NO Oxidation Performance Research Articles

Nonprecious mixed oxide catalysts Co3AlO and Co2NiAlO derived from nanoflowerlike cobalt-based hydrotalcites for highly efficient oxidation of nitric oxide

Nanoflowerlike Co3AlO-500 and Co2NiAlO-500 exhibit excellent NO oxidation performance upon abundant active sites Co3+/Ni3+–Oads through formation of bridged bidentate nitrate.

Potential synergic effect between MOR and BEA zeolites in NOx SCR with methane: A dual bed design approach

The selective catalytic reduction of NOx with methane (NOx CH4–SCR) under lean conditions was investigated with catalysts based on two different zeolite structures (MOR and BEA) containing Pd and Ce. The catalytic performance for NO oxidation to NO2 reaction, considered an important first key step in the NOx CH4–SCR mechanism, was also assessed.Pd(0.3)Ce(2)–HBEA was found to be very active for NO oxidation but exhibits poor activity for NOx CH4–SCR. Conversely, Pd(0.3)Ce(2)–HMOR presents modest activity for NO oxidation, compared to Pd(0.3)Ce(2)–HBEA, but exhibits mild activity for NOx CH4–SCR reaction. Characterisation by H2–TPR, DRS UV–vis, TEM/EDS and FTIR-CO allowed the identification of palladium stabilised as Pd2+ ions in exchange positions in both monometallic and bimetallic MOR based catalysts, whereas, in BEA catalysts, it is presented as PdO clusters. Cerium is stabilised in Pd(0.3)Ce(2)–HMOR as small CeO2 particles, whereas, in Pd(0.3)Ce(2)–HBEA, it is present as large clusters. Catalysts were also tested in dual bed configuration, in which Pd(0.3)Ce(2)–HBEA was placed as first layer and Pd(0.3)Ce(2)–HMOR as second layer in the catalytic bed. The catalytic performance was significantly improved (higher NOx conversion into N2 and higher CH4 selectivity to SCR reaction), when compared to the catalytic performance of each catalyst individually, suggesting the existence of a synergic effect. This synergy is explained by the complementary roles that each catalyst play in HC–SCR mechanism.

Preparation of graphene/carbon hybrid nanofibers and their performance for NO oxidation

A series of novel microdomain-graphitized polyacrylonitrile (PAN)-based nanofibers were prepared by adding varied amounts of graphene oxide into the precursor via the electrospinning method. These hybrid electrospun nanofibers with were stabilized in ambient atmosphere, carbonized in nitrogen atmosphere and treated in NH3 atmosphere for NO oxidation with low concentration (50ppm) at room temperature. The samples were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and nitrogen adsorption at 77K. Oxidation of NO into NO2 at room temperature was investigated in a fiber fixed-bed. The results demonstrated that the reduced graphene oxide sheets provide catalytic active sites embedded in the PAN-based nanofibers. In addition it was determined that nitrogen-containing functional groups played important roles in the enhancement of the catalytic oxidation of NO to NO2. The samples with 5wt.% GO exhibit the most catalytic oxidation of NO into NO2.

High performance of NO oxidation over Ce–Co–Ti catalyst: The interaction between Ce and Co

Ce0.2Co0.2Ti mixed oxide catalyst was synthesized by a facile sol–gel method and the catalytic activity was evaluated through NO oxidation. The catalyst was characterized by XRD, Raman, TEM, H2-TPR, O2-TPD and XPS. The results showed that Ce0.2Co0.2Ti exhibited high catalytic activity of NO oxidation with maximum conversion of 76% at 300°C under the condition of 400ppm NO, 8% O2 and 30000h−1 GHSV. The high activity was ascribed to the strong interaction between Ce and Co, which resulted in small particle, excellent redox and large amount of chemisorbed oxygen. These features were favorable for the high catalytic performance of NO oxidation.

YCeZrO Ternary Oxide Solid Solution Supported Nonplatinic Lean-Burn NOx Trap Catalysts Using LaCoO3 Perovskite as Active Phase

A series of nonplatinic ceria-based oxides supported catalysts LaCoO3/K2CO3/S (S=CeO2, Ce0.75Zr0.25O2 or 5%Y/Ce0.75Zr0.25O2) were prepared by successive impregnation and employed for lean-burn NOx trapping. It is found that the doping of Zr or YZr into CeO2 facilitates the formation of CeZrO binary or YCeZrO ternary solid solutions, increasing the specific surface area and improving the redox property of ceria. The results of EXAFS and H2-TPR reveal that the LaCoO3 in the solid solution supported catalysts possesses higher dispersion and better reducibility than that in CeO2 supported one. The result of O2-TPD shows that the surface active oxygen species are remarkably increased after loading LaCoO3 on the supports. The YCeZrO ternary solid solution supported catalyst containing 5 wt % K2CO3 exhibits the best performance for NO oxidation and reduction at 350 °C, showing a high NO-to-NO2 conversion (66.5%) at lean condition, and a very high NOx reduction percentage (98.2%) and an extremely high NOx-to-N2 s...

