Pt-Zn nanoparticles supported on porous polymeric matrix for selective 3-nitrostyrene hydrogenation

We report the promoting effect of Zn on performance of Pt-based catalyst in liquid-phase hydrogenation of 3-nitrostyrene (3-NS) to 3-vinylaniline (3-VA). Bimetallic Pt-Zn nanoparticles (NPs) were prepared within the hypercross-linked polystyrene (HPS) support. The nanoporous structure of HPS allows a size control of Pt-Zn NPs by confining them in the cavities (ca. 4-5 nm) of the polymeric matrix. The TEM analysis showed that the mean size of the resulted metal particles (4.7 nm) corresponds to the HPS pore size. The properties of the bimetallic catalyst were assessed by IR spectroscopy of chemisorbed CO that suggested the modification of Pt surface and electronic structure invoked by Zn incorporation. The catalytic results demonstrated an increased yield of 3-VA over Pt-Zn/HPS catalyst (97%) relative to monometallic Pt/HPS (16%). This is the highest result reported over Pt catalysts for NS hydrogenation without any additional reaction modifiers. Furthermore, stability of Pt-Zn/HPS under reaction conditions was confirmed over repeated reaction runs. Our results demonstrate the Pt modification with Zn as efficient means to control 3-VA selectivity, whereas HPS serves as a suitable support to control NP size and avoid metal leaching. (c) 2014 Elsevier Inc. All rights reserved.

Catalyst Development for Selective Hydrogenation of Functionalized Alkynes and Nitroarenes

Artur Yarulin

Catalyst design is of major importance for fine chemicals industry due to complexity of the synthesis and high product quality requirements. Moreover, the catalyst formulation has to comply with the standards of health, safety and environmental regulations. The conventional systems often do not satisfy the latter criteria and, therefore, have to be improved to become both efficient and eco-friendly. The advancing technologies of materials synthesis and characterization allow catalyst development from model systems (i.e. colloidal metal nanoparticles (NPs)) towards real heterogeneous catalysts for industrial implementation. The main approach taken in this thesis is based on surface and electronic structure design of the catalytically active NPs (Pd, Pt) by means of size control (2.1 – 9.8 nm) and modification by a second component (Ag, Cu, Zn) during the catalyst preparation. We analyzed the size effect of unsupported Pd NPs in the selective hydrogenation of alkynols with different alkyl chains, i.e. C16 in dehydroisophytol (to isophytol) and C1 in methylbutynol (to methylbutenol). Antipathetic structure sensitivity was established where larger Pd NPs exhibit intrinsically higher (up to ca. 2-fold) specific activity (per Pd surface atom). A higher Pd dispersion delivered greater yields to isophytol (89 -> 93%), while the product distribution in methylbutynol hydrogenation was insensitive to NP size. The distinct size effect on hydrogenation performance for both α-alkynols is associated with modifications in the adsorption strength linked to the hydrocarbon chain length. Furthermore, the incorporation of Ag or Cu in Pd NPs had a critical impact on yield to the target isophytol (up to 97%). This result is attributed to the dilution of the Pd surface sites by a second metal (Ag, Cu) and a modification of the Pd electronic properties. Pd-Ag NPs, having shown the highest selectivity, were further deposited on a structured support based on sintered metal fibers (SMF) coated with ZnO. The improved selectivity achieved over the unsupported Pd-Ag colloidal particles was retained over the structured catalytic system. The resulted Pd-Ag/ZnO/SMF (patent WO 2013/060821 A1) represents a viable alternative to the conventional Lindlar catalyst. Another bimetallic system was studied in selective 3-nitrostyrene hydrogenation, where Pt catalyst was modified by alloying with Zn through the reactive metal– support interactions. Pt/ZnO catalyst containing monodispersed Pt NPs (ca. 2.3 nm) favored 3-vinylaniline formation (97%) showing a remarkable activity (close to that of the benchmark Pt catalysts), i.e. the catalyst had superior combined selectivity/activity response as compared to the reported literature. Additionally, the catalytic tests were performed over bimetallic Pt-Zn NPs embeded within the hypercross-linked polystyrene (HPS) support. The controlled pore size of HPS (ca. 4 nm) allows immobilization and a NP size control by confining Pt within the nanocavities of the polymeric matrix. The catalytic results demonstrated boosted yields towards 3-vinylaniline (16 -> 97%) over Pt-Zn/HPS catalyst as compared to monometallic Pt/HPS. The findings presented here over monodispersed NPs establish the basis of catalyst development for the selective production of fine chemicals. The product distribution can be controlled on a nano-level by tuning the properties of the active phase through the particle size optimization and incorporation of a second metal.

EPFL2014

Structural characterisation of nanoalloys for (photo)catalytic applications with the Sapphire library

Kevin Rossi

A non-trivial interplay rules the relationship between the structure and the chemophysical properties of a nanoparticle. In this context, characterization experiments, molecular dynamics simulations and electronic structure calculations may allow the variables that determine a given property to be pinpointed. Conversely, a rigorous computational characterization of the geometry and chemical ordering of metallic nanoparticles and nanoalloys enables discrimination of which descriptors could be linked with their stability and performance. To this end, we introduce a modular and open-source library, Sapphire, which may classify the structural characteristics of a given nanoparticle through several structural analysis techniques and order parameters. A special focus is geared towards using geometrical descriptors to make predictions on a given nanoparticle's catalytic activity.

ROYAL SOC CHEMISTRY2022

Catalyst Development for Selective Hydrogenation of Functionalized Alkynes and Nitroarenes

Artur Yarulin

EPFL2014