Catalytic Oxidation Research Articles

Non-Noble Metal Catalysts for Electrooxidation of 5-Hydroxymethylfurfural.

2,5-Furandicarboxylic acid (FDCA) is a class of valuable biomass-based platform compounds. The creation of FDCA involves the catalytic oxidation of 5-hydroxymethylfurfural (HMF). As a novel catalytic method, electrocatalysis has been utilized in the 5-hydroxymethylfurfural oxidation reaction (HMFOR). Common noble metal catalysts show catalytic activity, which is limited by price and reaction conditions. Non-noble metal catalyst is known for its environmental friendliness, affordability and high efficiency. The development of energy efficient non-noble metal catalysts plays a crucial role in enhancing the HMFOR process. It can greatly upgrade the demand of industrial production, and has important research significance for electrocatalytic oxidation of HMF. In this paper, the reaction mechanism of HMF undergoes electrocatalytic oxidation to produce FDCA are elaborately summarized. There are two reaction pathways and two oxidation mechanisms of HMFOR discussed deeply. In addition, the speculation on the response of the electrode potential to HMFOR is presented in this paper. The main non-noble metal electrocatalysts currently used are classified and summarized by targeting metal element species. Finally, the paper focus on the mechanistic effects of non-noble metal catalysts in the reaction, and provide the present prospects and challenges in the electrocatalytic oxidation reaction of HMF.

Zeolite-induced defect engineering for synthesis of CuBTC-derived novel carbon-zeolite bifunctional support catalyst for multicomponent VOCs catalytic oxidation removal

In this study, a novel carbon-zeolite hybrid supported Cu catalyst (CuC@NaY) was facilely fabricated by zeolite-induced CuBTC self-assembled growth. The CuC@NaY-3 had a homogeneous spongy nanocage structure, coupled with rich active centers and most oxygen vacancy defects, making it have improved catalytic activity, multi-pollutant adaptability, as well as superior robustness and stability for practical applications. Proper volume of acetone enhanced the catalytic oxidation of toluene on CuC@NaY-3. The T90 for toluene and acetone mono-component catalytic oxidation on CuC@NaY-3 were 265.0 and 214.0 °C, respectively. Whereas for toluene/acetone mixture oxidation, due to the generated enol functional group (−o–) of acetone oxidation the T90 of toluene was reduced to 260.5 °C. The CuC@NaY-3 has also exhibited better water resistance and stability in the catalytic oxidation of toluene/acetone mixture. The DFT calculation proved that CuO led to a more pronounced activity in mono-component oxidation, while Cu2O played a facilitating role when the two pollutants co-exist.

Nanoconfined Cu clusters-activated peroxodisulfate for efficient wastewater decontamination via polymerization

In water treatment, the transition from mineralization to polymerization of organic pollutants is an essential step towards carbon and energy recovery. However, achieving efficient polymerization through the construction of heterogeneous catalysts remains a great challenge. In this work, we prepared Cu clusters nanoconfined in ZIF-derived carbon hollow structure to activate peroxodisulfate (PDS), achieving efficient wastewater decontamination via polymerization. The reaction rate is increased by a factor of 62. It shows excellent performance under different conditions (pH, anions, aqueous) as well as stability. Experiments and DFT calculations show that the removal of Bisphenol A was mainly by the direct oxidative transfer process, Cu–N and Cu clusters were involved in the catalytic oxidation. The removal of COD and TOC could reach 80% and 63.50%, respectively. This work provides technical support for the accelerated mechanism of oxidative polymerization during the treatment of toxic organic wastewater.

