Search Results (19)

The continuous tightening of emission regulations and the escalating costs of palladium (Pd) and rhodium (Rh) have renewed interest in platinum (Pt)-based three-way catalysts (TWCs) as cost-effective alternatives for gasoline aftertreatment. However, despite extensive studies on Pt/CeO₂ and Pt/Ba-based formulations, the cooperative roles of Ba and Ce and, in particular, the fundamental influence of the Ba/Ce ratio on oxygen mobility, NO_x storage behavior, and Pt–support interactions remain poorly understood. In this work, we address this gap by systematically tuning the Ba/Ce molar ratio in a series of Pt–Ba–Ce/Al₂O₃ catalysts prepared from Ba(CH₃COO)₂ and CeO₂ precursors, and evaluating their structure–function relationships in both fresh and hydrothermally aged states. Through comprehensive characterization (N₂ physisorption, XRD, XPS, H₂-TPR, NO_x-TPD, SEM, CO pulse adsorption, and dynamic light-off testing), we establish previously unrecognized correlations between Ba/Ce ratio–dependent structural evolution and TWC performance. The results reveal that the Ba/Ce ratio exerts a decisive control over catalyst textural properties, Pt dispersion, and interfacial Pt–CeO₂ oxygen species. Low Ba/Ce ratios uniquely promote Pt–Ce interfacial oxygen and O₂ spillover—providing a new mechanistic basis for enhanced low-temperature oxidation and reduction reactions—while higher Ba loading selectively drives BaCO₃ formation and boosts NO_x storage capacity. A clear volcano-type dependence of NO_x storage on the Ba/Ce ratio is demonstrated for the first time. Hydrothermal aging at 850 °C induces PtO_x decomposition, BaCO₃–Al₂O₃ solid-state reactions forming inactive BaAl₂O₄, and Pt sintering, collectively suppressing Pt–Ce interactions and reducing TWC activity. Importantly, an optimized Ba/Ce ratio is shown to mitigate these degradation pathways, offering a new design principle for thermally durable Pt-based TWCs. Overall, this study provides new mechanistic insight into Ba–Ce cooperative effects, establishes the Ba/Ce ratio as a critical and previously overlooked parameter governing Pt–support interactions and NO_x storage, and presents a rational strategy for designing cost-effective, hydrothermally robust Pt-based alternatives to Pd/Rh commercial TWCs. Full article

In this work, a series of Ba_xMn_0.7Cu_0.3O₃ samples (x: 1, 0.9, 0.8, and 0.7, BxMC) was synthesized, characterized, and used as catalysts for CO oxidation reaction. All formulations were active for CO oxidation in the tested conditions. A correlation between the electrical conductivity, obtained by impedance spectroscopy, and the reducibility of the samples, obtained by H₂-TPR, was observed. The Ba_0.8Mn_0.7Cu_0.3O₃ composition (B0.8MC) showed the best catalytic performance (comparable to that of the 1% Pt/Al₂O₃ reference sample) during tests conducted under conditions similar to those found in the exhaust gases of current gasoline engines. The characterization data suggest the simultaneous presence of a high Mn(IV)/Mn(III) surface ratio, oxygen vacancies, and reduced copper species, these two latter being key properties for ensuring a high CO conversion percentage as both are active sites for CO oxidation. The reaction temperature and the reactant atmosphere composition seem to be the most important factors for achieving a good catalytic performance, as they strongly determine the location and stability of the reduced copper species. Full article

The sol–gel method, adapted to aqueous media, was used for the synthesis of BaMn_0.7Cu_0.3O₃ (BMC) and Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (BMC-A, A = Ce, La or Mg) perovskite-type mixed oxides. These samples were fully characterized by ICP-OES, XRD, XPS, H₂-TPR, BET, and O₂–TPD and, subsequently, they were evaluated as catalysts for CO oxidation under different conditions simulating that found in cars exhaust. The characterization results show that after the partial replacement of Ba by A metal in BMC perovskite: (i) a fraction of the polytype structure was converted to the hexagonal BaMnO₃ perovskite structure, (ii) A metal used as dopant was incorporated into the lattice of the perovskite, (iii) oxygen vacancies existed on the surface of samples, and iv) Mn(IV) and Mn(III) coexisted on the surface and in the bulk, with Mn(IV) being the main oxidation state on the surface. In the three reactant atmospheres used, all samples catalysed the CO to CO₂ oxidation reaction, showing better performances after the addition of A metal and for reactant mixtures with low CO/O₂ ratios. BMC-Ce was the most active catalyst because it combined the highest reducibility and oxygen mobility, the presence of copper and of oxygen vacancies on the surface, the contribution of the Ce(IV)/Ce(III) redox pair, and a high proportion of surface and bulk Mn(IV). At 200 °C and in the 0.1% CO + 10% O₂ reactant gas mixture, the CO conversion using BMC-Ce was very similar to the achieved with a 1% Pt/Al₂O₃ (Pt-Al) reference catalyst. Full article

