Search

Wet scrubbing combined with ozone oxidation has become a promising technology for simultaneous removal of SO2 and NOx in exhaust gas. In this paper, a new 20-species, 76-step detailed kinetic mechanism was proposed between O3 and NOx. The concentration of N2O5 was measured using an in-situ IR spectrometer. The numerical evaluation results kept good pace with both the public experiment results and our experiment results. Key reaction parameters for the generation of NO2 and N2O5 during the NO ozonation process were investigated by a numerical simulation method. The effect of temperature on producing NO2 was found to be negligible. To produce NO2, the optimal residence time was 1.25sec and the molar ratio of O3/NO about 1. For the generation of N2O5, the residence time should be about 8sec while the temperature of the exhaust gas should be strictly controlled and the molar ratio of O3/NO about 1.75. This study provided detailed investigations on the reaction parameters of ozonation of NOx by a numerical simulation method, and the results obtained should be helpful for the design and optimization of ozone oxidation combined with the wet flue gas desulfurization methods (WFGD) method for the removal of NOx., (Copyright © 2015. Published by Elsevier B.V.)

This work has been undertaken to study the influences of pH value on the characteristics and activity of photocatalyst by deposition-precipitation method during its preparation process. A series of Pt-modified TiO2 were prepared by deposition-precipitation method at different pH values as well as wet impregnation method, and characterized by XRD, XPS, TEM, UV-Vis and photoluminescence (PL). It was found that the catalysts had the highest photocatalytic activity for NO conversion when pH value was kept at around 7. And the sample prepared by deposition-precipitation method showed higher activity than that by impregnation method. This was mainly due to their high value in highly-dispersed platinum oxides (PtOx) content on the surface of the catalysts. The results from UV-Vis absorption showed that highest absorbance was obtained for Pt/TiO2 prepared at pH values of around 7. And PL spectra results indicated that the recombination rate of photogenerated electrons and holes of the samples prepared by deposition-precipitation method was lower than that prepared by impregnation method. And in the zeta potential study, the pH values for the isoelectric point of the preparing slurry of 0.05 wt.%Pt/TiO2 and 0.5 wt.%Pt/TiO2 were determined to be 6.5-8.5, which further confirmed the enrichment of PtOx dopants for the catalysts repapered when pH value was around 7.

This study has been undertaken to investigate the roles of PtO and PtO(2) deposits in photocatalytic oxidation of NO over Pt-modified TiO(2) catalysts. These photocatalysts were prepared by neutralization method and characterized by XRD, BET, XPS, TEM and FTIR. It was found that Pt dopant existed as PtO and PtO(2) particles in as-prepared photocatalysts. And these Pt dopants would change their oxidation states during the photocatalytic oxidation reaction. An in situ XPS study indicated that a portion of PtO(2) on the surface of Pt/TiO(2) was reduced to PtO under UV irradiation. The migration of electrons to PtO(2) particles could separate the electrons and holes, resulting in the improvement of photocatalytic activity. And the depletion of PtO(2) by electrons could lead to the deactivation of Pt/TiO(2) catalyst. Moreover, PtO particles could be corroded to form Pt(2+) ions by HNO(3), which was one of the products of photocatalytic oxidation of NO. NO would adsorb on Pt(2+) related sites to form Pt(n+)-NO nitrosyls, retarding photocatalytic oxidation of NO to NO(2)., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A series of MnO(x)/TiO(2) composite nanoxides were prepared by deposition-precipitation (DP) method, and the sample with the Mn/Ti ratio of 0.3 showed a superior activity for NO catalytic oxidation to NO(2). The maximum NO conversion over MnO(x)(0.3)/TiO(2)(DP) could reach 89% at 250°C with a GHSV of 25,000h(-1), which was much higher than that over the catalyst prepared by conventional wet-impregnation (WI) method (69% at 330°C). Characterization results including XRD, HRTEM, FTIR, XPS, H(2)-TPR, NO-TPD and Nitrogen adsorption-desorption implied that the higher activity of MnO(x)(0.3)/TiO(2)(DP) could be attributed to the enrichment of well-dispersed MnO(x) on the surface and the abundance of Mn(3+) species. Furthermore, DRIFT investigations and long-time running test indicated that NO(2) came from the decomposition of adsorbed nitrogen-containing species., (Copyright © 2010 Elsevier Inc. All rights reserved.)

MnCe oxides were supported on TiO(2) and Al(2)O(3) by an ultrasonic impregnation method and used for selective catalytic reduction (SCR) of NO with NH(3) at low-temperature (80-220 degrees C). MnCe/TiO(2) showed a relatively higher SCR activity than MnCe/Al(2)O(3) at the temperature range of 80-150 degrees C. When the reaction temperature was higher than 150 degrees C, MnCe/Al(2)O(3) exhibited superior SCR activity to MnCe/TiO(2). NH(3) temperature programmed desorption study proved that MnCe/TiO(2) was mainly Lewis acidic, while MnCe/Al(2)O(3) could provide more Brönsted acid sites. These acid sites play an important role in SCR according to in situ diffuse reflectance infrared transform spectroscopy (DRIFT) analysis. The main SCR reaction was a typical Eley-Rideal mechanism on MnCe/TiO(2), which took place between coordinated NH(3)/NH(4)(+) and gas-phase NO. For MnCe/Al(2)O(3), the reaction mainly occurred via another pathway when the temperature exceeded 150 degrees C, which commenced with the adsorption and oxidation of NO and was followed by reaction between NO(2) or NO(2)-containing compounds and NH(3) adspecies. This reaction pathway makes a significant contribution to the improved NO conversion for MnCe/Al(2)O(3) at higher temperature., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

This study has been undertaken to investigate the relationship between Pd oxidation states on TiO(2) photocatalysts and their photocatalytic oxidation behaviors of NO. Three types of Pd-modified TiO(2) with different Pd oxidation states were prepared by wet impregnation method, neutralization method and photodeposition method, respectively. And these Pd-modified photocatalysts were characterized by X-ray diffraction analysis, X-ray photoelectron spectrum analysis (XPS), UV-Vis diffuse reflectance spectra and temperature programmed desorption (TPD). It was found from XPS results that the dominant oxidation states of Pd on these Pd-modified TiO(2) catalysts were Pd(2+), PdO, and Pd(0), respectively. NO-TPD results showed that the NO adsorption capacity was improved greatly by the modification of Pd(2+) ions. The activity tests showed that Pd-modified TiO(2) by a wet impregnation method increased photocatalytic activity compared to pure TiO(2) (Degussa P25). It was concluded that Pd(2+) ions on as-prepared TiO(2) catalysts provided key contributions to the improvement of photocatalytic activity. However, Pd(0) and PdO deposits on TiO(2) almost had no positive effect on NO oxidation. The mechanism of photocatalytic oxidation of NO in gas phase over Pd-modified TiO(2) was also proposed.

The composite titanium dioxide (TiO(2)) films coating on the woven glass fabric were prepared by a modified sol-gel process, using pre-calcinated TiO(2) nanoparticle or silica gel as filler. The characterized physicochemical properties of the prepared catalyst films showed that the specific surface area, the microstructure and the crystal structure of the catalysts were greatly affected by the fillers and the calcination temperature. The physicochemical properties of composite films and the photocatalytic activity of nitric oxide (NO) show that the pre-calcinated TiO(2) nanoparticle is more favorable than silica gel as filler. The pre-calcinated TiO(2) nanoparticle filler can increase the photocatalytic activities of the catalysts by increasing the specific surface area, introducing a bimodal mesoporous structure, and creating a polymorphous crystal structure. And the TiO(2)-TiO(2) film calcinated at 400 degrees C exhibits the highest photocatalytic activity for NO oxidation and is more active than Degussa P25.

Pd-modified TiO(2) prepared by thermal impregnation method was used in this study for photocatalytic oxidation of NO in gas phase. The physico-chemical properties of Pd/TiO(2) catalysts were characterized by X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller measurements (BET), X-ray photoelectron spectrum analysis (XPS), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), UV-vis diffuse reflectance spectra (UV-vis DRS) and photoluminescence spectra (PL). It was found that Pd dopant existed as PdO particles in as-prepared photocatalysts. The results of PL spectra indicated that the photogenerated electrons and holes were efficiently separated after Pd doping. During in situ XPS study, it was found that the content of hydroxyl groups on the surface of Pd/TiO(2) increased when the catalyst was irradiated by UV light, which could result in the improvement of photocatalytic activity. The activity test showed that the optimum Pd dopant content was 0.05 wt.%. And the maximum conversion of NO was about 72% higher than that of P25 when the initial concentration of NO was 200 ppm, which showed that Pd/TiO(2) photocatalysts could be potentially applied to oxidize higher concentration of NO.

Various surface platinized TiO(2) were prepared by four different preparation methods and investigated with respect to their behaviors in UV photocatalytic oxidation of nitric oxide. The physicochemical properties of the Pt modified TiO(2) were investigated by X-ray diffraction analysis, X-ray photoelectron spectrum analysis, transmission electron microscopy, and photoluminescence spectra. From the experimental results, it was found that new electronic states were observed above the valence bands of PtOx-TiO(2) and PtClx-TiO(2). And the lifetime of electrons and holes was found prolonged in the PtOx-TiO(2) catalysts. The activity tests showed that the dopants existed as metallic Pt and platinum chloride had little contribution to the photocatalytic oxidation of NO in gas phase. However, the dopant which existed as PtOx could improve the NO photocatalytic oxidation efficiency and the reaction rate. The photocatalytic activity of the 0.05 at% PtOx-TiO(2) was nearly three times higher than that of the pure Degussa P25 with an inlet NO concentration of 200 ppm.

A series of Si-doped TiO2 (Si/TiO2) photocatalysts supported on woven glass fabric were prepared by hydrothermal method for photocatalytic reduction of NO with NH3. The photocatalytic activity tests were carried out in a continuous Pyrex reactor with the flow rate of 2000mL/min under UV irradiation (luminous flux: 1.1x10(4)lm, irradiated catalyst area: 160cm2). The photocatalysts were characterized by X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrophotometer, transmission electron microscopy (TEM), photoluminescence (PL) and temperature-programmed desorption (TPD). The experiment results showed that NO conversion on Si/TiO2 at 323K could exceed 60%, which was about 50% higher than that on Degussa P25 and pure TiO2. With the doping of Si, photocatalysts with smaller crystal size, larger surface area and larger pore volume were obtained. It was also found that Ti-O-Si bands were formed on the surface of Si/TiO2 and that the surface hydroxyl concentration was greatly increased. As a result, total acidity and NH3 chemisorption amount were enhanced for Si/TiO2 leading to its photocatalytic activity improvement.

Gas-phase photocatalytic oxidation (PCO) of nitric oxide (NO) with immobilized TiO2 films was studied in this paper. The immobilized TiO2 films were synthesized by hydrothermal method. The characterization for the physicochemical properties of catalysts prepared under different hydrothermal conditions were carried out by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), Brunauer-Emmett-Teller measurements (BET) and scanning electron micrograph (SEM). It was found that the PCO efficiency of the catalyst was mainly depended on the hydrothermal conditions. The optimal values of hydrothermal temperature and hydrothermal time were 200 degrees C and 24 h, respectively. Furthermore, it was also known that the photocatalytic efficiency would decrease remarkably when the calcination temperature was over than 450 degrees C. Under the optimal conditions (hydrothermal condition: 200 degrees C for 24 h; calcination temperature: 450 degrees C), the photocatalytic efficiency of catalyst could reach 60% higher than that of Degussa P25.

