Catalytic Tests Research Articles

Optimizing reverse water gas shift catalysis: Minimizing metal loading and enhancing performance with Pt/ZrO2 catalysts through Rh incorporation

In this study, the optimization of catalysts for the reverse water gas shift reaction by minimizing metal loading and enhancing the performance of supported Pt catalysts through Rh incorporation was done. The catalysts were synthesized by the wet impregnation method, in which the metal noble load in bimetallic samples decreased by approximately one-third compared to the reference platinum catalyst, with varying Rh-Pt ratios. In all materials, m-ZrO2, obtained by the hydrothermal method, was used as support. In the catalytic tests in a continuous packed-bed flow reactor at atmospheric pressure, all samples were active to catalyze CO2 reduction between 200 and 300 °C. Bimetallic samples, particularly those with an Rh-Pt atomic ratio of 20–80, exhibited superior performance in the RWGS reaction despite their lower metal content. Based on the results of H2-TPR, FTIR in situ, and XPS, we propose that the enhanced CO production in bimetallic samples compared to Pt/ZrO2 catalysts can be attributed to Rh increasing the reduction extent of supported Pt. This enhancement facilitates the hydrogenation of bicarbonate species into formate species, which subsequently evolve into Pt0-CO and ultimately into CO. Additionally, Rh incorporation enables an alternative pathway for CO generation, where Pt0-carbonyls, known for their CO-producing capability, are formed via CO2 dissociation on the Pt0 surface. However, higher Rh concentrations favor the CO2 methanation rather than the RWGS reaction.

Bi-functional active sites Cu/MgO-La2O3 catalysts the selective hydrogenation of furfural to furfuryl alcohol

Selective hydrogenation of biomass with high efficiency to produce fine chemicals has high economic value and research significance. The Cu/MgO-La2O3 catalyst exhibits distinct active sites that facilitate the selective hydrogenation of furfural to furfuryl alcohol. Under optimal reaction conditions (90℃, 70 min) with the Cu/MgO-La2O3-6 catalyst, furfural conversion and furfuryl alcohol selectivity exceed 99.9 %. The catalyst’s activity remained approximately 97.6 % after five cycles. The combination of catalytic data, characterization tests, and density functional theory (DFT) calculations confirms that the addition of La promotes Cu reduction, resulting in a structured arrangement of highly hydrogenated copper sites (activation H2) and strongly adsorbed lanthanum sites (adsorbed furfural). Mechanistic studies indicate that the two active sites can simultaneously activate hydrogen and furfural. The strong adsorption of furfural enhances the hydrogenation reaction, while the weak adsorption of furfuryl alcohol inhibits side reaction pathways, thus achieving excellent catalytic selectivity.

Interface engineering in Ni(OH)2/NiOOH heterojunction to enhance energy-efficient hydrogen production via urea electrolysis

Electrochemical urea electrolysis has merged as a promising alternative to conventional water splitting methods for hydrogen fuel production due to its cost-effectiveness and superior energy efficiency. The utilization of heterostructures has been proposed as a viable strategy to improve the efficiency of the urea oxidation reaction (UOR) by augmenting the quantity of active sites and optimizing the electronic structure. In this study, a Ni(OH)2/NiOOH heterojunction, referred to as H-Ni, was synthesized via a straightforward hydrothermal synthesis method. The notable performance of H-Ni in UOR is ascribed to the synergistic interaction between Ni(OH)2 and NiOOH, which constitute the principal components of the catalyst. Density functional theory (DFT) calculations reveal that the H-Ni composite is capable of modulating the d-band center, thereby enhancing the adsorption and desorption of reaction intermediates and decreasing the Gibbs free energy (ΔG) associated with the rate-determining step (RDS) of the UOR. Experimental results from catalytic performance tests indicate that the H-Ni-140 catalyst attains a current density of 10 mA·cm−2 in 1 a M KOH electrolyte containing 0.33 M urea at a relatively low potential of 1.341 V versus reversible hydrogen electrode (RHE), thereby highlighting its superior electrocatalytic performance. Furthermore, the catalyst requires only a cell voltage of 1.78 V to achieve a current density of 100 mA·cm−2, which is approximately 120 mV lower than that required for water electrolysis. This work presents a straightforward methodology for the cost-effective development of heterojunction catalysts.

