Stéphane Siffert

The removal of NO and CO from CO ₂ industrial flue gases is achievable using Selective Catalytic Reduction (SCR) of NO by CO over transition‐metal‐based catalysts. In this work, CoCuAl mixed oxides were synthesized via the Layered Double Hydroxide (LDH) co‐precipitation route with hydrothermal aging at temperatures ranging from 40 to 110 °C. The influence of hydrothermal aging temperature on the physicochemical properties was investigated using X‐ray diffraction (XRD), N ₂ Physisorption, Raman spectroscopy, H ₂ Temperature‐Programmed reduction (H ₂ ‐TPR), Fourier‐transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Low to moderate hydrothermal treatment temperatures (40°C–60°C) promote enhanced crystallinity, cation incorporation, and carbonate intercalation within the LDH structure, whereas higher temperatures (> 80°C) induce CuO phase segregation with less anion intercalation. After CO ₂ treatment at 400°C, the mixed oxides prepared at low‐to‐moderate temperatures exhibited higher carbonate content and larger surface area (147–132 m ² .g ⁻¹ ). Pearson's Correlation analysis reveals the highest positive impact of carbonate content on NO reduction ( R = 0.94), whereas CuO shows a strong negative relationship ( R = −0.97) with N ₂ formation at higher treatment temperatures (> 80°C). These balanced properties, at low‐to‐moderate hydrothermal treatment temperatures, enhance CO oxidation (100% at 260°C) and promote higher N ₂ selectivity (51%–57% at 280°C–300°C).

The proposed study is devoted to highlighting the importance of mixed oxides preparation through the layered double hydroxide route for undesirable gas pollutants abatement. Different series of Cu/Al/Ce mixed oxides with similar or different stoichiometrics were prepared and compared for toluene and/or CO oxidation. Catalyst synthesis methods influence material properties and activity for oxidation reactions. The high activity for the oxidation reactions of mixed oxides derived from LDH is explained by the Cu/Ce synergy. The presence of CO in the CO/toluene mixture does not affect the total toluene oxidation, and the toluene does not affect the total oxidation of CO conversion at low temperatures. The most effective catalytic material (Cu₆Al_1.2Ce_0.8) presents a long lifetime stability for total toluene oxidation and resistance to CO poisoning in mixtures.

Cobalt-aluminum-layered double hydroxides containing carboxymethyl β-cyclodextrin (CMβCD) were synthesized by coprecipitation and evaluated as a cobalt source for the 4-nitrophenol reduction in an aqueous medium. Several physicochemical techniques (XRD, FTIR, TGA) indicated the intercalation of the anionic cyclodextrin without damages to the hydrotalcite-type structure. These lamellar cobalt-aluminum hybrid materials (CoAl_CMβCD) were evaluated in the 4-nitrophenol reduction and showed higher activities in comparison with the CMβCD-free standard material (CoAl_CO₃). To rationalize these results, a set of experimental controls going from physical mixtures of CoAl_CO₃ with different cyclodextrins to other cobalt-based materials were investigated, highlighting the beneficial effects of both the layered double hydroxide and CMβCD-based hybrid structures. CMβCD also showed a beneficial effect as an additive during the 4-nitrophenol reduction. CoAl_CO₃, dispersed in a fresh CMβCD solution could be re-used for five successive cycles without the loss of activity.

Catalytic total oxidation is an effective technique for the treatment of industrial VOCs principally resulting from industrial processes using solvents and usually containing mono-aromatics (BTEX) and oxygenated compounds (acetone, ethanol, butanone). The aim of this work is to deposit gold nanoparticles on CoAl mixed oxide issued from layered double hydroxide (LDH) precursor by using the deposition precipitation (DP) method, which is applied with two modifications, labeled method (A) and method (B), in order to enhance the interaction of the HAuCl₄ precursor with the support. Method (A) involves the hydrolysis of the HAuCl₄ precursor after addition of the support, while in method (B), the gold precursor is hydrolyzed before adding the support. The two methods were applied using as support the CoAl mixed oxide and the LDH precursor. Samples were characterized by several physical chemical techniques and evaluated for ethanol total oxidation. Method (B) allowed the ethanol oxidation activity to be enhanced for the resulting Au/CoAlOx catalysts thanks to the high surface concentration of Co²⁺ and improved reducibility at low temperature. The presence of gold permits to minimize the formation of by-products, notably, methanol, allowed for a total oxidation of ethanol at lower temperature than the corresponding support.

In this work, the LDH approach was used to prepare MnCoAl mixed oxides with various textural and structural frameworks for the purpose of enhancing the total oxidation of ethanol. Our results showed that the catalytic activity of the MnCoAl oxides was influenced by the Mn/Co ratio and the gas atmosphere used during synthesis and thermal treatment. Rietveld refinement was processed to estimate the proportion of phases presented in the prepared materials. Our findings indicated that the generation of Mn₂CoO₄ spinel and Mn₅O₈ lamellar phases improved the redox properties and enhanced the active sites in the MnCoAl oxides. Notably, we observed that the catalytic activity at low temperatures of the catalyst increased with the decrease in the cobalt amount. It was also demonstrated that using an N₂ atmosphere during the preparation of the materials is a promising route to prevent the formation of undesirable phases in the LDHs and their corresponding oxides. The presence of an O₂-free atmosphere during the LDH synthesis positively affects the total ethanol transformation to CO₂ over the oxide catalysts.

Chemical Synthesis is an open access peer-reviewed journal publishing original research involving all areas of the chemical sciences. The journal aims to be the premier resource of seminal and insightful research and showcases for researchers in both academia and industry, providing a platform of inspiration for the future of chemistry. Chemical Synthesis intends to serve as the preeminent international chemistry journal and has the ambition to be among the first choices of chemists for publication of their discoveries.

Catalytic total oxidation is an efficient technique for treating VOCs, which are mainly emitted by solvent-based industrial processes. However, studies of the catalytic oxidation of VOCs in combination with other pollutants are very limited, despite the fact that this is a key step of knowledge before industrial application. During the oxidation reaction, the behavior of a molecule may change depending on the reaction mixture. For the treatment of an effluent loaded with VOCs, it is necessary to carefully select not only the catalytic material to be used but also the reaction conditions. Indeed, the catalytic oxidation of a component in a VOCs mixture is not predicted solely from the behavior of individual component. Thus, the objective of this small review is to carry out a study on the effect observed in the case of the oxidation of a VOCs mixture or in the presence of water, NO_X or sulfur compounds.