Structure sensitivity of selective acetylene hydrogenation over the catalysts with shape-controlled palladium nanoparticles

The structure sensitivity of acetylene hydrogenation on catalysts with controlled shape of palladium nanoparticles was studied. Palladium particles of cubic (Pdcub), cuboctahedral (Pdco) and octahedral (Pdoct) shapes were obtained by a colloidal method. Poly(N-vinyl)pyrrolidone (PVP) was used as the stabilizer of colloidal solutions. In order to eliminate the effect of the polymer on the properties of the catalyst, PVP was removed from the surface of the particles after their transfer to the support by simultaneous treatment with ozone and UV radiation. This allowed complete cleaning of the catalyst surface from the organic stabilizer without any change in the morphology of particles. The effectiveness of this treatment method was confirmed by X-ray photoelectron spectroscopy and scanning electron microscopy. It was found experimentally that the shape of nanoparticles does not influence the catalyst selectivity, but the activity decreases in the order Pdoct > Pdco > Pdcub. Since octahedrons consist of (111) faces, the cubes contain only (100) faces, and the cuboctahedrons are composed of faces of both types, Pd111 is more active than Pd100. Calculations with the use of a statistical method showed that the ∼3-nm Pd octahedrons are nanoparticles with optimum shape and size, giving maximum catalyst activit

Structure sensitivity of selective acetylene hydrogenation over the catalysts with shape-controlled palladium nanoparticles

The structure sensitivity of acetylene hydrogenation on catalysts with controlled shape of palladium nanoparticles was studied. Palladium particles of cubic (Pd-cub), cuboctahedral (Pd-co) and octahedral (Pd-oct) shapes were obtained by a colloidal method. Poly(N-vinyl)pyrrolidone (PVP) was used as the stabilizer of colloidal solutions. In order to eliminate the effect of the polymer on the properties of the catalyst, PVP was removed from the surface of the particles after their transfer to the support by simultaneous treatment with ozone and UV radiation. This allowed complete cleaning of the catalyst surface from the organic stabilizer without any change in the morphology of particles. The effectiveness of this treatment method was confirmed by X-ray photoelectron spectroscopy and scanning electron microscopy. It was found experimentally that the shape of nanoparticles does not influence the catalyst selectivity, but the activity decreases in the order Pd-oct > Pd-co > Pd-cub. Since octahedrons consist of (111) faces, the cubes contain only (100) faces, and the cuboctahedrons are composed of faces of both types, Pd-111 is more active than Pd-100. Calculations with the use of a statistical method showed that the similar to 3-nm Pd octahedrons are nanoparticles with optimum shape and size, giving maximum catalyst activity

Size-Effect of Pd-(Poly(N-vinyl-2-pyrrolidone)) Nanocatalysts on Selective Hydrogenation of Alkynols with Different Alkyl Chains

We have studied the effect of unsupported Pd nanoparticle (NP) size in the selective C C semi-hydrogenation of alkynols with different alkyl chains, i.e., C-16 in dehydroisophytol (DIP) (to isophytol (IP)) vs C-1 in 2-methyl-3-butyn-2-ol (MBY) (to 2-methyl-3-buten-2-ol (MBE)). The Pd NPs were synthesized via colloidal technique with poly(N-vinyl-2-pyrrolidone) (PVP) as stabilizing agent where a range of crystal sizes (2.1-9.8 nm; confirmed by HRTEM) was generated. Both reactions show antipathetic structure sensitivity consistent with higher specific activity (TOF) over larger Pd NPs where the structure sensitivity effect is more pronounced for NPs = 88%) selectivity to the target alkenol product at almost complete (98%) conversion. Increased IP selectivity (S-IP; (XDIP=98%) ca. 95%) was observed over smaller (2.1-3.0 nm) Pd NPs while ca. 98% selectivity to MBE (S-MBE; XDIP=98%) is obtained irrespective of particle size. The kinetic results were consistent with a Langmuir-Hinshelwood model. The observed Pd NPs size effect on catalytic response is ascribed to a contribution of Pd electronic surface modifications, fraction of Pd-plane active sites and the steric effects which impact akynol/alkenol adsorption constants. The results obtained in this work provide a powerful tool for catalyst design for industrial applications

Shape-dependence of Pd nanocrystal carburization during acetylene hydrogenation

This interdisciplinary work combines the use of shape- and size-defined Pd nanocrystals (cubes of 10 and 18 nm, and octahedra of 37 nm) with in situ techniques and DFT calculations to unravel the dynamic phenomena with respect to Pd reconstruction taking place during acetylene hydrogenation. Notably, it was found that the reacting Pd surface evolved at a different pace depending on the shape of the Pd nanocrystals, due to their specific propensity to form carbides under reaction conditions. Indeed, Pd cubes (Pd(100)) reacted with acetylene to form a PdC0.13 phase at a rate roughly 6-fold higher than that of octahedra (Pd(111)), resulting in nanocrystals with different degrees of carburization. DFT calculations revealed changes in the electronic and geometric properties of the Pd nanocrystals imposed by the progressive addition of carbon in its lattice

Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts

In the present work, hollow PdAg-CeO2 heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO2 counterpart in an additive manner. The PdAg-CeO2 NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO2 moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance