Selective Catalytic Oxidation Of NO Research Articles

Supported Mn2O3-based catalysts for NO-SCO: an experimental study.

In this paper, the NO-SCO (the selective catalytic oxidation of NO) experiments of single-phase Mn2O3, supported Mn2O3/Al2O3, and the Ce-doped MnxCey/Al catalyst system were carried out. The physical and chemical properties of the catalysts were analyzed by XRD, BET, XPS, SEM, O2-TPD, and H2-TPR. The effects of loading and Ce doping on catalyst activity were studied. The results show that the Mn2O3 catalyst exhibited the best activity at 300 ℃, and the NO conversion rate of Mn2O3 was 78.2%. The relative content of Oα adsorbed on the surface of the Mnx/Al catalyst decreased obviously by loading Mn2O3 on γ-Al2O3, which led to the decrease in catalyst activity. And the temperature window moved to the high-temperature region. After doping Ce, the dispersion of Mn enhanced, and the relative content of oxygen Oα adsorbed on the surface increased. The low-temperature activity and fluidity of oxygen in catalysts were improved. Among them, the Mn0.2Ce0.08/Al catalyst obtained a high specific surface area, good pore structure, large oxygen storage capacity, and excellent surface oxygen species. The corresponding NO conversion rate reached 83.5% at 290 ℃. Then, the effects of operating parameters such as space velocity, NO concentration, and O2 content on the catalytic activity of Mn0.2Ce0.08/Al were discussed. The experimental results show that the NO conversion rate of Mn0.2Ce0.08/Al decreased with increasing NO concentration and space velocity. The O2 content had a positive effect on the catalytic activity of the catalyst. However, the NO conversion rate tended to be stable due to the saturation of oxygen adsorbed on the catalyst. Through cycling experiments, we found that Mn2O3, Mn0.2/Al, and Mn0.2Ce0.08/Al catalysts showed good oxidation stabilities for NO oxidation. The evaluation of the water and sulfur resistance of the catalyst shows that the toxicity of SO2 was reduced by the aqueous atmosphere to a certain extent. Through the structural optimization of the basic model and the calculation of the NO-SCO reaction path, the results show that the NO-SCO reaction on the Mn2O3 (110) face followed the ER mechanism more. For the Mn2O3/Al2O3 (110) surface, the LH-MvK hybrid mechanism can greatly reduce the desorption energy barrier of the reaction intermediates, which is more favorable for the NO-SCO reaction. The catalytic mechanisms of the MnxCey/Al catalysts require further in-depth research.

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

Nitric oxides (NOx, 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 NOx 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.

Catalytic oxidation mechanism of NO to HNO3 on TiO2 (101) and (001) surfaces and the influence factors on NO removal: A DFT study

Theoretical study on the selective catalytic oxidation of NO to form HNO3 on the different TiO2 (001) and (101) surfaces was performed by DFT calculations. The addition of additional NO molecules to the oxidation process also is discussed. The result shows that HNO3 is more easy to generate on (001) than (101) surface. The adsorbed H atom on surface is beneficial for the transformation of O2 to the superoxide radical (O2·−) that has a favorable role for the oxidation of NO on surface. In addition, it is manifestly demonstrated that the participation of the additional NO in the reaction of NO and O2 not only modifies the known NO oxidation pathway (NO→NO2→HNO3), but also affects the existence of the product HNO3. The trans-ONONO2 can firstly be formed if the additional NO molecule involves in the oxidation reaction in the beginning. When the additional NO molecule encounter with the precursor (H···NO3) of oxidation product (HNO3), it can improve the formation of HONO not HNO3. This study gains more insight into the mechanism of NO oxidation and has a potential atmospheric importance.

Fully selective catalytic oxidation of NO to NO2 over most active Ga-PCH catalyst

The series of xGa-PCH catalysts were prepared by the impregnation method for low temperature selective catalytic oxidation of NO in the excess of O2 and characterized by N2 adsorption-desorption, XRD, SEM, Py-FTIR, XPS, O2-TPD, and NO-TPD. The experimental study and characterization results were demonstrated that among all the samples, the 24Ga-PCH catalyst was highly active and had superior catalytic properties and never has been reported yet. The 24Ga-PCH catalyst exhibited high catalytic efficiency and 100 % NO oxidation at low temperature (150 °C). The effect of gallium loading, the effect of carriers, influence of O2, temperature and catalytic oxidation of NO with function time-on-stream were studied in detail. Meanwhile, the NO conversion experiment, SEM and Py-FTIR tests indicated that a small amount of gallium oxide on PCH result on considerable improvement in the catalytic performance, because of the higher acidic site and amorphous formation which were beneficial for NO oxidation at low temperature.

