Automobile Exhaust Purification Research Articles

Double-stable Ce-based oxide: Capturing atomic precious metals via Ostwald ripening for multicomponent three-way catalysts construction

Precious metal catalysts have been widely used to catalyze various reactions, particularly three-way catalysts for automobile exhaust purification. Pt, Pd, and Rh, which are dispersed on Ce-based oxides that store and release oxygen, serve as the active center of a catalyst. However, methods to construct multifunctional three-way catalysts to maximize their efficiency and stabilize them are lacking. In this study, Ce-based oxides with a double-stable mode were synthesized to capture and stabilize the precious metals Pt and Rh migrated by Ostwald ripening (OR), and a multicomponent three-way catalyst was accurately synthesized, which showed good catalytic activity and thermal stability. The origin of Ce-based oxides with a dual-stable mode was studied by TEM, XRD, oxygen storage/release capacity and rate test, and XPS. AC-STEM, EXAFS, in situ diffuse reflectance Fourier transform infrared, and H2 temperature-programmed reduction studied the OR migration of precious metals and the composition change after aging. Results showed that in the lean/rich oxygen alternating shift atmosphere containing CO, the proportion of OR migration of Pt and Rh precious metals whose initial state is single atoms can reach 100 %. This discovery provides a basic understanding of the sintering mechanism of precious metals, which is of great importance for the development and industrial application of three-way catalysts.

Removal of PM and oil mist from automobile exhaust by a “hamburger” structured conjugated microporous polymers membrane

The purification treatment of automobile exhaust has attracted great attention because of the severe harm of automobile exhaust to the global environment and human health. Herein, inspired by capillarity, we adopted a very simple face-to-face constrained growth method to prepare a conjugated microporous polymers membrane (C-CMPs-M) with a “Hamburger” structure through Sonogashira-Hagihara (S-H) coupling reaction for purification and filtration of gaseous, solid and liquid pollutants in automobile exhaust. Thanks to such a special structure, the C-CMPs-M−1 membrane shows an extremely high efficiency of capture and interception of PM2.5 and PM10 (greater than99.5 %) and PM0.3 (greater than95%) in the exhaust gas obtained at different engine speeds. Unlike those hydrophilic filtration materials which suffer the drawback of less tolerance in high humidity conditions, the unique superhydrophobic chemistry of the CMPs membrane makes it possible to efficiently intercept PM under high humidity conditions, and the filtration efficiency basically remains unchanged within 10 h. More interestingly, the super lipophilicity of the membrane endows it excellent oil absorption performance, e.g., high absorption of 907.61 % of its own weight for engine oil was detected and consequently good oil retention performance was also obtained. It also has a strong absorption performance for the unburned oil mist ejected from the exhaust. Based on its ideal porous structure, high interception efficiency, and good physicochemical stability at high humidity and high temperatures conditions, therefore, our C-CMPs-M−1 shows great potential in automobile exhaust purification applications.

Study on the performance of environmental micro-surfacing for exhaust purification

In order to endow pavement materials with environmental protection properties such as automobile exhaust purification, an environmentally friendly micro-surfacing material with exhaust purification was prepared. Functional materials with photocatalytic activity were prepared by sol-gel method. The best preparation scheme of composite modified asphalt was determined by comparative test. The mix proportion of micro-surfacing mixture was designed to determine the optimal preparation process of micro-surfacing. Based on rutting test, wet wheel wear test and pendulum test, the road performance of protective environmental micro-surfacing with exhaust purification function is studied. An exhaust gas purification test equipment is improved to determine the test method and analyze the exhaust gas purification performance of protective environmental micro-surfacing materials. The results showed that when the molecular weight ratio of Ti : N : Fe was 1 : 0.7 : 0.005, the photocatalytic performance of the prepared environmental functional material with tail gas purification effect was the best. The availability of photocatalytic materials is increased, and the photocatalytic performance is the optimum. When 3% functional materials and 5% SBR latex are used as composite modifier of emulsified asphalt, the consistency, cracking resistance and high temperature performance of composite modified emulsified asphalt are the optimum. The micro-surfacing mixture prepared with 7% oil-stone ratio and 6%–7% external water has good high temperature stability, water stability and skid resistance. When the molecular weight ratio of Ti : N : Fe is 1 : 0.7 : 0.005, the HC purification efficiency reaches 12%, the CO purification efficiency reaches 15%, and the NOX purification efficiency reaches 30%, which has good road performance and exhaust purification effect.

