Catalytic Activity For NO Oxidation Research Articles

The effect of copper-doped SBA-15 on catalytic oxidation of NO

Surface-loaded CuO species of SBA-15 exhibit excellent catalytic activity for NO oxidation.

Sr doping effect on the structure property and NO oxidation performance of dual-site doped perovskite La(Sr)Co(Fe)O3

In this work, the physico-chemical properties of the La1-xSrxCo0.8Fe0.2O3 (x = 0, 0.3，0.4，0.5，0.6) catalysts were systematically studied as well as their catalytic activity for NO oxidation. When Sr2+ substituted at La3+ site, [CoO6] octahedral distortion is amended and the crystal structure transited from rhombohedral to cubic. Co(III) electronic configuration turned from high/intermediate spin state to low spin sate with empty eg filling. Imbalanced positive charge induced by Sr2+ was compensated by tetravalent Co(IV) ions and oxygen deficiencies together. All these factors resulted in better reducibility of Co, increasing oxygen deficiencies and more mobile oxygen species. Thus, NO conversion of 67–69% was attained over the Sr-doped catalysts at 300 °C, much higher than the undoped catalysts (NO conversion of 24.3%). A significant decrease of the apparent activation energy (Ea), from 68 kJ/mol down to ~52 kJ/mol, was observed as well. Based on the kinetics results, NO oxidation over the perovskite catalysts is a typical superficial process determined by adsorbed NO and surface oxygen species.

Efficient and stable catalyst of α-FeOOH for NO oxidation from coke oven flue gas by the catalytic decomposition of gaseous H2O2

Goethite (α-FeOOH) possesses excellent catalytic activity, high selectivity and good stability as a catalyst for NO oxidation through the catalytic decomposition of gaseous H2O2. as the primary reactive oxygen species is involved in the NO oxidation process together with ·OH, and N2O5 is found for the first time in the products of NO oxidation.

Effect of praseodymium substitution on La1-xPrxMnO3 (x=0–0.4) perovskites and catalytic activity for NO oxidation

La1-xPrxMnO3(x = 0, 0.05, 0.1, …, 0.4) perovskites were prepared readily via citric acid sol–gel method in the present study. Several characterization techniques have been employed, such as X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Brunauer-Emmett-Teller (BET), N2 adsorption–desorption analyses, Oxygen temperature-programmed desorption (O2-TPD), Hydrogen temperature-programmed reduction (H2-TPR) and NO temperature-programmed desorption (NO-TPD), with the aim of exploring the effects of Pr substitution. Then the samples were submitted to activity test in catalytic NO oxidation. NO conversion was improved with the increase of Pr substitution when x ≤ 0.2, and then decreased with further addition of Pr. The most excellent catalytic activity with NO conversion of 91% at 260 °C was observed on La0.8Pr0.2MnO3. It was revealed that the appropriate Pr addition (x ≤ 0.2) at A-site led to the modified reducibility of LaMnO3, as well as the increased molar ratio of Mn4+/Mn3+ and Oads/Ototal, which was benificial for NO oxidation. Moreover, the increase of NO adsorption amount and the shift of the decomposition temperature of nitrates to lower temperautre with the aid of appropriate Pr component accounted for the enhanced activity.

Electrospun YMn2O5 nanofibers: A highly catalytic activity for NO oxidation

Nanofiber catalysts are potentially promising to be equipped in the lean-burned vehicle exhaust emission system considering its facile synthesis, low-cost, long durability in contrast to the traditionally complicated powder based catalyst. Here, via electrospinning method, we synthesized YMn2O5 nanofibers (average diameter: ˜93 nm) including nanowire stacked with particles, and hollow tubes with or without inside nanowires. The morphologies remained even after hydrothermal aging at 800 ℃ for 10 h with 10% H2O stream. X-ray photoelectron spectrum revealed Mn4+/Mn3+ ratio 0.589 on the surface of YMn2O5 catalyst (YMO), indicating the existence of oxygen vacancies. The highest conversion of electrospun mullite fibers at 310 ℃ is ˜18% higher than powder-based YMO at 352 ℃ in the presence of 5% H2O at WHSV = 240,000 ml g−1 h−1. The extracted activation energy from NO-to-NO2 conversion curves of YMO nanofiber (61.68 kJ/mol) is slightly lower than that of powder-based mullite (91.45 kJ/mol), consistent with calculated 68.16 kJ/mol on the fiber YMO surface (121) with a rate-limiting step of the NO2 desorption. The catalytic activity can be attributed to the unit occupy of the eg (dz2 and dx2-y2) orbitals of Mn-dimer atoms around fermi level based on the combination of the theoretical calculations and DRIFTS spectra analysis. Importantly, after the hash hydrothermal-aging, the highest NO oxidation conversion of powder-based mullite is less than 50%, while the fiber maintains a conversion of 62%. Moreover, the fresh YMO fiber maintained superior oxidation stability for 12 h at its maximum conversion of 66%. This work provides the possibility for mullite oxide fibers to replace powder-based precious metal catalyst coating on monolith converter.