Effect of rhenium on the activity of ZrO2-supported copper catalysts for hydrodeoxygenation of m-cresol

This work studies the effect of adding different loadings of Re on the performance of ZrO2-supported Cu catalysts for hydrodeoxygenation (HDO) of m-cresol. H2-TPR and XPS show a synergistic effect between Cu and Re, decreasing the reduction temperature of both metals and promoting the reduction of Re oxide. Moreover, the addition of Re changes Cu dispersion and acid properties of all catalysts. High Re contents results in a coverage of Cu surface. Catalytic tests reveal that HDO reaction rate and product distribution vary considerably depending on the Re loading. Cu catalyst was inactive for HDO reaction, forming only hydrogenation products. In contrast, Re catalyst stood out for its high capacity to promote HDO reaction, with significant production of toluene. For the bimetallic catalysts, the addition of Re increases HDO reaction rate from 0 to 0.39 mmol gmetal−1 min−1 and the selectivity towards toluene (0–82.6 %), whereas the formation of hydrogenation and dehydration products decreases.

Effects of nickel-deactivations on zeolites-Y of different SiO2/Al2O3 ratios in catalytic cracking of hydrocarbons

Effects of nickel deactivation on catalytic activities of three types of zeolites-Y (Y-5.1, USY-5.2, and VUSY-12) with varying SiO2/Al2O3 ratios were studied in cracking of hydrocarbons. Physicochemical characteristics such as crystalline phases, Ni oxidation states, morphology, acidity, surface area, and thermal stability of the samples were analysed. XRD revealed the absence of observable nickel compounds below 5 wt%, with NiO phase emerging at higher concentrations. Surface areas decreased from 826 to 615 m2/g (Y-5.1), 786–686 m2/g (USY-5.2), and 762–571 m2/g (VUSY-12) at 30 wt% Ni. The total acid sites also reduced from 17.247 to 9.826 µmol/g (Y-5.1), 15.464–8.854 µmol/g (USY-5.2), and 7.094–4.876 µmol/g (VUSY-12). XPS confirmed Ni2+ states. Catalytic cracking tests using n-Heptane demonstrated increases in C5-C6 alkanes, olefins, hydrogen, and methane yields as nickel concentration increased, with respective values of 64 %, 28 %, 79 % and 68 % for Y-5.1; 62 %, 28 %, 76 %, and 62 % for USY-5.2; and 58 %, 21 %, 75 %, and 60 % for VUSY-12. A corresponding decrease in heavier components were observed. The study demonstrates that nickel modification significantly impacts the physicochemical properties and catalytic performance of zeolite-Y and these depend strongly on the SiO2/Al2O3 ratios. The study gives further insights into the structural and catalytic modifications induced by nickel doping in zeolites, highlighting the potential of nickel-modified zeolites in promoting undesirable hydrogen and gas.

Simultaneous Catalytic Oxidation of Benzene and Toluene over Pd-CeZrOx Catalysts

Since actual industrial emissions contain a wide range of volatile organic compounds, studies into the simultaneous catalytic degradation of multi-component VOCs are essential. This work developed Pd-CeZrOx samples for the simultaneous elimination of benzene and toluene. Firstly, CeZrOx supports were synthesized using several methods (co-precipitation, CTAB template co-precipitation, and sol–gel method). Pd active species were then added into the 1.0Pd-CeZrOx samples using the impregnation procedure. XRD, BET, NH3-TPD, Raman, EPR, XPS, and H2-TPR were utilized to analyze the as-prepared Pd-CeZrOx samples. The catalytic performance tests reveal that the performance of 1.0Pd-CeZrOx-CTAB outperforms that of 1.0Pd-CeZrOx-PM and 1.0Pd-CeZrOx-CASG, and 1.0Pd-CeZrOx-CTAB displays superior catalytic activity for both benzene and toluene oxidation. The improved redox properties, the abundant surface oxygen vacancies, and the surface Pd2+ species of the 1.0Pd-CeZrOx-CTAB sample may be responsible for the simultaneous degradation activity of benzene and toluene.

The Synergic Effect of h-MoO3, α-MoO3, and β-MoO3 Phase Mixture as a Solid Catalyst to Obtain Methyl Oleate.