Synergetic effects of surface free Co3O4 species on catalytic oxidation of NO over cerium-cobalt solid solution

The xCo3O4/Ce0.85Co0.15-3xO2-δ catalyst was prepared by a sol-gel method for selective catalytic oxidation of NO. The experimental results showed that the highest catalytic activity reached 60.2% at 300 °C. In addition, the Raman spectra and XPS results confirmed that the Ce-Co catalyst contained surface free Co3O4 species and Co ions in the Ce0.85Co0.15-3xO2-δ solid solution. Surface free Co3O4 species could be removed by hydrochloric acid, leading to decrease of the catalyst activity. For the xCo3O4/Ce0.85Co0.15-3xO2-δ catalyst, the surface free Co3O4 species and the Ce0.85Co0.15-3xO2-δ solid solution enhanced catalytic performance, and the former provided the adsorption sites of NO and the latter promoted the activation of oxygen. This research studied the synergetic effects of Co3O4 species and Ce0.85Co0.15-3xO2-δ solid solution on the process of NO oxidation. For the xCo3O4/Ce0.85Co0.15-3xO2-δ catalyst, the enhanced catalytic performance was due to the synergy between the surface Co3O4 species and the Ce0.85Co0.15-3xO2-δ solid solution, as the former provided the sites for NO chemisorption and the latter promoted the activation of oxygen.

The inhibition effect and deactivation mechanism of H2O and SO2 on selective catalytic oxidation of NO over the Mn–Ca–Ox–(CO3)y catalyst

H2O and SO2 had an inhibition effect on NO oxidation. SO2 increased the particle size of the catalyst. H2O decreased the particle size of the catalyst.

Sol–gel synthesis of CuO-TiO2 catalyst with high dispersion CuO species for selective catalytic oxidation of NO

In this study, CuO-TiO2 (Cux-Ti) mixed-oxide catalysts with different Cu content prepared by sol-gel method were firstly used to selective catalytic oxidation (SCO) of NO. The catalytic activity test revealed that catalysts, especially Cu0.07-Ti, exhibited much higher catalytic performance than CuO supported TiO2 (Cu0.07/Ti) catalyst. XRD, EDS, Raman, XPS, H2-TPR, O2-TOD, NO-TPD and DRIFT measurements were used for characterizing the catalysts. The results of characterizations reveled that Cu0.07-Ti catalysts possessed high dispersed CuO. This feature of Cu0.07-Ti resulted in a strong interaction of Cu species with TiO2 support in compared to Cu0.07/Ti. This strong interaction not only enhanced amounts of active oxygen species by promoting the formation of oxygen vacancies, but also activated adsorbed NO over Cu0.07-Ti catalysts. In addition, on the basis of NO2 formation, it also promoted the decomposition of nitrate species to NO2 over Cu0.07-Ti catalyst. Based on the above mentioned favorable properties, Cu0.07-Ti catalysts had an excellent NO-SCO performance.

Influence of Ca doping and calcination temperature on selective catalytic oxidation of NO over Mn–Ca–Ox–(CO3)ycatalysts

Selective catalytic oxidation (SCO) is an unconventional technology for denitration.

Promotional effect of N-doped CeO2 supported CoOx catalysts with enhanced catalytic activity on NO oxidation

A series of neoteric CoOx/N-doped CeO2 catalysts were synthesized by partly substituting the lattice oxygen of CeO2 with nitrogen by a simple g-C3N4-modified sol–gel method and comprehensively characterized by XRD, H2-TPR, XPS, BET, TEM, TG, UV–vis DRS, PL, EIS, NO(O2)-TPD and EPR. The results demonstrated that: (1) The N-doped catalysts showed larger surface areas and pore volumes, which were favorable for the adsorption of reactant gas; (2) Replacing O with N could promote the reduction of resultant catalysts and assist cobalt oxide in changing the valence and the support in supplying the oxygen; (3) By a sol–gel method, the CoOx crystallites in these catalysts were encapsulated by CeO2 with only a small fraction of Co ions on the surface and strongly interacting with CeO2. Such structure maximized the interaction between CoOx and CeO2 in three dimensions, resulting in unique redox properties. Moreover, the prepared materials were evaluated in the selective catalytic oxidation of NO. The results showed that the N-doped materials exhibited higher catalytic activity than the un-doped one due to those physicochemical changes. An enhanced mechanism on the improvement of catalytic performance was proposed, and this could pave the way for the designed and synthesis of new highly catalytic activity catalysts.