Performance and mechanism comparison of manganese oxides at different valence states for catalytic oxidation of NO

Manganese oxides with different valences (MnO2, Mn2O3 and Mn3O4) synthesized by a hydrothermal synthesis method were investigated to evaluate their catalytic performances for NO oxidation. MnO2 with the Mn4+ ion exhibited the best catalytic activity with a maximum NO conversion of 91.4% at 250 °C under the GHSV of 48 000 mL g−1 h−1, and the low-temperature catalytic activity for NO oxidation decreased in the order of MnO2 > Mn2O3 > Mn3O4. Compared with Mn2O3 and Mn3O4, the catalytic performance of MnO2 was less affected by NO concentrations, O2 contents, GHSV, H2O and SO2, though all the three catalysts show stable catalytic properties. To investigate the factors influencing the catalytic activity, their properties were characterized by XRD, SEM, N2 adsorption, H2-TPR, O2-TPD and XPS, and these results indicated that the redox property and active oxygen species of MnO2 were proposed to be the main factors that contributed to the excellent performance in NO oxidation. For the three catalysts, in-situ DRIFTS studies further indicated that both the lattice oxygen and the chemically adsorbed oxygen participated in the NO oxidation process, but the adsorbed species were more easily desorbed from MnO2, probably benefiting for the catalytic performance of MnO2.

Effect of surface morphology on catalytic activity for NO oxidation of SmMn2O5 nanocrystals

SmMn2O5 has been reported to be a promising alternative to substitute the current commercial Pt-based catalysts for NO oxidation. In this work, single-crystalline orthorhombic SmMn2O5 nanorods and nanoparticles are successfully synthesized through a tunable hydrothermal route. The pH value of the precursor solution is a decisive factor for morphology control of SmMn2O5 nanocrystals, with decreasing pH value the morphology of SmMn2O5 nanocrystals converts from nanoparticles to nanorods. The nanoparticles exhibit a better catalytic activity for NO oxidation than the nanorods, because they can efficiently convert NO at lower temperature. By the analysis of X-ray photoelectron spectrum and high-resolution transmission electron microscope, the oxidation activity is found to be dependent on the high specific surface area and surface crystal planes of SmMn2O5 nanocrystals, which widens and deepens the oxygen chemistry and NO oxidation mechanism on the surfaces of SmMn2O5. This work could not only provide new insights into the morphology control of SmMn2O5 nanocrystals, but also pave a new way for the crystal planes modification of SmMn2O5 nanocrystals as NO oxidation catalyst to achieve an enhanced performance for environmental applications.

Preparation of a silicalite/ACF composite and its catalytic activity for NO oxidation to NO2

Preparation of a silicalite/ACF composite and its catalytic activity for NO oxidation to NO2

Preparation of a silicalite/ACF composite and its catalytic activity for NO oxidation to NO2

A silicalite/activated carbon fiber (ACF) composite was prepared by a two-step method, in which nitric acid oxidation was used to incorporate hydrophilic groups to improve crystal seed impregnation and a hydrothermal process was used to grow silicalite on the ACFs. The samples were characterized by SEM, XRD and N2 adsorption. Results showed that the surface of the ACFs was covered with a silicalite layer, and the specific surface area, pore volume and average pore size of the composite were 826 m2·−1, 0.42 cm3·−1 and 0.64 nm, respectively. The catalytic activity of the ACFs for NO oxidation to NO2 was higher than that of a composite loaded with 10 wt% silicalite under dry conditions. However, the latter had a much better resistance to vapor and exhibited a more stable catalytic activity than the ACFs under moist conditions.

Promotional role of La addition in the NO oxidation performance of a SmMn2O5 mullite catalyst

A series of LaxSm1−xMn2Oδ (x = 0, 0.1, 0.3, 0.5) catalysts were synthesized through a co-precipitation method. The catalytic activity for NO oxidation was enhanced with La substitution, and the maximum activity was achieved at x = 0.3.

