Reactions, Volume 7, Issue 1 (March 2026) – 21 articles

This work presents the synthesis, characterization, and application of zirconium oxide (ZrO₂)-based catalysts, modified with macro (silica nanospheres, NSP-SiO₂) and mesopore templates (Pluronic 123), impregnated with tungstophosphoric acid (TPA), in the catalytic pyrolysis of tomato agro-industrial residues. The NSP-SiO₂ (SXX) and P123 (PYY) amount mainly influences the ZrO₂SXXPYY-specific surface area (S_BET) and average pore diameter (D_p). ³¹P MAS NMR and FT-IR characterization results show that TPA (H₃PW₁₂O₄₀) was partially transformed into [P₂W₂₁O₇₁]⁶⁻ and [PW₁₁O₃₉]⁷⁻ during the synthesis steps. The acidic properties of ZrO₂SXXPYY samples containing 25 and 50 wt% of TPA (ZrO₂SXXPYYT25 and ZrO₂SXXPYYT50, respectively) are dependent on both the TPA content and the support nature. Bio-oil composition and product selectivity were strongly influenced by the textural and acid-based properties of the catalysts. Notably, non-catalytic pyrolysis favored pathways leading to C2 compounds, with a high content of acetic acid and hydroxyacetone. In contrast, the use of catalysts promoted the formation of higher molecular weight oxygenated compounds (C5–C6), specifically furans, aldehydes, and ketones. Full article

Linear alkylbenzene (LAB) is the main raw material used to make biodegradable detergents, and its production process is based on aromatic alkylation. HY zeolites that have undergone controlled dealumination and desilication have led industrial standards amongst solid acid catalysts because of their controllable acidity and hierarchical pore structure. Coke formation in such systems can assume a dual role, which is dependent on its condition. Though the over-deposition is known to cause deactivation by blocking the micropores, Bronsted acid-site masking, and diffusion collapse, the low-level deposition could also be done to increase the monoalkylate selectivity by the pore mouth catalysis, steric modulation, and selective suppression of secondary alkylation pathways. The critical review is done on the structural-kinetic interaction that determines the coke evolution in HY-based catalysts. In order to moderate the acid-site density and enhance hydrothermal stability, dealumination (Si/Al optimization of about 2.5 to 30–100) occurs, but to reduce deep-pore coke formation, desilication (interconnected mesopores) is created. The bimodal porosity and regulated acidity are found to be synergistic, as hierarchical HY zeolites produced through successive cycles of steam and alkaline treatments not only show LAB selectivity in excess of 90% but also exhibit much longer catalyst lifetimes. Quantitative research on the beneficial coke regime revealed that it was composed of about 36 wt% hydrogen-rich species, which were localized at the pore mouths, hence enhancing monoalkylation selectivity by 15–40%. Beyond a critical transition window (e.g., 8–12 wt.%), coke formation to condensed polyaromatic and graphitic products leads to fast deactivated coke formation, which is due to percolation limits and transport-controlled kinetics. More advanced techniques of characterization of the coke, e.g., temperature-programmed oxidation (TPO), ²⁷Al MAAS NMR, and UV-Raman spectroscopy, indicate how the coke is changed to highly structured graphitic deposits of high oxidation activation energy. Activity recovery of 85–98% is obtained in regeneration processes, including controlled oxidative calcination, microwave-based and plasma-based processes, and thermal management protocols, and it would be determined by the chemistry of the coke, its spatial distribution, and the regeneration protocols. This paper has developed a mechanistic coke control system by cross-tuning the acidity and development of an effective pore network, which led to a sustainable aromatic alkylation reaction with minimal activity loss, high selectivity, and long life. Full article

