Search Results (13)

In the presented work, titanosilicate with the MWW structure (Ti-MWW) was hydrothermally synthesized using boron and titanium precursors, with piperidine as a structure-directing agent. The resulting layered zeolite precursor, with a Si/Ti molar ratio of 50, was treated in an HNO₃ solution to remove extraframework Ti and B species. The acid-modified zeolite was functionalized with transition metal cations (Cu²⁺, Fe²⁺, Mn²⁺) and trinuclear oligocations (Fe(3) and Mn(3)). The application of this catalytic system is supported by the presence of titanium in the catalytic support structure—similar to a commercial system, V₂O₅–TiO₂. The obtained samples were characterized with respect to their structure (P-XRD, DRIFT), textural parameters (low-temperature N₂ sorption), surface acidity (NH₃-TPD), transition metal content (ICP-OES) and form (UV–vis DRS) as well as catalyst’s reducibility (H₂-TPR). Ti-MWW zeolite samples modified with transition metals were evaluated as catalysts for the selective catalytic reduction of NO with ammonia (NH₃-SCR). The effective temperature range for the NO conversion varied depending on the type of active phase used to functionalize the porous support. The catalytic performance was influenced by transition metal content, its form, and accessibility for reactants as well as interactions between the active phase and titanium-containing support. Among the catalysts tested, the copper-modified Ti-MWW zeolite showed the most promising results, maintaining 90% NO conversion rates across a relatively broad temperature range from 200 to 325 °C. This catalyst meets the requirements of modern NH₃-SCR installations, which aim to operate in the low-temperature region, below 250 °C. Full article

Metal oxide semiconductor-based photocatalysis and advanced oxidation processes (AOPs) are effective in treating various recalcitrant pollutants such as organic dyes present in industrial wastewater streams. AOPs rely on the highly reactive hydroxyl radicals (OH^•) that facilitate the non-selective destruction of most organic pollutants. Here, we present the novel synthesis of mesoporous FeTiO₃ catalyst via a simple, hard template-free, aqueous-solution-based hydrothermal synthesis method. The surfactant, tetradecyltrimethylammonium bromide (TTAB), was used as the structure-directing agent, the removal of which led to the formation of the mesoporous structure. The catalyst was characterized by thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Branauer–Emette–Teller analysis (BET), X-ray diffraction (XRD), and scanning electron microscope (SEM) techniques. The obtained catalyst has been studied for its photocatalytic application in the presence of H₂O₂ towards the degradation of organic dyes as representative pollutants, namely, rhodamine B (RhB) and methylene blue (MB) under direct solar light irradiation. The various characterizations confirm the formation of mesoporous FeTiO₃ with a pore size of ≈7.5 nm and a specific surface area of 65 ± 5 m²/g. The influence of H₂O₂ oxidant on the removal of the said dyes has also been studied at various concentrations in the presence of the synthesized catalyst to determine the optimum dosage of H₂O₂. The catalyst was efficient in the complete synergistic adsorption-led photo-Fenton-like removal of MB in just 30 min of irradiation time, while the 96% RhB was degraded in 240 min. Moreover, this catalyst has also shown potential for fluoride adsorption that reaches up to more than 50% in 90 min. Full article

Fabrication of chitosan and ilmenite sand-based novel photocatalysts through the catalytic graphitization of chitosan is reported. Nanocomposites consisted of TiO₂, Fe₂O₃ and Fe nanoparticles dispersed on a nitrogen-doped graphitic carbon framework. The surface area, pore volume and macropore structure of the carbon matrix is disturbed by the heterogeneously distributed nanoparticles. The extent of graphitization expanded with increasing metal loading as indicated by variation in the I_D/I_G ratio. The nanomaterial’s surface consists of Fe³⁺ and Ti⁴⁺, and graphitic, pyridinic and pyrrolic nitrogen were found in the carbon matrix. The band gap values of the composites varied in the 2.06–2.26 eV range. The photocatalytic activity of the synthesized nanomaterials was determined, and the highest rate constant for the photodegradation of methylene blue under sunlight was 4.4 × 10⁻³ min⁻¹, which resulted with 10 mg/L MB and 25 mg of the best-performing catalyst. The rate constant rose with increasing concentrations of persulfate added to the medium. The rate constant greatly diminished with the addition of isopropyl alcohol as it scavenged hydroxyl radicals. The presence of co-pollutants including Pb²⁺, rhodamine B, PO₄³⁻ and Cl⁻ curtailed the rate of reaction. The activity reduced with an increasing number of uses of the catalyst. Full article

