Active oxygen-promoted NO catalytic on monolithic Pt-based diesel oxidation catalyst modified with Ce

Co,Ce nanoparticles supported on stacked wire mesh cartridges. Activity and stability in diesel soot combustion

In this work, Co3O4 nanoparticles were successfully synthesized by precipitating a precursor salt solution in the form of microdroplets generated by a nebulizer, as an efficient, fast and low-cost approach. After drying and calcination, synthesized particles were deposited on stacked wire mesh monoliths by immersing the structures in a suspension containing synthesized Co3O4 particles and commercial ceria nanoparticles as a binder. These structured catalysts were evaluated for the combustion of diesel soot which constitutes a crucial step in the regeneration of catalytic particulate filters (CDPFs). Thermal and mechanical stability of Co,Ce washcoated monoliths were investigated. For this, successive catalytic evaluations of the structured system, with intermediate treatments at 900 °C (accelerated aging), were carried out indicating a very good activity and stability of the catalysts developed. Adherence tests showed good adhesion of the catalytic layer to the metallic substrate. Fresh and aged catalysts were fully characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Laser Raman Spectroscopy (LRS) and Temperature-Programmed Reduction (TPR). It was found that the catalytic coating resulted composed of nanometric CeO2 and Co3O4 along with chromium, iron and manganese oxides coming from the migration of the metallic substrate, in the catalytic cartridge calcined at 600 °C. Despite after calcination at 900 °C spinels of Co, Fe, Cr and Mn were observed, these oxides did not significantly affected the catalytic activity. Although this aging treatment at 900 °C was severe and is not expected under real conditions, it highlights the potential application of the catalytic metallic cartridges here developed.

Catalytic Oxidation Activity of NO over Mullite-Supported Amorphous Manganese Oxide Catalyst

Nitric oxide (NO) can pose a severe threat to human health and the environment. Many catalytic materials that contain noble metals can oxidize NO into NO₂. Therefore, the development of a low-cost, earth-abundant, and high-performance catalytic material is essential for NO removal. In this study, mullite whiskers on a micro-scale spherical aggregate support were obtained from high-alumina coal fly ash using an acid-alkali combined extraction method. Microspherical aggregates and Mn(NO₃)₂ were used as the catalyst support and the precursor, respectively. A mullite-supported amorphous manganese oxide (MSAMO) catalyst was prepared by impregnation and calcination at low temperatures, in which amorphous MnO_x is evenly dispersed on the surface and inside of aggregated microsphere support. The MSAMO catalyst, with a hierarchical porous structure, exhibits high catalytic performance for the oxidation of NO. The MSAMO catalyst, with a 5 wt% MnO_x loading, presented satisfactory NO catalytic oxidation activity at 250 °C, with an NO conversion rate as high as 88%. Manganese exists in a mixed-valence state in amorphous MnO_x, and Mn⁴⁺ provides the main active sites. The lattice oxygen and chemisorbed oxygen in amorphous MnO_x participate in the catalytic oxidation of NO into NO₂. This study provides insights into the effectiveness of catalytic NO removal in practical industrial coal-fired boiler flue gas. The development of high-performance MSAMO catalysts represents an important step towards the production of low-cost, earth-abundant, and easily synthesized catalytic oxidation materials.

A comparative investigation between particle oxidation catalyst (POC) and diesel particulate filter (DPF) coupling aftertreatment system on emission reduction of a non-road diesel engine

Non-road emission regulations are becoming increasingly rigorous, which makes it necessary for non-road engines to adopt aftertreatment systems. The commonly used aftertreatments mainly include diesel oxidation catalytic (DOC), diesel particulate filter (DPF), particle oxidation catalyst (POC), selective catalytic reduction (SCR) and ammonia purification catalyst (ASC). The purpose of this study is to investigate the effects of using an integrated system (DOC + DPF/POC + SCR + ASC) on non-road diesel engine emissions under steady-state and transient operating conditions, respectively. The major works are the comparison between POC and DPF from the viewpoint of emission reduction. The results show that both POC and DPF can effectively reduce particulate matter (PM) and nitrogen oxide (NO_X) emissions under steady-state conditions, and DPF has better purification effect than POC, especially for PM. The PM conversion rate of DPF is up to 87%, while that of POC is only 60% under the non-road steady-state test cycle (NRSC). Both NO_X and hydrocarbon (HC) conversion rates are high, exceeding 95%. The conversions of PM, NO_X, HC, and carbon monoxide (CO) of DPF in the non-road transient test cycle (NRTC) are 92.83%, 96.99%, 96.86% and 81.45%, respectively, while those of POC are 60.12%, 95.45%, 92.82% and 79.51%, respectively. Both the POC and DPF systems can meet the emission regulation limits. As a result, POC has the potential to substitute DPF in non-road engines due to its lower product and maintenance costs. We hope that the comparison study will provide useful guidance for improving the emissions performance of non-road diesel engines.

