Structure, Interaction, and Dynamics of Au/Pd Bimetallic Nanoalloys Dispersed in Aqueous Ethylpyrrolidone, a Monomeric Moiety of Polyvinylpyrrolidone

Abstract

Bimetallic nanoparticles (NPs) have been shown to exhibit certain advantages over pure NPs in catalysis due to a synergistic effect. It is common to disperse NPs in a polymer matrix such as polyvinylpyrrolidone (PVP) to prevent flocculation, which imparts considerable electronic effects on the NPs. In the present study, the interactions between aqueous solutions of N-ethylpyrrolidone (EP, system chosen to model the monomeric form of PVP) and Au/Pd bimetallic NPs, which are relevant in catalysis, have been investigated using molecular dynamics simulations and density functional theory (DFT) method. The adequacy of the force fields used was assessed based on their ability to reproduce the structures and adsorption energies obtained using DFT calculations. The interactions of NPs with the environment were studied at various concentrations of aqueous solutions of EP to examine the strength of NP–EP and NP–water interactions. Free energy calculations and local mole fraction enhancement values show that that the EP adsorption on NPs is preferred over the adsorption of water. Extensive analysis of the interactions of the NPs with various concentrations of aqueous EP suggests the existence of isolated water molecules that may take part in reactions. Adsorption of unexpectedly large numbers of EP molecules was found to be possible leading to accumulation of the electron density on the Au/Pd NPs, which have previously been shown to enhance the catalytic activity of NPs. This study emphasizes the importance of including the electronic effects on the NPs due to the adsorption of stabilizing agents in modeling and demonstrates the utility of MD simulations to generate appropriate model chemistries for studying catalysis at higher level quantum chemical and density functional theory calculations.

Gold‐Palladium Nanocluster Catalysts for Homocoupling: Electronic Structure and Interface Dynamics

“…The Au 0.5 Pd 0.5 :PVP system shows the best performance of the catalytic activity for ArCl coupling . Therefore, to examine this catalytic reaction, we adopted Au 10 Pd 10 NC model whose composition accords with the best Au−Pd ratio of 1 : 1 ,,. In Au−Pd:PVP system, the previous theoretical works,, as well as XPS measurements suggest that the Au−Pd NC supported by PVP is negatively charged.…”

“…We also worked on the synergetic alloy effects and metal‐support interaction of metal NC catalysts. For the alloy effect, we have intensively investigated the colloidal phase Au−Pd bimetallic NC catalysts for homocoupling of ArCl ,,. For the metal‐support interaction, we have investigated the selective hydrogenation on Ag NC/Al 2 O 3 and CO oxidation on M 1 /Al 2 O 3 etc ,.…”

“…Previously, MD simulations have been used to obtain atomistic level details of NCs adsorbed to proteins, DNA, lipids and dendrimers ,. Most of these studies used Lennard‐Jones (LJ) potentials for the metal NCs, and this methodology was shown to reasonably reproduce the energetics and geometric features obtained using DFT methods . Recently, Heinz and coworkers have developed a method based on the combination of LJ potential, harmonic bond stretch potential and a Coulomb electrostatic term to include the polarization effects.…”

“…In the series of works, we have theoretically investigated the origin of the catalytic activity of the Au−Pd NC catalysts using the DFT calculations, GA approaches, and MD simulations with respect to (1) the geometric and electronic/spin structures of Au−Pd NC,, (2) the reactive sites on the NC surface,, (3) the electronic effects of surrounding PVP, (4) the reaction cycle or entire reaction mechanism, (5) the inverse halogen dependence, and (6) the solvation dynamics at interface between polymer dispersed NC and solution . In this review article, we overview our theoretical works focusing on these issues of the Au−Pd NC catalyst for the homocoupling reaction of aryl chlorides.…”

Catalytic activation of nitrobenzene on PVP passivated silver cluster: A DFT investigation

“…DFT computations have proved to be very useful in investigating the interaction, studying the electronic effect of stabilizers and proposing the mechanism for catalytic activity of nanoparticles in several reactions . Recently, Gupta et al investigated the interactions between aqueous solutions of N ‐ethylpyrrolidone (EP, the monomeric form of PVP) and Au/Pd bimetallic nanoparticles using molecular dynamics simulations and DFT calculation . They also described the electronic effect of EP on the bimetallic NP.…”