Progress in Reaction Kinetics and Mechanism

The antioxidant properties of the synthesised 5-tert-butylbenzene-1,2,3-triol (system A) and the designed 3,5-di-tert-butylbenzene-1,2-diol (system B) have been explored through density functional theory at the M05-2X/6-31+G(d,p) level of theory. The quantum mechanics-based test for overall free radical scavenging activity (QM- ORSA) protocol has been employed to account for their radical-scavenging capacity against the hydroperoxyl radical (HOO•) in the gas phase and in toluene solvent as a mimic lipid medium. The different mechanisms of the chemical reactions of the studied systems with HOO• have been considered, namely (i) the hydrogen atom transfer (HAT), (ii) the single electron transfer followed by proton transfer and (iii) the radical adduct formation. Our calculations provide evidence that HAT is the most favoured reaction mechanism in both the gas phase and in lipid media and the calculated thermodynamic and kinetic parameters indicate that the designed compound is more efficient than the synthesised system A and the reference system (α-tocopherol).

BiVO₄/InVO₄ and BiVO₄/InVO₄/g-C₃N₄ were prepared by hydrothermal and ultrasonic-assisted hydrothermal methods respectively. All prepared samples were characterised by X-ray diffraction, scanning electron microscopy and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activity of the prepared catalysts was determined by degradation of Acid Blue 92 (AB92) under visible light. The rate constant and efficiency of AB92 degradation over BiVO₄/InVO₄/g-C₃N₄ was higher than that over BiVO₄/InVO₄ which indicates better photocatalytic activity of BiVO₄/InVO₄/g-C₃N₄. This enhancement can be attributed to the suitable dispersion of BiVO₄ and InVO₄ particles on the g-C₃N₄ surface. Furthermore, the conduction band and valence band edge potentials of InVO₄, BiVO₄ and g-C₃N₄ extend the life-time of electron–hole pairs which is beneficial for the improvement of photocatalytic efficiency.

The mechanism of action of nucleophilic and non-nucleophilic bases in the system “acetic acid (HOAc) – epichlorohydrin (ECH) – R₃X (R = alkyl, X = N, P)” has been studied. The observed orders of the reaction with respect to the components were found. It has been proved that the catalytic activity of the starting bases is determined by their nucleophilicity, rather than basicity. It is shown that the crucial stage of the reaction is the quaternisation of the starting base with the formation of a reactive intermediate, the acetate anion. Monitoring of possible paths of oxirane ring-opening by the initial base and the acetate anion was carried out. The behaviour of the model base, triphenylphosphine, in the quaternisation reaction was studied by UV spectroscopy. The rate constants of quaternisation in the reaction of tribenzylamine and triphenylphosphine with ECH have been estimated. The activation parameters of the stages of oxirane ring-opening by trimethylamine and the acetate anion were calculated using a quantum chemical method. It has been shown that the starting base attacks only the activated oxirane, while the acetate anion is capable of nucleophilic opening of both activated and non-activated ECH rings. A scheme for the catalytic opening of the oxirane ring by the bases in the system “ECH – HOAc – R₃X” is proposed, which includes a series of both consecutive and parallel stages leading to the formation of the reaction product.

In this work, SiO₂-supported Co–Rh bimetallic catalysts were prepared by adopting a method of impregnation and were used to catalyse the hydroformylation of dicyclopentadiene (DCPD) to diformyltricyclodecanes. Firstly, the hydroformylation of DCPD was carried out and three reaction stages were observed. In the first stage, a sharp decrease of reaction pressure was observed within 4 minutes. In the next stage, almost no reaction pressure decrease was detected over a relatively longer reaction time (70 minutes). In the final stage, the reaction pressure decreased at a relatively gentle rate, with barely any decrease of reaction pressure being observed at 460 minutes. Secondly, the hydroformylation of monoformyltricyclodecenes (MFTD) with various reaction times was carried out; the catalyst that was used at various reaction times was also recovered. Finally, the catalyst that had been used at various reaction times was characterised and analysed and the relationship between the catalytic performance and the structure of the catalysts was confirmed. In addition, combined with triphenylphosphine, the influence of pressure on the activity of Co–Rh bimetallic catalysts was investigated for the hydroformylation of MFTD.

