Single-Atom Pd Catalysts Supported on Covalent Triazine Frameworks for Hydrogen Production from Formic Acid

According to our knowledge, single-atom Pd catalysts supported on covalent triazine frameworks (CTF) have not been studied in the production of hydrogen from formic acid. Therefore, we synthesized 1 wt % Pd single-atom catalysts based on CTF-1, pyCTF, and bipyCTF supports and tested them in the gas-phase decomposition of formic acid. The results were compared with those obtained for a Pd catalyst supported on mesoporous graphitic-type carbon (Pd/C) with nanoparticles (∼2.3 nm). The catalysts were characterized by high-angle annular dark-field/scanning transmission electron microscopy (HAADF/STEM), extended X-ray absorption fine structure/X-ray absorption near-edge structure (EXAFS/XANES), and X-ray photoelectron spectroscopy (XPS) methods. The following order of catalytic activity was obtained: Pd/CTF-1 > Pd/C > Pd/pyCTF ≥ Pd/bipyCTF. The best performance of the Pd/CTF-1 catalyst was associated with Pd2+–C2N2 sites. Pd2+–N4 sites formed on pyCTF and bipyCTF supports showed lower catalytic activity. The selectivity trend at temperatures above 500 K was as follows: Pd/bipyCTF > Pd/pyCTF > Pd/CTF-1 > Pd/C. For the Pd/bipyCTF catalyst, the selectivity reached 99.8%, which is very high for this temperature range. These results may be important for the development of CTF-based catalysts for hydrogen production reactions.