Search Results (12)

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

It has previously been shown that an Ag/CZA catalyst can simultaneously remove NOx and soot from an oxygen-rich exhaust gas at low temperatures, by utilising the N₂O generated preferentially during incomplete NOx reduction. Here, we examine the effect of reformulating the catalyst to include potassium, which is a known promoter of soot combustion. On including 2 wt% K, NOx-reduction occurs both in the absence and presence of soot, but the N₂O formed does not play a part in the oxidation of soot. At higher K loadings (5, 10 and 15 wt%), NOx reduction is almost completely disabled, and only contributes to the activity of the catalyst containing 5 wt% K when tested in the presence of soot. At a loading of 20 wt% K, the potassium phase segregates, leaving NO and NH₃ adsorption sites exposed. In the absence of soot, this catalyst can remove NOx by reduction on the Ag/CZA component and through nitration of the potassium phase. Although the presence of potassium lowers the onset temperature for soot oxidation to within the range of NOx reduction over Ag/CZA, the mobile K species prevents the desirable C+N₂O reaction. Full article

The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NO_x and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an after-treatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NO_x under lean-burn operation conditions are selective catalytic reduction (SCR) and the lean NO_x trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NO_x and soot abatement strategies. The main focus of this review is on combined technologies for NO_x removal (i.e., LNT–SCR) and for the simultaneous removal of NO_x and soot, like SCR-on-Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems. Full article

Plasma science has attracted the interest of researchers in various disciplines since the 1990s. This continuously evolving field has spawned investigations into several applications, including industrial sterilization, pollution control, polymer science, food safety and biomedicine. nonthermal plasma (NTP) can promote the occurrence of chemical reactions in a lower operating temperature range, condition in which, in a conventional process, a catalyst is generally not active. The aim, when using NTP, is to selectively transfer electrical energy to the electrons, generating free radicals through collisions and promoting the desired chemical changes without spending energy in heating the system. Therefore, NTP can be used in various fields, such as NO_x removal from exhaust gases, soot removal from diesel engine exhaust, volatile organic compound (VOC) decomposition, industrial applications, such as ammonia production or methanation reaction (Sabatier reaction). The combination of NTP technology with catalysts is a promising option to improve selectivity and efficiency in some chemical processes. In this review, recent advances in selected nonthermal plasma assisted solid–gas processes are introduced, and the attention was mainly focused on the use of the dielectric barrier discharge (DBD) reactors. Full article

Vehicular pollution has become a major problem in urban areas due to the exponential increase in the number of automobiles. Typical exhaust emissions, which include nitrogen oxides (NO_x), hydrocarbons (HC), carbon monoxide (CO), soot, and particulate matter (PM), doubtless have important negative effects on the environment and human health, including cardiovascular effects such as cardiac arrhythmias and heart attacks, and respiratory effects such as asthma attacks and bronchitis. The mitigation measures comprise either the use of clean alternative fuels or the use of innovative technologies. Several existing emission control technologies have proven effective at controlling emissions individually, such as selective catalytic reduction (SCR) and lean NO_x trap (LNT) to reduce NO_x and diesel particulate filter (DPF) specifically for PM abatement. These after-treatment devices are the most profitable means to reduce exhaust emissions to acceptable limits (EURO VI norms) with very little or no impact on the engine performances. Additionally, the relative lack of physical space in which to install emissions-control equipment is a key challenge for cars, especially those of small size. For this reason, to reduce both volume and cost of the after-treatment devices integrated catalytic systems (e.g., a sort of a “single brick”) have been proposed, reducing both NO_x and PM simultaneously. This review will summarize the currently reported materials for the simultaneous removal of NO_x and soot, with particular attention to their nature, properties, and performances. Full article

Herein, a novel process of diesel exhaust purification by non-thermal plasma combined with wood fiber has been investigated to understand the effect of purification efficiency on the emission. The dielectric barrier discharge (DBD) and wood fiber (WF) improved removal efficiency of nitrogen oxide (NO_x) owing to the positive activity of oxygen-containing functional groups (such as O–H groups or C–O groups) on the wood surface, which promoted the removal of NO_x by 10%–13%. The mechanism to remove NO_x in the presence of wood fibers was also deduced through FTIR spectra. When carbon black was loaded on the wood fiber, there was simultaneous removal of carbon soot and NO_X. Although complete purification was not achieved, a high purification efficiency was obtained under the conditions of room temperature and no catalysts. These advantages highlight the importance of use of wood and non-thermal plasma (NTP), and this research work opens new avenues in the field of emissions treatment. Full article