Manganese oxides and iron-manganese oxides supported on TiO2 were prepared by the sol-gel method and used for low-temperature selective catalytic reduction (SCR) of NO with NH3. Base on the previous study, Mn(0.4)/ TiO2 and Fe(0.1)-Mn(0.4)/TiO2 were then selected to carry out the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigation for revealing the reaction mechanism. The DRIFT spectroscopy for the adsorption of NH3 indicated the presence of coordinated NH3 and NH4+ on both of the two catalysts. When NO was introduced, the coordinated NH3 on the catalyst surface was consumed rapidly, indicating these species could react with NO effectively. When NH3 was introduced into the sample preadsorbed with NO + O2, SCR reaction would not proceed on Mn(0.4)/TiO2. However, for Fe(0.1)-Mn(0.4)/ TiO2 the bands due to coordinated NH3 on Fe2O3 were formed. Simultaneously, the bidentate nitrates were transformed to monodentate nitrates and NH4+ was detected. And NO2 from the oxidation of NO on catalyst could react with NH4+ leading to the reduction of NO. Therefore, it was suggested that the SCR reaction on Fe(0.1)-Mn(0.4)/TiO2 could also take place in a different way from the reactions on Mn(0.4)/TiO2 proposed by other researchers. Furthermore, the SCR reaction steps for these two kinds of catalysts were proposed.

Photothermal effect was for the first time utilized to capture the energy from infrared light and to promote the photocatalytic oxidation activity of NO by a simply mechanical mixing of traditional photocatalysts and core-shell structured Fe 3 O 4 @SiO 2 . Fe 3 O 4 @SiO 2 absorbed the infrared light, transferred it into thermal energy based on photothermal effect, which then accelerated the NO photocatalytic activity of traditional photocatalysts. This promotion effect led by the addition of Fe 3 O 4 @SiO 2 was confirmed by several classical photocatalysts such as TiO 2 , g-C 3 N 4 , BiOI and CeO 2 . To quantitatively characterize the photothermal effect, thermo images were taken with a thermo imager to obtain the average temperature rise of samples under the illumination of simulated solar light. Specially, P25/Fe 3 O 4 @SiO 2 was studied in depth for illustration of the promotion mechanism. Experimental results showed that with the contribution of SiO 2 shell, the photocorrosion of Fe 3 O 4 didn’t occur during photocatalytic oxidation process and the photothermal effect of Fe 3 O 4 was maintained. The quantity of Fe 3 O 4 @SiO 2 was a vital factor for promotion of photocatalytic activity and the optimum mass ratio of P25 and Fe 3 O 4 @SiO 2 was 3–1. After 120 min of illumination, the temperature of optimum P25/Fe 3 O 4 @SiO 2 rose to 57.4 °C from 25 °C and its NO conversion capability showed an enhancement of 38.9% with the comparison to pure P25. The experimental results confirmed that the rise of temperature was attributed to the photothermal effect and its contribution was the same as the directly heating of photocatalysts. Furthermore, the enhancement of NO conversion capability around 30–40% was observed for the Fe 3 O 4 @SiO 2 mixed anatase TiO 2 , g-C 3 N 4 , ZnO, BiOI and CeO 2 . In sum, we developed a new strategy for utilization of NIR light of solar energy to facilitate the photocatalytic reactions. [ABSTRACT FROM AUTHOR]

Palladium-modified titanium dioxide, prepared using a one-step hydrothermal synthesis method, was employed for the photocatalytic oxidation of nitric oxide in gas phase. It was found that palladium dopants in the prepared photocatalysts existed as Pd2+ ions, palladium oxide particles, and metallic triphenylphosphine palladium. Pd2+ ions provided key contributions to the improvement of photocatalytic activity, while triphenylphosphine palladium and palladium oxide deposits on titanium oxide had almost no positive effect on nitric oxide oxidation. Results of the study indicated that photogenerated electrons and holes were efficiently separated after palladium doping. The bimodal pore-size distribution of the catalysts enhanced the speed of the photocatalytic reaction. Activity tests showed that the optimum palladium dopant content was 0.05% and the maximum conversion of nitric oxide was about 72.6% higher than that using titanium dioxide powder at 100 ppm. Results of this study show that palladium/titanium dioxide prepared using the one-step hydrothermal method may be more efficient in oxidizing nitric oxide than titanium dioxide powder. [ABSTRACT FROM AUTHOR]