Study of Ce, Ca, Fe, and Mn-Doped LaCoO3 Perovskite Oxide for the Four-Way Purification of PM, NOx, CO, and HC from Diesel Engine Exhaust.

Perovskite-type catalysts were widely used in the field of automobile exhaust purification due to their inherent physicochemical properties and excellent doping characteristics. A series of La1−xMxCo1−yNyO3 (M = Ce, Ca; N = Fe, Mn) perovskite-type catalyst samples were prepared by sol-gel method for the four-way purification of PM, NOx, CO, and HC emitted by diesel exhaust. The activity of catalyst samples was tested by simulation experiments and hydrogen temperature-programmed reduction (H2-TPR). Catalyst samples were characterized by means of XRD, FT-IR, SEM, BET, and XPS analysis. The results demonstrated that the perovskite-type catalyst samples with a particle pore size of 3–5 μm can be prepared by sol-gel method. When A-site of LaCoO3 perovskite-type oxide was doped by cerium ions, the catalyst samples produced small distortion. The doping of cerium ions to A-site was more conducive to the four-way purification of diesel exhaust than calcium ions. La0.8Ce0.2CoO3 perovskite-type samples showed the best purification efficiency, and the purification efficiencies of PM, NOx, CO, and HC were 90%, 85%, 94%, and 100%, respectively. When the B-site of La0.8Ce0.2CoO3 perovskite was doped with iron ions, the purification efficiency of catalyst samples for PM and NOx can be further enhanced. When the B-site of La0.8Ce0.2CoO3 perovskite was doped with manganese ions, the purification efficiency of the catalyst samples for PM can be further enhanced. It can be seen from the simulation experiments that La0.8Ce0.2Co0.7Fe0.3O3 perovskite was the best doping amount, and the purification efficiencies of PM, NOx, CO, and HC were 95%, 92%, 94%, and 100%, respectively.

Preparation of Cerium - Zirconium - Based Catalyst for Automobile Exhaust Purification

Preparation of Cerium - Zirconium - Based Catalyst for Automobile Exhaust Purification

Electrocatalytic property of nitrogen-doped graphite-supported CeO2-CoOx

Ceria has been widely used as a catalyst in photocatalysis, automobile exhaust purification, and organic degradation. However, ceria has poor intrinsic catalytic performance and usually requires modifications. In this study, N-doped graphite was used as a substrate, and then CeO2-CoOx was attached to N-doped graphite. Afterward, the effects of the recombination with N-doped graphite and those of Co doping on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic ability of CeO2 were studied. The experimental results showed that the electrocatalytic performance of CeO2-CoOx/N-rGO is higher than that of pure CeO2 and CeO2/N-rGO. After the N-doped graphite recombination, the number of transferred electrons increased at high potential, which fully illustrates that graphite can effectively reduce the overpotential of ORR. The 0.56 eV shift of the C1s in CeO2-CoOx/N-rGO to high binding energy revealed that CeO2-CoOx and N-rGO were combined with each other through covalent bonds. In addition, the increased pyridine nitrogen of N-rGO after the recombination improved the electrocatalytic performance of CeO2-CoOx/N-rGO. Overall, the catalytic ability of CeO2 was greatly improved, and the modified CeO2-CoOx/N-rGO composite showed better catalytic performance for the ORR and OER compared with Pt/C and RuO2.

Laboratory Study on Performance Evaluation and Automobile Exhaust Degradation of Nano‐TiO2 Particles‐Modified Asphalt Materials

