Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂

Abstract

This work aims to clarify the nanostructural transformation accompanying the loss of activity and selectivity for the hydrogen peroxide synthesis of palladium and gold-palladium nanoparticles supported on N-functionalized carbon nanotubes. High-resolution X-ray photoemission spectroscopy (XPS) allows the discrimination of metallic palladium, electronically modified metallic palladium hosting impurities, and cationic palladium. This is paralleled by the morphological heterogeneity observed by high-resolution TEM, in which nanoparticles with an average size of 2 nm coexisted with very small palladium clusters. The morphological distribution of palladium is modified after reaction through sintering and dissolution/redeposition pathways. The loss of selectivity is correlated to the extent to which these processes occur as a result of the instability of the particle at the carbon surface. We assign beneficial activity in the selective hydrogenation of oxygen to palladium clusters with a modified electronic structure compared with palladium metal or palladium oxides. These beneficial species are formed and stabilized on carbons modified with nitrogen atoms in substitutional positions. The formation of larger metallic palladium particles not only reduces the number of active sites for the synthesis, but also enhances the activity for deep hydrogenation to water. The structural instability of the active species is thus detrimental in a dual way. Minimizing the chance of sintering of palladium clusters by all means is thus the key to better performing catalysts.

Single Isolated Pd2+ Cations Supported on N-Doped Carbon as Active Sites for Hydrogen Production from Formic Acid Decomposition

“…line is in agreement with the recent results of Arrigo et al 28 showing a significant increase of the peak in the same region after deposition of PdAu nanoparticles on N-functionalized carbon nanotubes.…”

“…The presence of nitrogen leads to stabilization of a supported phase, changing its chemical and electronic properties or even to creation of novel active sites for catalytic reactions. [24][25][26][27][28][29] Recently, Arrigo et al 27 reported a study of interaction of N-doped carbon nanotubes with Pd species deposited from Pd(NO 3 ) 2 and Na 2 PdCl 4 and of reactivity of the obtained catalysts in different reactions like oxygen reduction, CO oxidation and hydrogenation. Our present work is focused to understanding of the nature of Pd species active in decomposition of formic acid and the character of interaction of these Pd species with the N-doped carbon surface.…”

CO oxidation as a test reaction for strong metal–support interaction in nanostructured Pd/FeO powder catalysts

“…At 336.6 eV (FWHM = 1.50) another palladium species can be fitted that we tentatively attributed to SMSI. As reported for similar metal-oxide interfaces [4,[43][44][45] the palladium at the particle surface can be shifted to higher binding energy when being in contact with an iron oxide overlayer. The integrated amount of the new species of 29% would exactly represent the content of Pd atoms at the surface of the particles in the present Pd particle size, according to the dispersion calculation.…”

Understanding Heteroatom-Mediated Metal–Support Interactions in Functionalized Carbons: A Perspective Review

“…Arrigo et al [60,77] proposed a convincing rationalization of the Pd 3d XPS signal of Pd NPs supported on nitrogen-doped carbon nanotubes. Four components were separated under the broad and complex Pd 3d signal (Figure 6).…”