Search Results (101)

This review examines the research progress on non-noble-metal-based catalysts for formaldehyde (HCHO) oxidation at room temperature. It begins with an introduction to the hazards of HCHO as an indoor pollutant and the urgency of its removal, comparing several HCHO removal technologies and highlighting the advantages of room-temperature catalytic oxidation. It delves into the classification, preparation methods, and regulation strategies for non-precious metal catalysts, with a focus on manganese-based, cobalt-based, and other transition metal-based catalysts. The effects of catalyst preparation methods, morphological structure, and specific surface area on catalytic performance are discussed, and the catalytic oxidation mechanisms of HCHO, including the Eley–Rideal, Langmuir–Hinshelwood, and Mars–van Krevelen mechanisms, are analyzed. Finally, the challenges faced by non-precious metal catalysts are summarized, such as issues related to the powder form of catalysts in practical applications, lower catalytic activity at room temperature, and insufficient research in the presence of multiple VOC molecules. Suggestions for future research directions are also provided. Full article

Progressive research on reducing engine emissions is highly valued due to the emissions’ significant environmental and health impacts. This comprehensive comparative study examines the catalytic efficiency of manganese (Mn) and cerium silica (Ce-Si) synthesis catalyst-based molds in a diesel engine using a selective catalytic reduction (SCR) technique with diesel and diesel–plastic oil blend (DPB) (B50). In addition to Fourier transform infrared spectroscopy (FTIR) studies, X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer–Emmett–Teller (BET) method are utilized to characterize the produced molds before and after exhaust gas passes. The Ce-Si-based mold demonstrates superior redox capacity, better adsorption capacity, and better thermal stability, attributed to enhanced oxygen storage and structural integrity compared to the Mn-based mold. Under minimum load conditions, nitrogen oxide (NO) reduction efficiency peaks at 80.70% for the Ce-Si-based mold in the SCR treatment with DPB fuel. Additionally, significant reductions of 86.84%, 65.75%, and 88.88% in hydrocarbon (HC), carbon monoxide (CO), and smoke emissions, respectively, are achieved in the SCR treatment under optimized conditions. Despite a wide temperature range, Ce-Si-based mold promotes high surface area and superior gas diffusion properties. Overall, the Ce-Si-based mold provides efficient emission control in diesel engines, which paves a path for developing better environmental sustainability. The outcomes contribute to advancing environmental sustainability by supporting the achievement of SDGs 7, 11, and 13. Full article

Zinc–air batteries (ZABs) are crucial for renewable energy conversion and storage due to their cost-effectiveness, excellent safety, and superior cycling stability. However, developing efficient and affordable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) at the air cathode remains a significant challenge. Manganese (Mn)-based materials, known for their tunable oxidation states, adaptable crystal structures, and environmental friendliness, are regarded as the most promising candidates. This review systematically summarizes recent advances in Mn-based bifunctional catalysts, concentrating on four primary categories: Mn–N–C electrocatalysts, manganese oxides, manganates, and other Mn-based compounds. By examining the intrinsic merits and limitations of each category, we provide a comprehensive discussion of optimization strategies, which include morphological modulation, structural engineering, carbon hybridization, heterointerface construction, heteroatom doping, and defect engineering, aimed at enhancing catalytic performance. Additionally, we critically address existing challenges and propose future research directions for Mn-based materials in rechargeable ZABs, offering theoretical insights and design principles to advance the development of next-generation energy storage systems. Full article

Current research on the synthesis of isonicotinic acid (INA) has focused on the development of catalysts by mixing transition metal oxides such as vanadium, titanium and zirconium in the desired molar ratio. These materials have good catalytic activity (CA) but have drawbacks, including low resistance to deactivation and limited ability to control reaction selectivity. In the present study, two- and three-component catalysts containing vanadium were successfully synthesized and their compositions and properties were studied. The experimental results showed that the efficiency of V-Ti-Mn-O catalyst was superior to V-Ti-O. Selectivity analysis showed that V-Ti-Mn-O was the most efficient catalyst, reaching a maximum value of 67.17% at 320 °C. Scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) were used to characterize the catalysts. The corresponding experimental results showed that the superior performance of the V-Ti-Mn-O catalyst was attributed to both the smaller size of the catalyst particles and their more uniform distribution. In the oxidation of 4-methylpyridine (4-MP), the V-Ti-O catalyst showed lower CA and stability compared to the V-Ti-Mn-O catalyst, which can be attributed to its limited CA and potential deactivation at higher temperatures, probably due to excessive oxidation. Full article

