Search Results (75)

The mixed oxides of Ni/ZrO₂, Ni-Ca/ZrO₂, Ni-Ba/ZrO₂, and Ni-Ba-Ca/ZrO₂ were prepared using the co-precipitation method at a pH of precisely 8.3. The catalytic mixed oxides of Ni/ZrO₂, Ni-Ca/ZrO₂, Ni-Ba/ZrO₂, and Ni-Ba-Ca/ZrO₂ were characterized using x-ray diffraction XRD, Brunauer Emmett Teller (BET), scanning electron microscopy (SEM), and metal dispersion for the screening of phase purity, surface area, and morphology. The mixed oxides are subjected to CO₂-TPD to quantify the basicity of every composition. The mixed oxide catalysts of Ni/ZrO₂, Ni-Ca/ZrO₂, Ni-Ba/ZrO₂, and Ni-Ba-Ca/ZrO₂ were screened for oxythermal reforming of CH₄ with CO₂ in a fixed bed tubular reactor at 800 °C. Among all catalysts, the Ba- and Ca- loaded Ni-Ba-Ca/ZrO₂ showed high conversion by the decomposition of methane and CO₂ disproportionation throughout the time on stream of 29 h. The high activity with stability led to less coke formation over Ni-Ba-Ca/ZrO₂ over the surface. The stable syngas production with an active catalyst bed contributed to the improved bimetallic synergy. The high surface basicity of Ni-Ba-Ca/ZrO₂ may keep actively gasifying the formed soot and allow for further stable reforming reactions. Full article

Non-catalytic partial oxidation (POX) of natural gas is gaining importance in low-carbon energy systems for methane conversion to acetylene, syngas, and olefins. However, uncontrolled polycyclic aromatic hydrocarbons (PAHs) and soot formation remain challenges. This work developed a Hierarchical-Integrated Mechanism (HI-Mechanism) by constructing detailed C₀-C₆, C₅-C₁₅ and C₁₆ mechanisms, and then hierarchically simplifying C₅-C₁₅ subsystems, ultimately integrating them into a final mechanism with 397 species and 5135 reactions. The HI-Mechanism accurately predicted shock tube ignition delays and major species concentrations. Microkinetic analyses, including production rates and reaction sensitivity, revealed key pathways and enabled reliable product distribution prediction. The HI-Mechanism provides theoretical guidance for optimizing POX of natural gas processes and can be extended to complex systems like heavy oil cracking, supporting clean energy technology development. Full article

Biomorphic mineralization was employed to synthesize novel Mn–Ce and Mn–Co–Ce oxide fibers using commercial cotton as a biotemplate, aiming to assess their catalytic performance in diesel soot combustion and CO oxidation. Two synthesis protocols—one with and one without citric acid—were investigated. The inclusion of citric acid led to fibers with more uniform morphology, attributed to improved precursor distribution, although synthesis yields decreased for Co-containing systems. In soot combustion tests, Mn–Ce catalysts synthesized with citric acid outperformed their monometallic counterparts. While cobalt incorporation enhanced the mechanical robustness of the fibers, it did not significantly boost catalytic activity. Selected formulations were also evaluated for CO oxidation, with Mn–Co–Ce fibers achieving T₅₀ values in the 240–290 °C range, comparable to Co–Ce nanofibers reported in the literature. These results demonstrate that biomorphic fibers produced through a simple and sustainable route can offer competitive performance in soot and CO oxidation applications. Full article