Ag/CeO₂-ZrO₂-Al₂O₃, a known catalyst for the simultaneous removal of NOx and soot, was modified by the addition of K, and was prepared using various techniques: wet impregnation, incipient wetness, and chemical vapor impregnation at different temperatures. The effect of the preparation method on catalyst activity was studied. It was found that catalysts prepared via wet impregnation, incipient wetness, and chemical vapor impregnation at 80 °C were able to utilize in situ formed N₂O at low temperatures, to simultaneously remove NOx and soot. The difference in preparation method affected the catalyst’s ability to produce and use N₂O as an oxidant for soot. The temperature at which chemical vapor impregnation was performed greatly influenced the catalyst’s ability to oxidize soot. The introduction of K to the Ag/CeO₂-ZrO₂-Al₂O₃ vastly improved the soot oxidation activity, particularly for the catalyst prepared via wet impregnation. However, the incorporation of K had an adverse effect on the reduction of NOx. 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

The challenge that needs to be overcome regarding the removal of nitrogen oxides (NO_x) and soot from exhaust gases is the low activity of the selective catalytic reduction of NO_x at temperatures fluctuating from 150 to 350 °C. The primary goal of this work was to enhance the conversion of NO_x and soot simulant by employing a Ag/α-Al₂O₃ catalyst coupled with dielectric barrier discharge plasma. The results demonstrated that the use of a plasma-catalyst process at low operating temperatures increased the removal of both NO_x and naphthalene (soot simulant). Moreover, the soot simulant functioned as a reducing agent for NO_x removal, but with low NO_x conversion. The high efficiency of NO_x removal required the addition of hydrocarbon fuel. In summary, the combined use of the catalyst and plasma (specific input energy, SIE ≥ 60 J/L) solved the poor removal of NO_x and soot at low operating temperatures or during temperature fluctuations in the range of 150–350 °C. Specifically, highly efficient naphthalene removal was achieved with low-temperature adsorption on the catalyst followed by the complete decomposition by the plasma-catalyst at 350 °C and SIE of 90 J/L. Full article

NO_x storage-reduction (NSR) is a potential approach for the effective removal of NO_x under the lean conditions in lean-burn engines. Herein, manganese-doped mixed oxides (Mn/MgAlO_x) with high performance for low temperature NO_x storage and release were derived from hydrotalcites precursors prepared by a facile coprecipitation method. The catalysts were characterized by X-ray diffraction (XRD), SEM, N₂ adsorption-desorption, H₂-TPR, FT-IR, and X-ray photoelectron spectroscopy (XPS) techniques. The Mn-doped MgAlO_x catalysts exhibited high NO_x storage capacity (NSC) at low temperature range (150–300 °C), which was related to their increased surface area, improved reducibility and higher surface Mn³⁺ content. The largest NSC measured, 426 μmol/g, was observed for NO_x adsorption at 200 °C on Mn15 catalyst (the sample containing 15 wt% of Mn). The in situ DRIFTS spectra of NO_x adsorption proved that the Mn-doped hydrotalcite catalysts are preferred for low temperature NO_x storage and release due to their ability to store NO_x mainly in the form of thermally labile nitrites. NSR cycling tests revealed the NO_x removal rate of Mn15 sample can reach above 70% within the wide temperature range of 150–250 °C. Besides, the influence of CO₂, soot, H₂O and SO₂ on NO_x storage performance of Mn15 catalyst was also studied. In all, owning to their excellent NO_x storage capacity, NSR cycling performance, and resistance to CO₂, soot, SO₂ and H₂O, the Mn-doped MgAlO_x NSR catalysts have broad application prospects in NO_x control at low temperatures. Full article

Alumina-supported manganese catalysts with cryptomelane and/or birnessite structure have been prepared using a simple method based on the thermal decomposition of potassium permanganate. The samples have been characterized by XRD, FTIR, TGA, DSC, N₂ adsorption at −196 °C, SEM, H₂-TPR and XPS, and their catalytic activity for soot combustion has been tested and compared to that of a reference Pt/alumina catalyst. The thermal decomposition of alumina-supported KMnO₄ yields a mixture of supported birnessite and potassium manganate which is the most effective, among those prepared, to lower the soot combustion temperature. However, this material is not useful for soot combustion because the accelerating effect is not based on a catalytic process but on the oxidation of soot by potassium manganate. A suitable soot combustion catalyst is obtained after potassium manganate is removed by water washing, yielding only the birnessite phase on the γ-Al₂O₃ support. This birnessite phase can be transformed into cryptomelane by calcination at 600 °C. These two samples, γ-Al₂O₃-supported birnessite and cryptomelane are suitable catalysts for soot combustion in NO_x/O₂ mixtures, as their catalytic activity is based on the NO₂-assited mechanism, that is, both catalysts accelerate the oxidation of NO to NO₂ and NO₂ promotes soot oxidation. The soot combustion temperatures obtained with these birnessite/cryptomelane alumina-supported catalysts are similar to that obtained with the reference Pt/alumina catalyst. Full article