Rhizopus oryzae lipase (ROL) is a key enzyme involved in olive oil spoilage and acts as a virulence factor in fungal infections. Natural lipophilic lipase inhibitors are crucial for mitigating economic losses resulting from lipid degradation in stored or decaying olive fruits. This study evaluated a series of enzymatically synthesized piperate esters with varying alkyl chain lengths (butyryl, C4; octyl, C8; dodecyl, C12) for their inhibitory effects on ROL activity. Octyl piperate (C8) demonstrated the highest potency, with IC₅₀ values of 0.05 mg/mL using methods B and C or 0.25 mg/mL using method A. Molecular docking indicated that C8 achieved the most favorable predicted binding energy (Gscore: –11.134 kcal/mol), primarily through hydrophobic interactions (Val329, Ala212, Phe209) and hydrogen bonds with oxyanion hole residues (Ser268, Thr206, Gln241). Molecular dynamics simulations confirmed that C8 maintained stable binding and stabilized the catalytic residues. In comparison, C4 exhibited weaker interactions, and the longer C12 chain induced conformational instability and steric hindrance. These results establish a parabolic structure–activity relationship, identifying the octyl chain (C8) as optimal for ROL inhibition among the tested derivatives. The rational design of lipophilic, biodegradable lipase inhibitors thus positions octyl piperate as a promising candidate for extending olive storage and shelf life, and as a scaffold for developing natural antifungal agents targeting virulent R. oryzae strains. Full article

Hydrodynamic cavitation (HC) is an efficient technique for biodiesel production. The main contribution of this study is the development of a modular reactor with a universal stainless steel joint, whose design facilitates the installation, replacement, and maintenance of the orifice plate by eliminating flanges and bolts during assembly. Using this reactor, the study evaluated the synergistic interaction between feed pressure and methanol:oil molar ratio in the transesterification of soybean oil, employing a 3² factorial design. The orifice plate was 3 mm thick and had 19 holes with a diameter of 1.0 mm, installed downstream of the pump. The process was carried out for 45 min, using NaOH at 1 wt% relative to the oil and at 60 ± 5 °C. Feed pressures of 1.72, 2.41, and 3.10 bar and methanol:oil molar ratios of 6:1, 8:1, and 10:1 were evaluated, reaching a maximum yield of 92.98% at 3.10 bar and 8:1. Analysis of variance (ANOVA) confirmed a significant interaction (p < 0.0001) and allowed a second-order polynomial model to be fitted (R² = 0.9981). In contrast, conventional mechanical agitation required 90 min to achieve 95% yield. The biodiesel produced met most American Society for Testing and Materials (ASTM) D6751 requirements, confirming the potential of HC as a viable alternative for intensifying biodiesel production. Full article

Ethanol is widely used as an additive in fuels, so its effect on the electrochemical oxidation of triethanolamine was investigated on a 25 μm platinum microelectrode. Ethyl acetate was applied as a cosolvent to increase the permittivity of the medium. A hydrocarbon n-heptane, typically present in gasohol samples as the main component, was studied, and its solutions prepared with ethanol in the entire concentration range (between 0 and 100 v/v% ethanol contents) were mixed with ethyl acetate. The as-prepared liquid mixtures were prepared separately, and they were mixed with ethyl acetate in uniform ratios. Triethanolamine, the selected redox-active compound, exhibited a sharp peak in ethyl acetate at the 15 mM concentration. The changes in the voltammograms served as a good template for quantitative analysis of ethanol content. The most suitable analytical signal used for it was the current minimum after the anodic peak, and this parameter proved more sensitive and reproducible than the anodic peak height itself. The scatterings of the current minimum values were typically within some nanoamperes. MTBE (methyl tert-butyl ether) was added to the apolar mixtures of ethanol, and this ether had a negligible interfering effect on the estimation of ethanol content. Full article