Influence of the sol–gel preparation method on the photocatalytic NO oxidation performance of TiO2/Al2O3 binary oxides

In the current work, TiO2/Al2O3 binary oxide photocatalysts were synthesized via two different sol–gel protocols (P1 and P2), where various TiO2 to Al2O3 mole ratios (0.5 and 1.0) and calcination temperatures (150–1000°C) were utilized in the synthesis. Structural characterization of the synthesized binary oxide photocatalysts was also performed via BET surface area analysis, X-ray diffraction (XRD) and Raman spectroscopy. The photocatalytic NO(g) oxidation performances of these binary oxides were measured under UVA irradiation in a comparative fashion to that of a Degussa P25 industrial benchmark. TiO2/Al2O3 binary oxide photocatalysts demonstrate a novel approach which is essentially a fusion of NSR (NOx storage reduction) and PCO (photocatalytic oxidation) technologies. In this approach, rather than attempting to perform complete NOx reduction, NO(g) is oxidized on a photocatalyst surface and stored in the solid state. Current results suggest that alumina domains can be utilized as active NOx capturing sites that can significantly eliminate the release of toxic NO2(g) into the atmosphere. Using either (P1) or (P2) protocols, structurally different binary oxide systems can be synthesized enabling much superior photocatalytic total NOx removal (i.e. up to 176% higher) than Degussa P25. Furthermore, such binary oxides can also simultaneously decrease the toxic NO2(g) emission to the atmosphere by 75% with respect to that of Degussa P25. There is a complex interplay between calcination temperature, crystal structure, composition and specific surface area, which dictate the ultimate photocatalytic activity in a coordinative manner. Two structurally different photocatalysts prepared via different preparation protocols reveal comparably high photocatalytic activities implying that the active sites responsible for the photocatalytic NO(g) oxidation and storage have a non-trivial nature.

Effect of Thermal Degradation on the CO, C3H6, and NO Oxidation Performance of Pt/Al2O3 with a Zoned Distribution of Pt

Temperature-programmed oxidation (TPO) experiments were used to evaluate the performance of uniformly (standard) and nonuniformly (zoned) distributed Pt/Al2O3 catalysts after homogeneous and heterogeneous thermal degradation. Both catalysts were homogeneously aged in an oven by exposing the entire catalyst to 750 °C in air for 4 h at atmospheric pressure. In heterogeneous aging, only the back of the catalysts was exposed at 675 °C, whereas the temperature at the inlet section did not exceed 550 °C. This was accomplished by introducing pulses of C3H6 and O2, with an inert gas between each pulse, for 50 cycles and using the heat generated by the exothermic oxidation reaction to thermally age zones of the samples. The zone-coated catalyst, with more Pt concentrated in the front of the monolith, showed better performance than the standard sample after heterogeneous aging. The reason is that most of the Pt in the zoned sample, which was located in the front half, was not affected by the more significant aging at the back of the monolith. On the other hand, at a higher total flow rate and higher temperature, the performance of the homogenously aged zoned catalyst was worse than that of the standard sample, because the effect of the Pt-rich upstream area of the zoned catalyst was lost through the formation of larger particles, widening the reaction zone into the less Pt-rich downstream region.

Au nanoparticles enhanced rutile TiO2 nanorod bundles with high visible-light photocatalytic performance for NO oxidation

A novel Au/TiO2 visible photocatalyst with Au nanoparticles (NPs) uniformly dispersed onto rutile TiO2 nanorod bundles was developed and used in photocatalytic NO oxidation for air cleaning. The Au NPs photosensitized TiO2 in visible-light area via plasma effect. They also reduced photoelectron–hole recombination by accelerating electron transfer and promoted NO molecule activation via strong adsorption. The TiO2 acted as a semiconductor photocatalyst and its nanorod bundle structure promoted light harvest by multiple reflections. Moreover, it also acted as a support to highly disperse and stabilize Au nanopaticles. These cooperative promoting effects resulted in the high activity and strong durability of Au/TiO2 in photocatalytic NO oxidation.

Catalytic performance of NO oxidation over LaMeO3 (Me = Mn, Fe, Co) perovskite prepared by the sol–gel method

Abstract The catalytic performance of LaMeO 3 (Me = Mn, Fe, Co) perovskite prepared by a sol–gel method was studied. These catalysts were characterized by X-ray diffraction (XRD), N 2 adsorption (BET), H 2 temperature programmed reduction (TPR), NO temperature programmed desorption (TPD) and CO–O 2 pulse. LaCoO 3 exhibited the best activity than that of LaFeO 3 and LaMnO 3 even after hydrothermal ageing. The activity sequence is in accordance with the reducibility of the samples. The activated oxygen species and adsorbed NO play key roles in the NO oxidation reaction.