In recent years, extensive attention has been paid to advanced oxidation processes (AOPs) with peracetic acid (PAA), a widely used disinfectant, using transition metal ions for the degradation of organic contaminants within water environments. Mn(II) has been widely used as an effective homogeneous transition metal catalyst for oxidant activation, but it has shown poor performances with PAA. Since the stability of manganese species can be enhanced through the addition of ligands, this study systematically investigated a novel AOP for the oxidation of carbamazepine (CBZ) using an Mn(II)/PAA system with several different ligands added. The reactive species were explored through UV-vis spectrometry, scavengers, and probe compounds. The results suggest that Mn(III)–ligand complexes and other high-valent Mn species (Mn(V)) were generated and contributed obviously toward efficient CBZ oxidation, while radicals like CH₃CO₂^• and CH₃CO₃^• were minor contributors. The oxidation efficiency of Mn(II)/PAA/ligands depended highly on ligand species, as ethylene diamine tetraacetic acid (EDTA) and oxalate (SO) could promote the oxidation of CBZ, while pyrophosphate (PPP) showed modest enhancement. The results obtained here might contribute to the removal of residue pharmaceuticals under manganese-rich waters and also shed light on PAA-based AOPs that could help broaden our present knowledge of manganese chemistry for decontamination in water treatment. Full article

A novel amorphous Fe-doped manganese carbonate (a-FeMn-1) was synthesized via a facile co-precipitation method and evaluated as an efficient heterogeneous catalyst for the activation of peroxymonosulfate (PMS) in the degradation of Orange II. Among various Fe/Mn molar ratios, the 1:1 composition (a-FeMn-1) showed optimal catalytic activity, achieving 98% removal efficiency within 60 min under near-neutral pH conditions. Characterization results indicated that Fe doping effectively induced an amorphous structure and increased surface area and oxygen defects, promoting PMS activation. The system displayed broad pH applicability and resistance to Cl⁻ and natural organic matter, while degradation was inhibited by HCO₃⁻ and PO₄³⁻. EPR and quenching experiments confirmed that surface-bound sulfate radicals (SO₄^•−), hydroxyl radicals (^•OH), and singlet oxygen (¹O₂) were the primary reactive species. XPS analysis further revealed the redox cycling of Fe and Mn and the involvement of defect oxygen in the PMS activation process. The catalyst also demonstrated excellent reusability over five cycles without significant loss in efficiency. This work provides insights into the rational design of amorphous bimetallic materials for sulfate radical-based advanced oxidation processes. Full article

The production of formic acid (FA) from lignocellulose and its derived sugars represents a pivotal upgrading reaction in biorefinery. This work prepared a Mn-Mo doped carbon nanotube composite catalyst for the catalytic oxidation of glucose into FA in an O₂ atmosphere, under extremely low Mn (3.27%) and Mo (0.40%) loading conditions, displaying a comparable performance with the traditional vanadium-based catalyst suffering from toxicity issues. It was confirmed that the doping of Mo led to the formation of MnMoO_X and increased the contents of low-valence Mn species (Mn²⁺ + Mn³⁺), lattice oxygen (O_latt), and surface adsorbed oxygen (O_ads) based on various characterization methods, such as XRD, XPS, TEM and ICP, which were beneficial to improve the catalytic performance. The maximum FA yield of 58.8% could be achieved over Mn₉Mo₁O_X@MWCNT after reaction for 6 h at 140 °C, which was far more than that obtained with undoped MnO_X@MWCNT (14.5%) at the identical conditions. Glyoxylic acid and arabinose were identified as two main intermediates, suggesting that the transformation of glucose into FA over Mn₉Mo₁O_X@MWCNT involved two different paths. This work proved that manganese-based catalyst was a green alternative for upgrading lignocellulose via catalytic oxidation. Full article

