Search Results (224)

This study examines the surface chemistry of platinum, palladium, rhodium, and ruthenium-substituted lanthanum strontium cobaltate perovskite catalysts in the context of the dry reforming of methane (DRM). The catalysts were synthesized by the solution combustion method and characterized by using a series of techniques. To explore the effect of noble metal ion substitution on the DRM, surface reaction was probed by CH₄/CO₂ TPSR using mass spectroscopy. It was recognized that La_1−xSr_xCo_1−yPd_yO₃ show the best activities for the reaction in terms of the temperature but became deactivated over time. CH₄/CO₂ temperature-programmed surface reactions (TPSRs) were set up to unravel the details of the surface phenomena responsible for the deactivation of the DRM activity on the LSPdCO. The CH₄/CO₂ TPSR analysis conclusively demonstrated the importance of lattice oxygen in the removal of carbon, which is responsible for the stability of the catalysts on the synthesized perovskites upon noble metal ion substitution. Full article

To ensure the sustainable use of limited resources, it is essential to establish selective and efficient recycling technologies for platinum group metals (PGMs). This study focused on the selective precipitation-based separation of Pt(IV) from hydrochloric acid (HCl) solutions in the presence of various metal ions, using trans-1,4-bis(aminomethyl)cyclohexane (BACT) as a precipitating agent. By using BACT, we succeeded in the selective separation of Pt(IV) by precipitation from HCl solutions containing Pd(II) and Rh(III). Notably, selective and efficient recovery of Pt(IV) was accomplished across various HCl concentrations, with a small amount of BACT and within a short shaking time. To evaluate the practical applicability of the method, Pt(IV) was recovered and purified from the HCl leachate of spent automotive exhaust gas purification catalysts using BACT. As a result, a high Pt recovery of 95.6% and a high purity of 99.3% were achieved. Although Pt(IV) was recovered as a precipitate containing BACT, it was found that Pt black could be readily obtained by dissolving the precipitate in HCl solution followed by reduction with sodium borohydride. Detailed structural analysis of the Pt(IV)-containing precipitate revealed that it is an ionic crystal composed of [PtCl₆]²⁻ and protonated BACT. The selective formation of this ionic crystal in HCl solution, along with its stability under such conditions, is the key to the selective recovery of Pt(IV) using BACT. Full article

In water-scarce regions, natural ecosystems and agriculture increasingly compete for limited water resources, intensifying stress during periods of drought. To assess these competing demands, we applied a modified PT-JPL model that incorporates the thermal inertial approach as a substitute for relative humidity (RH) in estimating soil evaporation—a method that significantly outperforms the original PT-JPL formulation in Mediterranean semi-arid irrigated areas. This remote sensing framework enabled us to quantify spatial and temporal variations in water use across both natural and agricultural systems within the UNESCO World Heritage site of Doñana. Our analysis revealed an increasing evapotranspiration (ET) trend in intensified agricultural areas and rice fields surrounding the National Park (R = 0.3), contrasted by a strong negative ET trend in wetlands (R < −0.5). These opposing patterns suggest a growing diversion of water toward irrigation at the expense of natural ecosystems. The impact was especially marked during droughts, such as the 2011–2016 period, when precipitation declined by 16%. In wetlands, ET was significantly correlated with precipitation (R > 0.4), highlighting their vulnerability to reduced water inputs. These findings offer crucial insights to support sustainable water management strategies that balance agricultural productivity with the preservation of ecologically valuable systems under mounting climatic and anthropogenic pressures typical of semi-arid Mediterranean environments. Full article

The composition of platinum group minerals localized in sulfide droplets from peridotites of the Zhelos intrusion was studied on a scanning electron microscope and on an electron probe microanalyzer. As part of this study, also an analytical approach based on the variation in accelerating voltage, electron beam intensity and probe diameter is considered in order to estimate the X-ray generation region, when analyzing PGM microinclusions comparable in size to the radiation generation region or smaller. Estimates were made of the possibility of reducing the size of the local analysis area when the accelerating voltage was reduced. The influence of the matrix composition on the results of the local analysis of PGM microphases and accuracy of the Pd and Pt content determination was also evaluated. The findings of the experiments conducted allowed for the successful identification of elements belonging to the PGM microphases and the host matrix. This approach enabled the estimation of the precise levels of impurity elements in their composition. Using a scanning electron microscope in the automatic scanning mode for the detection of heavy elements, 10 single and composite grains of three platinum group minerals larger than 5 µm and 22 microphases ranging in size from 0.3 to 4 µm were detected in the sulfide droplets. The large phases are merenskyite, omeiite and michenerite, with merenskyite being predominant. Among the microscopic inclusions were identified Pd-Bi-Te, Os-Ru-As and Rh-As-S phases. The composition of the studied palladium bismuthotelluride samples indicates a formation temperature range of 489–700 °C. Full article