Extensive research in the last few decades has conclusively demonstrated the significant influence of experimental conditions, surfactants, and synthesis methods on semiconductors' properties in technological applications. Therefore, in this study, the synthesis of molybdenum oxide (MoO3) was reported by the addition of 2.5 (MoO3_2.5), 5 (MoO3_5), 7.5 (MoO3_7.5), and 10 mL (MoO3_10) of nitric acid, obtaining the respective concentrations of 0.6, 1.10, 1.6, and 0.6 mol L-1. In this study, all samples were synthesized by the hydrothermal method at 160 °C for 6 h. The materials obtained were structurally characterized by X-ray diffraction (XRD) and structural Rietveld refinement, Raman spectroscopy, and infrared spectroscopy (FTIR), confirming the presence of all crystallographic planes and bands associated with active modes for the pure hexagonal phase (h-MoO3) when the solution's concentration was 0.6 mol L-1 of nitric acid. For concentrations of 1.10, 1.60, and 2.10 mol L-1, the presence of crystallographic planes and active modes associated with the formation of mixtures of molybdenum oxide polymorphs was confirmed, in this case, the orthorhombic, monoclinic, and hexagonal phases. X-ray photoelectron spectroscopy reveals the occurrence of the states Mo4+, Mo5+, and Mo6+, which confirm the predominance of the acid Lewis sites, corroborating the analysis by adsorption of pyridine followed by characterization by infrared spectroscopy. The images collected by scanning electron microscopy confirmed the information presented in the structural characterization, where microcrystals with hexagonal morphology were obtained for the MoO3_2.5 sample. In contrast, the MoO3_5, MoO3_7.5, and MoO3_10 samples exhibited hexagonal and rod-shaped microcrystals, where the latter morphology is characteristic of the orthorhombic phase. The catalytic tests carried out in the conversion of oleic acid into methyl oleate, using the synthesized samples as a heterogeneous catalyst, resulted in conversion percentages of 52.5, 58.6, 69.1, and 97.2% applying the samples MoO3_2.5, MoO3_5, MoO3_7.5, and MoO3_10, respectively. The optimization of the catalytic tests with the MoO3_10 sample revealed that the conversion of oleic acid into methyl oleate is a thermodynamically favorable process, with a variation in the Gibbs free energy between -67.3 kJ mol-1 and 83.4 kJ mol-1 as also, the energy value of activation of 24.6 kJ mol-1, for the temperature range from 80 to 140 °C, that is, from 353.15 to 413.15 K, respectively. Meanwhile, the catalyst reuse tests resulted in percentages greater than 85%, even after the ninth catalytic cycle. Therefore, the expressive catalytic performance of the mixture of h-MoO3 and α-MoO3 (MoO3_10) phases is confirmed, associated with the synergistic effect, mainly due to the increase in the surface area and available Lewis sites of these phases.

Rational screening of metal single-atom-doped ZSM-5 to promote ring-opening cracking of cycloalkanes to light olefins

The ring-opening cracking of cycloalkanes to light olefins poses a formidable challenge due to the sluggish activation of the C–C bond. In this study, we realize the rational screening of various single metal doped M−ZSM−5 catalysts (M = Mn, Co, Ni, Cu, Zn, Zr, Ru, Rh, Pd, Ag, Pt) to promote the ring-opening cracking of cycloalkanes to light olefins. Our calculation results show that methyl cyclopentane, a model compound of cycloalkanes, tends to adsorb in the form of a “half-chair” configuration in the intersecting channels of the M−ZSM−5, which is caused by the drastic distortion of the five-membered ring, accompanied by large changes in the bond angles. Based on the host–guest interaction between the active site and hydrocarbon in ring-opening cleavage, we reveal that the binding energies of metals to H and C can respectively quantify the metal’s ability to activate C–H and C–C bonds in cycloalkanes. By solving the microkinetic model, we plot activity-selectivity TOF volcano diagrams, where Mn, Ru, Rh-ZSM-5 within the EH range of −2.5 to −3.5 eV and the EC range of −6 to −8 eV can efficiently induce the ring-opening reaction of cycloalkanes without excessive dehydrogenation leading to aromatic hydrocarbon formation. The calculation shows good agreement with catalytic experimental tests and in situ DRIFT spectra results, providing a series of potential candidate catalysts for the ring-opening cracking of cycloalkane-rich diesel fuel.