The high efficiency and low consumption green wastewater treatment technology has important practical significance for the recycling of printing and dyeing wastewater. The efficiency of visible light catalytic degradation of organics is greatly affected by the performance of the catalyst and the photo reactor. Therefore, Bi₂WO₆/TiO₂/Fe₃O₄ (mBT) visible light photocatalyst was accurately prepared by the ammonia iron double drop method. In order to improve the photodegradation efficiency, a tubular magnetic field-controlled photocatalytic reactor (MPR) was developed. The novel mBT-MPR visible light photocatalytic system was proposed to treat RhB simulated wastewater. The experimental results showed that when the dosage of mBT catalyst was 1 g/L and visible light was irradiated for 60 min, the average removal rate of rhodamine B (RhB) with initial an concentration of 10 mg/L in the simulated wastewater for four times was 91.7%. The mBT-MPR visible light photocatalysis system is a green and efficient treatment technology for organic pollutants in water with simple operation, low energy consumption, and no need for catalyst separation. Full article

In the present study, the objective was to probe the capacity of the Fe₂O₃/Bentonite/TiO₂ (Fe₂O₃/B/TiO₂) nanoparticles to act as a catalyst in degrading the reactive red 198 (RR198) dye and textile factory wastewater, utilizing irradiation with visible and UV light. The efficiency of this degradation was studied for a variety of experimental parameters by employing real samples of textile wastewater. After 60 min of reaction time, complete degradation of the target pollutant was visible using the synthesized catalyst, i.e., Fe₂O₃/B/TiO_2, under UV light; the same effect was noted after 90 min under visible light. Further, the ease of separation and quick collection of the synthesized Fe₂O₃/B/TiO₂ can result in keeping the photocatalytic efficiency high, as well as raising the reusability. The photocatalytic processes under UV and visible light were found capable of converting the non-biodegradable textile wastewater into biodegradable one. Besides, with the introduction of Daphnia manga, the toxicity of the effluent was examined. Through photocatalysis, utilizing both techniques, the dye toxicity in the solution was fully neutralized, and the intensity of toxicity of the textile effluent was lowered by around 70%. The conclusion drawn in this study showed that the synthesized catalyst displayed good efficiency in removing organic compounds from the textile effluents by both photocatalytic processes using UV and visible light. 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

ZnFe₂O₄ microspheres were prepared by solvothermal method, and a novel ZnFe₂O₄@TiO₂ core-shell composite photocatalyst was prepared by ultrasonic (denoted as ZT-x) and mechanical stirring (denoted as ZTM-1.2). The morphology, structure, magnetic, and optoelectronic properties of the catalyst were investigated comprehensively, and the degradation performance of the catalyst was explored through the photocatalytic degradation of Rhodamine B (RhB) under UV light. The concentration of RhB was 10 mg/L, and the catalyst concentration was 0.3 g/L. ZT-1.2 showed the best photocatalytic degradation activity, and the degradation rate of RhB reached 97.3% within 60 min. The degradation ability of the catalyst was further evaluated by Methylene blue (MB), Methyl orange (MO), Phenol, and Ofloxacin (OFX). ZT-1.2 also exhibited excellent stability. The improved catalyst degradation performance was attributed to constructing a Z-type heterojunction. Moreover, the low-efficiency degradation of ZTM-1.2 was caused by catalyst agglomeration and low TiO₂ loading, confirming the superiority of the ultrasonic method and providing a new method for the preparation of magnetically recoverable TiO₂-based core-shell photocatalyst. Full article

