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The storage and reduction of NO x was examined over a series of mechanically mixed LaMn 0.9 Fe 0.1 O 3 (LMF) + Ba/Al 2 O 3 (BA), Pt-LMF + BA and LMF + BA + Pt/Al 2 O 3 (PA) catalysts in order to investigate the function of Pt in plasma-assisted NSR reaction. Efforts were also made to optimize the location of Pt to give the best H 2 reduction ability. [ABSTRACT FROM AUTHOR]

A series of WO 3 -doped Mn–Zr mixed oxide catalysts were investigated for the selective catalytic reduction of NO x by NH 3 (NH 3 –SCR). It was found that the added WO 3 significantly enhanced the catalytic performance of Mn–Zr mixed oxide catalyst for NH 3 –SCR of NO x . In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) studies revealed that the highly dispersed WO 3 not only resulted in more acid sites formed on the catalyst surface, but also inhibited the adsorption of the inactive nitrate specie, leaving more active sites available for the adsorption of NH 3 . In addition, the synergetic effect between W and Mn contributes to improving the redox property of the catalyst. Therefore, the high catalytic deNO x performance was obtained over WO 3 -promoted Mn–Zr mixed oxide catalyst. [ABSTRACT FROM AUTHOR]

We have reported a LaMnO-based, Pt free lean NO trap (LNT) catalyst shows promising NO reduction activities, but the mechanism of NO reduction or the role of the perovskite over this catalyst has not been addressed. This paper presented our investigation on the mechanistic aspects of NO adsorption and reduction over several LaMnO-based LNT catalysts. NO can be effectively oxidized to NO on LaMnO at 350 °C, while little NO (NO + NO) can be stored verified by the following temperature programmed desorption experiment; under the same conditions, a significant amount of NO (41 μmol NO/g washcoat) were stored over BaO/AlO/LaMnO indicating NO are adsorbed mainly on the BaO/AlO. The temperature programmed surface reaction with CO demonstrated that although it can store NO during the lean period, failed to reduce NO by CO over the BaO/AlO/LaMnO catalyst. After adding Pd into BaO/AlO/LaMnO, NO can not only be stored during the lean conditions but also reduced. It could be concluded that the Pd catalyst, not perovskite, is responsible for NO reduction during the rich conditions. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] CeO2-MoO3/TiO2 catalyst is much more active than CeO2/TiO2 for the NH3-SCR. [•] The existed MoO3 can prevent the formation of inactive nitrate species. [•] More Brønsted acid sites formed on the catalyst surface due to the presence of Mo. [•] The activated NH x species react with NO or adsorbed NO2. [ABSTRACT FROM AUTHOR]

This study provides insight into the mechanistic and performance features of the cyclic reduction of NO by CO in the presence and absence of excess water on a Pt-Rh/Ba/AlO NO storage and reduction catalyst. At low temperatures (150-200 °C), CO is ineffective in reducing NO due to self-inhibition while at temperatures exceeding 200 °C, CO effectively reduces NO to main product N (selectivity >70 %) and byproduct NO. The addition of HO at these temperatures has a significant promoting effect on NO conversion while leading to a slight drop in the CO conversion, indicating a more efficient and selective lean reduction process. The appearance of NH as a product is attributed either to isocyanate (NCO) hydrolysis and/or reduction of NO by H formed by the water gas shift chemistry. After the switch from the rich to lean phase, second maxima are observed in the NO and CO concentrations versus time, in addition to the maxima observed during the rich phase. These and other product evolution trends provide evidence for the involvement of NCOs as important intermediates, formed during the CO reduction of NO on the precious metal components, followed by their spillover to the storage component. The reversible storage of the NCOs on the AlO and BaO and their reactivity appears to be an important pathway during cyclic operation on Pt-Rh/Ba/AlO catalyst. In the absence of water the NCOs are not completely reacted away during the rich phase, which leads to their reaction with NO and O upon switching to the subsequent lean phase, as evidenced by the evolution of N, NO and CO. In contrast, negligible product evolution is observed during the lean phase in the presence of water. This is consistent with a rapid hydrolysis of NCOs to NH, which results in a deeper regeneration of the catalyst due in part to the reaction of the NH with stored NO. The data reveal more efficient utilization of CO for reducing NO in the presence of water which further underscores the NCO mechanism. Phenomenological pathways based on the data are proposed that describes the cyclic reduction of NO by CO under dry and wet conditions. [ABSTRACT FROM AUTHOR]

