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1.
Ja Hun Kwak Do Heui Kim Jnos Szanyi Charles H.F. Peden 《Applied catalysis. B, Environmental》2008,84(3-4):545-551
In this work, we investigated the NOx storage behavior of Pt/BaO/CeO2 catalysts, especially in the presence of SO2. High surface area CeO2 (110 m2/g) with a rod like morphology was synthesized and used as a support. The Pt/BaO/CeO2 sample demonstrated slightly higher NOx uptake in the entire temperature range studied compared with Pt/BaO/γ-Al2O3. More importantly, this ceria-based catalyst showed higher sulfur tolerance than the alumina-based one. The time of complete NOx uptake was maintained even after exposing the sample to 3 g/L of SO2. The same sulfur exposure, on the other hand, eliminated the complete NOx uptake time on the alumina-based NOx storage catalysts. TEM images show no evidence of either Pt sintering or BaS phase formation during reductive de-sulfation up to 600 °C on the ceria-based catalyst, while the same process over the alumina-based catalyst resulted in both a significant increase in the average Pt cluster size and the agglomeration of a newly formed BaS phase into large crystallites. XPS results revealed the presence of about five times more residual sulfur after reductive de-sulfation at 600 °C on the alumina-based catalysts in comparison with the ceria-based ones. All of these results strongly support that, besides their superior intrinsic NOx uptake properties, ceria-based catalysts have (a) much higher sulfur tolerance and (b) excellent resistance against Pt sintering when they are compared to the widely used alumina-based catalysts. 相似文献
2.
Yuanjing Zheng Anker Degn Jensen Jan Erik Johnsson Joakim Reimer Thgersen 《Applied catalysis. B, Environmental》2008,83(3-4):186-194
In this work, deactivation of a commercial type V2O5-WO3-TiO2 catalyst by aerosols of potassium compounds was investigated in two ways: (1) by exposing the catalyst in a lab-scale reactor to a layer of KCl particles or fly ash from biomass combustion; (2) by exposing full-length monolith catalysts to pure KCl or K2SO4 aerosols in a bench-scale reactor. Exposed samples were characterized by activity measurements, SEM-EDX, BET/Hg-porosimetry, and NH3 chemisorption. The work was carried out to support the interpretation of observations of a previous study in which catalysts were exposed on a full-scale biomass fired power plant and to reveal the mechanisms of catalyst deactivation.Slight deactivation (about 10%) was observed for catalyst plates exposed to a layer of KCl particles at 350 °C for 2397 h. No deactivation was found for catalyst plates exposed for 2970 h to fly ash (consisting mainly of KCl and K2SO4) collected from an SCR pilot plant installed on a straw-fired power plant. A fast deactivation was observed for catalysts exposed to pure KCl or K2SO4 aerosols at 350 °C in the bench-scale reactor. The deactivation rates for KCl aerosol and K2SO4 aerosol exposed catalysts were about 1% per day and 0.4% per day, respectively.SEM analysis of potassium-containing aerosol exposed catalysts revealed that the potassium salt partly deposited on the catalyst outer wall which may decrease the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the average K/V ratios (0.5–0.75) in the catalyst structure are high enough to explain the level of deactivation observed. The catalyst capacity for NH3 chemisorption decreased as a function of exposure time, which reveals that Brønsted acid sites had reacted with potassium compounds and thereby rendered inactive in the catalytic cycle. The conclusion is that chemical poisoning of active sites is the dominating deactivation mechanism, but physical blocking of the surface area may also contribute to the loss of activity in a practical application. The results support the observation and mechanisms of deactivation of SCR catalysts in biomass fired systems proposed in a previous study [Y. Zheng, A.D. Jensen, J.E. Johnsson, Appl. Catal. B 60 (2005) 253]. 相似文献
3.
