Reactions, Volume 3, Issue 4 (December 2022) – 11 articles

This study focuses on the synthetic approach influence in morphostructural features and catalytic performances for Ni/CeO₂ catalysts. Incipient wetness impregnation, coprecipitation and nitrate combustion were studied as catalyst preparation approaches, and the materials were then tested at 700 °C for methane dry reforming (MDR). The morphostructural properties of the materials were deeply studied using several techniques, such as temperature programmed reduction (TPR), to investigate reducibility and support-metal interaction, N₂ physisorption to evaluate the porosity and the surface area, scanning electron microscopy (SEM) and X-ray diffraction (XRD) to estimate Ni dispersion, and temperature programmed oxidation (TPO) to identify the type and amount of coke formed on catalysts’ surface after reaction. From the data obtained, coprecipitation turned out to be the most suitable technique for this application because this catalyst was able to reach 70% of CO₂ conversion and 30% methane conversion, with an H₂ yield of 15% and 30% yield of CO at the end of the 30 h test. Moreover, it was also the catalyst with the highest metal dispersion, the strongest interaction with the support, and the lowest coke deposition. Full article

A new three-component condensation of β-ketonitriles, 4-fluorobenzaldehyde, and secondary cyclic amines was developed. A possible reaction mechanism has been proposed including Knoevenagel condensation followed by aromatic nucleophilic substitution. It was found that in the case of 3-oxopropanenitrile bearing the 6-amino-1,3-dimethyluracil moiety, the reaction is not accompanied by fluorine substitution in the Knoevenagel adduct, and the Michael addition of a secondary amine occurs followed by oxidation. Full article

A systematic study of the Diels–Alder reaction of α-nitrocinnamate was performed. The reaction of p-substituted α-nitrocinnamate with 2,3-dimethyl-1,3-butadienes smoothly proceeded regardless of the p-substituent, which was either an electron-donating or -withdrawing group. A control reaction revealed that α-nitrocinnamate isomerized during the reaction. Danishefsly’s diene (1-methoxy-3-trimethylsiloxy-1,3-butadiene) facilitated cycloaddition under mild conditions to afford a cycloadduct without the alternation of the diastereomeric ratio. Moreover, the desilylation of the cycloadduct furnished multiple functionalized cyclohexanones. Full article

Anisole is a straw-colored aromatic compound mainly used in making solvents, flavoring agents, perfumes, fuel additives, and in the synthesis industries. Anisole, also known as methoxybenzene, is synthesized from sodium phenoxide or phenol using various methylating agents. The use of dimethyl ether (DME) as an alkylating agent is seldom reported in the literature. Herein, we have synthesized anisole through the O-alkylation process of phenol and DME to obtain zero discharge from this process. The thermodynamic equilibrium for the reaction of phenol and DME is simulated by using Aspen HYSYS (Hyprotech and Systems). The O-alkylation of phenol has been investigated using phosphotungstic acid (PTA) over γ-Al₂O₃ with appropriate acidity. Active metal loadings of various percentages were studied and the conversion was optimized at 46.57% with a selectivity of 88.22% at a temperature of 280 °C. The liquid products from the continuously stirred reactor were analyzed with liquid G.C. and the conversion and selectivity were calculated. A comparison of the O-alkylation and C-alkylation of phenol at different temperatures, reactant ratios, residence times, and recyclability was explored, as well as the impact of these factors on the yield of the desired anisole. The catalyst was characterized by XRD, BET, HR-TEM, FE-SEM, elemental mapping, XPS, and DRIFT studies. Full article

Studies of the processes of the hydrolytic oxidation of disaccharides are the first step towards the development of technologies for the direct conversion of plant polysaccharides, primarily cellulose, into aldonic and aldaric acids, which are widely used in chemical synthesis and various industries. In this study, heterogeneous catalysts based on a porous matrix of hypercrosslinked polystyrene (HPS) and noble metals (Pt, Au, Ru, and Pd) were proposed for the hydrolytic oxidation of cellobiose to gluconic and glucaric acids. The catalysts were characterized using low-temperature nitrogen adsorption, hydrogen chemisorption, electron microscopy, and other methods. In particular, it was shown that the Pt-containing catalyst contained, on average, six times more active centers on the surface, which made it more promising for use in this reaction. At a temperature of 145 °C, an O₂ pressure of 5 bars, and a substrate/catalyst weight ratio of 4/1, the yields of gluconic and glucaric acids reached 21.6 and 63.4%, respectively. Based on the data obtained, the mathematical model of the cellobiose hydrolytic oxidation kinetics in the presence of 3% Pt/HPS MN270 was developed, and the parameter estimation was carried out. The formal description of the kinetics of cellobiose hydrolytic oxidation was obtained. Full article

A method is presented to study the decomposition of urea deposited on Cu/HZSM-5 SCR catalysts and therewith the ability of the Cu/HZSM-5 SCR catalyst to be regenerated when being overdosed with SCR urea fluids during operation. This straightforward laboratory method could speed up calibration of exhaust gas aftertreatment systems. As an example, the removal of adsorbed urea to the SCR substrate due to dosage malfunction is studied. To study the removal of adsorbed urea on the catalyst substrate, FTIR experiments have been conducted to investigate the state of the catalyst. Besides Cu/HZSM-5 also HZSM-5 and CuOx were studied as model compounds to provide more inside on the processes occurring at the Cu/HZSM-5 surface upon urea decomposition. To simulate exposure of the SCR catalyst to overdosing of the urea solution, samples were impregnated with a 32 wt% urea solution, which correlates to that of commercial heavy duty diesel urea solutions. After impregnation, the samples were heated at various temperatures in the 133–400 °C temperature region, typically the operation window of a SCR catalyst. After heating, the samples were cooled to room temperature and measured in FTIR. The obtained spectra were compared with various literature reports to correlate the observed absorption bands to urea, urea related compounds and decomposition compounds. The concentration of these adsorbed species decreases at increased thermolysis temperature and is no longer visible at temperatures >250 °C. Extended heat treatment at 200 °C revealed only minor loss of adsorbents after 6 h and were still observable in the FTIR spectra after 24 h. Urea derived adsorbents were completely removed when simulating catalyst regeneration under SCR operation conditions under continuous air flow with a humidity of 10% and at elevated temperatures (400 °C). Full article