Abstract: Alkaline (earth-) carbonates are applied in NO x storage and reduction catalysts, given their ability to accumulate NO2 in excess oxygen environments, and releasing it under rich-burn conditions. The dependency of their conductivity on the NO x loading state makes them suitable as NO2 sensitive layers and enables the in situ characterization of the status of such catalyst systems. The conductivity of the NO x trap components BaCO3 and K2CO3, with different morphologies, is analyzed in various NO x containing atmospheres by impedance spectroscopy. While the stepwise uptake of NO2 can be detected electrically on both carbonates, only a weak corresponding influence of NO is detected. The increase in the conductivity of the carbonates during NO2 accumulation can be described as a diffusion controlled process with a characteristic nucleation delay in the case of BaCO3. Arrhenius-like plots comparing the conductivities of the carbonates in the unloaded and NO2 saturated states from 250 to 600°C reveal that the conductivity of BaCO3 is more sensitive to NO2 than those of K2CO3/La-Al2O3, but the latter exhibiting about five orders of magnitude higher conductivity. [Copyright &y& Elsevier]

Highlights: [•] A multifunctional catalyst/storage material is prepared to maximize NO removal. [•] The role of the different active sites in the lean/rich cycles is established. [•] The cobalt catalytic function oxidizes the NO to NO2. [•] The basic properties of the Co/Mg/Al mixed oxide are enhanced by doping with Na. [•] The introduction of V enables the reduction of the nitrate decomposition products. [ABSTRACT FROM AUTHOR]

Abstract: Alumina-supported In2O3, Ga2O3 and B2O3 were investigated as catalysts for lean NO x reduction with DME as reducing agent and compared to pure Al2O3 and In2O3. The In2O3-promoted alumina catalysts showed the highest NO x conversion at low temperatures, although with a narrow temperature window. Pure In2O3, on the other hand, was inactive for NO x reduction with DME. The Ga2O3- and B2O3-promoted alumina catalysts gave the highest NO x conversion at higher temperatures, showed a temperature window similar to pure alumina, but were less sensitive to H2O inhibition. Possible reasons for these observations are discussed. [Copyright &y& Elsevier]

Novel Fe–Mn mixed-oxide catalysts were prepared for the low-temperature selective catalytic reduction (SCR) of NOxwith ammonia in the presence of excess oxygen. It was found that Fe(0.4)–MnOxcatalyst showed the highest activity, yielding 98.8% NOxconversion and 100% selectivity of N2at 120 °C at a space velocity of 30 000 h–1. XRD results suggested that a new crystal phase of Fe3Mn3O8was formed in the Fe–MnOxcatalysts. TPR and Raman data showed that there was a strong interaction between the iron oxide and manganese oxide, which is responsible for the formation of the active center―Fe3Mn3O8. Intensive analysis of fresh, used, and regenerated catalysts by XPS revealed that electron transfer between Fen橷 Mnn誉 in Fe3Mn3O8may account for the long lifetime of the Fe(0.4)–MnOxcatalyst. In addition, the SCR activity was suppressed a little in the presence of SO2and H2O, but it was reversible after their removal. [ABSTRACT FROM AUTHOR]

It is shown that palladium-cobalt oxide-cerium catalyst deposited on cordierite catalyzes the reduction of nitrogen(II) oxide with carbon monoxide, and cobalt-iron catalysts in simultaneous reduction of NO + NO with C-C alkanes retained high activity in the presence of water vapor and sulfur dioxide. The Pd-CoO/cordierite catalyst exceeds the Pt-CoO/codierite catalyst in the conversion of NO and CO in the reaction mixture CO + NO + O + HO + SO. Modification of the Pd-CoO/cordierite with cerium oxide considerably increases its sulfur resistance. [ABSTRACT FROM AUTHOR]

A test reactor was designed and built for investigating liquid reducing agents in the selective catalytic reduction (SCR) process in the laboratory. The design of the experimental setup is described in detail and its performance was evaluated. Using a glass nebulizer, liquid reducing agents were sprayed directly onto a catalyst positioned in a heated glass reactor with a length of 250 mm and an internal diameter of 20.4 mm or 40 mm. Model exhaust gases were mixed from individual gas components and were heated up to 450 °C in a heat exchanger before entering the reactor. The off-gas was analyzed using two complimentary techniques, a multi-component online FTIR gas analysis and a liquid quench gas absorption setup, to detect higher molecular compounds and aerosols. Due to the versatility of construction, processes not related to SCR, but involving three-phase reactions with gases, liquids and a catalyst, can also be investigated. [ABSTRACT FROM AUTHOR]