The electrocatalytic hydrogenation (ECH) of biomass-derived phenolic compounds is a promising approach to the production of value-added chemicals and biofuels in a sustainable way under moderate reaction conditions. This study provides a comprehensive comparison of electrochemical and thermochemical hydrogenation processes, highlighting their relative advantages in terms of energy efficiency, product selectivity, and environmental impact. Several electrocatalysts (Pt, Pd, Rh, Ru), membranes (Nafion, Fumasep, GO-based PEMs), and reactor configurations are tested for the selective conversion of model compounds such as phenol, guaiacol, furfural, and levulinic acid. The contributions made by the electrode material, electrolyte composition, membrane nature, and reaction conditions are critically evaluated in relation to Faradaic efficiency, conversion rates, and product selectivity. The enhancement in the performance achieved by a new catalyst architecture is emphasized, such as MOF-based systems and bimetallic/trimetallic catalysts. In addition, a demonstration of graphite-based membranes and membrane-separated slurry reactors (SSERs) is provided, for enhanced ion transport and reaction control. The results illustrate the potential of using ECH as a low-carbon, scalable, and tunable method for the upgrading of biomass. This study offers valuable insights and guidelines for the rational design of next-generation electrocatalytic systems toward green chemical synthesis and emphasizes promising perspectives for the strategic development of electrochemical technologies in the pathway of a sustainable energy economy. Full article

This study explores the selective hydrogenation of cinnamaldehyde using a series of metal catalysts supported on reduced graphene oxide (rGO) and conventional activated carbon (AC). Catalysts based on Pt, Pd, Rh, Ru, and Co were synthesized with controlled metal loading and characterized by XRD, SEM-EDS, XRF, and TEM. Among all tested materials, Pd supported on rGO synthesized via the Tour method (Pd/rTOGO) exhibited the highest catalytic activity, achieving 62% conversion of cinnamaldehyde and superior selectivity toward hydrocinnamaldehyde (HCAL). The support material had a significant influence on performance, especially for Pd catalysts, where 2D rGO outperformed 3D AC in both conversion and selectivity. In contrast, other metals (Pt, Rh, Ru, Co) showed only modest activity and limited selectivity tuning via support choice. Notably, GC-MS analysis revealed the formation of a previously underreported side product, 3-isopropoxy-propan-1-yl benzene (ether), likely formed via reductive etherification in isopropanol. The combined kinetic and selectivity data enabled the proposal of reaction pathways, including rapid transformation of cinnamylalcohol (COL) to hydrocinnamal alcohol (HCOL) and HCAL to ether. These findings emphasize the importance of support structure and surface functionality, particularly in 2D carbon materials, for designing efficient and selective hydrogenation catalysts. Full article

Carbon monoxide (CO) is an important air pollutant generated from the incomplete combustion of fossil fuels, particularly in industrial processes such as iron and steel smelting, power generation, and waste incineration, posing environmental challenges that demand effective removal strategies. Recent advances in noble metal catalysts for catalytic oxidation of CO, particularly Pt-, Pd-, and Rh-based systems, have been extensively studied. However, there is still a lack of systematic review on noble metal-based catalytic oxidation of CO, especially regarding the effects of different active components of the catalysts and the mechanism of sulfur resistance. Based on extensive research and literature findings, this study comprehensively concluded the advances in noble metal-based catalytic oxidation of CO. The effects of preparation methods, supports, and physicochemical properties on the catalytic performance of CO were explored. In addition, the mechanism of the catalytic oxidation of CO were further summarized. Furthermore, given the prevalence of SO₂ in the flue gas, the mechanism of sulfur poisoning deactivation of catalysts and the anti-sulfur strategies were further reviewed. Exploration of new supporting materials, catalyst surface reconstruction, doping modification, and other catalyst design strategies demonstrate potential in improving sulfur resistance and catalytic efficiency. This study provides valuable insights into the design and optimization of noble metal-based catalysts for the catalytic oxidation of CO. Full article

Compressed natural gas (CNG) in dual-fuel diesel engines offers environmental benefits but significantly increases unburned methane (CH₄) emissions, especially at low engine loads. This study investigates the effectiveness of different catalytic converters in methane oxidation under transient test conditions (WHTC). Three types of catalysts (Pt-, Rh-, and Pd-based) were evaluated using a combined approach of empirical engine bench tests and mathematical modelling. The results showed that, under actual exhaust gas temperature conditions, the average methane conversion efficiencies were 3.7% for Pt, 17.7% for Rh, and 31.3% for Pd catalysts. Increasing the exhaust gas temperature by 50% improved the conversion efficiencies to 7.3%, 51.8%, and 69.2%, respectively. Despite this enhancement, none of the catalysts reached the 90% efficiency threshold required to increase the CNG content of the fuel beyond 6% without exceeding emission limits. The results highlight the need for high-activity Pd-based catalysts and optimised thermal management strategies to enable the broader adoption of dual-fuel engines, while complying with Euro VI standards. Full article