Magnesium-sulfur (Mg-S) batteries present a compelling energy storage solution, characterised by their remarkable theoretical energy density and economic viability. Nonetheless, challenges arise, including swift capacity degradation and suboptimal polysulfide (acting as an electronic and ionic insulator) utilisation, mainly due to a phenomenon known as the polysulfide “shuttle effect.” This effect also leads to a decline in battery performance. The Becke, 3-parameter, Lee-Yang-Parr (B3LYP) functional and 6-311G (d,p) basis set were used to examine the optoelectronic and charge-transfer properties of a polyaniline-pyrrole (PANIPyr) composite, emphasising interatomic and electronic interactions that enhance charge transport and oxidation of MgS₂. The findings demonstrate the presence of coordination bonding between hydrogen in pyrrole and the N⁻ ion in quinonediimine of polyaniline, significantly enhancing the electrical properties of PANI. The PANIPyr_P1 (P1-pyrrole attached at position one) configuration exhibits the lowest Ɛ_gap and the highest charge-transfer capacity, compared to other studied molecules in this work, thereby improving reactivity towards polysulfides in comparison to pure PANI. Significant electrical interactions at this site establish accessible electrophilic and nucleophilic regions that stabilise the ionic sides of the polysulfides, thus reducing the shuttle effect and improving charge transport at the interface. PANIPyr_P1 demonstrates viability for minimising polysulfide migration and enhancing cathodic efficiency in Mg-S batteries, thereby laying a foundation for future investigations into polymer-based cathode modifiers. Full article

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are two processes that occur during the operation of the cathodic electrode in Zn–Air batteries, which enable the integration of alternative energy sources into electrical energy distribution systems. Transition metal oxides, such as perovskites based on LaNiO₃, are promising electrocatalysts for the ORR and OER in alkaline medium due to their versatile structure, allowing for the substitution of certain atoms with dopants, which enhances the catalytic activity for both reactions. This work reports an electrochemical study of the catalytic activity toward ORR and OER of perovskite catalysts (LaNiO3 doped with transition metals (Fe, Mn, or Pd)) in the presence of carbon-based materials as supports (multiwalled carbon nanotubes (MWCNT), graphene oxide nanosheets (GO), and graphitic carbon (C)). The results revealed interesting catalytic properties in both reactions, particularly La(Ni_0.9Pd_0.1)O₃/MWCNT, which showed an ORR activation potential of 0.87 V vs. RHE, comparable to that of the commercial Pt/C catalyst (0.99 V vs. RHE), while the overpotential for OER was lower than that of the Pt/C catalyst (1.68 V vs. RHE for La(Ni_0.9Pd_0.1)O₃/MWCNT and 1.79 V vs. RHE for the commercial Pt/C). Full article

Guanidines are structurally unique, highly basic, nitrogen-containing organic compounds with strong hydrogen-bonding ability and biological activity, providing valuable functionality in medicinal chemistry, organocatalysis, and materials science. Among modern strategies for assembling guanidine-containing molecules, cycloaddition reactions have emerged as powerful tools due to their efficiency, stereoselectivity, and ability to rapidly build molecular complexity. Recent innovations have expanded cycloaddition methodologies for generating guanidine functionalities, incorporating guanidine-containing substrates, and using guanidine-based catalysts. This review summarizes these advances and highlights the current trends in guanidine-related cycloaddition chemistry. Full article

This study systematically investigates the role of Ni in Co₂SiO₄ in a bimetallic (Co²⁺,Ni²⁺)₂SiO₄ olivine-type system and the materials’ catalytic efficiency in a model Heck–Mizoroki coupling reaction. Thus, a series of olivines with varying (Co²⁺,Ni²⁺)₂SiO₄ compositions (0–100% Ni) was synthesised and characterised by ICP-OES, FTIR/Raman, P-XRD and XPS analysis. Ideal mixing of metals was achieved with (49:51) Co:Ni. Catalytic testing revealed distinct conversion vs. time profiles, with the (69:31) Co:Ni olivine exhibiting the best overall performance, combining good reactivity with near-perfect selectivity (>99%) and improved stability. Mechanistic pathways were probed through product scope analysis, reactant–product temporal profiling, leaching and radical scavenging experiments. Results suggest a radical-assisted Heck–Mizoroki mechanism. Spectroscopic data correlated Co²⁺ and Ni²⁺ incorporation with M1 and M2 site occupancy, where Ni²⁺ M2 sites enhanced reactant activation and intermediate stability and Co²⁺ in the M1 site enhanced product release, though also homocoupling in Co₂SiO₄. Minimal leaching was observed for all bimetallic catalysts. These findings highlight the tunability of bimetallic olivines for C–C coupling reactions via controlled cation distribution. Full article

