Effect of Polyvinyl Alcohol Ligands on Supported Gold Nano-Catalysts: Morphological and Kinetics Studies

Abstract

The effect of polyvinyl alcohol (PVA) stabilizers and gold nanoparticles supported on active carbon (AuNPs/AC) was investigated in this article. Polymers with different molecular weights and hydrolysis degrees have been synthesized and used, like the stabilizing agent of Au nano-catalysts obtained by the sol-immobilization method. The reduction of 4-nitrophenol with NaBH4 has been used as a model reaction to investigate the catalytic activity of synthesized Au/AC catalysts. In addition, we report several characterization techniques such as ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) in order to correlate the properties of the polymer with the metal nanoparticle size and the catalytic activity. A volcano plot was observed linking the catalytic performance with hydrolysis degree and the maximum of the curve was identified at a value of 60%. The Au:PVA-60 weight ratio was changed in order to explain how the amount of the polymer can influence catalytic properties. The effect of nitroaromatic ring substituents on the catalytic mechanism was examined by the Hammett theory. Moreover, the reusability of the catalyst was investigated, with little to no decrease in activity observed over five catalytic cycles. Morphological and kinetic studies reported in this paper reveal the effect of the PVA polymeric stabilizer properties on the size and catalytic activity of supported gold nanoparticles.

Controlling the Production of Acid Catalyzed Products of Furfural Hydrogenation by Pd/TiO2

“…One such study was published by Dimitratos et al , where they reported that encapsulation of colloidal Au NPs with longer polymer chains (M W ≥23,300 g mol −1 ). Capping of the Au colloid using PVA with high M W proved to be preferential for ensuring a stable colloid, however, the final supported NP catalyst displayed decreased catalytic activity [59] . This was rationalized by increased steric and electronic effects of the polymer chains inhibiting access to the catalyst surface, and has been corroborated by similar studies of PVP‐capped Au colloids [60] …”

Effect of the Colloidal Preparation Method for Supported Preformed Colloidal Au Nanoparticles for the Liquid Phase Oxidation of 1,6-Hexanediol to Adipic Acid

“…The supported Au catalysts were prepared by using the sol-immobilization method [31,[47][48][49]. Tetra chloroauric(III) acid (Sigma Aldrich, 99.99 %) (Milan, Italy), poly(vinyl alcohol) (PVA, Sigma Aldrich, MW 13,000-23,000 g mol −1 , hydrolysed 87-89 %), poly(vinyl pyrrolidone) (PVP, Sigma Aldrich, MW 29,000 g mol −1 ), poly(ethylene glycol) (PEG, Sigma Aldrich, MW 8000 g mol −1 ), sulfuric acid (Sigma Aldrich, 98%), sodium borohydride (Sigma Aldrich, powder, ≥98.0%), and activated carbon SX1G (AC, Norit) were used for catalyst preparation and were purchased from Sigma Aldrich.…”

Getting Greener with the Synthesis of Nanoparticles and Nanomaterials

“…The catalytic activity of metallic nanoparticles is very often governed by the method of preparation, which determines the particle size and structure of nanoparticles. This was demonstrated in the work of Scurti et al [11]. The authors studied the effect of polymeric stabilizers on gold nanoparticle size and activity in hydrogenation of 4-nitrophenol.…”

“…However, a high quantity of the polymer at the metal surface inhibited the catalytic activity of gold due to the steric and electronic effects. In addition, it was demonstrated that the catalytic activity is dependent on the degree of polymer hydrolysis and a volcano plot was observed between the hydrolysis degree of the polymer and the apparent kinetic constant in the 4-nitrophenol hydrogenation [ 11 ]. The optimum catalytic activity was observed for the sample synthesized with polyvinyl alcohol hydrolyzed at 60%.…”

“…The optimum catalytic activity was observed for the sample synthesized with polyvinyl alcohol hydrolyzed at 60%. These studies emphasized the crucial role of ligand–nanoparticle interaction in the catalytic mechanism of hydrogenation reaction [ 11 ]. The importance of the interaction between metal and the support in catalytic processes was also highlighted by Zhu et al [ 12 ].…”