A series of novel NNN pincer manganese complexes based on pyrazole skeleton 4 were efficiently synthesized in a two-step process. All of the new complexes were fully characterized by ¹H, ¹³C NMR spectra. Furthermore, the molecular structures of complexes 4a and 4c were also determined by X-ray single-crystal diffraction. The manganese(I) catalysts obtained showed efficient catalytic activity in the α-alkylation reaction of ketones with alcohols. Under optimal reaction conditions, the expected products were procured with moderate to high yields. Full article

Transfer hydrogenation is a crucial technology for synthesizing fine chemicals and pharmaceuticals, offering improved safety and convenience over traditional hydrogen methods, although it typically requires external bases. While isopropanol is commonly used as a hydrogen source, methanol is superior but faces challenges due to its high dehydrogenation energy barrier, limiting its use under mild conditions. This study focuses on investigating the differences in the electrogenerated base-driven transfer hydrogenation of aromatic ketones in isopropanol and methanol solvents, using Mn(CO)₅Br and cyclohexanediamine derivatives as the catalyst. The research demonstrates that high enantiomeric excess (ee) values were obtained in isopropanol in the presence of chiral Mn-based catalysts, while only racemic products were observed in methanol. The results indicate a strong dependence of the catalytic pathway on the choice solvent: in isopropanol, the catalyst operates via a metal–ligand cooperative transfer hydrogenation, resulting in high ee values, whereas in methanol, transfer hydrogenation occurs through metal hydride transfer with no stereoselectivity. Full article

Manganese-based oxides with good redox properties exhibit high soot oxidation activity. To further enhance their catalytic performance, introducing additional metal elements into manganese-based oxides is considered an effective approach. Herein, two rare earth elements (Sm and Ce)-modified MnO_x catalysts were prepared by the co-precipitation method. The synthesized MnO_x catalyst primarily consists of the Mn₃O₄ phase, with trace amounts of Mn₅O₈. The addition of Sm or Ce maintains the predominance of the Mn₃O₄ phase, increases the proportion of Mn₅O₈, and enhances the redox properties, thereby boosting the catalytic activity for NO and soot oxidation. Notably, the coexistence of Sm and Ce achieves optimal soot oxidation activity, with T₁₀ reaching 306 °C. Comprehensive physicochemical characterization elucidates the underlying structure–performance relationships of these catalysts. Full article

This study explores the synergistic interactions between photocatalysis, ozone treatment, and metal catalysts in the decomposition of acetaldehyde, a representative volatile organic compound (VOC). The study addresses the growing need for efficient air purification technologies by integrating advanced oxidation processes. Metal catalysts, particularly manganese oxide-based materials, were combined with photocatalysis and ozonation to investigate their impact on acetaldehyde removal efficiency. Experimental results revealed that the treatment integrating these methods significantly outperformed conventional single-process treatments. Metal catalysts facilitated the initial oxidation of acetaldehyde, while photocatalysis accelerated subsequent stages, including the mineralisation of intermediates. Ozone contributed additional reactive oxidative species, further enhancing decomposition rates. These findings provide valuable insights into the design of efficient VOC removal systems, demonstrating that integrating metal catalysts with photocatalytic and ozonation processes offers a promising strategy for improving air purification technologies. This approach has potential applications in environmental remediation and indoor air quality management. Full article

2,5-furandicarboxaldehyde (DFF) is one of the most promising biomass-based building blocks for the synthesis of biobased polymers. DFF can be obtained from 5-hydroxymethylfurfural (HMF), a fructose derivate, and it is a key molecule in the sequence of reactions of furan chemistry to develop biobased plastics. In this frame, four manganese(III)–Schiff base complexes 1–4 have been obtained. The general formula for the complexes, MnLⁿ(OCN)(H₂O/CH₃OH)_m (Lⁿ being the Schiff base ligands L¹–L⁴, formed as the result of the condensation of different substituted hydroxybenzaldehydes with diverse diamines, and m = 1–3), has been confirmed by characterization through different analytical and spectroscopic techniques. X-ray crystallographic studies for 1 and 2 showed tetragonally distorted octahedral structures, where the Schiff base was placed in the equatorial coordination positions of the Mn(III) ion. Complexes 1 and 2 behaved as efficient catalysts in the oxidation of HMF to DFF in an electrolytic reaction at pH 8.5, with phosphate buffer at room temperature, with conversion rates of 70–80%. On the other hand, complexes 3 and 4, where the axial position was sterically less accessible, yielded only an 11% conversion of HMF to DFF. The results indicate that a correct selection of metal complexes allows the development of a new efficient way to obtain DFF. Full article