ChemInform Abstract: Enhanced Catalytic Activity for NO Oxidation over Ba Doped LaCoO3 Catalyst.

AbstractA series of A‐side modified La1‐xBaxCoO3 (x = 0, 0.1, 0.2, 0.3) perovskites is prepared by a modified sol‐gel method using citric acid and EDTA as complexons with aqueous solutions of the metal nitrate precursors followed by drying and calcining in air (700 °C, 5 h).

Enhanced catalytic activity for NO oxidation over Ba doped LaCoO3 catalyst

Introduction of Ba enhanced the catalytic activity of NO oxidation dramatically compared with Ba-free catalyst and exhibited much better performance than the commercial Pt-based catalysts.

High NO oxidation catalytic activity on non-noble metal based cobalt-ceria catalyst for diesel soot oxidation

In this study, we have explored commercial ceria, commercial cobalt oxide (Co3O4) and a laboratory synthesized nano-ceria supported cobalt oxide (Co3O4) for catalytic NO oxidation, which is an important reaction for soot oxidation in diesel particulate filters (DPF), used for vehicle exhaust emissions control. Ceria supported cobalt oxide has been synthesized by incipient wetness impregnation method, and shows high catalytic activity for NO oxidation at moderate temperature. The catalytic activity is even comparable to reported noble metal based NO oxidation catalysts, and could be mainly due to the high dispersion of Co3O4 nanoparticles on ceria support with enhanced catalyst support interaction. This has also resulted in improved redox properties of Co3O4-ceria catalyst.

A simple co-nanocasting method to synthesize high surface area mesoporous LaCoO3 oxides for CO and NO oxidations

High surface area mesoporous LaCoO3 oxides (270m2g−1) with well crystallized perovskite framework have been successfully prepared via a simple one-step co-nanocasting method using the mesoporous SiO2 (KIT-6) template. The prepared mesoporous LaCoO3 material shows relatively high catalytic activity for CO oxidation and the complete CO conversion has been achieved at about 190°C, which is about 75°C lower than that of the non-mesoporous LaCoO3. Moreover, compared with non-mesoporous counterpart, the prepared mesoporous LaCoO3 possesses much higher catalytic activity for NO oxidation, showing rather higher NOx storage capacity. The NO removal ratio is high up to 64% under low temperature (310°C). The enhanced catalytic activity of the mesoporous LaCoO3 for CO and NO oxidation is attributed to its high surface area and crystal lattice defects. A catalytic mechanism of CO and NO oxidation was proposed.

NO Reactions Over Ir-Based Catalysts in the Presence of O2

The behaviour of a series of Ir-based catalysts supported on SiO2, ZSM-5 and γ-Al2O3 with various Ir loadings prepared by impregnation method was conducted by temperature programmed reaction (TPR) technique. The result implies that NO is oxidized to NO2while simultaneously being reduced to N2or N2O in the NO reactions over iridium catalysts. The surface active phase over iridium catalysts that promote the NO reactions is IrO2. The catalytic activity increases with the increase of the Ir loading and support materials have a little effect on the catalytic activity. When the loading is less than 0.1%, the catalytic activity was found to be dependent on the nature of support materials and in order: Ir/ZSM-5>Ir/γ-Al2O3>Ir/SiO2. When the loading is higher than 0.1%, the catalytic activity for NO oxidation is in order: Ir/ZSM-5>Ir/SiO2>Ir/γ -Al2O3, which is correlated with Ir dispersion on the surface of support materials and the catalytic activity for NO reduction is in sequence: Ir/γ -Al2O3>Ir/SiO2>Ir/ZSM-5, which is attributed to the adsorbed-dissociation of NO2. Compared to Pt/γ-Al2O3, Ir/γ-Al2O3catalyst is more benefit for the NO reduction.

Influence of the physico-chemical properties of CeO 2–ZrO 2 mixed oxides on the catalytic oxidation of NO to NO 2

Commercial and home-made Ce–Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N 2 adsorption at −196 °C and XPS, and were tested for NO oxidation to NO 2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce–Zr catalysts. As a general trend, Ce–Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce–Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t′′ for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce–Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.

