro compounds hydrogenation catalyzed by N-doped carbon-supported Co single atom (Co₁/NC) was taken as a model to uncover the mechanism of the reversible deactivation phenomenon. Co₁/NC exhibited moderate adsorption towards the substrate molecules (i.e., nitro compounds or related intermediates), which could be strengthened by the confinement effect from the porous structure. Consequently, substrate molecules tend to accumulate within the pore channel, especially micropores that host Co₁, making it difficult for the reactants to access the active sites and finally leading to their deactivation. The situation could be even worse when the substrate molecules possess a large size. Nevertheless, the catalytic activity of Co₁/NC could be restored via a simple thermal treatment, which could remove the adsorbates within the pore channel, hence releasing active sites that were originally inaccessible to reactants.