Formation and growth of palladium nanoparticles inside porous poly(4-vinyl-pyridine) monitored by operando techniques: The role of different reducing agents

Abstract

In this work we followed the formation of palladium nanoparticles, starting from palladium (II) acetate precursor, inside a poly(4-vinylpyridine-co-divinylbenzene) polymer in presence of different reducing agents. The formation and growth of palladium nanoparticles in presence of H2was followed as a function of temperature by simultaneous XANES-SAXS techniques, coupled with DRIFT spectroscopy in operando conditions. It was found that the pyridyl functional groups in the polymer plays a fundamental role in the stabilization of the palladium (II) acetate precursor, as well as in the stabilization of the palladium nanoparticles. The effect of a thermal treatment in alcohol (ethanol and 2-propanol) was preliminarily investigated by means of DRIFT spectroscopy in operando conditions. We found that alcohols act as reducing agents for Pd(OAc)2. The obtained palladium nanoparticles were preliminarily characterized by means of IR spectroscopy using CO as probe molecule.

DFT-Assisted Spectroscopic Studies on the Coordination of Small Ligands to Palladium: From Isolated Ions to Nanoparticles

“…Several studies have been reported using advanced characterization techniques (e.g., SAXS, liquid cell transmission electron microscopy, and extended X-ray absorption fine structure) to provide a molecular-level understanding of the roles of capping agents during the formation of MNPs. 7 , 11 , 17 , 19 − 21 , 29 − 43 Here, we employ a combination of UV–visible (UV–vis) and Fourier transform infrared (FT-IR) spectroscopies and density functional theory (DFT) modeling to investigate the coordination of small ligands (diols and amino alcohols) to Pd 2+ ions and Pd NPs. The complementary use of conventional spectroscopic techniques and theoretical modeling has already been demonstrated to be a powerful tool in investigating metal–ligand interactions in Au and Ag NPs.…”

“…For these reasons, a significant amount of research has been devoted recently to investigate the connection between metal–capping agent interactions and the formation mechanisms of MNPs in solution, as well as the nature and role of the local ligand environment of metal species in solution. Several studies have been reported using advanced characterization techniques (e.g., SAXS, liquid cell transmission electron microscopy, and extended X-ray absorption fine structure) to provide a molecular-level understanding of the roles of capping agents during the formation of MNPs. ,,,− ,− Here, we employ a combination of UV–visible (UV–vis) and Fourier transform infrared (FT-IR) spectroscopies and density functional theory (DFT) modeling to investigate the coordination of small ligands (diols and amino alcohols) to Pd 2+ ions and Pd NPs. The complementary use of conventional spectroscopic techniques and theoretical modeling has already been demonstrated to be a powerful tool in investigating metal–ligand interactions in Au and Ag NPs. − ,, The pH dependence of interaction strength and conformation of thiolate and thione molecules at the surface of Au NPs has been studied by means of surface-enhanced Raman spectroscopy (SERS) combined with DFT modeling by Ansar et al The synthesis of amidine-stabilized Ag NPs via hydrogenolysis of silver amidinate in the presence of hexadecylamine was explored by Cure et al through nuclear magnetic resonance and SERS spectroscopies in combination with DFT simulations devoted to unraveling the coordination of ligands to Ag NPs .…”

Dynamic Behavior of Pd/P4VP Catalyst during the Aerobic Oxidation of 2-Propanol: A Simultaneous SAXS/XAS/MS Operando Study

“…Recently, we have been involved in the study of the chemistry of Pd­(OAc) 2 inside a porous, divinylbenzene cross-linked, pyridine-containing polymer (P4VP). − In the freshly prepared form, this system might be seen as the heterogeneous counterpart of Pd­(OAc) 2 /pyridine, and this stimulated us to explore its behavior during the aerobic oxidation of an alcohol in the gas phase, as a function of the reaction conditions. In particular, we applied synchronous, time-resolved, SAXS/XAS/MS techniques to obtain a dynamical picture of the changes occurring to the Pd species (in terms of oxidation state, aggregation, and local structure) under transient reaction conditions.…”

Characterization of metallic species on porous materials by in situ XAS

“…), LDH-derived oxides, 22 carbons, [23][24][25][26] polymers, [27][28] zeolites, [29][30] MOFs, [31][32] ordered mesoporous materials, [33][34] clays, 35 among others. Apart from nanoparticle stabilization, the support can help in the tuning of nanoparticles properties.…”

“…Moreover, no extraframework or M-O-M contributions were observed, which indicated that both heteroelements were present as isolated species within the microporous matrix. 121 Although the study of the local environment of aluminum in zeolites by 27 Al NMR is a consensus and wellestablished in the zeolitic community, 122 there are also some studies of Al speciation by XAS. [123][124] However, aluminum is a light element and its study by X-ray absorption spectroscopy requires soft X-rays, complicating in situ and operando studies due to the high absorption of soft X-rays by matter in general.…”