Monodispersed Pd Nanoparticles for Acetylene Selective Hydrogenation: Particle Size and Support Effects

Abstract

Monodispersed Pd nanoparticles (8, 11, and 13 nm in diameter) as confirmed by high resolution transmission electron microscopy were prepared via the reverse microemulsion method and deposited on structured supports consisting of carbon nanofibers (CNF) grown on sintered metal fibers (SMF). The CNF/SMF supports were subjected to oxidative treatments to introduce O-functional groups on the CNF surface. These groups were characterized by temperature-programmed decomposition (TPD) and X-ray photoelectron spectroscopy. The catalysts were used to study (a) the effect of Pd size and (b) the effect of the support nature on the selective acetylene hydrogenation. Antipathetic size dependence of TOF disappeared at particle size bigger than 11 nm. Initial selectivity to ethylene was found size-independent. The deactivation due to coke deposition was faster for smaller particles. The structure-sensitivity relations for the catalysts investigated are discussed in terms of "geometric" and "electronic nature" of the size effect and rationalized regarding Pd-C x phase formation which is size-dependent. Supports with increased acidity diminished the formation of coke and changed the byproduct distribution toward ethane.

Combined XPS and TPD study of oxygen-functionalized carbon nanofibers grown on sintered metal fibers

“…Desorption of CO 2 and CO commenced at the same temperature. In comparison to TPD under flowing He which has been carried out previously [16] the peaks observed in UHV-TPD are broader. This could indicate a non-uniform temperature of the sample.…”

“…Additionally however, a broad CO peak at around 500-600 K can be observed for the ozone activated sample and two smaller peaks around 600 and 800 K for the H 2 O 2 activated sample. CO formation is usually assigned to the decomposition of phenols, ethers and carbonyls/quinones at high temperature (>800 K) [14,16,17]. However, as referenced in the introduction the interpretation of TPD spectra in the literature is ambiguous.…”

“…The aim of this work is the characterization of oxygencontaining groups created on the surface of CNFs grown on inconel sintered metal fiber material (CNF/SMF Inconel ) [15][16][17] by two different oxidative methods. For this purpose, we have coupled a step-wise TPD with XPS in the same UHV apparatus.…”

Recent Advances in the Liquid‐Phase Synthesis of Metal Nanostructures with Controlled Shape and Size for Catalysis

“…When ME-derived monodispersed Pd nanoparticles of 8, 11, and 13 nm diameter were used for the size effect studies, TOF reached a constant value at 11 nm (114). Selectivity to ethylene stayed constant independently on the particle size (19,114). Geometric effect allowed explaining this behaviour.…”

“…Thus, the active sites involve the relatively large ensembles of Pd surface atoms. Taking into account that the coverage of the surface by carbon is very high, it was suggested that the ensemble (geometric) effect was responsible for the structure sensitivity of this reaction (19,114).…”