Abstract: Platinum plays an important, multi-functional role during NOx storage and reduction (NSR). Understanding and predicting the effect of Pt loading is essential to optimize the lean NOx trap. In this study, a microkinetic model is developed for NOx storage on a series of Pt/BaO/Al2O3 catalysts with a range of Pt loadings (0–3.7wt.%). A classification of the Ba sites into two storage site populations, proximal and non-proximal (bulk), is presented. A simple model for estimating the capacities of the two Ba site populations using the Pt loading is used to explain trends in the storage of NO/O2 and NO2/O2. The model integrates existing literature models for NO2 storage on BaO/Al2O3, Pt-catalyzed NO oxidation to NO2, and spillover chemistry involving NO2. Wherever possible, simplifications in the model are made based on sensitivity analyses. Literature estimates of kinetic parameters are adjusted if estimates of spillover rate constants are not sufficient to predict the storage data. The dual-site model comprises proximal storage sites that participate in the spillover chemistry and non-proximal sites that involve NO2 that is generated by the Pt-catalyzed NO oxidation. The model shows reasonable agreement with the measured storage of NO and NO2 in O2 at 340°C for a range of storage times and Pt loading. The model helps to elucidate the storage dynamics and the roles of Pt and should be useful for incorporation into a complete NOx storage and reduction model. Some further refinements to the model are discussed. [Copyright &y& Elsevier]

Abstract: The behaviour of a perovskite SrTiCuO3 as NSR catalyst has been studied by simultaneous DRIFTS and activity measurement. The amount of NOx stored on the perovskite SrTiCuO3 (41μmol/m2 at 300°C) is much higher, when compared on a surface area basis, than on noble metal-containing reference catalysts (0.3–23μmol/m2). The perovskite SrTiCuO3 is able to perform both the NO oxidation to NO2 and the NOx storage, and copper enhances both the NO oxidation and NOx chemisorption capacities of copper-free SrTiO3 perovskite. During NOx chemisorption on SrTiCuO3, the following process have been identified (i) NO chemisorption and nitrite formation or NO oxidation to gas phase NO2 and further chemisorption of NO2 with nitrites or nitrates formation, (ii) nitrite oxidation to nitro and/or nitrates, and (iii) nitro and/or nitrate decomposition with release of NO2. NOx chemisorption at 300°C is more effective than chemisorption at 350°C, while regeneration at 350°C is more effective than regeneration at 300°C because: (i) decreased NOx slip (only for CO regeneration) and (ii) maintains the same chemisorption capacity of the perovskite after regeneration. H2 is a better reductant than CO, and the differences between both reducing gases are much higher at 300°C than at 350°C. [Copyright &y& Elsevier]

This work tried to identify the relationship between the internals of selective catalytic reduction (SCR) system and mixing performance for controlling ammonia (NH3) slip. In the SCR flow section, arranging the flow-guided internals can improve the uniformity of velocity distribution but is unfavorable for the uniformity of NH3 concentration distribution, The ammonia injection grids (AIG) with four kinds of nozzle diameters (i.e., 1.0 mm, 1.5 mm, 2.0 mm, and mixed diameters) were investigated, and it was found that the AIG with mixed nozzle diameters in which A3, A4, B3, and B4 nozzles' diameters are 1.0 mm and other nozzles' diameters are 1.5 mm is the most favorable for the umformity of NH3 concentration distribution. In the SCR reactor section, the appropriate space length between two catalyst layers, which serves as gas mixing in order to prevent maldistribution of gas concentrations into the second catalyst layer, under the investigated conditions is about 100, 1000, and 12 mm for honeycomb-like cordierite catalyst, plate-type catalysts with parallel channel arrangement, and with cross channel arrangement, respectively. Therefore, the cross channel arrangement is superior to the parallel channel arrangement in saving the SCR reactor volume. [ABSTRACT FROM AUTHOR]

Abstract: In order to elucidate the effect of washcoat composition on lean NO x trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that in all cases aging resulted in deterioration of the NO x conversion as a consequence of impaired NO x storage and NO x reduction functions, while increased selectivity to NH3 was observed in the temperature range 250–450°C. Elemental analysis, H2 chemisorption and TEM data revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the catalysts, associated with the Ba phase, decreased catalyst NO x storage capacity. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NO x spillover from Pt to Ba during NO x adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NO x spillover during catalyst regeneration. For the aged catalysts, halving the Pt loading from 100 to 50g/ft3 was found to result in a significant decrease in overall NO x conversion, while for catalysts with the same 100g/ft3 Pt loading, increasing the relative amount of Pt on the NO x storage components (BaO and La-stabilized CeO2), as opposed to an Al2O3 support material (where it was co-located with Rh), was found to be beneficial. The effect of Rh loading on aged catalyst performance was found to be marginal within the range studied (10–20g/ft3), as was the effect of BaO loading in the range 30–45g/L. [Copyright &y& Elsevier]

Abstract: A dual catalyst system for the Selective Catalytic Reduction of NO x with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NO x emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NO x reduction activity in comparison with Pt/Al2O3, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H2SO4 and HNO3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NO x reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase. [ABSTRACT FROM AUTHOR]