Among biomass gasification syngas cleaning methods, non-catalytic reforming emerges as a sustainable and high-efficiency alternative. This study employed integrated experimental analysis and kinetic modeling to examine non-catalytic reforming processes of biomass-derived producer gas utilizing a synthetic tar mixture containing representative model compounds: naphthalene (C₁₀H₈), toluene (C₇H₈), benzene (C₆H₆), and phenol (C₆H₅OH). The experiments were conducted using a high-temperature fixed-bed reactor under varying temperatures (1100–1500 °C) and equivalence ratios (ERs, 0.10–0.30). The results obtained from the experiment, namely the measured mole concentration of H₂, CO, CH₄, CO₂, H₂O, soot, and tar suggested that both reactor temperature and O₂ content had an important effect. Increasing the temperature significantly promotes the formation of H₂ and CO. At 1500 °C and a residence time of 0.01 s, the product gas achieved CO and H₂ concentrations of 28.02% and 34.35%, respectively, while CH₄, tar, and soot were almost entirely converted. Conversely, the addition of O₂ reduces the concentrations of H₂ and CO. Increasing ER from 0.10 to 0.20 could reduce CO from 22.25% to 16.11%, and H₂ from 13.81% to 10.54%, respectively. Experimental results were used to derive a kinetic model to accurately describe the non-catalytic reforming of producer gas. Furthermore, the maximum of the Root Mean Square Error (RMSE) and the Relative Root Mean Square Error (RRMSE) between the model predictions and experimental data are 2.42% and 11.01%, respectively. In particular, according to the kinetic model, the temperature increases predominantly accelerated endothermic reactions, including the Boudouard reaction, water gas reaction, and CH₄ steam reforming, thereby significantly enhancing CO and H₂ production. Simultaneously, O₂ content primarily influenced carbon monoxide oxidation, hydrogen oxidation, and partial carbon oxidation. Full article

This article discusses the possibility of using a liquid catalyst in selected vegetable fuels. The fuels selected for study are rapeseed oil methyl ester and hemp oil methyl ester. The aim of the research presented in this paper is to evaluate the operating and environmental performance of an engine fueled with selected fuels with a catalytic additive. The tests were carried out on a dynamometer bench using a Fiat 1.3 JTD common rail engine. During the tests, parameters such as engine torque and power, specific fuel consumption, and the emission of nitrogen oxides, hydrocarbons, carbon dioxide, and soot were measured. The tests were carried out on fuels with and without a catalytic converter. The results show that the use of a catalytic additive reduces nitrogen oxides and hydrocarbon emissions for all fuels tested. Full article

Diesel particulate matter (DPM) represents a deleterious environmental contaminant that necessitates the development of effective catalytic oxidation methodologies. This research delineates a comparative analysis of silver-supported metal oxide catalysts (Ag/Al₂O₃, Ag/TiO₂, Ag/ZnO, and Ag/CeO₂), with an emphasis on the effects of silver distribution and the metal-support interaction on the oxidation of DPM. An array of characterization techniques including XRD, HRTEM, XPS, H₂-TPR, TEM, GC-MS, TGA, and in situ DRIFTS was employed. The novelty of this study resides in elucidating the oxidation mechanism through a tripartite pathway and recognizing Ag⁰ as the predominant active species involved in soot oxidation. The Ag/Al₂O₃ catalyst demonstrated superior catalytic performance, achieving a reduction in the ignition temperature by more than 50 °C, attributable to the optimal dispersion of Ag nanoparticles and a balanced metal-support interaction. Conversely, an excessive interaction observed in Ag/ZnO resulted in diminished catalytic activity. The oxidation of DPM transpires through the volatilization of VOCs (<300 °C), the oxidation by reactive oxygen species, and the combustion of soot (>300 °C). This investigation offers significant contributions to the formulation of highly efficient silver-based catalysts for emissions control, with a particular focus on optimizing Ag dispersion and support interactions to enhance catalytic efficacy. Full article

Noble metals are still in high demand for exhaust control catalysts in mobile sources. Designing highly efficient and less costly catalysts for soot purification from engine emissions is a challenge. Herein, the Ni-Co spinel oxide catalyst made of earth-abundant elements was synthesized by a precipitation method. Based on the test results of powder X-ray diffraction (XRD), N₂ adsorption–desorption experiments, the temperature-programmed oxidation of soot (soot-TPO), the temperature-programmed oxidation of NO (NO-TPO), the temperature-programmed reduction in H₂ (H₂-TPR), and the advantages of Ni-Co synergistic catalysts relative to pure NiO and Co₃O₄ oxides were systematically investigated. The NiCo₂O₄ catalyst exhibits excellent catalytic performance and stability during soot oxidation compared with NiO and Co₃O₄ catalysts, i.e., its T₁₀, T₅₀, T₉₀ and S_CO2^m are 316, 356, 388 °C and 99.95%, respectively. The mechanism of the Ni-Co synergy effect for boosting soot oxidation on the spinel oxide catalyst is proposed according to the experimental results of in situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) and the theoretical knowledge of coordination chemistry of metal–NO. This study lays a good foundation for exhaust purification by non-noble metal catalysts for pollution control and sustainable environmental practices. Full article