Catalytic oxidation of CO over CuO@TiO2 catalyst: The relationship between activity and adsorption performance

AbstractThe emission of CO toxic gases seriously endangers environmental safety and human health. At present, the use of catalysts for catalytic oxidation of CO has become the mainstream research direction. In this study, CuO@TiO2 catalysts with different ratios were prepared by solvent hydrothermal method, and the effects of reaction pretreatment temperature and other factors on the catalytic oxidation performance of CO were investigated. The experimental results show that the catalyst can achieve 100% conversion of CO at 115°C under the condition of pretreament at 350°C for 2 h. This excellent performance is due to the uniform distribution of the active component on the surface of the TiO2 support, and the large pore structure constructed by the solvent hydrothermal method enhances the adsorption and activation of CO. This work provides an idea for the preparation of CO oxidation catalysts.

Iron and nitrogen co-doped biochar membrane for SMX removal in water by filtration and catalytic oxidation

Iron and nitrogen co-doped biochar membrane for SMX removal in water by filtration and catalytic oxidation

Enhanced photo-assisted thermal catalytic oxidation of formaldehyde via abundant surface adsorbed oxygen in Co3O4 with the assistance of natural zeolite

Photo-assisted catalytic oxidation is a promising and sustainable method for the formaldehyde (HCHO) degradation. Catalyst loading and surface adsorbed oxygen species are common strategies to enhance the efficiency of photo-assisted catalytic oxidation. In this work, acid-treated zeolite-based natural zeolites (mordenite and stellerite) were used as supports, to obtain Co3O4-natural zeolite composites by impregnation and MOF-templated methods. Under the combined action of visible light irradiation and heat condition, the photo-assisted thermal catalytic performance of different composites was determined. Among these composites, the Co-AS (Co3O4-acid-treated stellerite) composite exhibited the best HCHO mineralization performance. The use of acid-treated stellerite as a catalyst carrier effectively reduced the crystallite size of Co3O4, improved its dispersibility, and increased the surface adsorbed oxygen species, contributing to enhanced catalytic efficiency. The in-situ DRIFTs results showed that the main intermediates of photo-assisted thermal catalysis degradation were dioxymethylene (DOM) and HCOO-. Additionly, the reusability performance of the composites was also investigated. Experimental results showed that the composite had good photo-assisted thermal catalytic performance and durability, making it a promising catalyst for indoor air purification.

Mofs-derived transition metal carbon-based compounds supported Au-Pt catalyst for the catalytic oxidation of glycerol to glyceric acid

Accurately controlling the directional activation of the primary and secondary hydroxyls and preventing the deep oxidation of oxygen-containing functional groups and the degree of C–C cleavage is still a great challenge for the selective oxidation of glycerol to glyceric acid. Hence, a series of bimetallic Au-Pt/MxOyCz catalysts (M = Cu, Co, Ce, Mn, Ni, Zn, Zr) were prepared using MOFs-derived transition metal carbon-based compounds as the support. These catalysts were utilized for glycerol catalytic oxidation to glyceric acid under basic conditions. The experimental date indicated that the type of transition metal makes a big difference on the conversion of glycerol and the selectivity of glyceric acid under the mild condition of 60 ℃. Among them, the Mn-modified carbon-based compound supported Au-Pt/MnxOyCz catalyst has the best catalytic activity. After reaction for 2 h, the conversion of glycerol could reach 100 %, and the selectivity of glyceric acid could reach 57.3 %. The reason for the best activity of the Au-Pt/MnxOyCz catalyst is that the particle size of active molecules is small, and the strong metal-support interaction produces more active sites. Specifically, Au-Pt/MnxOyCz catalyst forms an Au-Pt alloy, and the synergy between alloyed Au-Pt and Mn&+ enhances the acidity of the catalyst, causing it to produce the most acidic sites and promoting the dispersion of metal nanoparticles. The strong basic site of the catalyst can promote Au-Pt electron transfer, which in turn changes the reducing properties of Au-Pt and enriches the oxygen vacancies of the catalyst. Therefore, the synergistic interaction between the acidic sites and strong basic sites promotes the activation of Au-Pt, which in turn promotes the reduction of Mn-based oxides and the activation and migration of oxygen. This work will offer some new recommendations for the development of MOFs-derived transition metal-based catalysts for the catalytic oxidation of bio-polyols under mild conditions.