Variable temperature adsorption of nitric oxide on MoO3 supported on tetragonal zirconia (MoOx/t-ZrO2), obtained by slurry deposition, was investigated by EPR spectroscopy. The influence of molybdenum loading and co-adsorbed oxygen on the adsorption process of NO was elucidated. Particular attention was devoted to redox character of NO activation. Another important aspect concerned is the nature of surface nitrosyl complexes of molybdenum and their thermal stability. The role of oxygen in NO transformation over catalyst surface was also discussed. 相似文献
4.
A NO
x
trap that uses only high-surface-area alumina as the NOx-storage material appears to provide significant advantages over
the conventional baria-based trap for exhaust-gas after-treatment in low-temperature exhaust (∼250 °C) characteristic of light-duty
diesel-powered vehicles operating at low speed/load conditions. In particular, an alumina trap provides better low-temperature
NO
x
conversion and also allows more efficient de-sulfurization than a baria-based trap in laboratory evaluations. Both of these
features are ascribed to the difference in basicity of the NO
x
-storage materials, which leads to thermally less stable nitrate (nitrite) and sulfate compounds in the case of alumina compared
to conventional traps with high levels of alkali or alkaline-earth metal oxides. Further studies, extending the laboratory
experiments to engine and vehicle evaluations, are still needed, however, in order to fully assess the true potential of the
alumina trap.
Article note George Graham—retired 相似文献
5.
Transient TPSR, DRIFTS-MS and TGA studies of a Pd/ceria-zirconia catalyst in CH4 and NO2 atmospheres
In this study, the parameters governing the activity of Pd/ceria-zirconia catalysts in the selective catalytic reduction (SCR) of NOx assisted by methane are investigated using a combination of temperature-programmed spectroscopic and thermogravimetric techniques and transient SCR conditions. By DRIFTS of adsorbed CO, it is established that Pd species on Ce0.2Zr0.8O2 are mainly present in cationic form but exhibit high reducibility. As found by temperature-programmed surface reaction (TPSR) in CH4 + NO2 atmosphere, the CH4-SCR reaction is initiated at 280 °C on Pd/Ce0.2Zr0.8O2 and yields almost 100% N2 above 500 °C. DRIFTS-MS and TGA experiments performed under transient SCR conditions show that DeNOx activity is due to a surface reaction between some methane oxidation products on reduced Pd sites with ad-NxOy species presumably located on the support. The detrimental effect of O2 on DeNOx is explained by the promotion of the total combustion of methane assisted by the ceria-zirconia component at the expense of the SCR reaction above 320 °C. 相似文献
6.
R. Burch J.P. Breen C.J. Hill B. Krutzsch B. Konrad E. Jobson L. Cider K. Eränen F. Klingstedt L.-E. Lindfors 《Topics in Catalysis》2004,(1):19-25
The effect of the addition of hydrogen on the SCR of NO
x
with a hydrocarbon reaction was investigated. It was found that hydrogen had a remarkable effect on the temperature range over which NO
x
could be reduced during the SCR reaction with octane. Reduction of NO
x
was initiated at as low a temperature as 100 °C and >95% NO
x
conversion was achieved over a temperature range of 200–450 °C. Hydrogen has the effect of activating octane at lower temperatures and also promotes the oxidation of NO to NO2 in the absence of hydrocarbon. Transient kinetic and in situ DRIFTS measurements indicated that hydrogen has a direct role in the reaction mechanism by either promoting the formation and storage of an organic C = N species which can then readily reduce NO
x
and/or removing a species which acts as a poison to the SCR reaction at low temperatures. 相似文献
7.
8.
This research investigated how the physical and chemical properties of Pt/TiO2-based catalysts with high activity in SCR reaction are affected by the preparation conditions (type of TiO2, Pt content and calcination temperature) using XRD, BET and TPR analysis. The catalyst preparation conditions that achieve optimum reactivity were identified by examination of how the physical and chemical properties relate to catalytic activity. According to the results, Pt content over 2 wt% causes a phenomenon in which Pt agglomeration increases linearly according to the surface area of the limited support. However, Pt content over 3 wt% showed an increase in reducibility in the low temperature region that is proportional to the absolute amount of Pt has increased. Moreover, although increased calcination temperature did not result in phase transition of the TiO2 support, it did lead to reduction of the surface area by increasing crystallinity and sintering of Pt. 相似文献
9.