A new spinelized Ni catalyst (Ni-UGSO) using Ni(NO₃)₂·6H₂O as the Ni precursor was prepared according to a less material intensive protocol. The support of this catalyst is a negative-value mining residue, UpGraded Slag Oxide (UGSO), produced from a TiO₂ slag production unit. Applied to dry reforming of methane (DRM) at atmospheric pressure, T = 810 °C, space velocity of 3400 mL/(h·g) and molar CO₂/CH₄ = 1.2, Ni-UGSO gives a stable over 168 h time-on-stream methane conversion of 92%. In this DRM reaction optimization study: (1) the best performance is obtained with the 10–13 wt% Ni load; (2) the Ni-UGSO catalysts obtained from two different batches of UGSO demonstrated equivalent performances despite their slight differences in composition; (3) the sulfur-poisoning resistance study shows that at up to 5.5 ppm no Ni-UGSO deactivation is observed. In steam reforming of methane (SRM), Ni-UGSO was tested at 900 °C and a molar ratio of H₂O/CH₄ = 1.7. In this experimental range, CH₄ conversion rapidly reached 98% and remained stable over 168 h time-on-stream (TOS). The same stability is observed for H₂ and CO yields, at around 92% and 91%, respectively, while H₂/CO was close to 3. In mixed (dry and steam) methane reforming using a ratio of H₂O/CH₄ = 0.15 and CO₂/CH₄ = 0.97 for 74 h and three reaction temperature levels (828 °C, 847 °C and 896 °C), CH₄ conversion remains stable; 80% at 828 °C (26 h), 85% at 847 °C (24 h) and 95% at 896 °C (24 h). All gaseous streams have been analyzed by gas chromatography. Both fresh and used catalysts are analyzed by scanning electron microscopy-electron dispersive X-ray spectroscopy (SEM-EDXS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS) and BET Specific surface. In the reducing environment of reforming, such catalytic activity is mainly attributed to (a) alloys such as FeNi, FeNi₃ and Fe₃Ni₂ (reduction of NiFe₂O₄, FeNiAlO₄) and (b) to the solid solution NiO-MgO. The latter is characterized by a molecular distribution of the catalytically active Ni phase while offering an environment that prevents C deposition due to its alkalinity. Full article

An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO₂ and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid, was evaluated on the degradation of (i) p-nitrophenol under UV-A light (365 nm) and (ii) rhodamine B under LED visible light (395 nm), and compared to undoped TiO₂ film. The higher enhancement is obtained under the longer wavelength (395 nm). The possibility of producing photocatalytic films without any calcination step and active under low-energy LED light constitutes a step forward for an industrial development. Full article

Simultaneous generation of plasma by microwave irradiation of perovskite or the spinel type of silica supported porous catalyst oxides and their reduction by nitrogen in the presence of oxygen is demonstrated. As a result of plasma generation in air, NO_x generation is accompanied by the development of highly heterogeneous regions in terms of chemical and morphological variations within the catalyst. Regions of almost completely reduced catalyst are dispersed within the catalyst oxide, across micron-scale domains. The quantification of the catalyst heterogeneity and evaluation of catalyst structure are studied using Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and XRD. Plasma generating supported spinel catalysts are synthesized using the technique developed by the author (Catalysts; 2016; 6; 80) and BaTiO₃ is used to exemplify perovskites. Silica supported catalyst systems are represented as M/Si = X (single catalysts) or as M(₁)/M(₂)/Si = X/Y/Z (binary catalysts) where M; M(₁) M(₂) = Cr; Mn; Fe; Co; Cu and X, Y, Z are the molar ratio of the catalysts and SiO₂ support. Composite porous catalysts are synthesized using a mixture of Co and BaTiO₃. In all the catalysts, structural heterogeneity manifests itself through defects, phase separation and increased porosity resulting in the creation of the high activity sites. The chemical heterogeneity results in reduced and oxidized domains and in very large changes in catalyst/support ratio. High electrical potential activity within BaTiO₃ particles is observed through the formation of electrical treeing. Plasma generation starts as soon as the supported catalyst is synthesized. Two conditions for plasma generation are observed: Metal/Silica molar ratio should be > 1/2 and the resulting oxide should be spinel type; represented as M_aO_b (a = 3; b = 4 for single catalyst). Composite catalysts are represented as {M/Si = X}/BaTiO₃ and obtained from the catalyst/silica precursor fluid with BaTiO₃ particles which undergo fragmentation during microwave irradiation. Further irradiation causes plasma generation, NO_x formation and lattice oxygen depletion. Partially reduced spinels are represented as M_aO_b–c. These reactions occur through a chemical looping process in micron-scale domains on the porous catalyst surface. Therefore; it is possible to scale-up this process to obtain NO_x from M_aO_b for nitric acid production and H₂ generation from M_aO_b–c by catalyst re-oxidized by water. Re-oxidation by CO₂ delivers CO as fuel. These findings explain the mechanism of conversion of combustion gases (CO₂ + N₂) to CO and NO_x via a chemical looping process. Mechanism of catalyst generation is proposed and the resulting structural inhomogeneity is characterized. Plasma generating catalysts also represent a new form of Radar Absorbing Material (RAM) for stealth and protection from radiation in which electromagnetic energy is dissipated by plasma generation and catalytic reactions. These catalytic RAMs can be expected to be more efficient in frequency independent microwave absorption. Full article

