Poly(amic acid) salt‐mediated palladium and platinum nanoparticles as highly active and recyclable catalysts for hydrogenation of nitroarenes in water under ambient conditions

Abstract

Development of highly active and recyclable catalysts for selective hydrogenation of nitroarenes to amines in water at room temperature is always a challenge in chemical industry. This study reports a facile in situ method for synthesis of ultrafine palladium and platinum nanoparticles (NPs) stabilized by poly (amic acid) salt (PAAS) and their potential as catalysts for hydrogenation of nitroarenes with sodium borohydride or molecular hydrogen as reductant in water at room temperature. In the reduction of 4‐nitrophenol to 4‐aminophenol by sodium borohydride, the activity parameters of PdNPs–PAAS and PtNPs–PAAS catalyst is 6.66 × 103 and 5.58 × 103 s−1 M−1 respectively. In the hydrogenation of diverse nitroarenes under atmospheric hydrogen pressure, PdNPs–PAAS shows high activity but poor selectivity toward desired amines in some cases, while PtNPs–PAAS shows both high activity and high selectivity for selective hydrogenation of nitroarenes to corresponding anilines. The high efficiency of nanocatalyst is due to the quasi‐homogeneous dispersion of metal NPs and synergistic effects between metal NPs and PAAS. In addition, nanocatalyst can be easily recovered with pH‐sensibility of PAAS and reused at least six times without significant loss of catalytic activities.

Role of Polymer Structures in Catalysis by Transition Metal and Metal Oxide Nanoparticle Composites

“…Unremarkable catalytic properties in the 4-NP reduction were recently reported for Pd and Pt NPs in poly(amic acid) salt. 287 Ag or Au NPs with very broad NP size distributions were prepared via NaBH 4 reduction of Ag or Au precursors in the presence of calixarene-based coordination polymers containing Co or Ni ions, indicating that these polymers are poor capping agents. 288 The Ag and Au NPs showed some activity in the NaBH 4 4-NP reduction to 4-AP, especially in the case of Ag (the rate constant of 0.32 min −1 ), but it is unclear what is the role of coordination polymers, while simpler alternatives might be better suited for stabilization of Ag and Au NPs.…”

“…The rate constant achieved for this catalyst was 1.84 min –1 , justifying a multistep-process of the attachment of triazine groups. Unremarkable catalytic properties in the 4-NP reduction were recently reported for Pd and Pt NPs in poly­(amic acid) salt . Ag or Au NPs with very broad NP size distributions were prepared via NaBH 4 reduction of Ag or Au precursors in the presence of calixarene-based coordination polymers containing Co or Ni ions, indicating that these polymers are poor capping agents .…”

Hybrid Organic–Platinum Nanoparticles for Hydrogenation Reactions

“…The reduction of p -NP follows the one documented for o -NP. ,− The Pt-nanoclusters capped with MPA–PETMP 2:1 show an average rate constant of k = 3.5 × 10 –3 s –1 ( k = 1.9 × 10 –3 s –1 for Pt-MSA–PETMP 2:1). The velocity rises for Pt-MSA–PETMP 4:1 and Pt-MPA–PETMP 4:1 ( k = 6.6 × 10 –3 s –1 and k = 3.8 × 10 –3 s –1 ).…”

“…In comparison to literature, the system herein clearly falls in the upper end with high conversion rates and low catalyst demand (Table ). ,,− Also compared to other bi- or multimetallic compounds the rate constants found here are competitive. − The stabilizing compounds are cost-effective, and the preparation route avoids sophisticated purification steps. A critical issue may be seen in the first cycle, where the anionic groups may interfere with boronic acid, but from IR spectroscopy, it is evident that the main chemical structure remains intact (Figure S12).…”

Palladium‐immobilized polymer‐coated magnetic nanocomposites as reusable catalysts for the reduction of 4‐nitrophenol

“…[33][34][35][36] Importantly, 4-aminophenol (4AP), the major product of the reduction of 4NP, can be used as a main intermediate for the syntheses of pharmaceuticals, agricultural chemicals, polymers, dyestuffs and cosmetic products. [37][38][39][40] We herein designed and synthesized a novel polymer-coated MNP/Pd nanocomposite for use as a catalyst for the reduction of 4NP under mild conditions (Fig. 1).…”