The effects of structural and geometrical characteristics of wash-coated monolith catalysts on the NO-NO2/NH3selective catalytic reduction (SCR) activity were experimentally investigated over the same Cu-exchanged zeolite system coated onto honeycomb cordierite substrates with different cell densities, lengths, washcoat loads, and channel shapes. A stacked configuration was also tested. Contrary to previous reports, it was found that both interphase and intraphase diffusional limitations appreciably affected the deNOxefficiency at intermediate to high temperatures, whereas entrance effects did not play a noticeable role in enhancing the NOxconversion. A two-phase 1D dynamic mathematical model of SCR monolithic converters, which explicitly accounts for both gas/solid and intraporous mass-transfer resistances, successfully predicted all of the observed effects using a single set of rate parameters estimated from intrinsic kinetic runs performed over the same catalyst in powdered form, under diffusion-free conditions. [ABSTRACT FROM AUTHOR]

Abstract: Al species can be introduced to the framework of Si-MCM-41 support by isomorphous substitution or wet impregnation and Brønsted acid sites can be created in Al-MCM-41. Pt catalysts supported on Si-MCM-41 and Al-MCM-41 are studied for the selective catalytic reduction of NO by hydrogen in excess oxygen. The introduction of Al species to MCM-41 at suitable Si/Al ratio shows great promotion effect on H2-SCR over Pt/MCM-41. Pt catalyst supported on Al-MCM-41 prepared by isomorphous substitution with the Si/Al ratio of 10 exhibits the best catalytic performance and ca. 80% NO x conversion as well as ca. 85% N2 selectivity can be achieved at 140°C at high GHSV of 80,000h−1. The H2-SCR reaction over Pt/Al-MCM-41, together with Pt/Si-MCM-41, are investigated by means of in situ DRIFT spectra and the existence of Brønsted acid sites in Al-MCM-41 is found to play a decisive role on the H2-SCR reaction pathway. [ABSTRACT FROM AUTHOR]

Abstract: The mass transfer of wire mesh honeycomb is investigated, and a new correlation Sh =1.108 Re 0.5 Sc 1/3 is proposed based on data for the mass transfer limited performance for selective catalytic reduction of NO x by NH3 over wire mesh honeycomb catalysts. The numerical model is developed to evaluate the performance of wire mesh honeycomb, which is verified by the experiments. By measuring the NO x conversion over wire mesh honeycomb catalysts with different washcoat thickness and cell density, the intraporous diffusion and interphase diffusion are studied. The pressure drop of wire mesh honeycomb is low. Compared to ceramic monolith, wire mesh honeycomb catalysts possess high catalyst utilization relative to the geometric surface area and the catalyst weight. [ABSTRACT FROM AUTHOR]

The nature of stored NOx and mechanistic aspects of the reduction of NOx stored over a model Pt—K/Al2O3 catalyst sample are investigated in this paper, and a comparison with a model Pt—Ba/Al2O3 catalyst is also made.It is found that at 350 °C on both the catalysts the storage proceeds with the initial formation of nitrites, followed by the oxidation of nitrites to nitrates. A parallel pathway involving the direct formation of nitrates species is also apparent; at saturation, only nitrates are present on the catalyst surface over both Pt—K/Al2O3 and Pt—Ba/Al2O3. However, whereas bidentate nitrates are present in remarkable amounts on Pt—K/Al2O3, along with ionic nitrates, only very small amounts of bidentate nitrates were observed on Pt—Ba/Al2O3.Under nearly isothermal conditions, the reduction of the stored NOx with H2 occurs via an in series two-steps Pt-catalysed molecular process involving the formation of ammonia as an intermediate, like for the Pt—Ba/Al2O3 catalyst sample. However, higher N2 selectivity is observed in the case of the Pt—K/Al2O3 catalyst due to the similar reactivity of the H2 + nitrate and NH3 + nitrate reactions. Accordingly ammonia, once formed, readily reacts with surface nitrates to give N2, and this drives the selectivity of the reduction process to N2. Notably, a strong inhibition of H2 on the reactivity of NH3 towards nitrates is also pointed out, due to a competition of H2 and NH3 for the activation at the Pt sites. Finally, the effect of water and CO2 on the reduction process is also addressed. Water shows a slight promotion effect on the reduction of the nitrates by H2, and no significant effect on the reduction by ammonia, whereas CO2 has a strong inhibition effect due to poisoning of Pt by CO formed upon CO2 hydrogenation. [Copyright &y& Elsevier]

