Search Results (30)

The conversion of NO_x and the yield of N₂O during NH₃-SCR-DeNO_x below 473 K over TiO₂-supported transition metal oxide catalysts with equal loading of 20 wt.-% decreases in the following order of the supported oxides: MnO_x > CuO_x > CoO_x > FeO_x > NiO_x > CeO_x. The storage capacity for NH₃, characterized by the acid site density of the catalyst, is not directly correlated with the catalytic activity. Rather, the temperature range for the reduction of the supported transition metal oxides as determined by TPR-H₂ is the main governing factor for high NH₃-SCR-DeNO_x activity, especially in the temperature range below 473 K. At the same time, oxidation temperature range and the density of Lewis acid sites govern the formation of N₂O. The decomposition of NH₄NO₃ as an intermediate in the NH₃-SCR-DeNO_x reaction is determined by the redox property of TMO-based catalysts, which further influences both the windows of the decomposition temperature and the yield of N₂O. The correlation between the redox properties and the activity for NH₃-SCR-DeNO_x was confirmed for a series of MnO_x-CeO_x/TiO₂-SiO₂ mixed transition metal oxide catalysts as a promising combination of the less active and more selective CeO_x with less selective and highly active MnO_x. The linear correlation between reduction temperature range and the NH₃-SCR-DeNO_x activity indicates that the found relation can be transferred to other supported transition metal-containing catalysts for low-temperature NH₃-SCR-DeNO_x. Full article

This study investigated the influence of the ultraviolet (UV) dose (${\mathrm{D}}^{\mathrm{U}\mathrm{V}}$) on the photodeposition of MnO_x and Pd cocatalysts on 300-nm-thick anatase TiO₂ thin films, which were prepared via sol–gel dip-coating on a glass substrate. MnO_x and Pd were photodeposited using increasing UV doses ranging from 5 to 20 J cm⁻², from 5 mM aqueous electrolytes based on Mn²⁺/IO₃⁻ or Pd²⁺, respectively. The effect of the ${\mathrm{D}}^{\mathrm{U}\mathrm{V}}$ on the MnO_x photodeposition resulted in an increase in Mn²⁺ surface content, from 2.7 to 5.2 at.%, as determined using X-ray photoelectron spectroscopy (XPS). For Pd, increasing the UV dose led to a reduction in the oxidation state, transitioning from Pd²⁺ to Pd⁰, while the overall Pd surface content range remained relatively steady at 2.2–2.4 at.%. Both MnO_x/TiO₂ and Pd/TiO₂ exhibited proportional enhancements in photocatalytic activity towards the degradation of methylene blue. Notably, Pd/TiO₂ demonstrated a significant improvement in photocatalytic performance, surpassing that of pristine TiO₂. In contrast, TiO₂ samples functionalized through wet impregnation and thermal treatment in the same electrolytes showed overall lower photocatalytic activity compared to those functionalized via photodeposition. Full article

Batch heterogeneous catalytic ozonation experiments were performed using commercial and synthesized nanoparticles as catalysts in aqueous ozone. The transferred ozone dose (TOD) ranged from 0 to 150 μM, and nanoparticles were added in concentrations between 0 and 1.5 g L⁻¹, with all experiments conducted at 20 °C and a total volume of 240 mL. A Ce-doped TiO₂ catalyst (1% molar ratio of Ce/Ti) was synthesized via the sol–gel method. Response surface methodology (RSM) was applied to identify the most significant factors affecting the removal of selected pharmaceuticals, with TOD emerging as the most critical variable. Higher TOD resulted in greater removal efficiencies. Furthermore, it was found that the commercially available metal oxides α-Al₂O₃, Mn₂O₃, TiO₂, and CeO₂, as well as the synthesized CeTiO_x, did not increase the catalytic activity of ozone during the degradation of ibuprofen (IBF) and para-chlorobenzoic acid (pCBA). Carbamazepine (CBZ) and diclofenac (DCF) are compounds susceptible to ozone oxidation, thus their complete degradation at 150 μM transferred ozone dose was attained. The limited catalytic effect was attributed to the rapid consumption of ozone within the first minute of reaction, as well as the saturation of catalyst active sites by water molecules, which inhibited effective ozone adsorption and subsequent hydroxyl radical generation (^●OH). Full article