Bio-oils produced from three different biomass sources, namely cork, pinewood, and olive stones, are evaluated concerning their suitability and prospects of including their electrochemical transformations in a biorefinery scenario for the production of added-value compounds. Different types and concentrations of electrolytes (e.g., H₂SO₄, KOH) are added to the bio-oils to increase the samples’ initially low ionic conductivity. The samples prepared by mixing bio-oil with 2 M KOH aqueous solution (50 vol.%) lead to a stable and homogeneous bio-oil alkaline emulsion suitable for electrochemical studies. The bio-oil samples are characterized by physicochemical methods (e.g., density, viscosity, conductivity), followed by analyzing their electrochemical behavior by voltammetric and chronoamperometric studies. The organics electrooxidation and the hydrogen evolution reaction in the bio-oils are assessed using Pt electrodes. Single- and two-compartment cell laboratory bio-oil electrolyzers are assembled using nickel plate electrodes. Electrolysis is carried out at 2.5 V for 24 h. Attenuated Total Reflection-Fourier-Transform Infrared Spectroscopy and Mass Spectrometry are applied to identify possible changes in the bio-oil samples’ chemical structure during the electrolysis experiments. Comparing the analyses of the bio-oil samples subjected to electrolysis with the blank samples demonstrates that bulk electrolysis significantly changes the bio-oil composition. The bio-oil obtained from cork biomass shows the most promising results, but further studies are required to understand the nature of the actual changes. Full article

Alkene epoxidation with TBHP as an oxidising reagent using heterogeneous Mo(VI) catalyst is an environmentally friendly process since it eliminates acid waste and chlorinated by-products often associated with the conventional industrial method that uses stoichiometric peracid such as peracetic acid and m-chloroperbenzoic acid. Polybenzimidazole supported Mo(VI) complex, i.e., PBI.Mo has been successfully prepared, characterised and assessed for the epoxidation of 1,5-hexadiene in the presence of tert-butyl hydroperoxide (TBHP) as an oxidising reagent. A quadratic polynomial model has been developed, demonstrating the yield of 1,2-epoxy-5-hexene in four independent variables. The effects of different parameters such as reaction temperature, feed mole ratio of 1,5-hexadiene to TBHP, catalyst loading, and reaction time were studied. Response surface methodology (RSM) using Box-Behnken Design (BBD) was employed to study the interaction effect of different variables on the reaction response. This study presents the optimization of 1,5-hexadiene epoxidation in a batch reactor using TBHP as an oxidant and a polymer-supported Mo(VI) catalyst. Full article

Continuous flow calorimeters are a promising tool in process development and safety engineering, particularly for flow chemistry applications. An isoperibolic flow calorimeter is presented for the characterization of exothermic reactions. The calorimeter is adapted to commercially available plate microreactors made of glass and uses Seebeck elements to quantify the heat of reaction. For automation of calibration procedures and calorimetric measurements, the device is connected to a lab automation system. Reaction enthalpy of exothermic reactions is determined via an energy balance of the entire calorimeter. Characterization of reaction kinetics is carried out via a local balancing of the individual Seebeck elements without changing the experimental setup, while using the previous measurements and additional ones at higher flow rates. The calorimeter and the associated measurement procedures were tested with the oxidation of sodium thiosulfate using hydrogen peroxide. Reaction enthalpy was determined to be 594.3 ± 0.7 kJ mol⁻¹, which is within the range of literature values. Full article

A simple, metal-free, cost-effective, and eco-friendly protocol for the preparation of trisubstituted 1,3,5 triazine from metformin using benzotriazole chemistry is reported. Short reaction time, large-scale synthesis, easy and quick isolation of the product, and excellent yield are the main advantages of this procedure. Furthermore, the use of benzotriazole chemistry results in a product free from metal traces. Our optimized reaction condition and methodology overcome the challenges of using a metal catalyst, such as a longer reaction time, lower yields, and expensive starting materials. Full article

Liquid organic hydrogen carriers (LOHCs) are an interesting alternative for hydrogen storage as the method is based on the reversibility of hydrogenation and dehydrogenation reactions to produce liquid and safe components at room temperature. As hydrogen storage involves a large amount of hydrogen and pure compounds, the design of a three-phase reactor requires the study of gas and liquid-phase kinetics. The gas-phase hydrogenation kinetics of LOHC γ-butyrolactone/1,4-butanediol on a copper-zinc catalyst are investigated here. The experiments were performed with data, taken from the literature, in the temperature and pressure ranges 200–240 °C and 25–35 bar, respectively, for a H₂/γ-butyrolactone molar ratio at the reactor inlet of about 90. The best kinetic law takes into account the thermodynamic chemical equilibrium, is based on the associative hydrogen adsorption and is able to simulate temperature and pressure effects. For this model, the confidence intervals are at most 28% for the pre-exponential factors and 4% for the activation energies. Finally, this model will be included in a larger reactor model in order to evaluate the selectivity of the reactions, which may differ depending on whether the reaction takes place in the liquid or gas phase. Full article