In this study the effect of ceria addition on the performance of a model Ba-based lean NO
x
trap (LNT) catalyst was examined. The presence of ceria improved NO
x
storage capacity in the temperature range 200–400 °C under both continuous lean and lean-rich cycling conditions. Temperature-programmed
experiments showed that NO
x
stored in the ceria-containing catalyst was thermally less stable and more reactive to reduction with both H2 and CO as reductants, albeit at the expense of additional reductant consumed by reduction of the ceria. These findings demonstrate
that the incorporation of ceria in LNTs not only improves NO
x
storage efficiency but also positively impacts LNT regeneration behavior. 相似文献
10.
The present study explores the possibilities of catalysts of Ag/Al2O3, in which silver has been deposited using reverse microemulsions with the aim of getting maximum dispersion and homogeneity in the active superficial species, for the selective catalytic reduction of NOx in excess of oxygen, using both propene and ethanol as reductants and in the scope of the control of the emissions produced by vehicles that operate in conditions of lean mixture like the diesel engine or those of gasoline direct injection. The promotional effect of the hydrogen presence in the reactive mixture has also been analyzed. For both reductants, when in presence of hydrogen, an important enhancement in NOx conversion is produced, in particular for a catalyst with 3 wt.% silver. The production of acetaldehyde during the reaction employing ethanol is also analyzed and its role on the NOx reduction process has been examined. The interpretation of catalytic properties has been complemented by means of in-situ DRIFTS. 相似文献
11.
A series of transition metal oxides promoted titania catalysts (MO
x
/TiO2; M = Cr, Mn, Fe, Ni, Cu) were prepared by wet impregnation method using dilute solutions of metal nitrate precursors. The
catalytic activity of these materials was evaluated for the selective catalytic reduction (SCR) of NO with CO as reductant
in the presence of excess oxygen (2 vol.%). Among various promoted oxides, the MnO
x
/TiO2 system showed very promising catalytic activity for NO + CO reaction, giving higher than 90% NO conversion over a wide temperature
window and at high space velocity (GHSV) of 50,000 h−1. It is remarkable to note that the catalytic activity increased with oxygen, up to 4 vol.%, under these conditions leading
primarily to nitrogen. Our TPR studies revealed the presence of mixed oxidation states of manganese on the catalyst surface.
Characterization results indicated that the surface manganese oxide phase and the redox properties of the catalyst play an
important role in final catalytic activity. 相似文献
12.
Boxiong SHEN Ting LIU Zhanliang SHI Jianwei SHI Tingting YANG Ning ZHAO 《Frontiers of Chemical Engineering in China》2008,2(3):325-329
MnO
x
-CeO
x
/ACFN were prepared by the impregnation method and used as catalyst for selective catalytic reduction of NO with NH3 at 80°C-150°C.
The catalyst was characterized by N2-BET, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The fraction of the mesopore
and the oxygen functional groups on the surface of activated carbon fiber (ACF) increased after the treatment with nitric
acid, which was favorable to improve the catalytic activities of MnO
x
-CeO
x
/ACFN. The experimental results show that the conversion of NO is nearly 100% in the range 100°C-150°C under the optimal preparation
conditions of MnO
x
-CeO
x
/ACFN. In addition, the effects of a series of performance parameters, including initial NH3 concentration, NO concentration and O2 concentration, on the conversion of NO were studied.
__________
Translated from Chemical Industry and Engineering Progress, 2007, 27(1): 87–91 [译自: 化工进展] 相似文献
13.