Pseudo first-order rate constants, k _obs , for the alkaline hydrolysis of N-(o-aminophenyl) phthalimide, obtained at constant [CTABr]_T (total concentration of cetyltrimethylammonium bromide) and varying concentrations of inert salt MX (MX = sodium formate, sodium acetate, sodium propanoate, sodium butyrate, sodium valerate and sodium hexanoate) follow the relationship: k obs = ( k 0 + θ K X / S [ MX ] ) ( 1 + K X / S [ MX ] ) , where θ and K^X/S are empirical constants and S = HO^-. The values of K^X/S for each aliphatic acid decrease with an increase in [CTABr]_T. This relationship gives an empirical constant whose magnitude is the measure of the ability of an ion, X^-, to expel another counterion S^-, from the cationic micellar surface to the bulk aqueous phase. The values of the empirical constant, K^X/S, are used to derive the ion exchange constant, K^Br_X.

As bifunctional catalysts, metal-supported zeolites play an important role in refining and petrochemical processes, e.g. isomerisation, alkylation, etc. Reduction in acidity and acid strength of zeolites upon their impregnation with metals have been widely reported. Also hydrogen spillover vis-a-vis the closeness of two catalyst functions (acid and metal) has been discussed at length. Hydrogen spillover has been claimed to give rise to formation of additional acid sites on supports. Here quantification of acid sites for two zeolites, zeolite Y and ZSM-5, impregnated with different metals in various proportions after exposing them to hydrogen, has been attempted using ammonia temperature programmed desorption. The observed acidity values have been explained on the basis of metal cluster size.

Five types of 0.006 wt% Rh catalyst supported on the surfaces of Al₂O₃, ZnO, TiO₂(rutile), TiO₂(anatase) and CeO₂ were prepared by the incipient wetness method and used to catalyse the conversion of dicyclopentadiene (DCPD) to monoformyltricyclodecenes (MFTD). The 0.006 wt% Rh/ZnO catalyst showed the highest performance of the catalysts investigated and a 95.5% MFTD yield with 100% MFTD selectivity could be achieved. This suggested that there may be a key role for the carrier on the catalytic performance in the DCPD hydroformylation. Furthermore, the kinetic profiles for DCPD hydroformylation over the 0.006 wt% Rh/ZnO catalyst have been examined systematically to explore the effect of reaction temperature on the catalytic performance. These data collectively suggested that a specific reaction temperature might enhance DCPD hydroformylation, possibly owing to agglomeration of the active sites at higher reaction temperatures.

In this work, the sorptive removal assessment of methylene blue by spotted golden thistle stalks was enhanced. Sorption was positively impacted by increasing temperature, initial pH or ionic strength. The sorbent isoelectrical point is 2.6 according to zeta potential measurements. The Elovich and Avrami models best fitted the sorption kinetic data; and an original prediction of equilibrium time is proposed. At 25 °C and for optimal initial pH = 7, the experimental maximal sorption capacity is 75 mg g⁻¹. The Langmuir, Redlich–Peterson, Sips and Tóth models led to good correlations of isothermal data. Desorption percentages are important in both mineral and organic acidic media; the highest levels up to 91% were recorded for 1 × 10⁻² M HCl solutions. The pseudo second-order model fitted satisfactorily the desorption kinetics. An innovative concept of regeneration is proposed, which promises significant savings of eluent and operating time. The sorbent regeneration assessment showed constant uptake abilities after five cycles of use.

This study investigated the adsorption process of p-nitrophenol (p-NP) onto partially reduced graphene oxide (prGO) using both experiment and theoretical calculations. The maximum adsorption capacity of prGO at pH 6.0 and 293 K for p-NP was 29.94 mg g⁻¹ which was significantly higher than previously reported using a metal-doped reduced graphene oxide composite. Systematic, comparative theoretical calculations were used to investigate the adsorption mechanism of p-NP onto graphene oxide, prGO and graphene nanosheet (GN). Calculations revealed three types of adsorption site and indicated that the adsorption force and sites were significantly affected by the quantity and type of oxygen-containing functional groups on the GN. The adsorption affinity was mainly derived from hydrogen bonds and π-π stacking which was further demonstrated by FTIR analysis. Due to its excellent adsorption performance, good recyclability and easy separation, prGO can be a promising adsorbent for the efficient elimination of p-NP from wastewater in the future.