Promoting role of Ru species on Ir-Fe/BN catalyst in 1,2-diols hydrogenolysis to secondary alcohols

Noble metal-based-bimetallic catalysts have been highly investigated and applied in wide applications including biomass transformation via regioselective C−O hydrogenolysis while further modification especially with noble metal is highly promising yet still under investigation. Herein, Ru was found as an effective modifier among the screened noble metals (Ru, Pt, Rh, Pd, Au, and Ag) for Ir-Fe/BN (Ir = 5 wt%, Fe/Ir = 0.25) catalyst in terminal C−O hydrogenolysis of 1,2-butanediol (1,2-BuD) to 2-butanol (2-BuOH). Only trace amount of Ru (up to 0.5 wt%) was effective in terms of high 2-BuOH selectivity (> 60%) and activity (about twice). Larger amount of Ru species (3 wt%) highly enhanced the activity but gave low selectivity to 2-BuOH with by-products of terminal C−C bond scission. Optimized catalyst (Ru(0.5)-Ir-Fe/BN) was reusable at least 4 times and gave moderate 2-BuOH yield (47%) in hydrogenolysis of 1,2-BuD. The promoting effect of Ru addition (0.5 wt%) to Ir-Fe/BN on hydrogenolysis of various alcohols was also confirmed. Combining catalytic tests with various characterizations, the promotion mechanism of Ru species in trimetallic catalysts was clarified. The Ru species in Ru(0.5)-Ir-Fe/BN form alloy with Ir and are enriched at the interface with BN surface, and direct interaction between Ru and Fe was not necessary in Ru-Ir-Fe alloy. The interface of Ir and Fe on the surface of Ir-Fe alloy may work as active sites for 1,2-diols to secondary alcohols via direct C−O hydrogenolysis, in which Ru-modified Ir activates H2 to form hydride-like species. The activity of Ru species in C−C bond cleavage was highly suppressed due to the direct interaction with Ir species and less exposed to substrate. Larger loading amount of Ru species (3 wt%) led to the formation Ru-rich trimetallic alloy, which further works as active sites for C−C bond scission.

Catalytic performance of a single atom Pd1Ag10/Al2O3 catalyst for the selective hydrogenation of acetylene: The role of CO-induced segregation

The single-atom Pd catalysts based on silver-rich bimetallic compositions are known for their extremely high ethylene selectivity in the acetylene hydrogenation reaction; however, their activity is noticeably lower than that of traditional monometallic Pd catalysts. The aim of the work was to apply a method of CO-induced segregation to increase the concentration of single atom Pd1 sites on the surface of Pd1Ag10/Al2O3 catalyst without noticeable formation of multiatomic Pdn (n ≥ 2) ensembles. It has been experimentally established by DRIFTS-CO and XPS methods that the effect of 30 vol% CO exposure temperature on the increase of surface Pd1 sites concentration in the range of 50 to 350 °C has a volcano-like dependence with a maximum at ∼ 200–250 °C. The catalytic tests show a considerable enhancement in activity for samples treated in CO at 200–250 °C (the temperature of 100 % acetylene conversion is reduced by ∼ 30 °C), while the C2H4 selectivity was similar for both freshly reduced and CO-treated catalysts. These results demonstrate the use of CO-induced segregation as a promising method for the controlled increase in the concentration of isolated Pd1 sites to improve the activity of silver-rich palladium catalyst without compromising its selectivity.

Heterogeneous Activation of Persulfate by Petal-Shaped Co3O4@BiOI to Degrade Bisphenol AF

In catalytic tests, the results have shown that almost all the BPAF was removed within 30 min when the dosage of Co3O4@BiOI and sodium persulfate (PS) was 0.15 g and 0.1 mM, respectively. Acid conditions inhibited BPAF degradation, but the inclusion of a precise concentration of bicarbonate ions (HCO3−) promoted degradation. The presence of chloride (Cl−), sulfate ions (SO42−), and a high concentration of HCO3− inhibited the degradation process, whereas the addition of nitrate ions (NO3−) had a minor effect on the catalytic process. The presence of free radicals (sulfate (SO4•−), hydroxyl (•OH), and superoxide (O2•−)) and the non-free radical singlet oxygen (1O2) in the Co3O4@BiOI/PS system was determined by electron paramagnetic resonance (EPR) and quenching tests. We propose that the Co(II)/Co(III) and Bi(III)/Bi(V) redox pairs simultaneously activate PS where the Co3O4 and BiOI components work synergistically to promote the rapid oxidative degradation of BPAF in water.