Constructing a Pt/YMn2O5 Interface to Form Multiple Active Centers to Improve the Hydrothermal Stability of NO Oxidation

The hydrothermal stability of NO oxidation is the key to the practical application of diesel oxidation catalysts in diesel engines, which in the laboratory requires that NO activity does not decrease after aging for 10 h with 10% H₂O/air at 800 °C. On the one hand, the construction of a metal/oxide interface can lead to abundant oxygen vacancies (O_v), which compensate for the loss of activity caused by the aggregation of Pt particles after aging. On the other hand, YMn₂O₅ (YMO) has excellent thermal stability and NO oxidation capacity. Therefore, a Pt/YMn₂O₅-La-Al₂O₃ (Pt/YMO-LA) catalyst was prepared by the impregnation method. The support of the catalyst, YMn₂O₅-La-Al₂O₃ (YMO-LA), was obtained by mixing high specific surface LA and YMO ball-milling. Under laboratory-simulated diesel exhaust flow, the NO oxidation performance of Pt/YMO-LA did not decrease after hydrothermal aging. Combining high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and oxygen temperature-programmed desorption (O₂-TPD), the Pt/YMn₂O₅ interface was formed after hydrothermal aging, and the increased O_v can provide reactive oxygen to Pt and YMO. The cooperative catalysis of multiple active centers composed of Pt, YMO, and O_v is the crucial factor to maintain the NO oxidation performance. In addition, in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) show that an increase in O_v is beneficial to the adsorption and desorption of more nitrate and nitrite intermediates, thus achieving the hydrothermal stability of NO oxidation.

NO catalytic performance analysis of gasoline engine tapered variable cell density carrier catalytic converter

Improving the flow field uniformity of catalytic converter can promote the catalytic conversion of NO to NO₂. Firstly, the physical and mathematical models of improved catalytic converter are established, and its accuracy is verified by experiments. Then, the NO catalytic performances of standard and improved catalytic converters are compared, and the influences of structural parameters on its performance are investigated. The results showed that: (1) The gas uniformity, pressure, drop and NO conversion rate of the improved catalytic converter are increased by 0.0643, 6.78%, and 7.0% respectively. (2) As the cell density combination is 700 cpsi/600 cpsi, NO conversion rate reaches the highest, 73.7%, and the gas uniformity is 0.9821. (3) When the tapered height is 20 mm, NO conversion rate reaches the highest, 72.4%, and the gas uniformity is 0.9744. (4) When the high cell density radius is 20 mm, NO conversion rate reaches the highest, 72.1%, and the gas uniformity is 0.9783. (5) When the tapered end face radius is 20 mm, NO conversion rate reaches the highest, 72.0%, and the gas uniformity is 0.9784. The results will provide a very important reference value for improving NO catalytic and reducing vehicle emission.

Promotional effect of ZrO2 and WO3 on bimetallic Pt-Pd diesel oxidation catalyst

Diesel oxidation catalysts Pt-Pd-(y)ZrO₂-(z)WO₃/CeZrO_x-Al₂O₃ with total Pt & Pd loading of only 0.68 wt.% were prepared and investigated for oxidation activity and stability of CO, C₃H₆, and NO. Introduction of ZrO₂ greatly improved low-temperature activities and retained stability especially for CO and C₃H₆ oxidation after treated at 800 °C. With the optimal loading amount of 6 wt% ZrO₂, 2 wt% WO₃ was introduced to the system and showed higher activity. Reaction temperature for 50% CO and C₃H₆ conversion declined to 160 and 181 °C, and the maximal NO conversion increased to 50%. By using XRD, TEM, CO chemisorption, XPS, and H₂-TPR analysis, it was found that ZrO₂ could inhibit aggregation of Pt and Pd, improve metal dispersion, and increase surface-chemisorbed oxygen after high-temperature treatment, accounting for promoted performance. Also, there were more reducible oxide species in ZrO₂-doped catalysts. ZrO₂ could induce reduction of noble metal oxides and surface ceria by weakening Pt-O-Ce interaction, which increased the ability to dissociate H₂ and spillover effect of dissociated hydrogen to ceria. Doping WO₃ increased metal dispersion of fresh samples and brought more Pt⁰ species that were active sites for oxidation reactions. Thus, ZrO₂ and WO₃ could be effective additives for oxidation catalysts to synergistically improve their activities and thermal stability.