Various surface platinized TiO2 were prepared by four different preparation methods and investigated with respect to their behaviors in UV photocatalytic oxidation of nitric oxide. The physicochemical properties of the Pt modified TiO2 were investigated by X-ray diffraction analysis, X-ray photoelectron spectrum analysis, transmission electron microscopy, and photoluminescence spectra. From the experimental results, it was found that new electronic states were observed above the valence bands of PtOx-TiO2 and PtClx-TiO2. And the lifetime of electrons and holes was found prolonged in the PtOx-TiO2 catalysts. The activity tests showed that the dopants existed as metallic Pt and platinum chloride had little contribution to the photocatalytic oxidation of NO in gas phase. However, the dopant which existed as PtOx could improve the NO photocatalytic oxidation efficiency and the reaction rate. The photocatalytic activity of the 0.05at% PtOx-TiO2 was nearly three times higher than that of the pure Degussa P25 with an inlet NO concentration of 200ppm. [Copyright &y& Elsevier]

Abstract: A two-stage process incorporating photocatalytic oxidation (PCO) and wet absorption was developed in this study for the treatment of nitrogen oxides (NOx). At first, nitric oxide was converted to nitrogen dioxide by PCO. Then the nitrogen oxides were absorbed effectively in a wet scrubber by using sulfite solution as an absorbent. The experimental results showed that the removal efficiency of NOx by this combined process could reach 75%, when the inlet concentration of nitrogen oxides was 240ppm (200ppm NO). It was also observed that NOx removal efficiency had a maximum value when the absorbent concentration (Na2SO3) was 2wt%. The addition of Na2S2O3 could effectively retard the excessive oxidation of sulfite by oxygen. 0.5wt.% Na2S2O3 was considered the suitable inhibitor concentration. The main products of this combined process were nitrite and nitrate. [Copyright &y& Elsevier]

Abstract: In this paper, ceria supported on sulfated zirconia (CeSZ) as a superacid catalyst was synthesized and the resulted performances for selective catalytic reduction (SCR) of NO with NH3 were investigated. Experimental results revealed that the sulfation of zirconia supports could greatly improve the SCR activity of the catalysts. Among the tested samples, the CeSZ catalyst with Ce/Zr mole ratio at 0.095 possessed the highest NO conversion (i.e., 98.6% at ca. 420°C and 180,000h−1). The sulfation had led to a formation of pure tetragonal phase of ZrO2, a well dispersion of CeO2, abundant stable superacid sites, increasing surface area and enrichment of Ce3+ on the surface, all of which were responsible for its excellent performance in SCR of NO with NH3. [Copyright &y& Elsevier]

Abstract: A new cerium oxide catalyst supported on HNO3-treated carbon nanotubes (TCNTs) was prepared for the first time and used for the selective catalytic reduction of NO with ammonia. CeO2 located on the outer surface or in the tubular channel of CNTs could be observed. Among these tested samples, carbon nanotubes loading Ce with a Ce/C mole ratio of 0.003 (calcined at 350°C) obtained the best NO conversion in the medium temperature range of 250–400°C. The activity improvement of 0.3 Ce/TCNTs (350) was attributed to the enlarged surface area by HNO3 treatment, the suitable crystal size of CeO2 and the well dispersion of ceria on the surface of CNTs. [Copyright &y& Elsevier]

