The abatement of aromatic pollutants in water requires resource-intensive oxidation to nontoxic products by hydroxyl radicals (•OH). In this study, we elucidate the mechanisms of •OH-induced aromatic ring degradation by combining kinetic measurements, electron paramagnetic resonance spectroscopy, density functional theory (DFT) calculations, and kinetic modelling. We demonstrate that benzyl alcohol, a model aromatic compound, is oxidized by •OH radicals, generated by ultrasonic irradiation in an O2-rich environment, into aromatic compounds (benzaldehyde and phenol derivatives) and C1-C2 oxygenates (formic acid, glyoxal, and oxalic acid). Through pathways akin to atmospheric chemistry, these •OH radicals de-aromatize and fragment benzyl alcohol, producing 5-hydroxy-4-oxo-pentenal and other dicarbonyl products. Unique to the aqueous phase, however, superoxide (•O2–) is generated as a byproduct of •OH-benzyl alcohol reactions. •O2– acts as a potent nucleophile, oxidizing 5-hydroxy-4-oxo-pentenal into oxalic acid and C1 oxygenates via aldehyde and ketone intermediates. This process regenerates •O2– and does not consume •OH, thereby further degrading ring fragmentation products while preserving •OH to activate the refractory aromatic ring of benzyl alcohol. These nucleophilic •O2– reactions can therefore reduce the energy and chemical demands needed to degrade aromatic compounds, thus promoting the sustainable and scalable application of •OH-based oxidation processes in water treatment.

Sonochemistry has shown potential to facilitate chemical conversion under near-ambient conditions in water without any chemical additive or other external stimulus. With the help of catalytic cavitation agents, the generation of radicals from ultrasound-induced inertial cavitation can be enhanced and utilized more efficiently for selective chemical transformations. In this study, multicavity CuO (MC-CuO) microparticles were prepared and employed as catalytic cavitation agents to promote spatially selective cavitation and simultaneously catalyze sonochemical oxidation of glucose. Accordingly, the rate of production of OH radicals by sonolysis of water, inferred from titration, was directly related to the cavitation energy, which was determined by analyzing the acoustic signal during pulsed irradiation of 500 kHz ultrasound. Two reaction pathways for glucose oxidation were identified. First, the generation of OH radicals and possibly other reactive oxygen species in the bulk aqueous phase resulted in the formation of gluconic acid, together with other byproducts of C-C bond cleavage and ring opening. Second, the generation of OH radicals in close proximity to CuO resulted in the formation of glucuronic acid with the six membered ring preserved. The present study demonstrates that by appropriately controlling the acoustic parameters (e.g. duty cycle, peak negative pressure and irradiation time) and reaction conditions (e.g. gas atmosphere and the addition of catalytic cavitation agent), it is possible to steer the selectivity of sono-oxidation of glucose towards glucuronic acid, the most value-added product, whilst minimizing the energy input to drive the sonochemical oxidation reaction. Reactive oxygen species generated from the inertial collapse of a gas bubble trapped on the surface of an MC-CuO cavity selectively oxidize glucose into glucuronic acid.

Ultrasonic irradiation holds potential for the selective oxidation of non-volatile organic substrates in the aqueous phase by harnessing hydroxyl radicals as chemical initiators. Here, a mechanistic description of hydroxyl radical-initiated glyoxal oxidation is constructed by gleaning insights from photolysis and radiation chemistry to explain the yields and kinetic trends for oxidation products. The mechanistic description and kinetic measurements reported herein reveal that increasing the formation rate of hydroxyl radicals by changing the ultrasound frequency increases both the rates of glyoxal consumption and the selectivity towards C2 acid products over those from C-C cleavage. Glyoxal consumption also occurs more rapidly and with greater selectivity towards C2 acids under acidic conditions, which favor the protonation of carboxylate intermediates into their less reactive acidic forms. Leveraging such pH and frequency effects is crucial to mitigating product degradation by secondary reactions with hydroxyl radicals and oxidation products (specifically H2O2 and •O2–). These findings demonstrate the potential of ultrasound as a driver for the selective oxidation of aldehyde functions to carboxylic acids, offering a sustainable route for converting biomass-derived platform molecules into valuable products.