Three MnCeTiO_x catalysts with the same composition were prepared by conventional co-precipitation (MCT-C), reverse co-precipitation (MCT-R), and parallel co-precipitation (MCT-P), respectively, and their low-temperature SCR performance for de-NO_x was evaluated. The textural and structural properties, surface acidity, redox capacity, and reaction mechanism of the catalysts were investigated by a series of characterizations including N₂ adsorption and desorption, XRD, SEM, XPS, H₂-TPR, NH₃-TPD, NO-TPD, and in situ DRIFTs. The results revealed that the most excellent catalytic performance was achieved on MCT-R, and more than 90% NO_x conversion can be obtained at 100–300 °C under a high GHSV of 80,000 mL/(g_cat·H). Furthermore, MCT-R possessed optimal tolerance to H₂O and SO₂ poisoning. The excellent catalytic performance of MCT-R can be attributed to its larger BET specific surface area; higher contents of Mn⁴⁺, Ce³⁺, and adsorbed oxygen species; and more adsorption capacity for NH₃ and NO. Moreover, in situ DRIFTs results indicated that the NH₃-SCR reaction follows simultaneously the Langmuir–Hinshelwood and Eley–Rideal mechanisms at 100 °C. By adjusting the adding mode during the co-precipitation process, excellent low-temperature de-NO_x activity of MCT-R can be obtained simply and conveniently, which is of great practical value for the preparation of a MnCeTiO_x catalyst for denitrification. Full article

In view of the flue gas characteristics of cement kilns in China, the development of low-temperature denitrification catalysts with excellent anti-poisoning performance has important theoretical and practical significance. In this work, a series of MnCeO_x@TiO₂ and tourmaline-containing MnCeO_x@TiO₂-T catalysts was prepared using a chemical pre-deposition method. It was found that the MnCeO_x@TiO₂-T2 catalyst (containing 2% tourmaline) exhibited the best low-temperature NH₃-selective catalytic reduction (NH₃-SCR) performance, yielding 100% NO_x conversion at 110 °C and above. When 100–300 ppm SO₂ and 10 vol.% H₂O were introduced to the reaction, the NO_x conversion of the MnCeO_x@TiO₂-T2 catalyst was still higher than 90% at 170 °C, indicating good anti-poisoning performance. The addition of appropriate amounts of tourmaline can not only preferably expose the active {001} facets of TiO₂ but also introduce the acidic SiO₂ and Al₂O₃ components and increase the content of Mn⁴⁺ and O_α on the surface of the catalyst, all of which contribute to the enhancement of reaction activity of NH₃-SCR and anti-poisoning performance. However, excess amounts of tourmaline led to the formation of dense surface of catalysts that suppressed the exposure of catalytic active sites, giving rise to the decrease in catalytic activity and anti-poisoning capability. Through an in situ DRIFTS study, it was found that the addition of appropriate amounts of tourmaline increased the number of Brønsted acid sites on the catalyst surface, which suppressed the adsorption of SO₂ and thus inhibited the deposition of NH₄HSO₄ and (NH₄)₂HSO₄ on the surface of the catalyst, thereby improving the NH₃-SCR performance and anti-poisoning ability of the catalyst. Full article