Automobile exhaust pollution is a serious problem that restricts urban development, and it poses a serious threat to people’s lives and health and even the climate. At present, the treatment of automobile exhaust has attracted people’s attention, and numerous works have been focused on it thereafter. The purpose of the present study is to drive TiO2 nanoparticles application into pavement, and the study present an experimental investigation of performances and automobile exhaust purification of asphalt and its mixture modified by nano‐TiO2. In this work, a series of rheometer properties and pavement performances were studied, including penetration, softening point, ductility, DSR and BBR for asphalt binder, conventional pavement performances, and creep test for asphalt mixture. Moreover, the photocatalytic degradation test of automobile exhaust was conducted to assess degradation of TiO2 nanoparticles in the asphalt mixture on automobile exhaust. Results indicate that the TiO2 nanoparticle was beneficial to increase the viscosity and reduce the temperature sensitivity, which would enhance its high‐temperature stabilization capability of asphalt. Meanwhile, nano‐TiO2 can significantly enhance the rheometer properties of asphalt and its capacity of high‐temperature antirutting, and its low‐temperature performance could also comply with the specification. Besides, the incorporation of nano‐TiO2 in mixtures could effectively enhance the antirutting and anticracking as well as water stabilization. Moreover, the nano‐TiO2‐modified asphalt mixture possesses a positive impact on photocatalytic degradation of CH and NOx, which could provide a reference for the treatment of automobile exhaust. The photocatalytic degradation effect of asphalt mixtures modified by nano‐TiO2 on NOx is significantly better than that of CH.

Development Status and Trend Analysis of Four-way Purification Technology for Automobile Exhaust

Automobile exhaust has seriously polluted the environment and endangered human health, in order to satisfy strict China VI regulation, four-way purification technology will become effective engine after-treatment technology for purifying automobile exhaust. This paper firstly introduces reaction mechanism of purifying particular matter, nitrogen oxide, carbon monoxide and hydrocarbon. Secondly, this paper summaries the development status of four-way purification technology for automobile exhaust from two aspects. Finally, this paper suggests that automobile exhaust can be purified by plasma combined with modified perovskite catalyst technology, this method has the advantages of low back pressure, low cost, simple structure and strong stability compared with the traditional automobile exhaust purifier, which canachievethe purification of PM, NOx, CO and HC simultaneously, and open up a new direction for automobile exhaust purification technology.

Developed photocatalytic semi-flexible pavement for automobile exhaust purification using iron-doped titanium dioxide

To develop a green and sustainable photocatalytic semi-flexible pavement (SFP) for automobile exhaust (AE) purification using the iron (Fe)-doped titaniumdioxide (TiO2) loaded in the adsorbable hardened cement paste of SFP, the effects of Fe doping on microstructure and photoabsorption performances of TiO2 were discussed. Also, the catalytic purification efficiency of Fe-doped TiO2 to AE and its influences on pavement performances of SFP were investigated. Test results indicate that the prepared Fe-doped TiO2 is anatase phase. Fe ions are successfully doped into TiO2, improving its catalytic efficiency when exposed to visible light. The grain size of Fe-doped TiO2 is 14–18 nm. The doped Fe ion inhibits the growth of crystalline grain in TiO2. Also, the photoabsorption edge band shows an obvious red shift from ultraviolet to visible light region. The band gap of TiO2 is obviously decreased by the Fe doping, and the visible light absorbance of TiO2 is increased, improving its utilization efficiency of solar irradiation. Further, the Fe-doped TiO2 shows higher purification efficiency to HC and NOx, following the pseudo-first-order kinetics reaction model. The purification reaction of HC occurs to produce CO2 and H2O. Additionally, the acidulous NOx is easily adsorbed by alkaline cement paste in SFP, enhancing the photocatalytic purification to NOx. NOx is purified to generate nitrate and H2O. However, Fe-doped TiO2 shows unsatisfactory photocatalytic purification efficiency to CO and CO2 due to their reversiblereactions, not following the pseudo-first-order kinetics reaction model. The Fe-doped TiO2 dosage of 8% is proposed to add in cement slurry for prepare photocatalytic SFP. The prepared Fe-doped TiO2 shows slight effects on pavement performances of SFP, and can be used in SFP to develop a new sustainable and green pavement material.

Automobile exhaust purification over g-C3N4 catalyst material

In this work, graphite phase carbon nitride (g-C3N4) photocatalyst was prepared by thermal decomposition of dicyandiamide. By controlling the calcination temperature (450 °C, 500 °C, 550 °C and 600 °C)，g-C3N4 materials with different structure types were obtained. The prepared samples were used to test the degradation of automobile exhaust. The optimum preparation temperature could be obtained by measuring the purification efficiency for the automobile exhaust. Moreover, XRD, SEM, FT-IR, UV–vis, PL, AND TG-DSC tests were conducted to characterize the microstructures and properties of the samples. The results obtained are that when the calcination temperature was 600 °C, the obtained g-C3N4 material has the highest purification efficiency for the exhaust gas. Then the degradation rates for the four components of exhaust gas HC, CO, CO2, NOX were 0.16%, 0.42%, 0.29% and 15.41% respectively under ultraviolet irradiation (UV irradiation) in 60 min, and 9.7%, 4.77%, 6.86%, 35.45% respectively under visible light irradiation (Vis irradiation). It could provide a potential utilization for future exhaust gas treatment.

