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

Covalenttriazine frameworks (CTF) have been recently applied assupports for metal catalysts for different reactions. Varying thenature of the CTF support could improve catalytic properties due toa change in the nature of metal active sites presented in the formof 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 gasphase. The results were compared with those obtained for a Pd/g-C3N4 catalyst. The catalysts were characterized byhigh-angle annular dark-field/scanning transmission electron microscopy,X-ray absorption near edge structure/extended X-ray absorption finestructure and X-ray photoelectron spectroscopy. The activity of thePd/hatnCTF catalyst was significantly higher than those for Pd/acacCTFand Pd/g-C3N4, providing the reaction at a lowertemperature by & SIM;60 K. The high performance of this catalystwas attributed to single-atom Pd2+-C1N3 sites, which are the main active Pd species in thissample. The Pd/acacCTF sample contained single-atom Pd2+-O-4 sites and metallic Pd nanoparticles, whilethe Pd/g-C3N4 sample contained mainly metallicPd nanoparticles. The selectivity toward H-2 was high (>98%)for all catalysts even at 573 K. The obtained results could be usefulfor the development of different applications of CTF materials.