The substitution of ethyl acetate for ammonia in NH₃-SCR provides a novel strategy for the simultaneous removal of VOCs and NO. In this study, three distinct types of biochar were fabricated through pyrolysis at 700 °C. MnO_x and TiO₂ were sequentially loaded onto these biochar substrates via a hydrothermal process, yielding a family of biochar-based catalysts with optimized dosages. Upon exposure to xenon lamp irradiation at 240 °C, the biochar catalyst designated as 700-12-3GN, derived from Ginkgo shells, demonstrated the highest catalytic activity when contrasted with its counterparts prepared from moso bamboo and loofah. The conversion efficiencies for NO and ethyl acetate (EA) peaked at 73.66% and 62.09%, respectively, at a catalyst loading of 300 mg. The characterization results indicate that the 700-12-3GN catalyst exhibits superior activity, which can be attributed to the higher concentration of Mn⁴⁺ and Ti⁴⁺ species, along with its superior redox properties and suitable elemental distribution. Notably, the 700-12-3GN catalyst has the smallest specific surface area but the largest pore volume and average BJH pore size, indicating that the specific surface area is not the predominant factor affecting catalyst performance. Instead, pore volume and average BJH pore diameter appear to be the more influential parameters. This research provides a reference and prospect for the resource utilization of biochar and the development of photothermal co-catalytic ethyl acetate and NO at low cost. Full article

A novel Mn/TiO₂ catalyst, prepared through modification with the rare-earth metal Dy, has been employed for low-temperature selective catalytic reduction (SCR) denitrification. Anatase TiO₂, with its large specific surface area, serves as the carrier. The active component MnO_x on the TiO₂ carrier is modified using Dy. Dy_xMn/TiO₂, prepared via the impregnation method, exhibited remarkable catalytic performance in the SCR of NO with NH₃ as the reducing agent at low temperatures. Experiments and characterization revealed that the introduction of a suitable amount of the rare-earth metal Dy can effectively enhance the catalyst’s specific surface area and the gas–solid contact area in catalytic reactions. It also significantly increases the concentration of Mn⁴⁺, chemisorbed oxygen, and weak acid sites on the catalyst surface. This leads to a notable improvement in the reduction performance of the DyMn/TiO₂ catalyst, ultimately contributing to the improvement of the NH₃-SCR denitrification performance at low temperatures. At 100 °C and a space velocity of 24,000 h⁻¹, the Dy_0.1Mn/TiO₂ catalyst can achieve a 98% conversion rate of NO_x. Furthermore, its active temperature point decreases by 60 °C after the modification, highlighting exceptional catalytic efficacy at low temperatures. By doubling the space velocity, the NO_x conversion rate of the catalyst can still reach 96% at 130 °C, indicating significant operational flexibility. The selectivity of N₂ remained stable at over 95% before reaching 240 °C. Full article

Oil (and natural gas) field brines can be considered promising sources of lithium for the sustainable supply of a growing market. To date, many materials have been developed for direct lithium recovery from brines, but most often these materials have been tested under various conditions, what makes it impossible to compare them. The aim of this research is to provide knowledge that would enable the comparison and selection of effective sorbents for different types of brines. For this purpose, an eight-step experimental protocol was employed. The recovery tests started with a pure lithium solution (300 mg/kg), and then other salts were gradually added, resulting in a brine containing Li⁺ (220 mg/kg), Na⁺ (7.21 wt%), Ca²⁺ (3.0 wt%) and Mg²⁺ (1000 mg/kg). For selected cases, the effect of pH was also investigated. Fifty materials (including ion exchange resins, organophosphate extractants, mineral adsorbents) were examined, for which the distribution coefficient and lithium recovery were determined. Moreover, for the most promising materials, lithium over magnesium selectivity and lithium ion capacity were determined. Only γ-Al₂O₃, TiO₂ and MnO_x-based powders keep their effectiveness in ultra-high salinity ranges and in the presence of high concentrations of Ca²⁺ and Mg²⁺ in alkaline solution. Full article

