Particle Size Effect of Hydride Formation and Surface Hydrogen Adsorption of Nanosized Palladium Catalysts: L₃ Edge vs K Edge X-ray Absorption Spectroscopy

Abstract

The particle size effect on the formation of palladium hydride and on surface hydrogen adsorption was studied at room temperature using in situ X-ray absorption spectroscopy at the Pd K and L3 edges. Hydride formation was indirectly observed by lattice expansion in Pd K edge XANES spectra and by EXAFS analysis. Hydride formation was directly detected in the L3 edge spectra. A characteristic spectral feature caused by the formation of a Pd−H antibonding state showed strong particle size dependence. The L3 edge spectra were reproduced using full multiple scattering analysis and density of state calculations, and the contributions of bulk absorbed and surface hydrogen to the XANES spectra could be distinguished. The ratio of hydrogen on the surface versus that in the bulk increased with decreasing particle size, and smaller particles dissolved less hydrogen.

Effect of Particle Size and Adsorbates on the L3, L2 and L1 X-ray Absorption Near Edge Structure of Supported Pt Nanoparticles

“…The changes in the XANES increase as the particle size decreases below about 2 nm. Nearly identical behavior has been observed by Tew et al recently for the L 3 edge of Pd catalysts on various supports [48]. Previous studies have not always provided a consistent answer to the effect of particle size on XANES as some authors have found an increase in the L 3 edge intensity as particle size decreases [5,6].…”

Chemical Synthesis and Characterization of Pd/SiO2: The Effect of Chemical Reagent

“…During the refinement, we obtained the following lattice parameters: 3.907, 3.891, 3.893, and 4.01 Å for Pd-NPsNaBH₄, Pd-NPshydrazine, Pd-NPsammonia,hydrazine, and Pd-NPsPEG, respectively (see Table 1 for the error bars). These lattice parameters are also close to those reported for palladium NPs and bulk palladium materials [12,17,24,30,33]. According to the analysis of peaks broadening, the mean crystallite size was 6.1 nm in the case of palladium reduced by NaBH4, and in case of reduction by hydrazine using ethanol and ammonia, the crystallite sizes were 8.4 nm and 13.7 nm, respectively, which is reported in Table 1 together with TEM results.…”

“…As a general procedure, porous support such as amorphous carbons [20][21][22][23][24][25], alumina, silica, or other mesoporous oxides [19,[26][27][28][29] is precipitated by palladium precursor containing palladium in its ionic phase [30] with subsequent reduction to Pd 0 and formation of palladium NPs [31]. Size and shape distributions of the resulting NPs depend on different parameters, such as type of support [32], temperature, and duration of reduction [33]. The role of the reducing agent has also been studied [34].…”

“…The role of the reducing agent has also been studied [34]. In particular, reduction in H 2 atmosphere can lead to the formation of particles 1 to 10 nm in size [30,33]. Another approach is to use a reducing agent in liquid form.…”

Distinguishing surface adsorbed hydrogen from bulk-dissolved hydrogen in supported Pd nanoparticles using in situ Pd L3-edge XANES

“…Scanning transmission electron microscopy (STEM) measurements showed that the size was 10.5 nm for Pd/SiO 2 (10.5) and 2.8 nm for Pd/SiO 2 (2.8). The details of the synthesis and characterisation were described elsewhere [9].…”