The chemical challenge of economically splitting water into molecular hydrogen and oxygen requires continuous development of more efficient, less-toxic, and cheaper catalyst materials. This review article highlights the potential of iron sulfide-based nanomaterials as electrocatalysts for water-splitting and predominantly as catalysts for the hydrogen evolution reaction (HER). Besides new synthetic techniques leading to phase-pure iron sulfide nano objects and thin-films, the article reviews three new material classes: (a) FeS₂-TiO₂ hybrid structures; (b) iron sulfide-2D carbon support composites; and (c) metal-doped (e.g., cobalt and nickel) iron sulfide materials. In recent years, immense progress has been made in the development of these materials, which exhibit enormous potential as hydrogen evolution catalysts and may represent a genuine alternative to more traditional, noble metal-based catalysts. First developments in this comparably new research area are summarized in this article and discussed together with theoretical studies on hydrogen evolution reactions involving iron sulfide electrocatalysts. Full article

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi_0.8B_0.2O₃ lean NOx trap (LNT) catalyst has been analyzed. The BaTi_0.8B_0.2O₃ catalysts were prepared using the Pechini’s sol–gel method for aqueous media. The characterization of the catalysts (BET, ICP-OES, XRD and XPS) reveals that: i) the partial substitution of Ti by Mn, Co, or Fe changes the perovskite structure from tetragonal to cubic, whilst Cu distorts the raw tetragonal structure and promotes the segregation of Ba₂TiO₄ (which is an active phase for NOx storage) as a minority phase and ii) the amount of oxygen vacancies increases after partial Ti substitution, with the BaTi_0.8Cu_0.2O₃ catalyst featuring the largest amount. The BaTi_0.8Cu_0.2O₃ catalyst shows the highest NSC at 400 °C, based on NOx storage cyclic tests, which is within the range of highly active noble metal-based catalysts. Full article

Perovskite derived Ni catalysts offer the remarkable benefit of regeneration after catalyst poisoning or Ni particle growth through the reversible segregation of Ni from the perovskite-type oxide host. Although this property allows for repeated catalyst regeneration, improving Ni catalyst stability towards sulfur poisoning by H₂S is highly critical in solid oxide fuel cells. In this work Mn, Mo, Cr and Fe were combined with Ni at the B-site of La_0.3Sr_0.55TiO_3±δ to explore possible benefits of segregation of two transition metals towards sulfur tolerance. Catalytic activity tests towards the water gas shift reaction were carried out to evaluate the effect of the additional metal on the catalytic activity and sulfur stability of the Ni catalyst. The addition of Fe to the Ni perovskite catalyst was found to increase sulfur tolerance. The simultaneous segregation of Fe and Ni from La_0.3Sr_0.55Ti_0.95-xNi_0.05Fe_xO_3±δ (x ≤ 0.05) was investigated by temperature programmed reduction, X-ray diffraction and X-ray absorption spectroscopy and catalytic tests after multiple redox cycles. It is shown that catalytic properties of the active phase were affected likely by the segregation of Ni/Fe alloy particles and that the reversible segregation of Ni persisted, while it was limited in the case of Fe under the same conditions. Full article