Pd Active Sites on Covalent Triazine Frameworks for Catalytic Hydrogen Production from Formic Acid

Covalent triazine frameworks (CTF) have been recently applied as supports for metal catalysts for different reactions. Varying the nature of the CTF support could improve catalytic properties due to a change in the nature of metal active sites presented in the form of single atoms and dispersed nanoparticles. To understand these changes, for the first time, 1 wt % Pd catalysts supported on hatnCTF and acacCTF prepared from hexaazatrinaphthylene-tricarbonitrile and malonyldibenzonitrile, respectively, were tested in formic acid decomposition in the gas phase. The results were compared with those obtained for a Pd/g-C3N4 catalyst. The catalysts were characterized by high-angle annular dark-field/scanning transmission electron microscopy, X-ray absorption near edge structure/extended X-ray absorption fine structure and X-ray photoelectron spectroscopy. The activity of the Pd/hatnCTF catalyst was significantly higher than those for Pd/acacCTF and Pd/g-C3N4, providing the reaction at a lower temperature by ∼60 K. The high performance of this catalyst was attributed to single-atom Pd2+–C1N3 sites, which are the main active Pd species in this sample. The Pd/acacCTF sample contained single-atom Pd2+–O4 sites and metallic Pd nanoparticles, while the Pd/g-C3N4 sample contained mainly metallic Pd nanoparticles. The selectivity toward H2 was high (>98%) for all catalysts even at 573 K. The obtained results could be useful for the development of different applications of CTF materials.