Optimizing propylene production via acetone hydrodeoxygenation: Insights from catalytic studies with Cu/γ-Al2O3 and Hβ zeolite

Propylene is a crucial light olefin in the petrochemical industry and can be produced via acetone hydrodeoxygenation, which involves two sequential reactions: first, acetone undergoes hydrogenation catalyzed by metallic sites, followed by the dehydration of the resulting isopropanol catalyzed by acidic sites. In this study, propylene production through acetone hydrodeoxygenation was investigated using a physical mixture of 35 wt% Cu/γ-Al2O3 and Hβ zeolite to investigate how various reaction parameters affect acetone conversion and propylene yield. Using the experimental design methodology, empirical models were developed to correlate acetone conversion (Xacet) and propylene yield (Yprop) with the ratio of 35 wt% Cu/γ-Al2O3 to Hβ (CR), total catalyst weight (Cw), hydrogen volumetric flow rate (FH2) and reaction temperature (T). The maximum propylene yield achieved in the catalytic tests was 73.46 %. A long-term test demonstrated the catalyst's reusability, remaining active even after 22 hours of reaction with only a slight decrease in propylene yield. Analysis of the experimental data revealed that increasing T and Cw positively affected propylene yield, whereas higher CR and FH2 had negative effects. According to the Pareto chart, reaction temperature was the most influential variable for propylene yield, followed by CR, FH2 and Cw. For acetone conversion, the order of significance among the variables was T >CR >Cw >FH2.

Reaction ignition during the oxidative coupling of methane over Mn–Na2WO4/SiO2

The present study investigates the oxidative coupling of methane (OCM) as a viable solution for CH4 upgrading with the benchmark Mn–Na2WO4/SiO2 catalyst. The effects of space velocity on catalytic performance and ignition responses were evaluated. Experimental catalytic tests revealed a complex relationship between space velocity and C2+ product yields and a self-igniting behavior when the reaction temperature reached about 700 °C. The results indicated that the temperature difference (∆T) between the catalyst bed and the flowing gas increased with the feed flow rate and decreased with dilution of the catalyst bed (increasing with catalyst loading), which can allow the reaction ignition at lower temperatures. The present study sheds light on the interplay between reaction conditions and the ignition behavior, providing valuable insights for optimization of OCM processes and catalyst development.

Z-scheme heterojunction TNCoPc/BiOBr nanomicrospheres for efficient photodegradation of tetracycline and rhodamine B: Degradation performance, intrinsic mechanism and degradation pathway studies

The natural ecosystem has been significantly jeopardized due to the misuse of organic dyes and antibiotics. To treat organic wastewater safely and efficiently, this study synthesized a binary composite photocatalyst TNCoPc/BiOBr, using a solvothermal method that involved loading cobalt tetranitro phthalocyanine onto BiOBr. The results of the catalytic performance tests indicated that the composites exhibited the capacity to degrade rhodamine B and tetracycline hydrochloride by 97.75 % and 78.37 %, respectively. Moreover, the composite exhibited good cyclic stability. Subsequent analytical characterization confirmed the formation of a Z-scheme heterojunction, resulting in a synergistic effect. This Z-scheme heterojunction facilitated the capacity of photocatalyst to achieve enhanced light absorption, augmented photogenerated carrier separation efficiency, and augmented redox capacity. Additionally, theoretical calculations were employed to further elucidate the catalytic mechanism and synergistic effects. The results demonstrate that the Co-N4 sites are the active center of the TNCoPc and verify the contribution of nitro substitution to the photogenerated electron transfer mechanism on TNCoPc. Furthermore, a systematic degradation pathway was predicted and deduced based on Fukui indices and liquid chromatography-mass spectrometry data. This study presents a paradigm for the application of composite photocatalysts containing substituted phthalocyanines in the degradation of organic wastewater.