Abstract: This study has been undertaken to investigate the relationship between Pd oxidation states on TiO2 photocatalysts and their photocatalytic oxidation behaviors of NO. Three types of Pd-modified TiO2 with different Pd oxidation states were prepared by wet impregnation method, neutralization method and photodeposition method, respectively. And these Pd-modified photocatalysts were characterized by X-ray diffraction analysis, X-ray photoelectron spectrum analysis (XPS), UV–Vis diffuse reflectance spectra and temperature programmed desorption (TPD). It was found from XPS results that the dominant oxidation states of Pd on these Pd-modified TiO2 catalysts were Pd2+, PdO, and Pd0, respectively. NO-TPD results showed that the NO adsorption capacity was improved greatly by the modification of Pd2+ ions. The activity tests showed that Pd-modified TiO2 by a wet impregnation method increased photocatalytic activity compared to pure TiO2 (Degussa P25). It was concluded that Pd2+ ions on as-prepared TiO2 catalysts provided key contributions to the improvement of photocatalytic activity. However, Pd0 and PdO deposits on TiO2 almost had no positive effect on NO oxidation. The mechanism of photocatalytic oxidation of NO in gas phase over Pd-modified TiO2 was also proposed. [Copyright &y& Elsevier]

Abstract: Mn/TiO2 and ceria modified Mn/TiO2 were prepared by sol–gel method and used for low-temperature selective catalytic reduction (SCR) of NO with NH3 in the presence of SO2. The deactivation of Mn/TiO2 by SO2 was observed during SCR process and the depositions of (NH4)2SO4 and NH4HSO4 were detected on Mn/TiO2 surface. It was found that the resistance to SO2 could be greatly enhanced for Ce modified Mn/TiO2. It was because that the formation of Ti(SO4)2 and Mn(SO4) x was prevented and the depositions of (NH4)2SO4 and NH4HSO4 were significantly inhibited with the doping of ceria. [Copyright &y& Elsevier]

Graphical abstract Abstract The g-C 3 N 4 with different structures was prepared by heat treatment using urea (CN-U) and thiourea (CN-T) as precursors under the same conditions. The microstructure and optical properties of the photocatalyst were analyzed with advanced tools. The results showed that the CN-U has a porous structure, a high specific surface area and a wide band gap in comparison with CN-T. The in situ FT-IR technique was used to monitor the adsorption and reaction process of visible photocatalytic NO oxidation on g-C 3 N 4. The corresponding reaction mechanism was proposed based on the results of reaction intermediate observation and electron paramagnetic resonance (EPR) radical scavenging. It was revealed that (1) the presence of defective sites favored the adsorption of gas molecules and electronically compensated it leading to promoted formation of the final products; (2) the high separation efficiency of photogenerated electron-hole pairs enhanced the production of radicals during the photocatalytic reaction; (3) the hydroxyl radicals (OH) are not selective for the decomposition of pollutants, which are favorable to the complete oxidation of the reaction intermediates. The above three aspects are the main reasons for the CN-U possessing the efficient visible light photocatalytic activity. The present work could provide new insights and methods for understanding the mechanism of photocatalysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] The NO was oxidized to N2O5 and HNO3 when the O3/NO was over 1 and below 100°C. [•] The temperature rising led to the disappearance of high state nitrogen oxides. [•] The formation reaction of NO3 was the trigger reaction for N2O5 generation. [•] The oxidation of SO2 might be accelerated with NO x presenting when O3 was excess. [ABSTRACT FROM AUTHOR]

Abstract: Manganese-based catalysts have shown excellent low-temperature selective catalytic reduction (SCR) activity for NO x removal. However, they all suffer from the serious SO2 poisoning effect on activity. Ceria modification has been reported to be able to promote SO2 tolerance of SCR catalysts probably via the inhibition of surface sulfate species formation. In this study, in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigations were carried out to determine the role of Ceria in the improved resistance for a Ce-modified Mn/TiO2 catalyst. The results indicated that after the introduction of Ce, SO x ad-species preferentially formed on Ceria as bulk-like sulfate species and lessened the sulfation of the main active phase (MnO x ) during low-temperature SCR processes in the presence of SO2. Furthermore, the DRIFT and TG–DSC results also implied that Ce modification could reduce thermal stabilities of the sulfate species covered on catalyst surface, thereby promoting its decomposition. Both of these would be beneficial to the improved SO2 tolerance of Ce modified catalysts. [Copyright &y& Elsevier]