Optimal carbofuran degradation via CWPO in NOM-doped water by a framework Cu-doped aluminate perovskite catalyst derived from aluminum saline slags

This study is the first to propose the synthesis of LayAl1–xCuxO3–δ perovskite catalysts using Al recovered from acid leaching of saline slags. The effect of parameters such as the La/Al molar ratio was explored during the synthetic process. A suite of characterization techniques—including XRF, XRD, N2 adsorption, H2-TPR, FTIR, TGA-DTA, TEM, SEM, EDX, and XPS—confirmed the successful synthesis of high-purity (up to 90 %) perovskites with La and O vacancies, and a high concentration of Cu(I) active sites dispersed within the perovskite lattice. The best catalyst was used to optimize the degradation of carbofuran (CBF) in water doped with synthetic dissolved natural organic matter (NOM) using the Fenton-like catalytic wet peroxide oxidation (CWPO) approach. The effects of catalyst concentration, H2O2 dose, and pH on catalytic performance were investigated. Degradation, mineralization (COD removal), and H2O2 consumption were maximized, while Cu leaching was minimized using a statistical desirability function for multiple responses. Optimal conditions were found to be a catalyst concentration (mg Cu/mg H2O2) of 0.234 (2.0 g L–1), an H2O2 dose of 73.3 % (0.73 times the stoichiometric dose for full COD mineralization), and a remarkable circumneutral pH of 6.2. Under these conditions, degradation reached 94.1 %, and COD mineralization was 51 % under room temperature. Notably, the perovskite catalyst exhibited remarkable stability during reuse in up to three cycles, as demonstrated by the low Cu leaching (<1.30 mg L–1).

Geometrical features and chemical adsorptions of (Ag3Sn)n clusters

The Ag-Sn alloys are famous ancient intermetallics, with the Ag3Sn being a crucial component of the phase diagram. Recently, Ag3Sn nanoparticles showcase efficient catalytic CO oxidation capabilities. Here, structural features and stability of (Ag3Sn)n (n = 1–6) clusters are first analyzed in detail. The results reveal that structures of them evolve from cages to close-packed icosahedra, where Ag are distributed on cores and gradually aggregated, whereas Sn occupy edge positions and become dispersed. Moreover, the icosahedral (Ag3Sn)3 has a higher stability than that of its neighbors and can maintain the structural integrity at 700 K. The molecular orbitals reveal that the (Ag3Sn)3 has an electronic open-shell configuration of 1S21P61D102S21F1, which is confirmed by the density of states. Electrostatic potential surfaces show that (Ag3Sn)n have significant electron-deficient σ-hole regions at Ag sites, which can make CO stretching frequencies and bond lengths have red-shifts. Adsorption energies between (Ag3Sn)n and CO display odd–even oscillations, ranging from (0.43–0.68) eV, and the direction of charge flows is from CO → clusters. Our work provides inferences to structure evolutions and adsorptions of the Ag3Sn alloy at the atomic level.

Integrated syngas biorefinery for manufacturing ethylene, acetic acid and vinyl acetate

The paper presents the design of an innovative process for manufacturing sustainable biochemicals, as acetic acid, ethylene and vinyl acetate monomer (VAM), in an integrated syngas biorefinery using renewable feedstock as biomethane and captured CO2. The work is supported by full design and simulation of six plants imbedded in a large process: syngas1 H2/CO 2:1 by catalytic partial oxidation of methane, syngas2 H2/CO 1:1 by dry methane reforming, methanol, acetic acid by carbonylation, ethylene and vinyl acetate. A key contribution is the development of a novel acetic-acid-to-ethylene process starting from syngas. This consists of catalytic hydrogenation of acetic acid (exothermic) followed by catalytic ethanol dehydration (endothermic). The thermal integration of reactors leads to low energy process and superior sustainability measures versus petrochemical and methanol-to-olefin processes. The comprehensive simulation of the integrated biorefinery allows getting consistent mass and energy balances, performing energy analysis and capital cost estimation, and finally delivering reliable sustainability measures. Based on syngas the carbon-yield, mass-yield, carbon footprint (kg CO2/kg product) and energetic requirement (MJ/kg) are 78.6%, 34.7%, 1.6 and 11.2 for ethylene, and 80.8%, 46.8%, 1.5 and 11.9 for VAM. At high biomethane price the ethylene may be costly but manufacturing the higher value VAM is fully profitable.