The sonohydrothermal (SHT) treatment is an innovative technique allowing the simultaneous coupling of low frequency ultrasound and hydrothermal conditions for the synthesis of materials. The aim of the present work was to investigate, for the first time, the synthesis of zeolite A and its formation mechanism under SHT conditions. The zeolite synthesis was carried out under sonohydrothermal conditions using a specially designed reactor that allows the application of ultrasonic irradiation at 20 kHz in an autoclave-type reactor heated up to 200 °C under autogenous pressure. The conversion kinetics of the amorphous hydrogel to zeolite A and its further conversion to sodalite were studied. Syntheses were performed in the SHT reactor at 80 and 100 °C, varying the synthesis time from 15 minutes to several hours. The required time to obtain fully crystalline zeolite A under sonohydrothermal conditions was only 25 minutes, highlighting a significantly improved crystallization rate compared to silent conditions (a 9.6-fold kinetic gain). In addition, the resulting zeolite A has smaller particles and a more homogeneous particle size distribution than the zeolite synthesized by hydrothermal treatment. These results can be explained by the sonofragmentation of the amorphous gel and the concomitant enhanced mass transfer of the building units at the interface between the crystallite surface and the solution resulting from the acoustic cavitation activity under SHT conditions. Compared to classical hydrothermal heating, a drastic kinetic increase of the transformation of zeolite A into the more stable sodalite phase was also observed under sonohydrothermal conditions.

Efficient energy transfer management in catalytic processes is crucial for overcoming activation energy barriers while minimizing costs and CO2 emissions. We exploit here a concept of CuO particle design with multiple gas-stabilizing sites, engineered to function as cavitation nuclei and catalysts. This concept facilitates the selective and efficient acoustic energy transfer directly to the catalyst surface, avoiding the undesired dissipation of acoustic energy into the bulk solution while demonstrating superior cavitation properties at lower acoustic pressure amplitudes. Utilizing a chemical thermometric approach, we demonstrate that the local temperature on the surface of our CuO particles during cavitation bubble implosions can create an effective equivalent temperature of about 360 °C. This temperature effect facilitates the efficient catalysis of oxidative reactions using an organic pollutant probe molecule. Density functional theory (DFT) calculations were used to assess the decomposition of H2O2 and of pollutant probe molecule on CuO (111). Our work represents a significant advance in sonocatalytic systems, promising efficient energy use in catalytic reactions.

Wine made or stored in clayware ceramic pots attracts the attention of consumers, but this practice is less studied than when classic stainless steel tanks or wood barrels are used. It is known that wine can be influenced by the container in which it is aged. To analyse the influence of ceramics on the chemical composition of wine, Armenian clay-based ceramic tablets were immersed in model wine and aged from 1 hour up to 16 months at 25 °C in darkness. The concentrations of 26 elements (namely: Al, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sr, Ti, V, W and Zn) in 19 samples were determined by ICP-AES analysis. Proton time domain NMR relaxometry was used to characterise the iron redox processes that occurred in the model wine in contact with a ceramic. A fast increase in the pH of the model wine in contact with the bare ceramic tablet (from 2.35 to 5) was recorded in 4 days. The coating of the ceramic tablets with beeswax showed a significant effect on the interaction between the model wine and the ceramic.

Catalytic oxidation of low concentrations of ethanol was investigated in dry and humid air streams at low temperature (60 °C) over manganese oxide-based catalysts supported on a meso–macrostructured TiO2 using ozone as the oxidant. Ethanol was selected as a representative model VOC present in indoor air, and its concentration was fixed to 10 ppm. For that purpose, a series of Mn/TiO2 powder and monolithic catalysts was prepared, some doped with 0.5 wt% Pd. Whatever the catalyst, the presence of water vapor in the gas phase had a beneficial effect on the conversion of ethanol and ozone. The Pd–Mn/TiO2 catalyst containing 0.5 wt% Pd and 5 wt% Mn exhibited superior oxidation efficiency to the Mn/TiO2 counterparts by increasing ozone decomposition (77%) while simultaneously increasing the selectivity to CO2 (85%). The selectivity to CO2 approached nearly 100% by increasing the amount of catalyst from 20 to 80 mg. In a further step, alumina wash-coated cordierite honeycomb monoliths were coated with the 0.5Pd–5Mn/TiO2 catalyst. Full conversion of ethanol to CO2 without residual O3 emitted (less than 10 ppb) could be attained, thereby demonstrating that the proposed Pd–Mn/TiO2 monolithic catalyst fulfills the specifications required for onboard systems.