Abstract: Selective catalytic reduction of NOx with propene has been investigated over SnO2/Al2O3 catalysts prepared by impregnation and single step sol–gel methods. Catalyst preparation method exerts significant influence on the catalytic performance, and SnO2/Al2O3 prepared by the sol–gel method is more active than the impregnated catalyst. Moreover, its resistance against water is higher. The high surface area and the strong interaction between SnO2 and Al2O3 may be responsible for the high reduction activity of sol–gel SnO2/Al2O3 catalyst. The presence of oxygen strongly favours the NOx reduction process. FT-IR results have revealed that the role of oxygen is to contribute to the formation of formate, acetate and nitrate species, all of which are reactive intermediates for NOx reduction. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of a model PtBa/Al2O3 model NSR catalyst in both the NO x storage/reduction and soot oxidation is investigated in this work. It is found that the presence of soot negatively influences the NO x storage capacity of the catalyst, evaluated at 623K in presence of water and CO2 in the feed stream: in fact the amounts of NO x stored in presence of soot decrease by nearly 30% in the presence of roughly 10% (w/w) of soot. The presence of soot has a destabilizing effect on the NO x adsorbed species, which decompose to a large extent in the absence of gas phase NO and oxygen. This has also been confirmed by dedicated TPD and TPO experiments. However the presence of soot does not appreciably affect the behavior of the PtBa/Al2O3 catalyst in the reduction by H2 of the stored nitrates, being in all cases N2 the major reaction product along with minor amounts of ammonia. During the storage of NO x , soot oxidation takes place. Notably, the stored NO x participate in the soot oxidation upon release of NO2 and O2 which actively oxidize soot. However a direct participation of the adsorbed NO x species in the oxidation of soot cannot be excluded. [ABSTRACT FROM AUTHOR]

The present paper describes a novel, fully integrated after-treatment system based on the use of hydrogen for de-NOxpurposes, designed for light-duty diesel engine applications. Hydrogen is generated by an autothermal reformer, placed as a bypass unit of the close-coupled DOC and DPF, and it promotes an NOxreduction in a specific catalytic converter in the under-floor position. The results of the tests on commercial reforming catalysts and on H2-selected catalytic reductions (SCR) perovskite catalysts that were synthesized by our group are presented. The best catalyst, on the basis of TPRe activity tests, was La0.8Sr0.2Fe0.9Pd0.1O3. At a lab-scale, the fuel penalty of the system is around 4% for an NOxto N2conversion of 60%, under the best operating conditions. T50is very low (150 °C) compared to other de-NOxstrategies. The system was then integrated on board a vehicle, and several testing protocols were performed (NEDC2000 cycle, stationary driving conditions on the roller test bench, and real driving conditions on the road). It has been demonstrated that the system is able to work independently in many driving conditions and that the reforming reaction can be effectively controlled and maintained. The NOxemissions were kept below Euro 6 levels, even though undesired CO and HC secondary emissions were produced. This performance was reached with a fuel penalty of 10%. Although this value is presently too high to envisage direct application on the market, it has been demonstrated that this technology is already fully functional on board a real vehicle, which encourages further refining research activity. [ABSTRACT FROM AUTHOR]

This study gives an overview of zeolites used for hydrocarbon trapping, selective catalytic reduction of nitrogen oxides (NO) with NH (NH-SCR) and hydrocarbon NO reduction applications. We also discuss challenges for the use of zeolites in these applications and the material properties that require improvement. [ABSTRACT FROM AUTHOR]

Abstract: Zeolites In,H-ZSM-5 (Si/Al=29.7, 1.7wt% In) and In,H-mordenite (In,H-M, Si/Al=6.7, 3.5 wt% In) were prepared by reductive solid state ion exchange (RSSIE) method and studied in the selective catalytic reduction of NO (NO-SCR) by methane. The results suggested that the methane oxidation reactions proceed by redox type mechanisms over In+/InO+ sites. The NO reduction selectivity was shown to be related to the relative rates of In+ oxidation by NO and O2. Regarding the relative rates, the In+ density of the zeolite was the most important. Above about 673K the In,H-ZSM-5 (T-atom/In=102) had higher NO reduction selectivity than the In,H-mordenite (T-atom/In=46). The operando DRIFTS examinations suggested that NO+ and NO3 − surface species were formed simultaneously on InO+Z− sites, and were consumed together in the NO-SCR reaction with methane. The reduction of the NO3 − by methane gave an activated N-containing intermediate, which further reacted with the NO+ species to give N2. The NO-SCR properties could be significantly improved by adding small amount of Pd to the In,H-zeolite catalyst. The promoting effect of Pd was interpreted as a concerted action of InO+ and the Pd n+ sites. The interplay between these sites is twofold: the Pd speeds up the equilibration of the NO/O2 mixture, thereby, increases the formation rate and the steady state concentration of the activated nitrate species, whereas the In+/InO+ sites prevent the transformation of Pd-nitrosyls to less reactive isocyanate and nitrile species. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study of Pt/Ba/Al2O3, Co/Ba/Al2O3, Pt/Co/Al2O3 and Pt/Co/Ba/Al2O3 was performed in regards to their NO x storage capacities and NO oxidation abilities as a function of temperature. The nitrate stability and dynamic behaviors of NO x storage reduction during lean/rich fuel cycles using hydrogen as a reductant were also investigated over these catalysts. It was found that Pt/Co/Ba/Al2O3 possessed the largest NO x storage capacity within the temperature range of 200–350°C. The existence of Co not only improved the oxidation of NO to NO2 under lean conditions, but also enhanced the release and reduction of NO x during the rich phase. The Pt and Co co-supported catalysts showed better NO x storage reduction activity and higher N2 selectivity than Pt supported Ba/Al2O3 catalysts within the tested temperature range. As for Pt/Co/Ba/Al2O3, high conversion was obtained at either a low reductant concentration with long duration time or a high reductant concentration with short duration time during the rich phase. In situ FTIR studies showed that NO x adsorption over Co-containing catalysts takes “nitrite route” as an important pathway. The intimate contact of Co and Ba/Al could accelerate nitrite/nitrate formation and the synergistic effect of Pt and Co could accelerate NO x reduction. [ABSTRACT FROM AUTHOR]