Abstract: This study has been undertaken to investigate the roles of PtO and PtO2 deposits in photocatalytic oxidation of NO over Pt-modified TiO2 catalysts. These photocatalysts were prepared by neutralization method and characterized by XRD, BET, XPS, TEM and FTIR. It was found that Pt dopant existed as PtO and PtO2 particles in as-prepared photocatalysts. And these Pt dopants would change their oxidation states during the photocatalytic oxidation reaction. An in situ XPS study indicated that a portion of PtO2 on the surface of Pt/TiO2 was reduced to PtO under UV irradiation. The migration of electrons to PtO2 particles could separate the electrons and holes, resulting in the improvement of photocatalytic activity. And the depletion of PtO2 by electrons could lead to the deactivation of Pt/TiO2 catalyst. Moreover, PtO particles could be corroded to form Pt2+ ions by HNO3, which was one of the products of photocatalytic oxidation of NO. NO would adsorb on Pt2+ related sites to form Pt n+–NO nitrosyls, retarding photocatalytic oxidation of NO to NO2. [ABSTRACT FROM AUTHOR]

Abstract: A series of MnO x /TiO2 composite nanoxides were prepared by deposition-precipitation (DP) method, and the sample with the Mn/Ti ratio of 0.3 showed a superior activity for NO catalytic oxidation to NO2. The maximum NO conversion over MnO x (0.3)/TiO2(DP) could reach 89% at 250°C with a GHSV of 25,000h−1, which was much higher than that over the catalyst prepared by conventional wet-impregnation (WI) method (69% at 330°C). Characterization results including XRD, HRTEM, FTIR, XPS, H2-TPR, NO-TPD and Nitrogen adsorption–desorption implied that the higher activity of MnO x (0.3)/TiO2(DP) could be attributed to the enrichment of well-dispersed MnO x on the surface and the abundance of Mn3+ species. Furthermore, DRIFT investigations and long-time running test indicated that NO2 came from the decomposition of adsorbed nitrogen-containing species. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, Mn–Ce/TiO2 was prepared by sol–gel method and used for low-temperature selective catalytic reduction (SCR) of NO with NH3 in the presence of SO2 at different temperatures (100–200°C). SO2 had a poisoning effect on NO conversion of the Mn–Ce/TiO2 catalyst and this effect was directly related with reaction temperature. The higher the reaction temperature, the more rapidly the catalyst activity decreased. The results of in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectroscopy and temperature programmed desorption (TPD) profiles indicated that the active sites of the Mn–Ce/TiO2 catalyst were seriously sulfated at 200°C which led to an irreversible deactivation of the sample. While the formation and deposition of (NH4)2SO3 and NH4HSO4 were the main causes of catalyst deactivation when the SCR reaction was carried out at 100°C. This kind of deactivation could be almost completely recovered after water-washing treatment. [Copyright &y& Elsevier]

Abstract: This study has been undertaken to investigate the influences of the valence states of doped palladium on the photocatalytic oxidation behaviors of NO over palladium modified TiO2 catalysts. These Pd/TiO2 catalysts were prepared by thermal impregnation method and characterized by XRD, BET, XPS and UV–Vis diffuse reflectance spectra. It was found that Pd dopant existed as Pd2+ in as-prepared photocatalysts. And after photocatalytic oxidation reaction, both Pd0 and Pd4+ could be detected. The activity tests showed that the modification of Pd could enhance the photocatalytic activity. And it was concluded that Pd4+ could be attributed to the improvement of activity. [Copyright &y& Elsevier]