Hydrocarbon Assisted NO Oxidation with Non-thermal Plasma in Simulated Marine Diesel Exhaust Gases

The NO oxidation performance in a non-thermal plasma (NTP) reactor under realistic synthetic exhaust gas compositions is investigated. The gas compositions differ mainly in the NO–NO2 ratio and represent different modes of operation of a marine diesel engine. It is found that the maximum NO oxidation efficiency is independent on the NO–NO2 ratio. Up to 55 % of the NO is mainly oxidised to NO2 in all gas mixtures being analysed. However, the specific energy density needed to reach the highest NO oxidation varies with the gas composition between 15 and 60 J/L. The performance of the NTP-reactor was significantly improved by the addition of propene (C3H6) acting as an additional oxidising agent. The energy consumption for NO–NO2 conversion was found to be between 20 and 45 eV/NO, depending on the ratio of the added propene as well as the initial concentrations of nitrogen oxides.

Improved CO, hydrocarbon and NO oxidation performance using zone-coated Pt-based catalysts

The effect of an axial Pt distribution along a diesel oxidation catalyst (DOC) was investigated by comparing a standard catalyst, with a homogeneously distributed Pt amount along the length, with a non-homogeneously distributed catalyst (zoned). The zoned catalyst had more Pt located at the upstream portion, and less downstream, while maintaining the same total amount of Pt as the standard case. The effects of flow rate on NO, CO or C3H6 oxidation, and during oxidation of NO and C3H6 as a mixture, were used for the comparison. The reaction details along the catalyst were also resolved using spatially resolved, capillary inlet mass spectrometry (Spaci-MS). Results showed that the performance of the two catalysts were similar at low flow rate and with a single reacting gas, while the zoned sample worked better for CO and C3H6 oxidation as the flow rate increased, and better for NO oxidation in the NO/C3H6 gas mixture. With CO or C3H6 oxidation, the superior performance of the zoned sample was due to a larger, localized exotherm and a decreased self-poisoning effect. The exothermic heat produced in the front part of the zoned catalyst allowed it to reach higher temperature at the front faster than the homogeneous/standard sample and it also lowered the effect of self-poisoning by converting most of the reactants in the front part. NO oxidation, being kinetically more challenging, occurred along the entire length of catalyst at low temperature, not achieving near 100% conversion in these tests. Spatially resolved experiments during C3H6 and NO oxidation, as a mixture, showed that NO oxidation started after C3H6 was consumed. Therefore, for the zoned sample, C3H6 was oxidized closer to the inlet portion of the catalyst, where a higher density of Pt was located, leaving the rest of the catalyst available for NO oxidation. However, with the standard sample, C3H6 oxidation utilized a larger part of the catalyst leaving a smaller portion of the monolith for NO oxidation.

Deactivation mechanisms of Pt/Pd-based diesel oxidation catalysts

Currently precious metal-based diesel oxidation catalysts (DOC) containing platinum (Pt) and palladium (Pd) are most commonly used for the oxidation of hydrocarbon and NO in diesel exhaust hydrocarbon oxidation. The present work has been carried out to investigate the deactivation mechanisms of the DOC from its real-world vehicle operation by coupling its catalytic activity measurements with surface characterization including X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. A production Pt–Pd DOC was obtained after being aged on a vehicle driven for 135,000 miles in order to study its deactivation behavior. The performance of the vehicle-aged part was correlated with that of the simulated hydrothermal lab aged sample assuming that Pt–Pd sintering plays a major role in irreversible catalyst deactivation. In addition to the hydrothermal sintering, the deterioration of hydrocarbon and NO oxidation performance was caused by surface poisoning. The role of the various aging factors in determining long-term performance in mobile applications will be discussed.

Influence of Support Materials and Aging on NO Oxidation Performance of Pt Catalysts under an Oxidative Atmosphere at Low Temperature

The predominant factor in catalytic low-temperature NO oxidation under an oxidative condition over supported Pt, Pd and Rh catalysts was investigated and discussed using a thermodynamic calculation, XPS analysis, CO adsorption, and reaction evaluation. New insights were gained as follows; the resistance to metal oxide formation of these metals is important for NO oxidation activity under an excess oxygen condition. In the fresh catalysts, the oxidation status of Pt was affected by the electronegativity of the support cation, and the Pt supported on a more acidic support has a higher NO oxidation activity. After aging treatment, the oxidation status of Pt on each support was almost the same, and a large amount of surface metallic Pt favors Pt catalysts to have high activity. The analysis of the NO oxidation kinetics revealed that the affinity of Pt for NO molecules was improved with the aging treatment. It could be concluded that a suitable combination of Pt and the support facilitates high dispersion of the metallic Pt, even after the aging treatment, which is favorable for the NO oxidation in the presence of excess oxygen at low temperature.