Effect of chromium oxide as active site over TiO2-PILC for selective catalytic oxidation of NO

This study introduced TiO2-pillared clays (TiO2-PILC) as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350°C, the NO conversion was 61% under conditions of GHSV = 23600 hr−1. The BET data showed that the support particles had a mesoporous structure. H2-TPR showed that Cr(10)TiP (10 wt.% Cr doping on TiO2-PILC) clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO + O2 adsorption, the intensity of evolution of superoxide ions (O2−) increased. The content of Cr3+ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr3+ increased to 50.28%. Additionally, Oα/Oβ increased markedly through the oxidation process. The NO conversion decreased when SO2 was added into the system, but when the SO2 was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO42−.

Effects of Cr on the NO oxidation over the ceria–zirconia solid solution

CrOx, Ce0.5Zr0.5O2 and 10Cr/Ce0.5Zr0.5O2 catalysts were prepared to investigate the separate effect of Cr and Ce0.5Zr0.5O2 for selective catalytic oxidation of NO. It was found that the co-actions of CrOx and Ce0.5Zr0.5O2 exhibited the higher catalytic activity than separate effect of CrOx or Ce0.5Zr0.5O2. The separate effects of Cr and Ce0.5Zr0.5O2 on the structure of the catalysts were systematically examined by XRD, TEM, BET, XPS, NO-TPD and O2-TPD. The XPS results showed that Cr species were enriched on the surface and the amount of Cr6+ increased after Cr was loaded on the Ce0.5Zr0.5O2. TPD results showed that NO was adsorbed on the sites of Cr, and O2 was adsorbed and activated on the ceria–zirconia solid solution. Finally, the adsorbed NO interacted with the adsorbed O2 to generate NO2 in the Langmuir–Hinshelwood mechanism.

Selective catalytic oxidation of NO with O 2 over Ce-doped MnO x/TiO 2 catalysts

A series of Ce-doped MnO x /TiO 2 catalysts were prepared by impregnation method and used for catalytic oxidation of NO in the presence of excess O2. The sample with the Ce doping concentration of Ce/Mn=1/3 and calcined at 300°C shows a superior activity for NO oxidation to NO 2. On Ce(1)Mn(3)Ti catalyst, 58% NO conversion was obtained at 200°C and 85% NO conversion at 250°C with a GHSV of 41000 h −1, which was much higher than that over MnO x /TiO 2 catalyst (48% at 250°C). Characterization results implied that the higher activity of Ce(1)Mn(3)Ti could be attributed to the enrichment of well-dispersed MnO x on the surface and the abundance of Mn 3+ and Ti 3+ species. The addition of Ce into MnO x /TiO 2 could improve oxygen storage capacity and facilitate oxygen mobility of the catalyst as shown by PL and ESR, so that its activity for NO oxidation could be enhanced. The effect of H 2O and SO 2 on the catalyst activity was also investigated.

Selective catalytic oxidation of NO over iron and manganese oxides supported on mesoporous silica

The selective catalytic oxidation (SCO) of NO was studied on a catalyst consisting of iron-manganese oxide supported on mesoporous silica (MPS) with different Mn/Fe ratios. Effects of the amount of manganese and iron, oxygen, and calcination temperature on NO conversion were also investigated. It was found that the Mn-Fe/MPS catalyst with a Mn/Fe molar ratio of 1 showed the highest activity at the calcination temperature of 400 °C. The results showed that over this catalyst, NO conversion reached 70% under the condition of 280 °C, and a space velocity of 5000 h −1. SO 2 and H 2O had no adverse impact on the reaction activity when the SCO reaction temperature was above 240 °C. In addition, the SCO activity was suppressed gradually in the presence of SO 2 and H 2O below 240 °C, and such an effect was reversible after heating treatment.