This work presents a novel, highly sensitive, and directional piezoelectric cantilever-based micro-electro-mechanical system (MEMS) device conceived using a biomimetic approach of a fish’s lateral line system for marine sensing robotics. The device will consist of twelve cantilevers with different lengths in a cross-shaped configuration made with a piezoelectric thin film (PZT, ZnO, BaTiO₃) embedded between the top and bottom metals, Platinum (Pt) and Aluminum (Al), used as electrodes. This unique design of cantilevers in circular shapes has the advantage of directional response. A comparative study of these piezoelectric materials was performed analytically through the finite element method to design, model, and simulate our device in COMSOL software. Cantilever microstructures were simulated with lengths ranging from 100 to 1000 mm. The results show that PZT has the best performance with these materials. The maximum potential voltage was shown as 1.9 mV using the PZT material cantilever with 29 µm displacement. Full article

DeNO_x activity in a NSR–SCR hybrid system of two copper-containing chabazite-type zeolitic catalysts was addressed. A Pt-Ba-K/Al₂O₃ model catalyst was used as the NSR (NO_x storage and reduction) catalyst. For the SCR (selective catalytic reduction) system, two Cu-CHA zeolites were synthesized employing a single hydrothermal synthesis method assisted with ultrasound and incorporating Cu in a 2 wt.%, 2Cu-SAPO-34 and 2Cu-SSZ-13. The prepared catalysts were characterized, and the crystallinity, surface area, pore size, HR-TEM and EDX mapping, coordination of Cu ions and acidity were compared. The NH₃ storage capacity of the SCR catalysts was 1890 and 837 ${\mathsf{\mu }\mathrm{mol} \mathrm{NH}}_3{·\mathrm{g}}_{\mathrm{cat}}^{-1}$ for 2Cu-SAPO-34 and 2Cu-SSZ-13, respectively. DeNO_x activity was evaluated for the single NSR system and the double-bed NSR–SCR by employing alternating lean (3%O₂) and rich (1%H₂) cycles, maintaining a concentration of 600 ppm NO, 1.5% H₂O and 0.3% CO₂ between 200 and 350 °C. The addition of the SCR system downstream of the NSR catalyst significantly improved NO_x conversion mainly at low temperature, maintaining the selectivity to N₂ above 80% and reaching values above 90% at 250 °C when the 2Cu-SSZ-13 catalyst was located. The total reduction in the production of NH₃ and ~2% of N₂O was observed when comparing the NSR–SCR configuration with the single NSR catalyst. Full article

The main problem affecting the life of refractory linings in furnaces is alkaline corrosion formed during biomass combustion, especially in systems with SiO₂–Al₂O₃. This corrosion effect is very intensive compared to using conventional technologies designed for burning traditional fuels. This study focuses on the development of a new type of andalusite refractory material with a higher corrosion resistance to K₂CO₃ and fly ash after biomass combustion. The original andalusite refractory material is labeled A60PT0, with an oxide content of 60 wt.% Al₂O₃ and 37 wt.% SiO₂, a compressive strength parameter of 64 MPa, and an apparent porosity of 15%. In the experiment, four mixtures (labeled A60PT1–A60PT4) were modified primarily using the raw materials and granulometry. The fly ash was characterized by an X-ray diffraction analysis with the following phases: quartz, calcite, microcline, leucite, portlandite, and hematite. According to the X-ray fluorescence analysis, the samples contained the following oxides: 47 wt.% CaO, 12 wt.% K₂O, 4.6 wt.% SiO₂, 3.5 wt.% MgO, and some minority oxides such as P₂O₅, MgO, MnO, and Fe₂O₃ between 2 and 5 %. The tendency for slagging/fouling of the ash was determined with the help of the indexes B/A, TA, K_t, and Fu. The final material was a shaped andalusite refractory material labeled A60PT4 with a content of 65 wt.% Al₂O₃ and 36 wt.% SiO_2. The properties of the andalusite material were a compressive strength of 106.9 MPa, an apparent porosity of 13%, and the recommended temperature of use up to 1300 °C. For corrosion testing, a static crucible test was performed according to the norm ČSN CEN/TS 15418 and the company’s internal regulation. The exposure time of the samples was 2 h and 5 h at temperatures of 1100 °C and 1400 °C for K₂CO₃ and ash, respectively. For the evaluation of tested samples, an X-ray powder differential analysis, an X-ray fluorescence analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used. Full article

