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.

Formic acid is a promising liquid organic hydrogen carrier (LOHC) since it has relatively high hydrogen content (4.4 wt%), low inflammability, low toxicity and can be obtained from biomass or from CO2. The aim of the present research was the creation of efficient 1 wt% Pd catalysts supported on mesoporous graphitic carbon (Sibunit) for the hydrogen production from gas-phase formic acid. For this purpose, the carbon support was modified by pyrolysis of deposited precursors containing pyridinic nitrogen such as melamine (Mel), 2,2′-bipyridine (Bpy) or 1,10-phenanthroline (Phen) at 673 K. The following activity trend of the catalysts Pd/Mel/C > Pd/C ~ Pd/Bpy/C > Pd/Phen/C was obtained. The activity of the Pd/Mel/C catalyst was by a factor of 4 higher than the activity of the Pd/C catalyst at about 373 K and the apparent activation energy was significantly lower than those for the other catalysts (32 vs. 42–46 kJ/mol). The high activity of the melamine-based samples was explained by a high dispersion of Pd nanoparticles (~2 nm, HRTEM) and their strong electron-deficient character (XPS) provided by interaction of Pd with pyridinic nitrogen species of the support. The presented results can be used for the development of supported Pd catalysts for hydrogen production from different liquid organic hydrogen carriers.

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