Modification of Pd Nanoparticles with Lower Work Function Elements for Enhanced Formic Acid Dehydrogenation and Trichloroethylene Dechlorination

Abstract

Catalytic degradation of halogenated contaminants by palladium (Pd) is a promising technology for environmental remediation. However, the low utilization of H by Pd catalyst and its easy poisoning prevent its applications. Here, low work function elements (B or Ag) were incorporated into Fe@C-supported Pd nanoparticles (NPs) to alter their crystalline structure and induce electronic effects, addressing these issues. The Pd mass-normalized dechlorination rates of trichloroethylene (TCE) by Fe@C–Pd–B and Fe@C–Pd–Ag were 51 and 59 times higher than that of unmodified Fe@C–Pd, respectively. The H utilization efficiency of Fe@C–Pd–B and Fe@C–Pd–Ag was 5.4 and 7.2 times higher than that of unmodified Fe@C–Pd, respectively. Various characterizations suggest that the B or Ag incorporation induced the charge redistribution and elevated the electron density of Pd atoms, resulting in the enhanced formic acid (FA) dehydrogenation and TCE dechlorination. Although the Ag incorporation presented a relatively higher H utilization due to the suppressed combination of H and accumulation of unsaturated hydrocarbons (i.e., C2H4), the Fe@C–Pd–Ag was easily deactivated. In contrast, the B incorporation enabled the Pd NPs with a good stability. These findings can guide the rational design of robust Pd-based catalysts for efficient and selective FA dehydrogenation and chlorinated contaminant degradation.

Few-Atomic Zero-Valent Palladium Ensembles for Efficient Reductive Dehydrogenation and Dehalogenation Catalysis

“…However, enlarging the size of the Pd clusters to Pd NPs could result in diminished catalytic activity on FA dehydrogenation (Figure S13 and Figure b). The multilinear adsorption of the intermediate (i.e., formate) on the unsaturated surface metal atoms leads to the formation and stronger adsorption of CO, consequently causing catalyst poisoning . Nonetheless, the bridging adsorption of formate on Pd clusters consisting of a few zero-valent Pd atoms could promote the formation of CO 2 , resulting in the rapid H 2 accumulation through FA dehydrogenation.…”

“…The markedly higher H 2 formation and 4-CP degradation kinetics of Pd 1+c‑red /CN suggest that FA dehydrogenation and C–Cl bond cleavage primarily occur on the zero-valent Pd atoms rather than the positively charged Pd atoms. It is generally accepted that H 2 can be easily catalyzed to form atomic H*, and the adsorbed atomic H* is responsible for rapid dechlorination catalysis. ,− In this case, the FA dehydrogenation process may affect the C–Cl cleavage rate, and the reactivity of Pd 1‑ox /CN for 4-CP dechlorination could be underestimated. The added H 2 facilitated the dechlorination of 4-CP on Pd 1‑red /CN but not on Pd 1‑ox /CN catalysts surface (Figure S22), indicating that the formation of atomic H* via H 2 dissociation is hindered on the positively–charged Pd single atoms.…”

“…Moreover, the catalytic reactivity of the above three catalysts on dehydrogenation and dehalogenation reactions was assessed. FA serves as a representative hydrogen carrier as it is considered an ideal hydrogen storage material because of its high hydrogen storage density, non–toxic nature, and ease of storage and transport. , 4-CP, a typical industrial chlorinated phenol compound that is persistent in the environment and carcinogenic to humans, was selected as the reactivity probe. The Pd ensembles in Pd 1+c‑red /CN catalyst achieves an exceptional H 2 formation reactivity (0.56 μmol min –1 m –2 ) through FA dehydrogenation and 4-CP dechlorination reactivity at a rate of 0.19 L min –1 m –2 , the highest compared to reported works.…”

Potential–Rate Correlations of Supported Palladium-Based Catalysts for Aqueous Formic Acid Dehydrogenation

“…Researchers have explored various supported metal catalysts for efficient FAD, including Pd-based, − Au-based, , Co-based, Pt-based, and Mo-based catalysts . Among these options, Pd-based catalysts have shown great potential in meeting the demands for FAD and have been extensively studied .…”

Hydrogen Production via Cerium-Promoted Dehydrogenation of Formic Acid Catalyzed by Carbon-Supported Palladium Nanoparticles

“…As palladium (Pd) is the most active metal for aqueous formic acid dehydrogenation, Pd-based catalysts have been extensively used. Pd alloyed with Ag, Au, Cu, Co, or Ni showed considerably improved activity compared to monometallic Pd catalysts. ,− Adopting novel supports or modifying supports with dopants such as nitrogen, amine-functional groups, and metal oxide also was used in a way to enhance the activity of Pd-based catalysts. − ,− These enhanced catalytic activities were attributed to the particle size of active metals, ligand effect (electronic modification), strain effect (changes in lattice distance), and interaction of dopants with reactants or intermediates, and in most cases, a combination of these effects. Despite the considerable improvement in catalytic activity, ironically, such combined effects make it difficult to understand the independent role of each factor in the formic acid dehydrogenation reaction.…”