In addition to SCR systems, lean NO_X traps (LNTs) are also used for exhaust aftertreatment of lean burn internal combustion engines to sustainably reduce NO_X emissions. Modern LNTs consist of different functional compounds to maximize the performance during NO_X storage and regeneration. Based on the material analysis of a serial production LNT, PGM loaded BaO, Al₂O₃, MgAl₂O₄, and CeO₂ were identified as the main base materials. In this paper, the NO_X storage capacity (NSC) of these compounds is investigated both as single catalysts and as physical mixtures to identify possible synergistic effects. Therefore, commercially available support materials were loaded with Platinum and tested in granular form under realistic conditions. To optimize the performance by reducing the diffusion pathways for NO_X molecules during storage, PGM, BaO, and Ceria were combined in a composite by the incipient wetness impregnation of alumina. As a result, the temperature dependent NSC of the commercial LNT could be reached with the Pt/Rh/Ba₁₀Ce₂₅/Al₂O₃ infiltration composite, while reducing the oxygen storage capacity by about 45%. Without the additional Rhodium coating, the low-temperature NSC was insufficient, highlighting the important contribution of this precious metal to the overall performance of LNTs. Full article

The present study analyzed a computational model to evaluate the electromechanical properties of the AlN, BaTiO₃, ZnO, PVDF, and KNN-NTK thin-films. With the rise in sustainable energy options for health monitoring devices and smart wearable sensors, developers need a scale to compare the popular biocompatible piezoelectric materials. Cantilever-based energy harvesting technologies are seldom used in sophisticated and efficient biosensors. Such approaches only study transverse sensor loading and are confined to fewer excitation models than real-world applications. The present research analyses transverse vibratory and axial-loading responses to help design such sensors. A thin-film strip (50 × 20 × 0.1 mm) of each sample was examined under volumetric body load stimulation and time-based axial displacement in both the d₃₁ and d₃₃ piezoelectric energy generation modes. By collecting evidence from the literature of the material performance, properties, and performing a validated finite element study to evaluate these performances, the study compared them with lead-based non-biocompatible materials such as PZT and PMN-PT under comparable boundary conditions. Based on the present study, biocompatible materials are swiftly catching up to their predecessors. However, there is still a significant voltage and power output performance disparity that may be difficult to close based on the method of excitation (i.e., transverse, axial, or shear. According to this study, BaTiO₃ and PVDF are recommended for cantilever-based energy harvester setups and axially-loaded configurations. Full article

Plasma catalysis has been utilized in many environmental applications for removal of various hydrocarbons including tars. The aim of this work was to study the tars removal process by atmospheric pressure DBD non-thermal plasma generated in combination with packing materials of various composition and catalytic activity (TiO₂, Pt/γAl₂O₃, BaTiO₃, γAl₂O₃, ZrO₂, glass beads), dielectric constant (5–4000), shape (spherical and cylindrical pellets and beads), size (3–5 mm in diameter, 3–8 mm in length), and specific surface area (37–150 m²/g). Naphthalene was chosen as a model tar compound. The experiments were performed at a temperature of 100 °C and a naphthalene initial concentration of approx. 3000 ppm, i.e., under conditions that are usually less favorable to achieve high removal efficiencies. For a given specific input energy of 320 J/L, naphthalene removal efficiency followed a sequence: TiO₂ > Pt/γAl₂O₃ > ZrO₂ > γAl₂O₃ > glass beads > BaTiO₃ > plasma only. The efficiency increased with the increasing specific surface area of a given packing material, while its shape and size were also found to be important. By-products of naphthalene decomposition were analyzed by means of FTIR spectrometry and surface of packing materials by SEM analysis. Full article

A new type of amorphous barium aluminum oxide was synthesized using a polyol thermal method involving a mixture with Vulcan XC-72 carbon and supported with 20%Pt catalysts to enhance the activity of a methanol electrooxidation reaction (MOR). The maximum current density, electrochemically active surface area (ECSA), and electrochemical impedance spectra (EIS) of the obtained catalysts for MOR were determined. The MORs of barium aluminum oxide with different calcination temperatures and Ba and Al contact ratios were studied. The MOR of the uncalcined amorphous Ba_0.5AlO_x catalysts prepared with a mole ratio of 2/1 Ba/Al mixed with Vulcan XC-72 carbon and supported with 20%Pt catalyst (Pt-Ba_0.5AlO_x/C) was enhanced compared with that of 20%Pt-Al₂O₃/C and 20%Pt/C catalysts due to its obtained largest maximum current density of 3.89 mA/cm² and the largest ECSA of 49.83 m²/g. Therefore, Pt-Ba_0.5AlO_x/C could provide a new pathway to achieve a sufficient electrical conductivity, and possible synergistic effects with other active components improved the catalytic activity and stability of the prepared catalyst in MOR. Full article