Highly efficient Ru/CeO2 catalyst using colloidal chemical method for propane oxidation

Although supported-Ru catalysts have been widely studied for the light alkane oxidation root in their lower cost compared to Pt and Pd, developing Ru-based catalysts with high efficiency for low-temperature light alkane elimination remains a significant challenge. Herein, Ru/CeO2 catalysts were prepared utilizing the colloidal synthesis (Ru/CeO2-CS) and compared with the catalyst prepared with the traditional impregnation method (Ru/CeO2-IM) in the textural properties and catalytic propane oxidation. It was discovered that Ru/CeO2-CS sample contained a higher concentration of active Ru − O − Ce interface and oxygen vacancies attributed to the strong Ru-CeO2 interaction, which further enhanced the redox capacity. Besides, the lower valence state of Ru species and higher contents of Lewis acid sites on Ru/CeO2-CS sample boosted the adsorption, dissociation, and activation of propane, thus promoting the deep oxidation of propane to CO2 and H2O. The reaction mechanism of propane oxidation was revealed by in-situ DRIFTS, and both the catalysts showed bands related to acrylate species, suggesting that propane underwent an acrylate oxidation pathway on Ru/CeO2-CS and Ru/CeO2-IM samples. The distinct textural properties of these catalysts resulted in Ru/CeO2-CS synthesized by colloidal methods showing a T90 of 170 °C, and Ea of 50.9 ± 1.8 kJ·mol−1, markedly lower than Ru/CeO2-IM prepared with the traditional impregnation method. Apart from the activity, the Ru/CeO2-CS sample obtained superior water resistance, thermal stability, and durability. This comprehensive work provides promising insights into low-temperature propane oxidation.

Neuroprotective Effect of Natural Indole and β-carboline Alkaloids against Parkinson's Disease: An Overview.

Parkinson's disease (PD) is a devastating neurodegenerative condition that mostly damages dopaminergic neurons in the substantia nigra and impairs human motor function. Males are more likely than females to have PD. There are two main pathways associated with PD: one involves the misfolding of α-synuclein, which causes neurodegeneration, and the other is the catalytic oxidation of dopamine via MAO-B, which produces hydrogen peroxide that can cause mitochondrial damage. Parkin (PRKN), α-synuclein (SNCA), heat shock protein (HSP), and leucine-rich repeat kinase-2 (LRRK2) are some of the target areas for genetic alterations that cause neurodegeneration in Parkinson's disease (PD). Under the impact of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which is also important in Parkinson's disease (PD), inhibition of mitochondrial complex 1 results in enhanced ROS generation in neuronal cells. Natural products are still a superior option in the age of synthetic pharmaceuticals because of their lower toxicity and moderate side effects. A promising treatment for PD has been discovered using beta-carboline (also known as " β-carboline") and indole alkaloids. However, there are not many studies done on this particular topic. In the herbs containing β-carbolines and indoles, the secondary metabolites and alkaloids, β-carbolines and indoles, have shown neuroprotective and cognitive-enhancing properties. In this review, we have presented results from 18 years of research on the effects of indole and β-carboline alkaloids against oxidative stress and MAO inhibition, two key targets in PD. In the SAR analysis, the activity has been correlated with their unique structural characteristics. This study will undoubtedly aid researchers in looking for new PD treatment options.