The effect of cobalt precursors on NO oxidation over supported cobalt oxide catalysts

The effect of cobalt precursors such as cobalt acetate and cobalt nitrate on NO oxidation was examined over cobalt oxides supported on various supports such as SiO2, ZrO2, and CeO2. The N2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction with H2 (H2-TPR), NO chemisorptions, and temperature-programmed oxidation (TPO) with mass spectroscopy were conducted to characterize catalysts. The NO uptake as well as the catalytic activity for NO oxidation was dependent on the kinds of cobalt precursors and supports for supported cobalt oxides catalysts. Among tested catalysts, Co3O4/CeO2 prepared from cobalt acetate showed the highest catalytic activity. The catalytic activity generally increased with the amount of chemisorbed NO. Reversible deactivation was observed over Co3O4/CeO2 in the presence of H2O. On the other hand, irreversible deactivation occurred over the same catalyst even in the presence of 5 ppm SO2 in a feed. The strongly adsorbed SO2 can prohibit NO from adsorbing on the active sites and also can prevent formed NO2 from desorbing off the catalyst surface. The formation of SO3 cannot be observed from the chemisorbed SO2 on Co3O4/CeO2 during TPO.

Reaction of NO over Iridium Catalysts with Excess Oxygen

A series of iridium-supported catalysts with various Ir loadings were prepared by impregnation method. The support materials used were ZSM-5, γ-Al2O3, and SiO2. The Ir loadings examined were 0.02%, 0.1%, 1%, and 5% (w). The behavior of the catalysts for the NO reaction was analyzed by means of temperature programmed reaction (TPR) experiments. The reactions of NO over iridium include the oxidation of NO to NO2 and the reduction of NO to N2 or N2O. The iridium catalysts promote the reactions of NO and the catalytic activity increases with the increase of the Ir loadings. Further, support materials have a little effect on the catalytic activity. When the loading was less than 0.1%, the catalytic activity was found to be dependent on the property of support materials and the activity order was Ir/ZSM-5Ir/γ-Al2O3Ir/SiO2; when the loading was higher than 0.1%, the order of catalytic activity for NO oxidation was Ir/ZSM-5Ir/SiO2Ir/γ-Al2O3, which was correlated with Ir dispersion on the surface of support materials, and the order of catalytic activity for NO reduction was Ir/γ-Al2O3Ir/SiO2Ir/ZSM-5, which was attributed to the adsorbed-dissociation of NO2. Ir/γ-Al2O3 catalyst was more beneficial for the NO reduction than Pt/γ-Al2O3 catalyst.

Effect of alloy composition on dispersion stability and catalytic activity for NO oxidation over alumina-supported Pt–Pd catalysts

Applying a synthesis procedure that promotes alloy formation, highly-dispersed alumina-supported Pt–Pd catalysts spanning the Pt-rich half of the composition range were prepared, aged under oxygen-rich hydrothermal conditions, and characterized by CO chemisorption, XRD, and TEM. Anomalously large particles, typical of pure Pt catalysts treated under such conditions, were not found in any of the Pd-containing catalysts, and the extent of particle coarsening due to aging was found to decrease with increasing Pd content. Alloying appears to have little effect on the NO oxidation turn-over frequency, which increases with decreasing dispersion.

The effect of metal oxide additives (WO3, MoO3, V2O5, Ga2O3) on the oxidation of NO and SO2 over Pt/Al2O3 and Pt/BaO/Al2O3 catalysts

For NOx storage, the oxidation of NO to NO2 is an important step in the storage mechanism. In the firstpart of this work, model WO3/Pt/Al2O3, MoO3/Pt/Al2O3, V2O5/Pt/Al2O3, Ga2O3/Pt/Al2O3 and Pt/Al2O3 catalysts were prepared and used in flow reactor experiments. Heating ramp oxidation and steady state oxidation experiments were performed in order to investigate the catalytic activity for NO oxidation both in the presence and absence of SO2 in the reaction gas mixture. In the absence of SO2, the WO3 and MoO3 containing catalysts showed a significantly higher NO oxidation activity than the other catalysts. When SO2 was included in the reaction gas mixture, the NO oxidation activity decreased for all catalysts, but the MoO3 containing catalyst was less affected by the presence of SO2 and also showed the lowest SO2 oxidation activity. In the second part of this work, model Pt/BaO/Al2O3 and Pt/BaO/MoO3/Al2O3 catalysts were prepared and used in heating ramp oxidation and transient flow reactor experiments in order to investigate the effects of NO oxidation activity enhancement and suppression of the activity for SO2 oxidation on NOx storage capacity. Both catalysts showed equal NOx storage capacity in the sulphur free cycles. When SO2 was included in the reaction gas mixture, the NOx storage capacity declined faster for the Pt/BaO/MoO3/Al2O3 catalyst than for the Pt/BaO/Al2O3 catalyst, due to sulphur poisoning which resulted in a faster decrease in the regeneration capacity during rich periods.