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

Abstract

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.

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

“…Despite washing the samples in HCl, water, and tetrahydrofuran, X-ray photoelectron spectroscopy (XPS) analysis showed that some amounts of Zn and Cl were left in the hatnCTF sample (Table S1) but not in the acacCTF sample. This is in accordance with literature data for other CTF samples. , …”

“…Electron microscopy studies were performed using a double-corrected ThemisZ (Thermo Fisher Scientific) device in high-angle annular dark-field/scanning transmission electron microscopy (HAADF/STEM) and high-resolution transmission electron microscopy (HRTEM) modes with an acceleration voltage of 200 kV …”

“…The electronic state and surface contents of elements were determined using XPS. A SPECS photoelectron spectrometer equipped with a PHOIBOS-150-MCD-9 hemispherical analyzer and a FOCUS-500 X-ray monochromator (AlKα radiation, h ν = 1486.74 eV, 200 W) and a VG-Microtech Multilab 3000 spectrometer equipped with a semispherical electron analyzer and a Mg Kα ( h ν = 1253.6 eV) with a 300 W X-ray source were used. , …”

“…Thus, Zhang et al and Feng et al studied hydrogen production from formic acid decomposition in the liquid phase over Pd and PdCo nanoparticles supported on CTF, respectively, and reported their promising properties. Recently, we have shown that some CTF materials can stabilize 1 wt % Pd in the form of isolated atoms, thus forming single-atom catalysts . This type of catalyst is known for efficient usage of a noble metal and often higher intrinsic activity, selectivity, and stability in different reactions than those for catalysts containing supported metal nanoparticles.…”

Metallic active-site engineering: a bridge between covalent triazine frameworks and high-performance catalysts

“…78 By implanting metal single atoms into CTFs, the process of intermediate evolution and conversion happens more smoothly and the energy barrier will decrease because of the electron transfer and orbital overlaps between the d electrons of metals and the molecular orbitals of substrates. [79][80][81][82] As a representative work, Liang's group applied triazine COF supported Pd single atoms (Pd 1 /trzn-COF) in CO oxidation and illustrated the detailed roles of Pd single atoms and the trzn-COF as well as the corporative catalysis based on their chemical interactions. 14 Engineering active metals into CTFs for photocatalysis Photocatalysis, as a critical subclass of conversion and storage of solar energy, has gained huge popularity in the scientic fraternity.…”