The behavior and operation parameters were analyzed for the hybrid LNT-SCR (Lean NO_x-Trap–Selective Catalytic Reduction) system with advanced catalyst formulations. Pt-Ba-K/Al₂O₃ was used as an NSR (NO_x Storage and Reduction) or LNT catalyst effective in NO_x and soot simultaneous removal whereas Cu-SAPO-34 with 2 wt.% of copper inside the structure was the small pore zeolite employed as the SCR catalyst. Under alternating and cyclic wet conditions, feeding volumetric concentrations of 1000 ppm of NO, 3% of O₂, 1.5% of water, 0.3% of CO₂, and H₂ as a reductant, the NO_x-conversion values were above 95% and a complete mineralization to nitrogen was registered using θ ≤ 3 (20 s of regeneration) and a hydrogen content between 10,000 and 2000 ppm in the whole temperature range tested. An excess of hydrogen fed (above 1% v/v) during the rich phase is unnecessary. In addition, in the low temperature range below 250 °C, the effect is more noticeable due to the further ammonia production and its possible slip. These results open the way to the scale up of the coupled catalytic technologies for its use in real conditions while controlling the influence of the operation map. Full article

Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO₂ emissions than stoichiometric gasoline engines. However, NO_x reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NO_x storage and reduction (NSR), also known as lean NO_x trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NO_x emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NO_x removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO₃) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NO_x from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO₂ conversion, NO_x storage capacity, and NO_x reduction efficiency is addressed. Furthermore, the NO_x removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al₂O₃) in the absence and presence of SO₂ and H₂O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted. Full article

This work aimed to optimize the washcoat slurry for hydrotalcite-based lean NOx trap (LNT) catalyst. The effects of the slurry properties including pH, solid content, binder and additive on the hydrotalcite-based slurry viscosity were investigated. The particle size distribution of the optimal hydrotalcite-based slurry was measured. A cordierite material was used to coat the optimal slurry, and the washcoat was characterized by X-ray diffraction, scanning electron microscopy and N₂ adsorption. The optimal slurry containing Pt and Ba was coated on the cordierite for the preparation of hydrotalcite-based LNT catalyst, and the performances of this catalyst were evaluated by NOx storage test, temperature programmed desorption and NOx reduction. For comparison, the performance of the commercial LNT catalyst with Pt/BaO/Al₂O₃ was analyzed. After coating, the hydrotalcite-based washcoat was closely contacted with the support, being the main phase MgO and presenting a specific surface area of 86.3 m²/g. The hydrotalcite-based LNT catalyst had better NOx storage and desorption ability, selectivity to N₂ and LNT efficiency than the Pt/BaO/Al₂O₃ catalyst. Full article

Ceria/spinel-based lean NO_x trap compositions with and without barium were modified with MnO_x via incipient wetness impregnation. The effect of the MnO_x layer on the aged materials (850 °C) as to the NO_x storage and release properties was investigated via NO_x adsorption (500 ppm NO/5% O₂/balance N₂) carried out at 300 °C in a dual-bed with a 1% Pt/Al₂O₃ catalyst placed upstream of the samples to generate sufficient amounts of NO₂ required for efficient NO_x storage. Subsequent temperature programmed desorption (TPD) experiments were carried out under N₂ from 300 °C to 700 °C. The addition of MnO_x to the barium free composition led to a slightly reduced NO_x storage capacity but all of the ad-NO_x species were released from this material at significantly lower temperatures (ΔT ≈ 100 °C). The formation of a MnO_x layer between ceria/spinel and barium had a remarkable effect on ageing stability as the formation of BaAl₂O₄ was suppressed in favour of BaMnO₃. The presence of this phase resulted in an increased NO_x storage capacity and lower desorption temperatures. Furthermore, NO_x adsorption experiments carried out in absence of the Pt-catalyst also revealed an unexpected high NO_x storage ability at low NO₂/NO ratios, which could make this composition suitable for various lean NO_x trap catalysts (LNT) related applications. Full article

The effect of phosphorous exposure on the NO_x storage capacity of a Pt/Ba/Al₂O₃ catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H₂O and O₂. The NO_x storage capacity was measured before and after the phosphorus exposure and a significant loss of the NO_x storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N₂-physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P₄O₁₀. However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO₃⁻). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample. Full article