The cycloaddition reaction is one of the most common reactions in organic chemistry. It has been applied in various fields. Herein, we focus on the application of cycloaddition reactions in investigating biological molecules and materials using magnetic resonance techniques. To facilitate magnetic resonance studies such as electron paramagnetic resonance (EPR) spectroscopy and paramagnetic nuclear magnetic resonance (NMR) spectroscopy, there is often a requirement to attach spin labels and paramagnetic tags to the system of interest. The cycloaddition reaction is one of the ways to tether these spin labels and paramagnetic tags. In this review, we highlight the applications of various cycloaddition reactions such as the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction, the strain-promoted azide–alkyne cycloaddition (SPAAC) reaction and the Diels–Alder reaction in the interdisciplinary field of magnetic resonance studies of biomolecules, including proteins, nucleic acids, carbohydrates, lipids and glycans, as well as materials. Full article

Fumaric acid is one of the most important bio-based chemicals, with applications in the food, feed, polymer, pulp, and pharmaceutical industries. To overcome the limitations of the current petrochemical production process, alternative methods are being developed. Biotechnological production using wild-type fungi like Rhizopus sp. is a promising alternative. In this study, apple pomace was used as a carbohydrate source for fumaric acid production using Rhizopus arrhizus NRRL 1526. Our focus was on the use of free, non-structurally bound carbohydrates present in high amounts in apple pomace originating from direct apple juice processing. Three processes were compared: pressing, extraction, and a combination of both. Two cultivation strategies were applied: pre-culture and separate upstream biomass production. Using the pre-culture approach, a fumaric acid titer of 68.3 g/L was achieved with a yield of 0.53 g/g and a productivity of 0.29 g/(L·h) from synthetic apple pomace juice. Separate biomass production enabled growth-decoupled fumaric acid production, yielding 50.2 g/L and 79.3 g/L with yields of 0.82 g/g and 0.54 g/g and productivities of 0.17 g/(L·h) and 0.27 g/(L·h) from synthetic and real apple pomace juice, respectively. Thus, the efficient use of apple pomace for the fermentative production of fumaric acid is shown. Full article

The stability of perovskite materials in humid conditions significantly hinders their practical deployment. This study employed ab initio molecular dynamics (AIMD) simulations based on the Car–Parrinello approach to elucidate the adsorption mechanisms within two systems: CH₃NH₃PbI₃-15O₂-2H₂O and CH₃NH₃PbI₃-15O₂-5H₂O. The findings indicate that in the system with a higher water content (5H₂O), the degradation of the perovskite skeleton is more severe. Additionally, the adsorption energy of oxygen molecules significantly increases, along with more pronounced charge transfer between the oxygen and the perovskite material. The study also reveals that although water molecules contribute to the damage of the perovskite skeleton, oxygen molecules are the primary culprits. These insights not only clarify the specific impacts of various components in a mixed-gas environment on perovskite stability but also provide an essential theoretical basis for future modifications and optimizations of perovskite materials. Full article

Exploring effective oxygen reduction reaction (ORR) electrocatalysts is essential for advancing solid-state alkaline zinc–air batteries (ZABs). This paper presents the synthesis of silver–manganese dioxide–carbon nanotubes (SMC) ternary composites as an electrocatalyst for air electrodes, achieved through one-step pyrolysis of silver permanganate under microwave irradiation. Characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersion spectrometer (EDS) consistently confirmed the composition of SMC, comprising silver and alpha-manganese dioxide anchored on the surface of carbon nanotubes (CNTs). Electrochemical tests including polarization and chronoamperometry curves demonstrated the superior electrocatalytic activity of SMC for ORR compared to chemically produced electrocatalysts in alkaline conditions. Furthermore, the performance of a solid-state zinc–air cell with SMC as the electrocatalyst was evaluated, showing a long discharge voltage plateau and a capacity of 60.03 mAh at 30 mA·cm⁻². The study also delves into the mechanism behind the enhanced electrocatalytic activity, concluding that the strategy and electrocatalyst developed in this research offer a promising approach for creating efficient oxygen reduction catalysts for solid-state zinc–air batteries. Full article