In this study, a series of cerium dioxide catalysts with varying hydrothermal temperatures and times were synthesized using the hydrothermal method, without the use of templates. The impact of varying hydrothermal conditions on the activity of cerium dioxide catalysts was investigated through experiments to examine their oxidation characteristics in soot combustion. Among the conditions tested, the hydrothermal conditions of 140 °C and 6 h yielded the most optimal catalytic oxidation of soot, with a combustion characteristic temperature (T_p) of 552 °C and a reduction of 122.9 °C. The integrated combustion index (S) and combustion stability coefficient (R_w) were found to be 27.97 × 10⁸ %²min⁻²°C⁻³ and 90.76 × 10⁵, respectively. The indices of S and R_w exhibited an improvement of 51.1% and 36.93%, respectively. 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

Purification of soot particles from automobile exhaust has closely to do with the synergistic effect between catalyst metals. Here, several binary Ni-Fe oxide catalysts were elaborately prepared via a modified solvothermal method. A non-noble-metal (Ni)-modified hexagonal Fe₂O₃ nano-sheet catalyst (Ni−Fe₂O₃) was prepared. The introduced heteroatoms replace some of the Fe atoms, which take up the surface of the [FeO₆] octahedron, and the synergistic effect formed between the heteroatoms which are on the surface and the adjacent Fe atoms promotes the formation of coordination unsaturated ions of the activated reactants. The optimal performance was obtained with the Ni-Fe₂O₃-20 composition, with catalytic soot oxidation resulting in T₅₀, SCO₂^m, E_a and TOF of 366 °C, 99.1%, 72.7 kJ mol⁻¹ and 0.156 min⁻¹ (at 310 °C), respectively. The combination of Ni and Fe₂O₃ cells increases the ratio of Fe³⁺/Fe²⁺, making the interaction among electrons between the Ni, which was proved highly dispersed over the catalyst, and the Fe₂O₃ strong. Both exist on the catalyst surface in the form of NiFe₂O₄. Ni atoms and Fe₂O₃, which demonstrate a synergistic effect, promoting the formation of coordination unsaturated ions of the activated reactants and generating more oxygen vacancies, thus promoting the adsorption of NO and accelerating the ignition of soot in O₂ at a low temperature. The novel Ni-Fe₂O₃-X oxide cocatalyst is an improved noble-free catalyst that promotes the synergistic effect between heteroatoms and metal oxides through surface regulation. This is of great significance for the further development of economic and efficient catalysts for soot particle removal from automobile exhaust. Full article

The problem of removing NO_x and carbon particle emissions from diesel engines has been a challenge in the field of environmental protection, which is prompting people to actively explore ways to improve the efficiency of pollutant emission treatment. Due to the high price of precious metals, developing an alternative catalytic material with high catalytic activity and stability is a difficult task. Perovskite, with its stable and flexibly variable crystal structure, has become a research hotspot in the field of catalysis. This paper discusses the structure of perovskite catalysts and the mechanism behind the simultaneous catalytic oxidation of diesel engine soot and NO_x. Meanwhile, it provides a comprehensive review of the preparation methods and A/B site modification strategies, establishing a foundation for the synthesis and A/B site modification of perovskite catalysts capable of catalyzing the oxidation of soot and NO_x simultaneously. Additionally, this article offers an outlook on the challenges and future development of perovskite catalysts in this field. Full article

A series of Co-Ce clay-based catalysts were prepared via the wet impregnation method and tested for the catalytic combustion of diesel soot and carbon monoxide. The objective of this work was to find a suitable catalyst with an optimized active phase composition in order to structure this system using a 3D-printing technique. The physicochemical characterization indicated that the support was mainly composed of kaolinite and quartz. When supported on commercial clay, the mixture of oxides (Co₃O₄ spinel and CeO₂ fluorite) had higher activity than the individual oxides. The formation of a solid Co-Ce solution was verified along with a synergistic effect between these two selected metal oxides. The optimal molar composition was Co:Ce = 90:10. The corresponding catalyst showed the highest catalytic activity for soot combustion, with 335 °C being the temperature of the maximum combustion rate. Also, it produced the best system for CO oxidation. This formulation showed a balanced proportion of Co³⁺ and Co²⁺ on the surface and had the highest content of Ce³⁺ surface species among the catalysts prepared, which played a key role in the oxidation reactions studied. Full article