The effects of regeneration-phase CO and/or H2, and their amounts as a function of temperature on the trapping and reduction of NOX over a model and a commercial NOX storage/reduction catalyst have been evaluated. Overall, for both catalysts, their NOX removal performance improved with each incremental increase in H2 concentration. For the commercial sample, using CO at 200 °C, beyond a small amount added, was found to decrease performance. The addition of H2 to the CO-containing mixtures resulted in improved performance at 200 °C, but the presence of the CO still resulted in decreased performance in comparison to activity when just H2 was used. With the model sample, the presence of CO resulted in very poor performance at 200 °C, even with H2. The data suggest that CO poisons Pt sites, including Pt-catalyzed nitrate decomposition. At 300 °C, H2, CO, and mixtures of the two were comparable for trapping and reduction of NOX, although with the model sample H2 did prove consistently better. With the commercial sample, H2 and CO were again comparable at 500 °C, but mixtures of the two led to slightly improved performance, while yet again H2 and H2-containing mixtures proved better than CO when testing the model sample. NH3 formation was observed under most test conditions used. At 200 °C, NH3 formation increased with each increase in H2, while at 500 °C, the amount of NH3 formed when using the mixtures was higher than that when using either H2 or CO. This coincides with the improved performance observed with the mixtures when testing the commercial. 相似文献
14.
Dekui Sun Qingya Liu Zhenyu Liu Guoqing Gui Zhanggen Huang 《Applied catalysis. B, Environmental》2009,92(3-4):462-467
V2O5/AC has been reported to be active for selective catalytic reduction (SCR) of NO with NH3 at around 200 °C and resistant to SO2 deactivation. To elucidate its SCR mechanism, adsorption and oxidation of NH3 over V2O5/AC are studied in this paper using TG, MS and DRIFTS techniques. It is found that the adsorption and oxidation of NH3 take place mainly at VO bond of V2O5. A higher V2O5 loading results in more NH3 adsorption on the catalyst. V2O5 contains both Brnsted and Lewis acid sites; NH4+ on Brnsted acid sites is less stable and easier to be oxidized than NH3 on Lewis acid sites. Gaseous O2 promotes interaction of NH3 with AC and oxidation of NH3 over V2O5/AC. NH3 is oxidized into NH2 and acylamide structures and then to isocyanate species, which is an intermediate for N2 formation. 相似文献
15.
The present study represents an effort to correlate the dependence of NOx emissions on heat losses to the atmospheric environment in a CH4/air fueled combustor. To this end, the numerical analysis was performed over a wide range of residence times, equivalence ratios and heat losses using a perfectly stirred reactor (PSR) code. The numerical results showed that the calculated NOx concentration initially increased, reached a maximum value and then decreased with increasing residence time when the heat loss was present. The similar variation was observed in changes in the thermal NO concentration that was evaluated by only considering the reactions associated with the thermal (Zeldovich) NO mechanism. With the heat loss increased, the calculated NOx concentration was substantially reduced for all equivalence ratios investigated. In addition, the reductions in the NOx concentration with respect to residence time became faster with increasing the equivalence ratio particularly for fuel rich conditions. The observed variations in the calculated NOx concentration over the residence time (NOx/τ) were found to fit well to the following correlation:ln(NOx/τ)=a(HLI)+b. In the correlation, HLI is the dimensionless heat loss parameter and coefficients a and b are constants expressed as a function of adiabatic flame temperature (for a given equivalence ratio) and equivalence ratio, respectively. 相似文献
16.
Effects of precursors on the surface Mn species and the activities for NO reduction over MnOx/TiO2 catalysts 总被引:1,自引:0,他引:1
Junhua Li Jianjun Chen Rui Ke Chuankui Luo Jiming Hao 《Catalysis communications》2007,8(12):1896-1900
TiO2-supported manganese oxide catalysts were prepared from two different precursors, manganese nitrate (MN) and manganese acetate (MA), and these samples were characterized by BET, XRD, TG/DTA, XPS and FT–IR. The characterization results showed that the MN precursor resulted primarily in MnO2, accompanied with some Mn-nitrate, while the MA precursor caused mainly Mn2O3 species. These two different precursors also led to different surface Mn atom concentrations indicated by XPS and NH3 adsorption. Consequently, the higher low-temperature activity of MnOx/TiO2 from MA precursor was attributed to higher surface Mn concentration and the surface Mn2O3 species. 相似文献
17.