In this study, the response surface method (RSM) was used to determine the best reaction conditions for the gas-phase hydrogenation of carbon dioxide on a commercial nickel-based catalyst. The RSM was applied in our previous study to find the optimal conditions for the same process carried out in laboratory-scale tubular reactors. The main benefits observed were fast detection of optimal conditions and the high precision of the optimum detected (which was experimentally confirmed). These advantages were due to the small number of experiments conducted and the simplicity of the models employed; only linear and quadratic models were developed. The successful result encouraged us to carry out experiments in a larger-scale reactor—an intermediate between a laboratory plant and a pilot plant. This approach helped us to fix some problems resulting from the larger scale of the process conducted. Despite the difficulties described in the main part of this article, we can recommend using the RSM as a tool for supporting experimentation and substantially speeding up the analysis of results and their introduction into practice. At the process scale considered, maximum carbon dioxide conversion was obtained at a temperature of 354 °C and a ratio of molar fluxes of H₂ to CO₂ equal to 3.9. It should be emphasized that this result was confirmed experimentally. Full article

Black liquor, the side stream from Kraft pulping, is a promising feedstock for the production of renewable fuels via hydrothermal liquefaction (HTL). However, further upgrading of the black liquor HTL oil is required to reduce the oxygen content for fuel use. In this work, the hydrodeoxygenation (HDO) of black liquor HTL oil model compounds was investigated to enhance the understanding of catalyst activity and selectivity under hydrothermal conditions. The study focused on isoeugenol and 4-methylcatechol as model compounds, representing different functionalities in black liquor-derived HTL-oil. Sulfided NiMo catalysts supported on titania, zirconia, activated carbon, and α-alumina were evaluated in batch mode at subcritical and supercritical upgrading using hydrogen gas. The results show that isoeugenol was fully converted in all experiments, while 4-methylcatechol conversion varied depending on the catalyst and reaction conditions. Phenols were obtained as the main products and the maximum degree of deoxygenation achieved was around 40%. This research provides insights into the potential of hydrothermal HDO for upgrading BL-derived biocrudes, emphasising the importance of catalyst selection and reaction conditions in hydrothermal conditions. Full article

The Sakurai reaction constitutes a valuable tool for carbon–carbon bond formation. The use of nontoxic allylic reagents as well as the atom economy of the global process has prompted the development of enantioselective (aza)-variants based on the use of chiral organo- and metal catalysts. This review collects the recent developments in catalytic enantioselective Sakurai reactions published since the beginning of 2011, including methodologies based on the use of chiral organocatalysts, metal/boron catalysts and multicatalyst systems. It is divided into three parts, dealing successively with enantioselective organocatalytic (aza)-Sakurai reactions, enantioselective metal/boron-catalyzed Sakurai reactions and enantioselective multicatalyzed (aza)-Sakurai reactions. It shows that, although still widely developed with aromatic aldehydes, the enantioselective catalytic Sakurai reaction has considerably matured in the last decade. Full article

Titanium oxide (TiO₂) is of great interest in solar cell manufacturing, hydrogen production, and organic compound photodegradation. The synthesis variables and methodology affect the morphology, texture, crystalline structure, and phase mixtures of TiO₂, which, in turn, affect the optical and catalytic properties of TiO₂. In this work, the effect of acetic acid as a catalyst and chelating agent on the morphology, texture, crystal structure, optical properties, and photocatalytic activity of TiO₂ samples obtained using the sol–gel method with sodium dodecyl sulfate (SDS) as a template was investigated. The results indicated that acetic acid not only catalyzes the hydrolysis of the TiO₂ precursor but also acts as a chelating agent, causing a decrease in crystallite size from 18.643 nm (T7 sample, pH = 6.8, without addition of acetic acid) to 16.536 nm (T2 sample, pH = 2). At pH 2 and 3, only the anatase phase was formed (T2 and T3 samples), whereas at pH 5 and 6.8, in addition to the anatase phase, the brookite phase (11.4% and 15.61% for samples T5 and T7, respectively) was formed. The band-gap value of TiO₂ decreased with decreasing pH during synthesis. Although the T2 sample had the highest specific surface area and pore volume (232.02 m²g⁻¹ and 0.46 gcm⁻³, respectively), the T3 sample had better efficiency in methylene blue dye photodegradation because its bird-nest-like morphology improved photon absorption, promoting better photocatalytic performance. Full article