Ba_1−xCe_xMnO₃ (BM-Ce_x) and Ba_1−xLa_xMn_0.7Cu_0.3O₃ (BMC-La_x) perovskite-type mixed oxides were synthesized using the sol–gel method adapted for aqueous media with different values of x (0, 0.1, 0.3, 0.6) to estimate the effect of the degree of the partial substitution of Ba by Ce or La on the structure and properties that are relevant for their use as catalysts for gasoline direct injection (GDI) soot oxidation. The samples were deeply characterized by ICP-OES, XRD, XPS, N₂ adsorption, H₂-TPR, and O₂-TPD, and their potential as catalysts for soot oxidation has been analyzed in various scenarios that replicate the exhaust conditions of a GDI engine. By comparing the catalytic performance for soot oxidation of the two tested series (BM-Cex and BMC-Lax) and in the two conditions used (100% He and 1% O₂ in He), it could be concluded that (i) in the absence of oxygen in the reaction atmosphere (100% He), BMC-La_0.1 is the best catalyst, as copper is also able to catalyze the soot oxidation; and (ii) if oxygen is present in the reaction atmosphere (1% O₂/He), BM-Ce_0.1 is the most-active catalyst as it presents a higher proportion of Mn(IV) than BMC-La_0.1. Thus, it seems that the addition of an amount of Ce or La higher than that corresponding to x = 0.1 in Ba_1−xCe_xMnO₃ and Ba_1−xLa_xCu_0.3Mn_0.7O₃ does not allow us to improve the catalytic performance of BM-Ce_0.1 and BMC-La_0.1 for soot oxidation in the tested conditions. Full article

Soot combustion experiments with 5%O₂/He were conducted using model soot, and four distinct compositions of Ce_xPr_1-xO_2-δ oxides of varying nominal cerium compositions (x = 0, 0.2, 0.3, and 1) were prepared. The catalyst samples were comprehensively characterized using techniques such as XRD, Raman spectroscopy, HR-TEM, N₂ adsorption at −196 °C, XPS, O₂-TPD, H₂-TPR, and work function measurements. The Pr-rich compositions, ranging from Ce_0.3Pr_0.7O_2-δ to PrO_2-δ, resulted in a significant increase in the total evolved O₂ amounts and enhanced catalyst reducibility. However, a decrease in the textural properties of the catalysts was noted, which was particularly important for the pure praseodymia under the synthesis route conducted. The catalytic activity was investigated under the two following contact modes of mixing between soot and catalyst: loose and tight. The results revealed that the catalytic performance is associated with the surface contact in tight contact mode and with the combination of surface/subsurface/bulk oxygen mobility and the BET surface area in loose contact mode. Notably, the temperatures estimated at 10% and 50% of the conversion (T₁₀ and T₅₀) parameters were achieved at much lower temperatures than the uncatalyzed soot combustion, even under loose contact conditions. Specifically, the 50% conversion was achieved at 511 °C and 538 °C for Ce_0.3Pr_0.7O₂ and Ce_0.2Pr_0.8O₂, respectively. While no direct correlation between catalytic activity and work function was observed, a significant relationship emerges between work function values and the formation of oxygen vacancies, whatever the conditions used for these measurements. On the other hand, the ability to generate a high population of oxygen vacancies at low temperatures, rather than the direct activation of gas-phase O₂, influences the catalytic performance of Pr-doped ceria catalysts, highlighting the importance of surface/subsurface oxygen vacancy generation, which was the parameter that showed a better correlation with the catalytic activity, whatever the soot conversion value or the mode of contact considered. Full article

A series of Ag-modified manganese-mullite (SmMn₂O₅) catalysts with different Ag contents (1, 3, and 6 wt.%) were prepared via a citric acid sol–gel method for catalytic soot oxidation. The catalysts were characterized by powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Raman spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy analysis (HRTEM), X-ray photoelectron spectroscopy (XPS), and H₂ temperature-programmed reduction (H₂-TPR). The soot oxidation activity of the mullite was significantly promoted by the addition of silver and affected by the loading amount of the metal. Herein, the influences of silver loading on the metal size distribution and its interactions with the mullite were studied. Based on these characterizations, a possible soot oxidation reaction mechanism was proposed for silver-modified SmMn₂O₅. Full article