Within the context of sustainable chemistry, sonochemistry is now emerging as an alternative unconventional technology in catalysis. While ultrasound-generated radicals can participate in chemical reactions, mastering the reaction selectivity of polyfunctional substrates remains an elusive task. To address this challenge, we designed nanostructured metal oxides with leaf-like morphologies (e.g., CuO) by sonochemical synthesis (20 kHz) and investigated their activity for controlling the selectivity of oxidation reactions under ultrasonic irradiation in aqueous solution. We demonstrated that colocalization of the cavitation event onto the CuO surface active sites enables the direct utilization of radicals generated by cavitation for chemo-selective chemical reactions. In particular, we provided evidence for an alternative reaction pathway in glucose selective oxidation through synergistic cavitation–catalyst interactions at 550 kHz. We showed that the unwanted H• radicals stemming from water sonolysis are trapped by the surface lattice oxygen of CuO, thereby increasing the coverage of •OH radicals on the catalyst surface, and steering the selective oxidation of glucose to glucuronic acid, a valuable chemical whose synthesis remains a formidable challenge in the field of catalysis. This work also highlights that the particle size of the sonocatalyst is a key parameter governing an optimal transfer of radicals from the cavitation bubbles to the catalyst surface.

Selective oxidation of terpenes is a key enabling route to produce value-added epoxides from renewable raw materials. In the present work, the photo-assisted oxygen atom transfer (OAT) to renewable monoterpenes, such as a-pinene, beta-pinene, camphene, (R)-(+)-limonene and (S)-(-)-limonene was evaluated with a dichloro-dioxoBipy molybdenum((VI)) complex (Bipy = 2,2' -bipyridine-4,4'-dicarboxylato) anchored on TiO2 nanotubes (labeled as Mo((VI))Cl(2)O(2)Bipy/TiO2-NT) using molecular oxygen as a primary oxidant under benign ambient conditions. Supported MoO3 on TiO2 nanotubes were also used for comparison purposes. Photooxidation of a-pinene with that MoO3/TiO2-NT catalyst resulted in a low conversion and in products distribution similar to that of the parent titania nanotubes, with the ketone as the main product due to a radical process. In contrast, all monoterpenes were successfully oxidized by the Mo((VI))Cl(2)O(2)Bipy/TiO2-NT catalyst to the desired epoxides with high selectivities due to the OAT with O-2 and UV-vis light. Additionally, the photo-stimulated OAT to (R)-(+)and (S)-(-)-limonene with the immobilized dioxo-Mo-(VI) complex resulted in a diastereomeric excess (d.e.) for the cis-limonene-1,2-epoxide isomers relative to the trans isomers (d.e. = 36 and 34 %, respectively), thereby suggesting that the chiral center in the (R)-(+)- and (S)-(-)-limonene governs the formation of the diastereoisomer. Although not chiral, the Mo((VI))Cl(2)O(2)Bipy/TiO2-NT catalyst was shown to act stereoselectively during the OAT process. The high stability of the Mo((VI))Cl(2)O(2)Bipy -catalyst under the reaction conditions was also ascertained by recycling studies.

This chapter deals with the use and development of heterogeneous non-precious metal oxide-based catalysts for aerobic oxidation reactions in gas–solid and liquid–solid phases. The main solid catalysts from transition metal ions (Mn, Cu, Fe, V, Ce, Nd, Mo, W) are described. Many examples are given about the reactions, catalytic performances, catalysts used and major industrial processes, either existing at present using petroleum-based raw materials or future processes using biomass-derived raw materials. It concerns selective oxidation and ammoxidation (NH3 + O2) reactions of alkanes to alkenes; alkanes to carboxylic acids, aldehydes and nitriles; olefins to carboxylic aldehydes and acids and aromatics to the corresponding acids or nitriles. Total oxidation reactions for depollution treatment and combustion are also briefly presented regarding atmospheric pollutants, such as industrial volatile organic compounds (VOCs). Some reaction mechanisms (radical-type or Mars and van Krevelen-type) along with concerns on the structure and size of active sites are discussed. Different reactor types, including packed bed, membrane and moving bed technology, are discussed depending on the intended reaction, as well as considerations on physical aspects of the solid catalysts, related to thermal and electrical conductivities, attrition resistance, deactivation and regeneration of the catalysts.

