Factors Influencing the Performance of Pd/C Catalysts in the Green Production of Hydrogen from Formic Acid

Abstract

Formic acid derived from biomass is known to be used for hydrogen production over Pd catalysts. The effects of preparation variables, structure of the carbon support, surface functional composition on the state of Pd, and catalytic properties of the samples in the vapor-phase decomposition of formic acid were studied. In all catalysts derived from Pd acetate, metal particles visible by conventional TEM had similar sizes, but the adsorption capacity towards CO responded strongly to N-doping of the carbon surface. Moreover, a decrease in the CO/Pd values was accompanied by a significant increase in the reaction rate. Taking account of X-ray photoelectron spectroscopy (XPS) and atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF/STEM) data, the trends observed were assigned to a larger fraction of single electron-deficient Pd atoms in the N-doped samples, which do not adsorb CO but interact with formic acid to produce hydrogen. This was confirmed by extended DFT studies. The obtained results are valuable for the development of Pd catalysts on carbon supports for different processes.

Highly Stable Single‐Atom Catalyst with Ionic Pd Active Sites Supported on N‐Doped Carbon Nanotubes for Formic Acid Decomposition

“…The observed shifts of Pd 3d 5/2 peaks for components Pd 1 and Pd 2 to higher values with respect to bulk metal and oxide may be related to extra‐atomic relaxation caused by small particle sizes . The XPS spectrum of the 0.2 wt % Pd/N‐CNTs sample shows only one state of palladium with a binding energy of 337.7 eV, which in the case of catalysts supported on N‐CNMs is assigned to isolated Pd 2+ ions coordinated by pyridinic nitrogen sites …”

“…Thus, the XPS studies give grounds to make a definite conclusion on the formation of highly stable Pd ions on the surface of N‐CNTs. Currently, in the literature the formation of Pd 2+ is attributed to the interaction of palladium with one, two,,, and even six pyridinic nitrogen atoms in the case of the g‐C 3 N 4 support . A substantial excess of pyridinic nitrogen atoms in 0.2 wt % Pd/N‐CNTs (N Py /Pd=24) makes it possible to stabilize palladium by any of the ways described above, including palladium coordination by sixfold N‐coordinating cavities, similarly to g‐C 3 N 4 .…”

“…Catalysts consisting completely of metal nanoparticles were less active in this reaction. In our earlier study, the high activity of palladium ions was attributed to the formation of active sites made of Pd 2+ coordinated by two pyridinic nitrogen atoms at the edges of graphite planes of N‐CNMs . According to our DFT calculations, such sites caused the cleavage of the C−H bond in the formic acid molecule to give an adsorbed hydrogen atom and a carboxyl fragment; in addition, it facilitated their interaction to produce molecular hydrogen and carbon dioxide.…”

Hydrogen Production from Formic Acid Attained by Bimetallic Heterogeneous PdAg Catalytic Systems

“…In this sense, there is an increasing number of publications reporting on the investigation of catalytic systems able to catalyse the reaction while exploring the features of either support or metal active phase. Special mention should be made of those breakthroughs achieved Xu et al [29][30][31][32][33][34], and Bulushev et al [47][48][49][50][51][52][53][54][55][56][57].Most of the heterogeneous catalysts used are based on metal nanoparticles immobilised on supports of diverse nature (i.e. carbon materials, MOF, zeolites, resins, etc.)…”

Boosting Hydrogen Production from Formic Acid over Pd Catalysts by Deposition of N-Containing Precursors on the Carbon Support

“…Catalysts containing no Pt-group metals [9,10] do not show promising properties as the catalysts with precious metals. Catalysts consisting of supported highly dispersed Pd particles [2,11,12] or even single Pd atoms [13][14][15] are often considered as the most efficient for the hydrogen production from formic acid. High dispersion of Pd implies high sensitivity of the metal properties to the support material.…”