Abstract: The effects of different regeneration times, but with a constant total amount of reductant delivered, were investigated over a model NO X storage and reduction (NSR) catalyst. The different regeneration times were 4, 8 and 16s with 4, 2, and 1% H2 as the reductant amounts, respectively. The lean time was kept the same during these experiments, resulting in a constant inlet NO X -to-reductant amount in the cycles. Overall, the results show clear improvements with longer regeneration times in both NO X trapping and overall reduction performance at all temperatures except 500°C. At 500°C, there was still an increase in trapping performance with longer regeneration time, but a more significant increased NO X release coincident with a small increase in the trapping performance resulted in an overall decrease in NO X conversion with increasing regeneration time. The data demonstrate that the different concentrations of H2 did not lead to different regeneration extents, but that the main factor for the improved performance was the regeneration time itself. With longer regeneration times, more nitrate/nitrite decomposition occurred, thereby leading to more extensive surface cleaning. [Copyright &y& Elsevier]

Abstract: Selective catalytic reduction (SCR) of NO from simulated flue gas by ammonia with Fe2O3 particles as the catalyst was performed using a magnetically fluidized bed (MFB). X-ray diffraction (XRD) spectroscopy and Brunauer–Emmett–Teller (BET) method were used to analyze Fe2O3 catalyst. Important effects of magnetic fields were observed in the SCR of NO by ammonia over Fe2O3 catalyst. The apparent activation energies of SCR were reduced by external magnetic fields, and the SCR activity of Fe2O3 catalyst was improved with the magnetic fields at low temperatures. Thus the scope of temperature with high efficiency of NO removal was extended from 493–523 K to 453–523 K by magnetic fields. Magnetic fields of 0.01–0.015 T were suggested for NO removal on Fe2O3 catalyst with MFB. The results suggested that the magnetoadsorption of NO onto Fe2O3 surface together with NH2 and NO free radicals effects induced by the external magnetic fields both acted to improve the rate of SCR of NO on Fe2O3 catalyst. On the other hand, magnetic field effects were also attributed to improved gas–solid contact in MFB. [Copyright &y& Elsevier]

Abstract: In this work, we simulated the whole processes of plasma-enhanced selective catalytic reduction for nitrogen oxides removal with hydrocarbon additive. The simulation model consists of plasma simulation and catalysis simulation. First, single filamentary microdischarge in dielectric barrier discharge was calculated to evaluate the radical production yield as a function of specific input energy. Second, the chemical reaction process in the discharge reactor was simulated to find the gas reforming property by the plasma. This plasma simulation was applied to NO oxidation process in atmospheric pressure N2/O2/NO/C3H6 mixtures under various discharge conditions. Finally, the catalytic reaction process was modeled using simple mass balance equations in gas-phase and on catalyst surface. The catalytic reaction simulation was tested for the reduction of nitrogen oxides on γ-Al2 O 3 catalyst in N2/O2/NO/C3H6 and in N2/O2/NO2/C3H6. [Copyright &y& Elsevier]