The cobalt manganese oxides, especially the spinels and related (multiphase) materials described with the formula Co_xMn_3−xO₄ (0 < x < 3), are widely used catalysts in a range of processes in significant industrial and environmental areas. The great diversity in the phase relations, composition, and metal ion valences, together with ion and vacancy site distribution variations, results in great variety and activity as catalysts in various industrially important redox processes such as the removal of CO or volatile organic substances (VOCs) from the air and oxidative destruction of pollutants such as dyes and pharmaceuticals from wastewater using peroxides. These mixed oxides can gain application in the selective oxidation of organic molecules like 5-hydroxyfurfural or aromatic alcohols such as vanillyl alcohol or in the production of fuels and other valuable chemicals (alcohols, esters) with the Fischer–Tropsch method. In this review, we summarize these redox-based reactions in light of the chemical and phase composition of the catalysts with the formula Co_xMn_3−xO₄ with 0 < x < 3. Full article

In this work, the origin of the synergetic effect in mixed Mn_xCo_3-xO₄ oxides with the spinel structure in the CO oxidation reaction was tested. A series of Mn_xCo_3-x oxide catalysts were synthesized by the coprecipitation method with further calcination at 600 °C and varying manganese content from x = 0 to x = 3. The catalysts were characterized using XRD, TEM, N₂ adsorption, TPR, EXAFS, and XPS. The catalytic activity of Mn_xCo_3-x oxide catalysts was tested in CO oxidation reactions. The addition of manganese to cobalt oxide results in the formation of mixed Mn-Co oxides based on a cubic or tetragonal spinel structure, a change in microstructural properties, such as surface area and crystal size, as well as local distortions and a decrease in the surface concentration of Co ions and Co in the octahedral sites in spinel structure; it also decreases catalyst reducibility. For all catalysts, the activity of CO oxidation decreases as follows: Mn_0.1Co_2.9 > Co₃O₄~Mn_0.3Co_2.7 > Mn_0.5Co_2.5 > MnO_x > Mn_0.7Co_2.3 > Mn_0.9Co_2.1~Mn_1.1Co_1.9~Mn_2.5Co_0.5 > Mn_2.9Co_0.1 > Mn_1.7Co_1.3 > Mn_2.1Co_0.9 > Mn_1.3Co_1.7~Mn_1.5Co_1.5~Mn_2.3Co_0.7. The Mn_0.1Co_2.9 catalyst displays the best catalytic activity, which is attributed to its small crystal size and the maximum surface ratio between Co³⁺ and Co²⁺. A further increase in the manganese content (x > 0.3) provokes drastic changes in the catalytic properties due to a decrease in the cobalt content on the surface and in the volume of mixed oxide, changes in the oxidation states of cations, and structure transformation. Full article

Methyl mercaptan is a sulfur-based chemical found as a co-product in produced natural gas and it causes corrosion in pipelines, storage tanks, catalysts, and solid adsorption beds. To improve the quality of methane produced, researchers have studied the use of metal oxides and aluminum silicates as catalysts for removing mercaptan. However, there are restrictive limitations on the efficiency of metal oxides or aluminum silicates as adsorbents for this application. Therefore, this study investigated the performance of these materials in a fixed-bed reactor with simulated natural gas streams under various operating conditions. The testing procedure includes a detailed assessment of the adsorbent/catalysts by several techniques, such as Braeuer–Emmett–Teller (BET), Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectrometry (EDS), and X-ray Photoelectron Spectroscopy. The results revealed that metal oxides such as copper, manganese, and zinc performed well in methyl mercaptan elimination. The addition of manganese, copper, and zinc oxides to the aluminum silicate surface resulted in a sulfur capacity of 1226 mg S/g of catalyst. These findings provide critical insights for the development of catalysts that combine metal oxides to increase adsorption while reducing the production of byproducts like dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) during methyl mercaptan removal. Full article