Influence of flue gas components on SO2 adsorption by activated carbon at low temperature

Activated carbon can adsorb SO2 in flue gas, whose performance is significantly enhanced when lowering the adsorption temperature; however, the characteristics and mechanism of SO2 adsorption under the action of complex flue gas components at low temperatures remain unclear. In this study, adsorption experiments were conducted to investigate the characteristics of SO2 adsorption on activated carbon and the impact of O2, H2O, and NO within −20 to 20 °C. The saturated adsorption of SO2 showed a 2.21-fold increase when the temperature was lowered from 20 °C to −20 °C. Within this temperature range, physical adsorption was dominant, accounting for 73.7–91.0 %. O2 and H2O inhibited the physical adsorption of SO2 and promoted its chemical adsorption. As the temperature was lowered, the promoting effect of O2 increased, while the influence of H2O shifted from promotion to inhibition. NO affects SO2 adsorption only when co-existing with O2. As the temperature decreased, the promoting effect of NO on both physical and chemical adsorption strengthened and was significantly higher than that of O2 and H2O. Based on desorption experiments and quantum chemical calculations, the mechanisms by which H2O and NO affect SO2 adsorption were proposed·H2O and SO2 share the same physical adsorption sites, with H2O being more strongly adsorbed, thus significantly inhibiting the SO2 physical adsorption. When NO coexists with O2, gaseous SO2 reacts with the NOx adsorption configurations to form C-SO3 and C-HSO3. Active atoms near C-SO3 and C-HSO3 can adsorb NO2, forming a co-adsorption configuration, which in turn enhances the nearby physical adsorption of SO2. Enhancing the catalytic oxidation and adsorption of NO through surface modification of activated carbon can improve the low-temperature adsorption performance of SO2.

Synthesis and carbon monoxide purification performance of ZSM-5 molecular sieve Co-doped Mn/V catalytic material

Trackless, rubber-tired, diesel-powered vehicles are widely used in the mining industry. In recent years, the use of high-performance catalysts to remove carbon monoxide (CO) from diesel vehicle exhaust has attracted much attention. In this paper, a series of manganese-vanadium doped ZSM-5 molecular sieve catalysts were prepared by an impregnation method. The structures of the catalysts were characterized and experiments were conducted to evaluate their performance. The CO catalytic oxidation performance experiments revealed that Mn0.6-V0.4-ZSM-5 had the best performance, with a conversion rate of 97.5 % at 300 °C. The catalyst was also tested for water resistance and stability. Kinetic measurements were performed and the fitted activation energy was 22.68 kJ/mol. Characterization studies revealed that the surface defects formed by Mn and V doping provided a large number of active sites and oxygen vacancies for CO oxidation, increased the number of adsorbed oxygen species on the surface, and enhanced the redox capacity through the interaction of Mn4+ and V5+ to improve the catalytic oxidation performance of the catalyst. The adsorption configurations, adsorption energy (Ebin), and formation energy of oxygen vacancies of CO at different adsorption sites and different active fractions were calculated with density functional theory. The Ebin of CO on Mn2V2O7, the active fraction of Mn0.6-V0.4-ZSM-5, was −1.29 eV, which was the most stable adsorption configuration. This configuration had good oxygen mobility, and was conducive to CO catalysis, confirming the characterization and performance experiments.

AMn2O4 (A = Ni, Co, Cu) oxygen carrier chemical looping reforming of benzene: Migration pathways of reactive oxygen species by experimental and DFT investigations

