Kinetic Analysis of 4-Nitrophenol Reduction by “Water-Soluble” Palladium Nanoparticles

Abstract

The most important model catalytic reaction to test the catalytic activity of metal nanoparticles is the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride as it can be precisely monitored by UV–vis spectroscopy with high accuracy. This work presents the catalytic reduction of 4-nitrophenol (4-Nip) to 4-aminophenol (4-Amp) in the presence of Pd nanoparticles and sodium borohydride as reductants in water. We first evaluate the kinetics using classical pseudo first-order kinetics. We report the effects of different initial 4-Nip and NaBH4 concentrations, reaction temperatures, and mass of Pd nanoparticles used for catalytic reduction. The thermodynamic parameters (activation energy, enthalpy, and entropy) were also determined. Results show that the kinetics are highly dependent on the reactant ratio and that pseudo first-order simplification is not always fit to describe the kinetics of the reaction. Assuming that all steps of this reaction proceed only on the surface of Pd nanoparticles, we applied a Langmuir−Hinshelwood model to describe the kinetics of the reaction. Experimental data of the decay rate of 4-nitrophenol were successfully fitted to the theoretical values obtained from the Langmuir–Hinshelwood model and all thermodynamic parameters, the true rate constant k, as well as the adsorption constants of 4-Nip, and BH4− (K4-Nip and KBH4−) were determined for each temperature.

Flow-Through PolyHIPE Silver-Based Catalytic Reactor

“…The reaction was described with the Langmuir–Hinshelwood mechanism [ 57 , 58 ]. However, the reaction can be relatively accurately described as an irreversible equimolar reaction between 4-NP and NaBH 4 to 4-AP [ 61 ]: …”

“…As the NaBH 4 concentration was in high excess [ 61 ], a solution with high pH was used [ 56 ], and oxygen was removed [ 59 , 60 ]; therefore, Equation (1) can be further simplified into pseudo-first-order reaction kinetics with an apparent rate constant [ 56 ]: for a continuous tubular reactor ( Figure 6 ), resulting in the following expression: where k’ is the apparent rate pseudo-first-order rate constant [min −1 ], k cat ’ is the apparent rate pseudo-first-order catalytic rate constant [min −1 g −1 ], A in / A out and C in / C out are the absorbance and concentration ratios of 4-NP at the inlet and outlet of the column with subtracted baseline (solution without 4-NP), F is the flow rate, V c is the column volume, ε is the column porosity, and t r is the residence time.…”

Cu/CuO Composite Track-Etched Membranes for Catalytic Decomposition of Nitrophenols and Removal of As(III)

“…The reduction of nitroaromatic compounds proceeds according to the Langmuir-Hinshelwood mechanism and was detailed in [69,[78][79][80][81]. According to this mechanism, hydrogenation of nitrobenzene and its derivatives takes place through two main stages [82]. In the first stage, borohydride and nitrophenolate ions in aqueous solution are reported to be adsorbed onto the nanocatalyst surface [83].…”

Silk Polymers and Nanoparticles: A Powerful Combination for the Design of Versatile Biomaterials

“…On the other hand palladium NPs are used as catalyzers mainly in C-C coupling reactions (Suzuki–Miyaura, Sonogashira and Mizoroki-Heck reactions), reduction of nitroarenes, hydrogenation of alkenes and alkynes, and oxidation of primary alcohols (Saldan et al, 2015 ). Both metal NPs have been used as well for depollution applications (Iben Ayad et al, 2020 ), photothermal treatments (Samadi et al, 2018 ; Yang et al, 2019 ) and as antibacterial/antifungal agents (Dumas and Couvreur, 2015 ; Pedone et al, 2017 ).…”