Enhanced selective oxidation of ethylarenes using iron single atom catalysts embedded in Nitrogen-Rich graphene

Heavily (19 % wt) Nitrogen doped graphene (N-G), with Nitrogen incorporated mainly as pyridinic species (77.8 %), was obtained by reacting fluorographene with ammonia under solvothermal conditions, at mild temperature (140 °C). N-G was used to stabilize single iron atoms (N-G-Fe) in two different configurations: low spin X-(FeIIN4)-Y and high spin X-(FeIIIN4)-Y. The resulting N-G-Fe single atom catalysts exhibit remarkable efficacy in the selective oxidation of ethylarenes, with activity comparable or even superior to state-of-the-art materials, converting ethylbenzene to acetophenone with an initial turnover frequency of 13400 h−1. Notably, N-G-Fe exhibits genuine catalytic activity since it is able to oxidize ethylbenzene using substoichiometric amount of peroxides, and exploiting molecular oxygen as the final oxidant. Moreover, N-G-Fe can be recycled without any metal leaching, and exhibits a broad catalytic scope. Multi-technique characterizations combined with rationally designed catalytic tests allowed us to identify the active sites and propose a plausible mechanism for the catalytic cycle.

Rational fabrication of two polyoxovanadate-based frameworks for efficient detoxifying mustard gas simulant

Two polyoxovanadates (POVs)-based cobalt–organic frameworks, namely [H2Co2(p-bix)4][V8O23] (1) and [Co(o-bix)][V2O6] (2) (where p-bix = 1,4-bis(imidazol-1-ylmethyl)benzene and o-bix = 1,2-bis(imidazol-1-ylmethyl)benzene), were synthesized via a hydrothermal process and thoroughly characterized structurally. Compound 1 features a three-dimensional framework where the inorganic layers {V8Co2}, containing circular [V4O12]4− ({V4}) dimers, are interconnected by p-bix ligands. While compound 2 forms a two-dimensional layer structure where the inorganic {V4} clusters are linked by four binuclear [Co2O3(o-bix)2]2− units through the sharing of O atoms from {V4} clusters. Given the catalytic prowess of POVs in oxidizing various organic substrates, we evaluated the catalytic performance of these two compounds as heterogeneous catalysts for detoxifying mustard gas simulant CEES (2-chloroethyl ethyl sulfide) into the non-toxic CEESO (2-chloroethyl ethyl sulfoxide). The catalytic tests revealed that both compounds effectively catalyze the oxidation of CEES, yielding solely CEESO. Particularly, catalyst 2 exhibited excellent catalytic properties, achieving nearly 100 % conversion and selectivity within just 40 min at room temperature. The prominent performance of 2 remains consistent through at least five recycling cycles, showcasing its durability and effectiveness. This exceptional performance of 2 was achieved due to the synergistic interaction between V and coordinatively unsaturated Co sites within the structure, as confirmed by detailed comparative studies of structure and catalytic activity as well as density functional theory (DFT) calculations.

3D printed steel monoliths for CO2 methanation: A feasibility study

Steel honeycomb monoliths have been manufactured by Fused Deposition Modelling-FDM 3D printing technology using 90 % 17–4 PH steel nanoparticles-loaded polymer filament. Pure steel monoliths were obtained after thermal removal of the polymer and steel sintering. NiO-CeO2 active phase nanoparticles were loaded on powder steel and on the steel monoliths, and the supported catalysts were tested in the hydrogenation of CO2 to CH4, paying special attention to the steel pretreatment before active phase loading. The catalytic experiments confirm that totally functional catalysts have been prepared, showing 100 % selective conversion of CO2 to CH4 above 225 ºC and stability in long-term experiments (18 hours at 325 ºC). The catalytic behaviour is improved by H2O2-pretreatment of the steel honeycomb monoliths before the active phase loading. XPS characterization confirms that the surface of the catalysts is oxidised on the fresh catalysts and gets even more oxidised after the catalytic tests. The H2O2-pretreatment of the steel support partially avoids the additional oxidation under reaction conditions, keeping chromium and cerium cations less oxidised than on the catalyst prepared with untreated steel. In addition, evidence about the electronic interaction between the steel support and the NiO-CeO2 (np) active phase are obtained.