Chemical looping reforming (CLR) provides a novel solution for clean and efficient utilization of biomass tar. The versatility of oxygen carrier (OC) is essential for improving reforming efficiency. The properties of Mn-based spinel OCs (AMn2O4, A = Ni, Co, Cu) were investigated in the CLR process using benzene as a tar model compound. Detailed characterization and experimental results demonstrate the excellent structural stability of Mn-based spinel. The NiMn2O4 showed the most prominent reforming effect on benzene with the highest conversion of 95.77 % at 850 °C, S/C = 1.0, and WHSV = 3.0 h−1. After 40 cycles, NiMn2O4 and CoMn2O4 maintained significant catalytic activity for benzene reforming, achieving conversions of 92.96 % and 90.07 %, respectively, in the final cycle. Density functional theory (DFT) calculations demonstrate that the addition of H2O increases the activity of NiMn2O4. Compared to benzene adsorption alone, the adsorption energy decreased from −2.20 eV to −2.54 eV after the addition of H2O. The migration path of NiMn2O4 (100) reactive oxygen species in the presence or absence of H2O is directly demonstrated. In the absence of H2O, the activation energy barrier for direct oxidation of C6H5* by NiMn2O4 lattice oxygen is dominant (0.98 eV), but OH* produced by dissociation of H2O exhibits high activity, and oxidation of C6H5* to produce the key intermediate product C6H5O* has an activation energy barrier of only 0.35 eV. In addition, H2O has a predominant role in the replenishment of oxygen vacancies. The elucidation of the oxygen migration mechanism provides new guidance for the design of efficient OCs for catalytic oxidation.

High-Valent Iron–Oxo species in heterogeneous Catalysis: Formation, Mechanism, and reactivity for the degradation of various emerging organic contaminants

High-valent iron–oxo species (FeⅣ/Ⅴ=O), generated via peroxide activation with Fe-based catalysts, have shown potential in the selective and efficient degradation of organic contaminants. However, a comprehensive understanding of the oxidative degradation mechanism induced by FeⅣ/Ⅴ=O is still pending. In this research, to unravel this oxidation mechanism, an Fe-single atom catalyst (FeN4-C) was synthesized, and FeⅤ=O was formed as the predominant reactive species upon peroxymonosulfate (PMS) activation. The FeN4-C/PMS system was experimentally studied on its catalytic oxidation behavior for the degradation of 34 typical emerging organic contaminants (EOCs) in water, exhibiting a significant variation in the pseudo first-order kinetic rate constants (kobs) among the EOCs. A quantitative structure–activity relationship (QSAR) model was established based on the molecular structure feature and measured kobs of the EOCs. The model infers that EOCs with higher electron donating ability (EHOMO) are more susceptible towards FeN4-C/PMS oxidation, implying an electrophilic reaction following the single electron transfer (SET) mechanism. Further exploration of the degradation pathways for seven representative EOCs revealed that the oxidation occurs through the abstraction of either a hydrogen atom or a nonbonded (or π) electron by FeⅤ=O, enabling processes such as C-, N-, and S-oxidation, along with N- and O-dealkylation and deamination, to effectively degrade EOCs. These research findings provide a robust theoretical framework for understanding the reaction mechanisms and predicting the degradability and removal of various EOCs by FeⅣ/Ⅴ=O for water purification.

Efficient catalytic oxidation of xylose to formic acid with the oxygen vacancies of CeO2 promoted the vanadium catalysts anchored on biochar

The catalytic oxidation of carbohydrates for the preparation of formic acid (FA) is an prominent route for high-value utilisation of biomass. Reforming xylose, a biomass derivative, into FA with high efficiency is essential for the advancement of non-homogeneous V-type catalysts. Here, we present the self-assembly of V and Ce onto a cellulose pulp for the synthesis of oxygen vacancy (Ov)-rich non-homogeneous-bimetallic catalysts (5Ce-VOx/BC-600). Under the optimised conditions, 71.46 % FA was obtained, which far exceeded the catalytic performance of the single-metal catalyst. Furthermore, the 5Ce-VOx/BC-600 catalyst showed excellent stability and reusability. Kinetic studies revealed that glyceric and glycolic acids served as the pivotal intermediates, undergoing subsequent deacidification and oxidation processes to yield FA and CO2. The analysis of the catalytic mechanism indicated that the incorporation of Ce enhanced the quantity of acidic sites and the concentration of Ov in the 5Ce-VOx/BC-600 catalyst, which promoted substrate adsorption and O2 activation. Meanwhile, the catalyst showed high lattice oxygen (OL) mobility and assisted the redox cycle of V5+/V4+ to oxidise xylose to FA. Significantly, the synergistic effect of Ce, V species and Ov enhances the OL mobility of the catalysts, thus promoting the efficient oxidation of xylose. The catalytic system was further extended to the oxidation of other biomass derivatives to FA, demonstrating excellent catalytic performance.