Multifunctional nickel nanofiber for effective air purification: PM removal and NO reduction from automobile exhaust

Particulate matter and NO pollution caused by automobile exhaust cause severe air pollution and respiratory diseases. Traditional gasoline particulate filter and three-way catalysts face the problem of high cost and no resistance to high temperature. Development of multifunctional filtration purification media with low cost and temperature resistance is necessary. In this paper, Ni nanofibers filter is easily fabricated by electrospinning, suitable for working environment with variable temperature. Moreover, between adjacent nanofibers, the preferable fused junction was formed which is beneficial to mechanical properties of the filter. The Ni nanofibers filter exhibits outstanding PM1 and NO gas removal ability. The PM1 filtration efficiency up to 99.86% @300 nm was achieved under wing speed of 5.3 cm/s. Moreover, the Ni nanofibers also achieve impressive NO-to-N2 and NO adsorption ability owing to the high specific surface area and activity of Ni nanofiber itself. As such, the multifunctional Ni nanofibers filter equips the potential for the actual application in automobile exhaust purification converter.

Cerium-bismuth solid solution material prepared and application in automobile exhaust purification

Due to the effect of human beings, the ecosystem of earth in which people can only live is encountering increasingly severe pollution. Environment pollution, especially the air pollution, has become a problem that cannot be ignored today. Therefore, this work is dedicated to make full use of light energy and combined with photocatalysis technology, to convert harmful pollutants to humans into clean substances, so as to achieve the purpose of purifying the air. This work prepared the cerium-bismuth solid solution material, which had a good effect on the purification of exhaust gas. The optimum ratio of cerium-bismuth in the solid solution material was obtained through the exhaust gas purification experiment. Moreover, the microscopic characterization tests of XRD, UV–Vis, FT-IR, SEM, EDS were conducted. The results obtained are that the molar ratio of cerium and bismuth is 0.5. In addition, under ultraviolet light conditions, the purification efficiency of cerium-bismuth solid solution material for HC, CO, CO2 and NOX were 3.6%, 22.22%, 13.56%, 26%. Under natural light conditions, the purification efficiencies for HC, CO, CO2 and NOX were 17.57%, 23.1%, 17.3% and 39.1%, respectively. The optical domain can be extended from ultraviolet light to visible light.

Effect of grain size on thermal stability and oxygen storage capacity of Ce0.17Zr0.73La0.02Nd0.04Y0.04O2 solid solutions

Nanostructured CeO2-ZrO2 materials are an irreplaceable constituent in catalytic systems for automobile exhaust purification due to their unique oxygen storage capacity (OSC). However, traditional CeO2-ZrO2 materials are easy to sinter at high temperature, which causes a sharp decrease of OSC. In this paper, La3+, Nd3+ and Y3+ are chosen as dopants for CeO2-ZrO2 to improve anti-sintering and OSC properties. The Ce0.17Zr0.73La0.02Nd0.04Y0.04O2 powders (CZLNY) were prepared by co-precipitation method. The effects of grain sizes with different mixed chlorinated solution concentrations on performances were investigated. X-ray diffraction (XRD) and transmission electron micrograph (TEM) were performed to calculate the grain sizes of CZLNY. The specific surfaces, OSC and redox properties were investigated by N2 adsorption/desorption and temperature programmed reduction (H2-TPR). The results show that introducing La3+, Nd3+ and Y3+ into CeO2-ZrO2 lattice can improve the stability of phase structure and anti-sintering ability. Moreover, low concentration of mixed chlorinated solution remarkably improves structural and textural properties of CZLNY. Relatively large fresh grain exhibits superior thermal stability and OSC under the condition of being calcined at 800 °C for 3 h. The specific surface and OSC are 42.37 m2/g and 333.13 μmol/g after calcining at 1000 °C for 10 h, respectively. This is owing to the low sintered driving force of large grain and long-range migration energy of large pores during the sintering process, which are beneficial to the stability of structure in CZLNY materials.