Earth abundant transition metal oxides are low-cost promising catalysts for the oxygen evolution reaction (OER). Many transition metal oxides have shown higher OER activity than the noble metal oxides (RuO₂ and IrO₂). Many experimental and theoretical studies have been performed to understand the mechanism of OER. In this review article we have considered four earth abundant transition metal oxides, namely, titanium oxide (TiO₂), manganese oxide/hydroxide (MnO_x/MnOOH), cobalt oxide/hydroxide (CoO_x/CoOOH), and nickel oxide/hydroxide (NiO_x/NiOOH). The OER mechanism on three polymorphs of TiO₂: TiO₂ rutile (110), anatase (101), and brookite (210) are summarized. It is discussed that the surface peroxo O* intermediates formation required a smaller activation barrier compared to the dangling O* intermediates. Manganese-based oxide material CaMn₄O₅ is the active site of photosystem II where OER takes place in nature. The commonly known polymorphs of MnO₂; α-(tetragonal), β-(tetragonal), and δ-(triclinic) are discussed for their OER activity. The electrochemical activity of electrochemically synthesized induced layer δ-MnO₂ (EI-δ-MnO₂) materials is discussed in comparison to precious metal oxides (Ir/RuO_x). Hydrothermally synthesized α-MnO₂ shows higher activity than δ-MnO₂. The OER activity of different bulk oxide phases: (a) Mn₃O₄(001), (b) Mn₂O₃(110), and (c) MnO₂(110) are comparatively discussed. Different crystalline phases of CoOOH and NiOOH are discussed considering different surfaces for the catalytic activity. In some cases, the effects of doping with other metals (e.g., doping of Fe to NiOOH) are discussed. Full article

In this study, Mn-Ce/Al₂O₃/TiO₂ catalyst prepared by impregnation method was used for synergistic O₃ oxidation NO. The catalyst prepared by impregnating Al₂O₃/TiO₂ at a Mn:Ce molar ratio of 4:1 showed the best catalytic activity. The catalyst performance showed that when the molar ratio of Mn:Ce was 4:1 and the volume ratio of O₃:NO was 1:4, the removal rate of NO could reach 63%, which could increase the removal rate by 40% compared with that of NO oxidized by O₃ alone. BET, XRD, and TEM characterization results showed that when the molar ratio of Mn:Ce was 4:1, the catalyst specific surface area, and pore capacity were the largest. A large amount of MnOx and CeOx were distributed on the catalyst surface. The XPS analysis showed that the oxidation-reduction and oxygen vacancy of Mn (IV)/Mn (III)/Mn (II) and Ce (IV)/Ce (III), had a synergistic effect on the decomposition of O₃ into reactive oxygen species(O*), thus improving the catalytic capacity of Mn-Ce/Al₂O₃/TiO₂ catalyst for O₃. The O₂-TPD analysis showed that the oxygen vacancies and oxygen species in the catalyst could be used as the active point of decomposition of O₃ into O*. The experimental results show that the prepared catalyst can significantly improve the efficiency of ozone oxidation of NO and reduce the amount of ozone. The catalyst can be applied to ozone oxidation denitrification technology. Full article

Chlorobenzene (CB) is a volatile and harmful organic molecule that may result in deformities, cancer, etc. Catalytic oxidization of CB may be a way to manage it. The development of nonprecious catalysts with high catalytic activity is the key but is still a challenge. In this work, a series of Ce-Mn-O_x/TiO₂ modified by citric acid monohydrate were developed and exhibited a composite pore structure. This pore structure leads to a large specific surface area, highly exposed activity sites, and excellent catalytic activity. The as-prepared 10C-CM/T exhibited nearly 100% efficiency for CB oxidization in the temperature range of 300–350 °C. The in situ DRIFT measurements demonstrated that the main intermediates at 250 °C are maleate and phenolic acid, whereas when the temperature is 350 °C, the main intermediates are carbonate, bidentate carbonate, and maleate. Full article