Nitramines are nitrogen-containing organic compounds with the formula R¹R²N–NO₂. They are well-known as explosives and have been produced industrially for more than a century. A few nitramine-containing natural products have also been identified in recent years. Nitramines have also found their way into specific synthetic procedures, usually as intermediates, and for the last decades, the implementation of amine-based carbon capture and storage (CCS) technologies to mitigate CO₂ emissions from fossil fuel combustion is of particular concern since small amounts are produced. Both environmental and health implications are of particular interest, and little is known today. The need for efficient and safe synthetic procedures is, therefore, vital for further research in the field. The present review gives a detailed summary of published methods and research post-millennium. Many new as well as well-established methods are presented. Representative examples with basic conditions and yields are given. Finally, indications for future research are discussed. Full article

The Kabachnik–Fields (KF) reaction is a versatile three-component method for the condensation of amines, carbonyl compounds, and P–H reagents, enabling efficient synthesis of α-aminophosphonates—key bioactive and functional molecules. This review critically examines the literature from the last 25 years. However, with regard to mechanistic aspects, selected earlier seminal studies are also considered when necessary to provide a coherent and comprehensive mechanistic framework. Advances in catalyst-free methodologies, sustainable synthetic approaches, and Lewis and Brønsted acid catalysis are discussed, alongside developments in enantioselective KF reactions in the presence of chiral metal complexes or organocatalysts. Full article

As the energy structure evolves, low-load operation of coal-fired boilers is becoming common, posing challenges to combustion stability. This study explored the co-combustion of brown gas (HHO) with bituminous coal and anthracite in a one-dimensional furnace. Results indicate that introducing HHO significantly elevated combustion temperatures, with maximum increases of 158 °C and 207 °C, respectively. In the premixed mode, the flame front shifted upstream, indicating advanced ignition timing. Moreover, HHO co-combustion notably enhanced the combustion stability of anthracite, as reflected in stabilized furnace temperatures. With increasing HHO flow rate, CO concentrations from both bituminous coal and anthracite were reduced by over 80%. The combustion efficiency of bituminous coal reached 98%, while the combustion efficiency of anthracite increased by 19% (premixed) and 13% (staged), confirming the premixed mode’s superiority in promoting complete combustion. HHO co-combustion increased SO₂ emissions but had a complex effect on NO_X emissions due to the competition between NO_X reduction caused by HHO and NO_X formation caused by the increased combustion temperature. HHO co-combustion changed the melting point of fly ash, increased the content of Al₂O₃, and reduced the content of Na₂O, K₂O, and MgO, influencing the slagging behavior of the boiler and the subsequent management of fly ash. Full article

This mini-review discusses recent advances in the rigorous application of Bonding Evolution Theory (BET) to elucidate electron rearrangements in cycloaddition reactions occurring in both ground and electronically excited states. Computational studies reveal that describing bond formation and cleavage through parametric polynomials derived from the Catastrophe Theory (CT) provides a deeper and more coherent understanding of chemical bonding and reactivity. However, several existing BET applications have adopted CT concepts without fully incorporating the mathematical rigor on which BET is based, resulting in conceptual ambiguities and inaccurate interpretations. A proper implementation of BET requires evaluating the Hessian matrix at potentially degenerate critical points (CPs) of the Electron Localization Function (ELF) and assessing their relative evolution along the reaction coordinate. This systematic protocol integrates key CT principles within BET’s original framework, restoring its formal consistency. The resulting analyses have revealed correlations between electron-density symmetry and CT polynomials, relationships between these polynomials and the homolytic or heterolytic character of bond dissociation, and the development of a CT-based model for scaling bond polarity. These findings demonstrate that incorporating CT-derived functions into BET is not merely a formal refinement but a fundamental step toward achieving a more rigorous and predictive understanding of electron rearrangements in cycloadditions. Full article