A protector-free one-pot strategy to synthesize highly dispersed Pd hydrogenation catalysts in a broad loading range on polystyrene

Abstract

Pursuing a strategy to feasibly acquire nanoparticles in a clean state (protector-free) and desired size range (ca. 3.0–5.0 nm) is a fundamental demand for the application of state-of-the-art precious metal catalysts. Herein, vinylbenzyl trimethylammonium chloride (VTC) was copolymerized on the surface of polystyrene (PS) as a capturing group. This capturing group anchored PdCl₄²⁻ via electrostatic state-of-the-art interaction to prepare PS supported Pd nanoparticles in one-pot system for the selective hydrogenation of phenylacetylene to styrene. Using a combination of inductively coupled plasma-optical emission spectrometry (ICP-OES), zeta potential analysis (ZPA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectra (FT-IR) techniques, it was demonstrated that introducing VTC on PS in a proper amount (VTC : styrene molar ratio of 0.05) was a key factor to optimize the electrostatic state of the polystyrene substrate, which facilitated uniform anchoring of PdCl₄²⁻ and the following in situ reduction to Pd particles under protector-free conditions, and led to the formation of particles in desired ca. 3.0–5.0 nm size range while broad Pd loading being adjusted in 20 times change (from 0.2–4.6 wt%). The catalytic measurements and corresponding kinetic analysis for the selective hydrogenation of phenylacetylene to styrene showed that the regular change of catalytic performance among the samples was directly governed by Pd particle size. In addition, the good stability of the present Pd catalyst was verified via leaching experiment and recycle use tests on typical samples. These results indicated that the present strategy was promising in acquiring clean and size-controllable metal nanoparticles, which could be inferred as a feasible system to obtain desired metal nanocatalysts for advanced heterogeneous catalysis applications.