Preparation of Pt/beta zeolite–Al 2O 3/cordierite monolith for automobile exhaust purification

A two-step route was developed to prepare zeolite beta coatings on structured monolith. Al 2O 3 layer was deposited on cordierite substrate by slurry dip-coating in the first step and beta zeolite layer was then coated on Al 2O 3/cordierite by direct dynamic hydrothermal synthesis in the second step. The as-prepared beta zeolite–Al 2O 3/cordierite was characterized by means of XRD and SEM techniques and the stability of beta coatings was studied. Based on these results, the advantages of the two-step method were discussed. After the introduction of Pt to beta zeolite–Al 2O 3/cordierite, the obtained Pt/beta zeolite–Al 2O 3/cordierite monolith was tested as promising catalyst for the purification of automobile exhaust from real lean-burn engine.

Effect of doping elements on catalytic performance of CeO 2-ZrO 2 solid solutions

CeZr, CeYZr, LaCeZr, LaCePrZr, LaCePrYZr, and LaCePr solid solutions were prepared via the coprecipitation method, and characterized by means of X-Ray Diffraction (XRD) and Brunauer-Emmett-Teller (BET) techniques. The oxygen storage capacity (OSC) of the solid solutions was evaluated by the pulse technique and the catalytic activity was assessed using a 4-channel catalysis device. It was seen that the solid solutions presented cubic structure. The specific surface area and thermal stability could be enhanced by doping Y into the solid solutions. Doping a small amount of La had a positive effect on the thermal durability while doping a large amount of La decreased the specific surface area and the thermal stability. LaCePrZr and LaCePrYZr solid solutions synthesized using Baotou rare earth mineral residue enriched with LaCePr after Nd extraction presented a certain higher value in specific surface area and thermal stability, thereby enabling to be used as economic catalysts for automobile exhaust purification. Coating Al 2O 3 or SiO 2 layer on the surface of ceria-zirconia solid solutions increased the specific surface area and thermal resistance.

Rapid synthesis of La 0.7Sr 0.3MnO 3+ λ catalysts by microwave irradiation process

Microwave irradiation processing (MIP) was considered as a potential method to synthesize perovskite-type oxides rapidly, cleanly and energy-efficiently. In this paper, La 0.7Sr 0.3MnO 3+ λ , a kind of promising catalyst for automobile exhaust purification, was successfully prepared by MIP in not more than 5 min. The sol–gel method was also used for comparison. All the samples were evaluated by catalytic activity tests in the simulated exhaust and characterized by XRD, BET, TEM and XRF analyses. The results showed that the integrated perovskite-type phase and uniform particle size were obtained in the microwave-treated samples. And those ones exhibited a better oxidation activity under slightly oxygen-rich condition than that by sol–gel method, which may be related to more A-site cation vacancies and larger bulk oxygen content generated in MIP. Possible formation mechanism of perovskites in MIP was also discussed.

Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated γ-Mo2N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N2 selectivity were achieved at 450 ○C. The amount of O2 taken up by γ-Mo2N increased with temperature rise and reached 3133.9 μmol g−1 at 450 ○C; we conclude that there formation of Mo2OxNy occurred. This oxygen-saturated γ-Mo2N material was catalytically active: NO conversion and N2 selectivity were 89 and 92% at 450 ○C. We found that by means of H2 reduction at 450 ○C, Mo2OxNy could be reduced back to γ-Mo2N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 μmol g−1) of γ-Mo2N suggest that γ-Mo2N is a promising catalytic material for automobile exhaust purification.

Use of noble metals in automobile exhaust catalysts

This is a review of recent literature involving laboratory work on catalytic reactions of interest in automobile exhaust purification. The review is concerned with the noble metals Pt, Pd, and Rh, the oxidation of CO and hydrocarbons, the reduction of NO, and the water-gas-shift and steam-re-forming reactions. Current thoughts are given about the mechanisms of these reactions, the dependence of the reaction rates on particle size, when known, and the role of the impurity SO/sub 2/. The current opinion that alloy formation between the noble metals is detrimental and segregation beneficial is supported by literature references.