Palladium supported on a novel ordered mesoporous polypyrrole/carbon nanocomposite as a powerful heterogeneous catalyst for the aerobic oxidation of alcohols to carboxylic acids and ketones on water.

Nasim Ganji,Sepideh Najafvand-Derikvandi,Babak Karimi,Hojatollah Vali

doi:10.1039/c9ra10941b

Abstract

Preparation of an ordered mesoporous polypyrrole/carbon (PPy/OMC) composite has been described through a two-step nanocasting process using KIT-6 as a template. Characterization of the PPy/OMC nanocomposite by various analysis methods such as TEM, XRD, TGA, SEM and N2 sorption confirmed the preparation of a material with ordered mesoporous structure, uniform pore size distribution, high surface area and high stability. This nanocomposite was then used for the immobilization of palladium nanoparticles. The nanoparticles were almost uniformly distributed on the support with a narrow particle size of 20–25 nm, confirmed by various analysis methods. Performance of the Pd@PPy/OMC catalyst was evaluated in the aerobic oxidation of various primary and secondary alcohols on water as a green solvent, giving the corresponding carboxylic acids and ketones in high yields and excellent selectivity. The catalyst could also be reused for at least 10 reaction runs without losing its catalytic activity and selectivity. High catalytic efficiency of the catalyst can be attributed to a strong synergism between the PPy/OMC and that of supported Pd nanoparticles.

Highlights

Oxidation of alcohols to carbonyl compounds is one of the most fundamental chemical reactions in organic synthesis both in academic and industrial areas,[1,2,3,4,5] because the corresponding products have wide applications in synthetic chemistry as important precursors and intermediates
Global production of aryl carboxylic acids is estimated to be more than 620 kilotons by 2023.8 large scale synthesis of these carbonyl compounds still relies on the oxidation of alcohols with stoichiometric amounts of hazardous and expensive oxidants,[9,10] such as permanganate, chromate and aDepartment of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), PO-Box 45195-1159, Gava-zang, Zanjan 45137-6731, Iran
Surface areas were calculated according to the BET equation, and pore size distribution (PSD) were evaluated through the BJH method using adsorption branches of the isotherms

Summary

Introduction

Oxidation of alcohols to carbonyl compounds is one of the most fundamental chemical reactions in organic synthesis both in academic and industrial areas,[1,2,3,4,5] because the corresponding products have wide applications in synthetic chemistry as important precursors and intermediates. Nitrogen adsorption– desorption isotherm of the Pd@PPy/OMC catalyst provided a strong evidence for the successful immobilization of the Pd species on the PPy/OMC material, by showing an appreciable decrease in the BET surface area and total pore volume from 822 m2 gÀ1 and 1.39 cm[3] gÀ1 for the PPy/OMC composite to 628 m2 gÀ1 and 1.18 cm[3] gÀ1 for the Pd@PPy/OMC catalyst, respectively (Table 1).

Results

Conclusion