Solar photothermo-catalysis is a fascinating multi-catalytic approach for volatile organic compounds (VOCs) removal. In this work, we have explored the performance and the chemico-physical features of non-critical, noble, metal-free MnO_x-ZrO₂ mixed oxides. The structural, morphological, and optical characterizations of these materials pointed to as a low amount of ZrO₂ favoured a good interaction and the ionic exchange between the Mn and the Zr ions. This favoured the redox properties of MnO_x increasing the mobility of its oxygens that can participate in the VOCs oxidation through a Mars-van Krevelen mechanism. The further application of solar irradiation sped up the oxidation reactions promoting the VOCs total oxidation to CO₂. The MnO_x-5 wt.%ZrO₂ sample showed, in the photothermo-catalytic tests, a toluene T₉₀ (temperature of 90% of conversion) of 180 °C and an ethanol T₉₀ conversion to CO₂ of 156 °C, 36 °C, and 205 °C lower compared to the thermocatalytic tests, respectively. Finally, the same sample exhibited 84% toluene conversion and the best selectivity to CO₂ in the ethanol removal after 5 h of solar irradiation at room temperature, a photoactivity similar to the most employed TiO₂-based materials. The as-synthetized mixed oxide is promising for an improved sustainability in both catalyst design and environmental applications. Full article

Soot particles in diesel engine exhaust is one of the main reasons for hazy weather and elimination of them is urgent for environmental protection. At present, it is still a challenge to develop new catalysts with high efficiency and low cost. In this paper, a kind of K modified three-dimensionally ordered macroporous (3DOM) MnCeO_x/Ti_0.7Si_0.3O₂ catalysts are designed and synthesized by a sample method. Due to the macroporous structure and synergistic effect of K, Mn, and Ce, the K_nMnCeO_x/Ti_0.7Si_0.3O₂ (K_nMnCeO_x/M-TSO) catalysts exhibit good catalytic performance for soot combustion. The catalytic activity of K_0.5MnCeO_x/M-TSO was the best, and the T₁₀, T₅₀, and T₉₀ are 287, 336, and 367 °C, respectively. After the prepared catalyst was doped with K, the physicochemical properties and catalytic performance changed significantly. In addition, the K_0.5MnCeO_x/M-TSO catalyst also somewhat exhibits sulfur tolerance owing to it containing Ti. Because of its simple synthesis, high activity, and low cost, the prepared K_nMnCeO_x/M-TSO catalysts are regarded as a promising candidate for application. Full article

The control of the spontaneous formation of nanostructures at the surface of thin films is of strong interest in many different fields, from catalysts to microelectronics, because surface and interfacial properties may be substantially enhanced. Here, we analyze the formation of nickel oxide nanocuboids on top of La₂Ni_1−xMn_1+xO₆ double perovskite ferromagnetic thin films, epitaxially grown on SrTiO₃ (001) substrates by radio-frequency (RF) magnetron sputtering. We show that, by annealing the films at high temperature under high oxygen partial pressure, the spontaneous segregation of nanocuboids is enhanced. The evolution of the structural and magnetic properties of the films is studied as a function of the annealing treatments at different temperatures. It is shown that the formation of NiOx nanocuboids leads to a nanostructured film surface with regions of locally different electrical transport characteristics. Full article

In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and electrochemical workstation. The results demonstrated that the complex inclusions formed in Cu-bearing steel were (Ti, Al, Mn)-O_x-MnS, which was similar to that in base steel. Hence, localized corrosion was initiated by the dissolution of MnS. However, the main inclusions in Ti-bearing steels were modified into TiN-Al₂O₃/TiN, and the localized corrosion was initiated by the dissolution of high deformation region at inclusion/matrix interface. With increased interface density of inclusions in steels, the corrosion rate increased in the following order: Base steel ≈ Cu-bearing steel < Ti-bearing steel. Owing to the existence of Cu-enriched rust layer, the Cu-bearing steel shows a similar corrosion resistance with base steel. Full article