Ultra-high-temperature (>1500 °C) sensors play vital roles in ensuring operational excellence in variety of energy-related applications, such as power plant boilers and gas turbine engines. Crystalline sapphire fibers have enormous potential to replace conventional expensive precious metal (e.g., Pt/Rh)-based high-temperature (>1500 °C) sensors by offering higher environmental robustness and distributed sensing capabilities. However, a lack of proper cladding substantially compromises the performance of the sensor. To overcome this fundamental limitation, we develop a hybrid growing method to fabricate low-loss clad crystalline sapphire fibers. We grow a higher-refractive-index doped crystalline sapphire fiber core using the laser-heated pedestal growth (LHPG) method and lower-refractive-index undoped crystalline sapphire fiber cladding using the liquid-phase epitaxy (LPE) method. Furthermore, due to the existence of this cladding layer, a single mode of operation can be achieved at a core diameter size of 30 μm. The experimental results confirm that the grown clad crystalline sapphire fiber can survive in extremely high-temperature (>1500 °C) harsh environments due to the matched coefficient of thermal expansion (CTE) between the fiber core and the cladding. The numerical results also indicate a temperature sensing accuracy of 3.5 °C. This opens the door for developing point and distributed fiber sensor networks capable of enduring extremely harsh environments at extremely high temperatures. Full article

Strict gaseous emission standards are applied globally to regulate the maximum amounts of pollutant emissions that can be produced from all vehicles. The exhaust aftertreatment systems used by automotive manufacturers rely on the utilization of precious metals (Pt, Pd, Rh). However, much effort has been devoted on the reduction or the replacement of the amount of Platinum Group Metals (PGMs) in three-way catalysts (TWC), both from a cost-effectiveness as well as an environmental point of view. PROMETHEUS catalyst, which was recently homologated for Euro 6 applications, is a low-cost, Cu-based TWC, which consists of a significantly lower quantity of PGMs compared to conventional state-of-the-art catalysts and achieves similar or even better catalytic efficiencies. In this review paper, a complex reaction scheme is proposed for the first time for a catalytic converter utilizing Cu and PGMs, following an extensive literature investigation of the available models. The scheme also accounts for the surface reaction mechanisms of the main processes and the side reactions potentially taking place during the TWC operation in the presence of Cu and at least one of the following PGMs: Pt, Pd or Rh. At a next step, the proposed reaction scheme will be validated based on experimental data, using mathematical modelling of a PROMETHEUS catalytic converter incorporating Cu and PGM nanoparticles. Full article

Metallic Pd/Ni gauzes, located downstream of the Pt/Rh ammonia oxidation catalyst nets in the Ostwald process, is the current technology for capturing volatile gas phase platinum and rhodium species lost from the Pt/Rh combustion catalyst through evaporation. In this screening study, we explore four oxide families, ABO₃ perovskites, (ABO₃)_n(AO) Ruddlesden–Popper (RP) phases, AO rock salt, and A₂O₃ sesquioxide type oxides, as alternative materials for platinum capture. It was found that all the tested nickelates, LaNiO₃, NdNiO₃, La₂NiO₄, and La₄Ni₃O₁₀, captured platinum well and formed A₂NiPtO₆. In contrast, La_0.85Sr_0.15FeO₃, LaFeO₃, and LaCoO₃ did not capture platinum. CaO, SrO, and Nd₂O₃ formed low-dimensional platinates such as Ca_xPt₃O₄, Sr₄PtO₆, and a newly discovered neodymium platinate, Nd_10.67Pt₄O₂₄. Gd₂O₃ did not capture platinum in bench-scale experiments in dry air, but did, however, seem to capture platinum under pilot plant conditions, likely due to the co-capture of Co lost from the N₂O abatement catalyst. The catalytic activity of both oxides and platinum-containing products were studied, toward NO_x and N₂O decomposition. None of the oxides showed significant activity toward NO_x decomposition, and all showed activity toward N₂O decomposition, but to different extents. An overall assessment of the screened oxides with respect to potential use in industrial Ostwald conditions is provided. All tested oxides except CaO and SrO withstood industrial conditions. From our assessments, the nickelates and A₂O₃ (A = Nd, Gd) stand out as superior oxides for platinum capture. Full article