Oxidative degradation of anionic dyes in wastewater by magnetic lignin micro-nano spheres catalyzed peroxymonosulfate

Lignin has gained significant attention in wastewater treatment due to its abundant resources and good adsorbability. In this work, magnetic lignin micro-nano spheres (Fe3O4@SiO2-LNS) was prepared using alkali lignin as the raw material, and was used as the adsorbent and catalyst to activate peroxymonosulfate (PMS) to build an inhomogeneous catalytic oxidation system (Fe3O4@SiO2-LNS/PMS). The system was then used to remove the stubborn acid blue 9 (AB9) dye in wastewater, and the effects of pH, catalyst dosage, PMS dosage of the system on the removal percentage of AB9 dye and the corresponding degradation mechanism were explored. The results showed that Fe3O4@SiO2-LNS/PMS system had good removal efficiency for AB9 in wastewater, and AB9 dye was completely oxidized and finally degraded into CO2 and H2O. The maximum removal percentage of AB9 was observed when the pH and temperature of the system were 6.0 and 313 K, and the removal percentage of AB9 achieved 100 % when the optimal dosage of Fe3O4@SiO2-LNS and PMS were 3.44 g/L and 53.15 mM, respectively. In addition, Fe3O4@SiO2-LNS had good stability and reusability. This work provides a promising approach for abatement of dyeing wastewater pollution and a new direction for high-value utilization of alkali lignin.

Catalytic oxidation of Mn(II) on ferrihydrite and goethite surfaces and the subsequent oxidation and immobilization of coexisting Cr(III)

Catalytic oxidation of Mn(II) on ferrihydrite and goethite surfaces and the subsequent oxidation and immobilization of coexisting Cr(III)

Facet-dependent effect of α-MnO2 on Ag atoms anchoring and low-temperature selective catalytic oxidation of ammonia

Ammonia (NH3) contributes greatly to haze formation, posing significant risks to ecology and health. As a typical NH3 selective catalytic oxidation (NH3-SCO) catalyst, Ag supported catalysts can balance activity and selectivity. In this research, Ag atoms were anchored on the various crystal facets ({310}, {110} and {100}) of α-MnO2 and were studied for the NH3-SCO. The facet-dependence on Ag atoms anchoring mechanism, as well as the anchored Ag structure, have all been revealed in detail. It was found that the capturing of Ag on the facets of α-MnO2 followed the terminal hydroxyl anchoring mechanism, and further confirmed the linear relationship between Ag capturing quantity and the amount of terminal hydroxyl groups. The {310} facet has a strong ability to activate water molecules to produce surface hydroxyl groups, thereby exhibiting a heightened capability to capture Ag atoms; Ag atoms are loaded in the form of fine nanoparticles on the {310} facet, while anchored in a highly dispersed form on the {110} and {100} facets. The anchoring of Ag significantly improves the NH3-SCO performance of α-MnO2, especially, the Ag/α-MnO2 catalyst with Ag anchoring on the {310} facets exhibited the best activity, achieving 100 % conversion and greater than 80 % N2 selectivity at as low temperature as 100 °C. Finally, the adsorption and possible NH3-SCO mechanism of Ag/α-MnO2 catalysts were also explored by in-situ DRIFTS. The aim of this research is to reveal the facet-dependence of α-MnO2on Ag atoms anchoring,and its effect on low-temperature NH3-SCO activity.