Mechanistic studies of the Suzuki-Miyaura reaction with aryl bromides using Pd supported on micro- and mesoporous activated carbons

Heterogeneous catalysis by ultra-small bimetallic nanoparticles surpassing homogeneous catalysis for carbon-carbon bond forming reactions

Palladium catalyzed cross-coupling reactions represent a significant advancement in contemporary organic synthesis as these reactions are of strategic importance in the area of pharmaceutical drug discovery and development. Supported palladium-based catalysts are highly sought-after in carbon-carbon bond forming catalytic processes to ensure catalyst recovery and reuse while preventing product contamination. This paper reports the development of heterogeneous Pd-based bimetallic catalysts supported on fumed silica that have high activity and selectivity matching those of homogeneous catalysts, eliminating the catalyst's leaching and sintering and allowing efficient recycling of the catalysts. Palladium and base metal (Cu, Ni or Co) contents of less than 1.0 wt% loading are deposited on a mesoporous fumed silica support (surface area SABET = 350 m2 g-1) using strong electrostatic adsorption (SEA) yielding homogeneously alloyed nanoparticles with an average size of 1.3 nm. All bimetallic catalysts were found to be highly active toward Suzuki cross-coupling (SCC) reactions with superior activity and stability for the CuPd/SiO2 catalyst. A low CuPd/SiO2 loading (Pd: 0.3 mol%) completes the conversion of bromobenzene and phenylboronic acid to biphenyl in 30 minutes under ambient conditions in water/ethanol solvent. In contrast, monometallic Pd/SiO2 (Pd: 0.3 mol%) completes the same reaction in three hours under the same conditions. The combination of Pd with the base metals helps in retaining the Pd0 status by charge donation from the base metals to Pd, thus lowering the activation energy of the aryl halide oxidative addition step. Along with its exceptional activity, CuPd/SiO2 exhibits excellent recycling performance with a turnover frequency (TOF) of 280 000 h-1 under microwave reaction conditions at 60 °C. Our study demonstrates that SEA is an excellent synthetic strategy for depositing ultra-small Pd-based bimetallic nanoparticles on porous silica for SCC. This avenue not only provides highly active and sintering-resistant catalysts but also significantly lowers Pd contents in the catalysts without compromising catalytic activity, making the catalysts very practical for large-scale applications.

Valorisation of Fruits, their Juices and Residues into Valuable (Nano)materials for Applications in Chemical Catalysis and Environment

One of the most abundant wastes from all around the world is nutrient resources. Among them, fruits, their extracts, and residues comprise a major portion, which contain many valuable components that get lost during disposal or become burden on the shrinking landfills. These concerns are addressed by seeking sustainable processing methods that would have a minimal environmental impact. The crops contain renewable chemicals which are useful for catalysis, wastewater treatment, or preparation of nanomaterials; there has been an upsurge for the industrial applications of (nano)materials as their environmental and catalytic appliances is a fascinating subject to design cheaper and safer catalytic systems. Due to the excellent chemical properties of the fruit extracts, they have garnered attention as cost-effective catalysts and support materials. This review focuses on the preparation of (nano)materials and their catalytic and environmental applications and highlights the potential appliances and industrial benefits derived from these low-cost renewable and sustainable greener sources thus essentially converting waste into wealth.

Microwave-Assisted Synthesis of Pd Nanoparticles and Catalysis Application for Suzuki Coupling Reactions

A facile and efficient method was developed for the synthesis of highly active palladium nanoparticles (PdNPs) by microwave-assisted chemical reduction. The PdNPs with different morphology were prepared with or without KBr (capping agent) using ethylene glycol (EG) and citric acid (CA) as reducing agent in the presence of polyvinylpyrrolidone (PVP), respectively. The as-prepared PdNPs were characterized by (UV-Visible Spectrophotometer) UV-Vis, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The results showed that the PdNPs reduced by EG without KBr (PdNPs-EG) has smaller particle size than other PdNPs. The remarkable catalytic activity of the PdNPs catalysts are obtained using a low amount of PdNPs (0.1 mmol‰) using K2CO3 as base and EtOH/H2O as solvent toward Suzuki coupling reactions of aryl bromides and phenylboronic acid for 15 min.

A mechanistic study of cross-coupling reactions catalyzed by palladium nanoparticles supported on polyaniline nanofibers

Pd/PANI nanocomposites effect C–C coupling reactions mainly through a homogeneous mechanism.

Highly dispersed Pd nanoparticles supported on nitrogen-doped graphene with enhanced hydrogenation activity

Pd nanoparticles supported on nitrogen-doped graphene (NG) were prepared as hydrogenation catalysts.