Glycerol was oxidized selectively to oxalic and tartronic acids in 78% yield over a highly crystalline CuO catalyst prepared within a few minutes by a sonochemical synthesis.

This chapter is focused on the use of high intensity ultrasound for the preparation of nanostructured materials with an emphasis on recent prominent examples of the production of dense or porous metal oxides through sonochemical and ultrasonic spray pyrolysis routes. Sonochemistry enables the synthesis of oxides that are often unachievable by traditional methods or affords known materials with shape, size, and nano/microstructure control under fast reaction conditions. The fundamental principles of acoustic cavitation, as well as the main ultrasonic parameters affecting the cavitation phenomenon, are first summarized. Next, the applications of ultrasound in the synthesis of nanostructured oxide materials following both preparation methods are reviewed. Particular focus is given to the ultrasound-assisted synthesis of metal oxide nanoparticles for energy applications.

In this review paper, we have assembled the main characteristics of partial oxidation reactions (oxidative dehydrogenation and selective oxidation to olefins or oxygenates, as aldehydes and carboxylic acids and nitriles), as well as total oxidation, particularly for depollution, environmental issues and wastewater treatments. Both gas–solid and liquid–solid media have been considered with recent and representative examples within these fields. We have also discussed about their potential and prospective industrial applications. Particular attention has been brought to new raw materials stemming from biomass, as well as to liquid–solid catalysts cases. This review paper also summarizes the progresses made in the use of unconventional activation methods for performing oxidation reactions, highlighting the synergy of these technologies with heterogeneous catalysis. Focus has been centered on both usual catalysts activation methods and less usual ones, such as the use of ultrasounds, microwaves, grinding (mechanochemistry) and photo-activated processes, as well as their combined use.

In the last two decades, the use of ionic liquids (ILs) in different areas of chemistry has increased considerably, especially for biomass conversion into fuels and chemicals. This chapter describes the investigations in strategies 288and innovations based on ILs in terms of dissolution and pretreatment methods and their uses as reaction solvents, catalysts and extraction solvents in biorefinery. Relevant literature examples related to the design of ILs for the valorization of cellulose, lignin and vegetable oil are reported, with emphasis on their impact on the reactivity and reaction pathways to further improve chemical yields. Additionally, several parameters involved in these processes such as the choice of the anion or/and cation of ILs are thoroughly discussed. Significant improvements have been made in recyclability of ILs for a wide range of reactions. This chapter also discusses the renewability and sustainability aspects related to biorefinery processes, where ILs are involved.

Catalytic ozone decomposition on various manganese oxide-based catalysts was investigated at 40 degrees C for ozone concentrations in the range 2-20 ppm in dry and humid conditions. Ozone conversion efficiency shows a slight dependence with ozone concentration, slightly decreasing when ozone concentration increases. A strong but reversible inhibiting effect was observed when water is present in the gas phase likely due to the reversible adsorption of water on ozone reaction sites. Whatever the catalyst used, the same behavior was observed which is characterized by a transient decrease in efficiency at the beginning of the reaction until reaching the steady-state. A kinetic model was developed, based on the mechanism of ozone decomposition proposed by Oyama and co-workers, allowing us to properly describe the reaction behavior of ozone on manganese oxide catalysts for variable initial reactant concentrations. Additionally, the transient behavior of the MnO2 catalysts experimentally observed at the beginning of the ozone decomposition reaction was kinetically described for the first time, as well as the steady-state.

The heterogeneous oxidation of vanillyl alcohol to vanillin was investigated on new grounds under eco-friendly conditions in the presence of hydrogen peroxide as an oxidant and water as solvent, coupled with low frequency ultrasonic irradiation. The sono-Fenton-like-assisted vanillyl alcohol oxidation was performed with a high-surface area nanostructured spinel cobalt oxide catalyst exhibiting small crystallites size. The catalytic reaction was also carried out under conventional heating conditions for comparison purposes. The influence of the reaction parameters, namely catalyst loading and hydrogen peroxide concentration was studied with the aim of determining the optimum yield and selectivity to the desired vanillin product. The chemical effects of ultrasound (ability to generate hydroxyl radicals) along with increased mass transfer appeared to be key prerequisites for enhancing the efficiency of the process, while decreasing the overall energy consumption.