The development of a selective separation and recovery method for platinum-group metals (PGMs) is in high demand to establish efficient and practical recycling technologies for different secondary materials such as industrial automobile catalysts. In this study, the highly selective precipitation of Pt(IV) from hydrochloric acid (HCl) solutions containing Pd(II), Pt(IV), and Rh(III) was successfully achieved using m-phenylenediamine dihydrochloride (MPDA) as a precipitant. Pt(IV) selectivity was observed at HCl concentrations higher than 7 M, whereas the co-precipitation of Rh(III) could not be suppressed using 3–7 M HCl solutions. Successful recovery of Pt(IV)-containing precipitates with high Pt yield (94.6%) and Pt purity (98.5%) was also achieved using an actual catalyst leaching solution with a complex composition containing PGMs, base metals, and rare metals. Structural analyses revealed that the Pt(IV)-containing precipitate forms ionic crystals composed of [PtCl₆]²⁻/protonated m-phenylenediamine (MPDA-2H⁺) in a 1:1 ratio. The high stability and insolubility of the Pt(IV)-containing ionic crystals, owing to their highly packed structure, resulted in the highly selective precipitation of Pt(IV) at high HCl concentrations. Full article

This study investigated Rhodamine B (RhB) degradation by electro-Fenton (EF), anodic oxidation (AO), and their combination (EF/AO), using a carbon felt cathode coupled to a sub-stoichiometric titanium dioxide Magnéli phase (Ti₄O₇) anode or a platinized titanium (Ti/Pt) anode. The results indicated that operational parameters influenced the kinetics of electrochemical reactions. An increase in current density from 10 to 50 mA cm⁻² significantly enhanced the RhB degradation rate; 30 mA cm⁻² was the optimal current density, balancing both energy efficiency and degradation performance. Moreover, higher RhB concentrations required longer treatment. The Microtox^® bioluminescence inhibition test revealed a significant toxicity decrease of the dye solution during electrochemical degradation, which was highest with EF/AO. Similarly, total organic carbon removal was highest with EF/AO (90% at pH 3), suggesting more efficient mineralization of RhB and its by-products than with EF or AO. Energy consumption remained relatively stable with all oxidation processes throughout the 480 min electrolysis period. High-resolution mass spectrometry elucidated RhB degradation pathways, highlighting chain oxidation reactions leading to the formation of intermediates and mineralization to CO₂ and H₂O. This study underscores the potential of EF, AO, and EF/AO as effective methods for RhB mineralization to develop sustainable and environmentally friendly wastewater treatment strategies. Full article

Calcium orthophosphate material (Ca_1-xCu_x)HPO₄.nH₂O (0.4 ≤ x ≤ 1) with the gradual replacement of Ca²⁺ with Cu²⁺ ions were synthesized by a chemical precipitation technique. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Then, the prepared powders were deposited onto an alumina substrate with interdigitated Pt electrodes by the spin coating method and polyvinyl alcohol (PVA) as a binder. Successively, the sensors were investigated from 0% to 90% at room temperature under various conditions, including humidity, nitrogenous oxide, methane, carbon dioxide and ammonia. The results evidenced that at 90% RH, the sensitivity of sensors significantly increased with the increase in the Cu content. Moreover, the sensors exhibited good repeatability and, after 1 year of aging, the sensor response was equal to 34% that of the freshly prepared sensor. Finally, there was no interference in the presence of other gases (nitrogenous oxide 2.5 ppm, methane 10 ppm, carbon dioxide 500 ppm and ammonia 4 ppm). Full article

Insufficient selectivity is a major constraint to the further development of metal oxide semiconductor (MOS) sensors for chemical warfare agents, and this paper proposed an improved scheme combining catalytic layer/gas-sensitive layer laminated structure with temperature dynamic modulation for the Mustard gas (HD) MOS sensor. Mustard gas simulant 2-Chloroethyl ethyl sulfide (2-CEES) was used as the target gas, (Pt + Pd + Rh)@Al₂O₃ as the catalytic layer material, (Pt + Rh)@WO₃ as the gas-sensitive layer material, the (Pt + Pd + Rh)@Al₂O₃/(Pt + Rh)@WO₃ sensor was prepared, and the sensor was tested for 2-CEES and 12 battlefield environment simulation gases under temperature dynamic modulation. The results showed that the sensor only showed obvious characteristic peaks in the resistance response curves to HD under certain conditions (100–400 °C, the highest temperature was held for 1 s and the lowest temperature was held for 2 s), and its peak height reached 6.12, which was far higher than other gases, thus realizing the high selectivity of the MOS sensor to 2-CEES. Meanwhile, the sensor also showed good sensitivity, detection limits, response/recovery times, anti-interference, and stability, which further verified the feasibility of the improved scheme. Full article