Topics in Catalysis - The influence of the combustion products of different lubrication oil additives and impurities in fuel or urea solution on the activity and selectivity of V2O5/WO3-TiO2... 相似文献
18.
FTIR and pulse thermal analysis were applied to investigate catalysts containing Pt (1 wt%)/Ba (17 wt%) supported on -Al2O3, SiO2 and ZrO2. The aim was to learn how the support material affects the thermal stability of barium carbonate and its activity in the reaction to bulk Ba(NO3)2. The lower thermal stability of BaCO3 in alumina supported samples was found to influence the formation of barium nitrate during the NO
x
storage process. Quantification of Ba(NO3)2 formed during NO
x
storage indicated that for alumina supported catalysts only ca. 30% of barium present in the sample is involved in the storage process. The low thermal stability found for alumina supported barium nitrite excludes its role in the formation of barium nitrate during interaction of NO
x
with the catalyst at 300 °C. The studies indicate that -Al2O3 plays a major role in influencing the thermal stability of BaCO3 and Ba(NO3)2. This finding seems to be relevant for the higher activity of -Al2O3-supported catalysts in NO
x
storage reduction reactions. 相似文献
19.
Pierre H. Ravelonandro Dominique H. Ratianarivo Claire Joannis-Cassan Arsène Isambert Marson Raherimandimby 《Food and Bioproducts Processing》2011,89(3):209-216
Arthrospira (Spirulina) platensis Toliara isolated from alkaline and salt lakes in the south-western area of Madagascar is a potential source of proteins that could efficiently fight against food deficiency in developing countries like Madagascar. Up to now, productivity in this country has been low, so a better understanding of the growth conditions of this species is needed to improve its production. Growth experiments were undertaken in bubble columns at laboratory scale. The influence of agitation of the culture, medium salinity (ranging from 13 to 35 g L−1) and CO2 addition (ranging from 0 to 2%, v/v) on growth and protein content was examined. Because Arthrospira cells are fragile, a bubble column without additional mixing gave the best growth. Arthrospira (Spirulina) platensis showed higher specific growth rate (μmax) and protein content for lower salinity. Addition of 1% of CO2 improved the productivity by near 60%. The feasability of semi-continuous culture was demonstrated and optimal culture conditions led to a mean productivity of 0.22 ± 0.03 g L−1 d−1, a mean specific growth rate of 0.015 ± 0.002 h−1 and a protein content of 53 ± 2% of total dry weight. 相似文献
20.
C.M.L. Scholz K.M. Nauta M.H.J.M. de Croon J.C. Schouten 《Chemical engineering science》2008,63(11):2843-2855
In this paper a global reaction kinetic model is used to understand and describe the NOx storage/reduction process in the presence of CO2 and H2O. Experiments have been performed in a packed bed reactor with a Pt–Ba/γ-Al2O3 powder catalyst (1 wt% Pt and 30 wt% Ba) with different lean/rich cycle timings at different temperatures (200, 250, and ) and using different reductants (H2, CO, and C2H4). Model simulations and experimental results are compared. H2O inhibits the NO oxidation capability of the catalyst and no NO2 formation is observed. The rate of NO storage increases with temperature. The reduction of stored NO with H2 is complete for all investigated temperatures. At temperatures above , the water gas shift (WGS) reaction takes place and H2 acts as reductant instead of CO. At , CO and C2H4 are not able to completely regenerate the catalyst. At the higher temperatures, C2H4 is capable of reducing all the stored NO, although C2H4 poisons the Pt sites by carbon decomposition at . The model adequately describes the NO breakthrough profile during 100 min lean exposure as well as the subsequent release and reduction of the stored NO. Further, the model is capable of simulating transient reactor experiments with 240 s lean and 60 s rich cycle timings. 相似文献