Abstract: A nanocomposite of Al2O3 and ZrO2–TiO2 solid solution (AZT) was synthesized for NO x storage-reduction (NSR) catalysts Pt/Rh/Ba/K/AZT, and the effect of calcination temperature on thermal stability was investigated. The catalyst containing AZT calcined at 1073K (AZT catalyst) had a high NO x storage capacity after thermal aging. This enhanced storage capacity was attributed to the fact that ZrO2–TiO2 solid solution (ZT) was crystallized and stabilized. The solid-state reaction of potassium, which was added as a NO x storage material, was inhibited in the AZT catalyst, relative to those containing AZT calcined at a low temperature. The AZT catalyst also showed excellent NO x storage performance after sulfur aging at 973K or higher, compared with the catalyst containing physically mixed Al2O3 and ZT (physically mixed catalyst). Furthermore, AZT catalysts inhibited the solid phase reaction of potassium with support materials and kept a high ratio of active potassium, which can store NO x . Further, because the barium in the AZT catalyst prevented sulfur poisoning, the ratio of active barium in the AZT catalyst was also larger than that in the physically mixed catalyst, probably because of the low basicity and high Pt dispersion of AZT. [Copyright &y& Elsevier]

Abstract: The effect of axial length on the NO x reduction performance of two different commercial Lean NO x Trap (LNT) monolithic catalysts was experimentally investigated in a bench flow reactor. The washcoat composition of one of the catalysts consisted of Pt and K on γ-Al2O3; whereas the other catalyst contained a complex mixture of Pt, Pd, Rh, Ba, Ce, Zr, Mg, Al and others. The NO x removal characteristics of cylindrical monolith segments of constant diameter (2.22cm) and axial lengths of 2.54, 5.08 and 7.62cm were evaluated using a simulated lean engine exhaust containing water and carbon dioxide at a constant space velocity of 30,000h−1. No significant effects of length were observed when the catalysts were fully reduced with hydrogen between NO x capture phases. However when the catalysts were only partially regenerated NO x reduction efficiency increased with monolith length. Intra-catalyst H2 measurements at different axial locations indicated that at least some of the efficiency loss during partial regeneration occurred when back-mixed H2 was directly oxidized and became unavailable for nitrate reduction. [Copyright &y& Elsevier]

Abstract: The preparation procedure of a structured NO x storage/reduction catalyst is investigated by optimizing washcoating of ceramic monoliths and subsequent incorporation of Pt and Ba as the active phases. Endurance and firm adherence of the alumina washcoat to the substrate has been achieved. Incorporation of platinum from Pt(NH3)4(NO3)2 has been studied by impregnation (filling the monolith channels) and adsorption from solution (ion exchange). Highly dispersed and well distributed platinum were obtained by the adsorption procedure at pH 11–12 and calcination temperature no higher than 450–500°C. Barium was incorporated by dry or wet impregnation. The dry impregnation procedure led to a more homogeneous barium distribution on the surface of washcoat. The sample prepared by adsorption from solution and dry impregnation, for incorporation of Pt and Ba respectively, showed the best storage capacity, ca. around 2.1μmol NO x per mg of BaO for a feedstream with 380ppm NO and 6% O2 in nitrogen, and a space velocity of 32,100h−1, and also complete release and reduction of the stored NO x when oxygen was shifted to 2.3% H2. Thus, a relation between good NO x storage behavior and Pt dispersion and Pt-Ba distribution, and the preparation procedure has been established. [Copyright &y& Elsevier]

Iron-containing zeolites are known to be promising catalysts for the NH3-SCR reaction. Here, we will investigate the catalytic activity of iron-based BEA catalysts, which was found to exhibit improved activities compared to previously described iron-containing zeolite catalysts, such as ZSM-5 and ZSM-12. Series of Fe-BEA zeolite catalysts were prepared using a range of different preparation methods. Furthermore, we found that an iron concentration around 3 wt% on BEA showed a small optimum in SCR activity compared to the other iron loadings studied. [ABSTRACT FROM AUTHOR]

Iron-containing zeolites are known to be promising catalysts for the NH3-SCR reaction. Here, we will investigate the catalytic activity of iron-based BEA catalysts, which was found to exhibit improved activities compared to previously described iron-containing zeolite catalysts, such as ZSM-5 and ZSM-12. Series of Fe-BEA zeolite catalysts were prepared using a range of different preparation methods. Furthermore, we found that an iron concentration around 3 wt% on BEA showed a small optimum in SCR activity compared to the other iron loadings studied. [ABSTRACT FROM AUTHOR]

Abstract: Surface dynamics of nitrates on NOx storage–reduction (NSR) catalysts are examined by means of in situ FT/IR. In the initial state of NOx storage, both nitrite and nitrates are formed on Pt–Ba/Al2O3 surface, and then nitrite become abundant with the increase of storage time. The initial rate of nitrate storage is faster in a flow of NO/O2 mixture than in a flow of NO2 without O2. The presence of oxygen is found to be essential for the conversion of surface nitrite to nitrates. The rate and amount of nitrate formation are strongly affected by type of supports. The storage ability is in the order of MgO>Al2O3 >ZrO2 >SiO2, which is in accordance with that of basicity of the supports. On the other hand, the rate of nitrate reduction by H2 is in the different order: Al2O3 >ZrO2 >SiO2 >MgO. The strong contribution of acid–base property of supports as a controlling factor is suggested. [Copyright &y& Elsevier]