Effects of Different Mixture Ratios of Methanol-Diesel on the Performance Enhancement and Emission Reduction for a Diesel Engine

To improve the combustion and emission characteristics of diesel engines, methanol-diesel fuels with different mixing ratios (DM0, DM10, DM20, DM30, and DM40) were used to investigate the effects of methanol addition on the combustion and emission of a four-stroke diesel engine in terms of cylinder pressure, brake power, brake-specific fuel consumption, and nitrogen oxides, soot, and carbon monoxide emissions. Firstly, an improved entire diesel engine model was developed using AVL-BOOST software and validated by the experimental results. The results showed that the increase of methanol content in the fuel mixture had a negative impact on the performance characteristic of the diesel engine, but significantly improved the emission characteristic of the diesel engine. With the methanol ratio in the mixed fuel increased to 10%, 20%, 30%, and 40%, the cylinder pressure of the engine increased by 0.89%, 1.48%, 2.29%, and 3.17%, respectively. However, the power decreased by 3.76%, 6.74%, 11.35%, and 15.45%, the torque decreased by 3.76%, 6.74%, 11.35%, and 15.45%, respectively, and the brake specific fuel consumption increased by 3.77%, 6.92%, 12.33%, and 17.61%, respectively. In addition, with the methanol ratio in the mixed fuel increased to 10%, 20%, 30%, and 40%, the carbon monoxide emission decreased by 21.32%, 39.04%, 49.81%, and 56.59% and the soot emission decreased by 0.25%, 8.69%, 16.81%, and 25.28%, respectively. Therefore, the addition of methanol to the fuel can improve the combustion and emission characteristics of the engine.

Recent advances in selective catalytic oxidation of nitric oxide (NO-SCO) in emissions with excess oxygen: a review on catalysts and mechanisms

Nitric oxides (NO_x, which mainly include more than 90% NO) are one of the major air pollutants leading to a series of environmental problems, such as acid rain, haze, photochemical smog, etc. The selective catalytic oxidation of NO to NO₂ (NO-SCO) is regarded as a key process for the development of selective catalytic reduction of NO_x by ammonia (via fast selective catalytic reduction reaction) and also the simultaneous removal of multipollutant (pre-oxidation and post-absorption). Until now, scholars have developed various types of NO-SCO catalysts, dividing the main groups into noble metals (Pt, Pd, Ru, etc.), metal oxides (Mn-, Co-, Cr-, Ce-based, etc.), perovskite-type oxides (LaMnO₃, LaCoO₃, LaCeCoO₃, etc.), carbon materials (activated carbon, carbon fiber, carbon nanotube, graphene, etc.), and zeolites (ion-exchanged ZSM-5, CHA, SAPO, MCM-41, etc.) in this review. This paper summarizes the recent progress of the above typical catalysts and mostly analyzes the catalytic performance for NO oxidation in terms of the H₂O and/or SO₂ resistances and also the influencing factors, and their reaction mechanisms are described in detail. Finally, this review points out the key problems and possible solutions of the current researches and presents the application prospects and future development directions of NO-SCO technology using the above typical catalysts.

In Situ Investigations on the Facile Synthesis and Catalytic Performance of CeO2-Pt/Al2O3 Catalyst

Ceria-modified Pt/Al2O3 catalyst has been commonly prepared by the impregnation of platinum on ceria-modified alumina and widely applied in the chemical industry and automotive industry. The in situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS), and thermogravimetric (TG) analysis techniques were employed to investigate the typical mechanisms of the bis(ethanolammonium)hexahydroxyplatinate(IV) and cerium nitrate decomposition catalyzed by Ptδ+ species for the facile synthesis of CeO2-Pt/Al2O3 catalyst. It was found that Pt4+-catalyzed decomposition of cerium nitrate leads to the higher dispersity of ceria and forming more active oxygen species, on the basis of X-ray diffraction (XRD) and H2 temperature-programmed reduction (H2-TPR) results. The in situ activity measurements were also performed to investigate the reaction mechanisms and the specific activities for the catalytic CO, NO, C3H6 and C3H8 co-oxidation. The results indicate that undesirable N2O by-product is formed by the selective catalytic reduction (SCR) of NO by C3H6 below 350 °C. The cerium addition effectively improves the activity of catalytic oxidation, but exhibits an increased N2O yield, due to the increased reducibility.

Improved low-temperature catalytic oxidation performance of Pt-based catalysts by modulating the electronic and size effects

The electronic effect between PVA and platinum could be modulated though reaction time, restraining the chain movement and affecting the platinum dispersion, both of which closely affects the low-temperature performance of the Pt-based catalyst.

Promotional effects of ascorbic acid on the low-temperature catalytic activity of selective catalytic oxidation of ammonia over Pt/SA: effect of Pt0 content

The amount of Pt species was increased by the addition of ascorbic acid to the Pt/SiAl catalyst, which shifted the temperature of the NH₃-SCO reaction between NH₃ and O₂ to a lower temperature.