Encapsulation of Cu/Fe3O4 With RT‐COF‐1 for Improved Stability in Water–Gas Shift Reaction

AbstractStability is crucial for the practical application of heterogeneous catalysts, particularly in industrial processes, where catalyst deactivation often occurs due to factors such as sintering, poisoning, and active site degradation. This study investigates the effectiveness of utilizing covalent organic frameworks (COFs), specifically RT‐COF‐1, to enhance the stability of Cu/Fe3O4 catalysts in harsh water–gas shift (WGS) reaction environments. By encapsulating Cu/Fe3O4 with trace RT‐COF‐1, we aimed to preserve the structural integrity and active interfaces between the metal components during catalytic reactions. Characterization techniques, including X‐ray photoelectron spectroscopy, nitrogen sorption, and high‐angle annular dark‐field scanning transmission electron microscopy, confirmed the successful COF coating and its role in preventing particle aggregation and maintaining active site structures over extended catalytic tests. Notably, Cu/Fe3O4@COF demonstrated significantly enhanced stability during a continuous 24‐h WGS test compared to uncoated catalysts, which exhibited rapid deactivation. Mechanistic insights indicated that COF coating reduced the number of active sites while preserving the overall morphology of the catalyst, contributing to its robust performance. Ultimately, this work highlights the potential of COF encapsulation as an effective strategy for enhancing the durability and efficacy of multifunctional catalysts in challenging reaction conditions.

Study of the Use of Oxygenated Water as a Non-Toxic Molecule Model for Catalytic Testing of Pozzolana-PN and Iron-Based NOx Reducing Catalysts

During previous catalytic tests on the reducing power of NOx catalysts based on pozzolana and PN-black citric acid polymer, it was found that the use of the NO<sub>2</sub> model molecule poses a significant health and environmental risk. Thus, a project was launched to find another, much less harmful model molecule. Hydrogen peroxide H<sub>2</sub>O<sub>2</sub> was chosen, a molecule naturally secreted by the body to prevent pigment synthesis, with disinfectant, antiseptic and whitening properties widely used in various activities, including cosmetics. Consequently, catalytic tests of NOx-reducing power using hydrogen peroxide H<sub>2</sub>O<sub>2</sub> as a model molecule were carried out on two catalysts based on pozzolana and PN-black polymer of citric acid, PNP-Fe-water-15% and PNP-Fe-ethanol-15%, differing in the solvent used during their syntheses according to a procedure detailed in the bibliography and this manuscript. Pozzolana is a volcanic rock widespread in the volcanic mountains in the Vakinankaratra region of Madagascar. Its use as a support for catalysts based on PN-black polymer of citric acid and Iron-Fe enabled us to synthesize various catalysts, the characteristics and synthesis methods of which are detailed in this manuscript. In short, the catalytic test with hydrogen peroxide was conclusive, enabling a pragmatic comparison of the two catalysts tested, with the result that the catalyst synthesized with water PNP-Fe-water-15% is more active than the catalyst synthesized with ethanol PNP-Fe-ethanol-15%. This is due to the quality and difference in dispersion of the PN-black polymer molecules depending on the solvent used, which can have an impact on the nature of the catalyst surfaces and certain characteristics such as porosity. This dispersion is confirmed and viewed using an optical microscope to visualize the surface of a catalyst grain. Kinetic results from two proposed mechanisms for the reduction of H<sub>2</sub>O<sub>2</sub> hydrogen peroxide molecules using PNP-Fe catalysts also confirmed not only the proposed mechanisms, but also the higher activity of PNP-Fe catalysts synthesized with water, whose kinetic constants are much higher than those synthesized with ethanol.

XPS study of the stability variations of [M(COD)Cl]<SUB>2</SUB> (M = Ir, Rh) complexes anchored on modified silica in reactions of spin-selective hydrogenation of unsaturated hydrocarbons by parahydrogen

Changes in the composition of anchored [M(COD)Cl]2–NH2–C3H6–SiO2 and [M(COD)Cl]2–P(Ph)2–C2H4–SiO2 (where M = Ir, Rh) catalysts in reactions of gas-phase selective hydrogenation of propene, propyne and 1,3-butadiene with parahydrogen (p-H2) were studied using XPS. The atomic ratio M/Cl has been proposed as an indicator of the stability of the structure of the anchored complex, both at the stage of sample preparation and in the reaction. Based on a comparison of XPS data and the results of catalytic testing using parahydrogen-induced polarization, it is shown that the stability of the anchored {[M(COD)Cl]2–Linker–SiO2} complex during hydrogen activation is a key factor in the catalytic behavior of systems. Such stability is influenced not only by the chosen metal and linker, but also by the nature of the hydrogenated substrate.