The selective catalytic reduction by NH3 of NO (“standard SCR”) and NO/NO2 mixtures (“fast SCR”) were compared over Fe-ZSM-5 catalysts of different Fe content ranging from 0.2 to 5 wt%. The Fe site structure was monitored by UV–vis spectroscopy. From the response of the reaction rates to the variation of the site structure, it was concluded that standard and fast SCR require different Fe sites; standard SCR proceeds both on isolated and oligomeric Fe oxo sites, whereas a small concentration of isolated Fe sites is sufficient to sustain the high reaction rates of fast SCR, with no discernible contribution of different sites. The response of both reactions to hydrothermal stress (with or without SO2 present) differs; strong deactivation in standard SCR accompanied by increasing NH3 oxidation activity being opposed to stable activity in fast SCR, suggesting that those isolated sites, which are responsible for fast SCR are very resistive toward clustering under the conditions of automobile exhaust catalysts. The potential of preparation procedures to improve the activity by increasing the Fe content is very different. The best performance was achieved using solid-state ion exchange with FeCl3, with NO x conversions >90% between 473 and 773 K obtained over the best catalyst. But if a concomitant increase of the aggregated site abundance cannot be avoided, then NH3 oxidation will effectively compete with fast SCR already at relatively low temperatures. The role of free NO2 in the reaction mechanism of standard SCR was assessed by comparing the SCR reaction rate with that of NO oxidation for all catalysts used. NO oxidation was significantly slower than NO reduction in all cases, which excludes free NO2 produced by NO oxidation as an intermediate of the standard SCR reaction. [Copyright &y& Elsevier]

In this paper, we report a novel electrochemically assisted NO x storage/reduction catalyst (Pt–KβAl2O3) that can operate over a range of reaction conditions for the effective removal of NO x . Under negative polarization, NO x was stored on the catalyst surface in form of potassium nitrates. Under positive polarization, the catalyst was regenerated, and the stored nitrates were efficiently desorbed and reduced to N2. The variation of the current under the applied polarizations allowed monitoring the progress of both the storing and the regeneration phases, and thus optimisation of the duration of both sequences in a technically feasible manner. In addition, the possibility of electrochemical regeneration of the catalyst surface allowed work under a fixed lean gas composition, which implies an important technological advance for the NSR process. The electrochemically assisted NO x storage/reduction experiments were supported by NO x -TPD and cyclic voltammetry measurements, which also revealed useful information about the chemisorption properties of the electrochemical catalyst. [Copyright &y& Elsevier]

Abstract: The kinetics of the selective catalytic reduction of NO in the presence of vanadium loaded carbon-based catalysts has been studied, by means of different techniques, such as transient response analysis, temperature programmed desorption and DRIFT spectrometry. The results point out to a reaction mechanism involving adsorbed species of ammonia, which react with the NO from the gas phase. The role of oxygen will be the regeneration of the spent catalytic sites. Finally, the Mars van Krevelen kinetic model was successfully used to fit the experimental data. [Copyright &y& Elsevier]

Abstract: Experimental results describing the product distribution during the reduction of NO by H2 on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts are presented in the temperature range 30–500°C and H2/NO feed ratio range of 0.9–2.5. A microkinetic model that describes the kinetics of NO reduction by H2 on Pt/Al2O3 is proposed and most of the kinetic parameters are estimated from either literature data or from thermodynamic constraints. The microkinetic model is combined with the short monolith flow model to simulate the conversions and selectivities corresponding to the experimental conditions. The predicted trends are in excellent qualitative and reasonable quantitative agreement with the experimental results. Both the model and the experiments show that N2O formation is favored at low temperatures and low H2/NO feed ratios, N2 selectivity increases monotonically with temperature for H2/NO feed ratios of 1.2 or less but goes through a maximum at intermediate temperatures (around 100°C) for H2/NO feed ratios 1.5 or higher. Ammonia formation is favored for H2/NO feed ratios of 1.5 or higher and intermediate temperatures (100–350°C) buts starts to decompose at a temperature of 400°C or higher. The microkinetic model is used to determine the surface coverages and explain the trends in the experimentally observed selectivities. [Copyright &y& Elsevier]

In order to improve the catalytic performance of supported-Ir catalysts for the selective reduction of NO with CO, the effect of H2 was investigated. While adding H2 showed no or negative effect on NO conversion on Ir/SiO2, Ba/Ir/SiO2 and Ir/WO3/SiO2 catalysts, the activity of Ba-doped Ir/WO3/SiO2 catalyst for NO reduction was significantly increased by H2 addition. The role of H2 was found to stabilize the catalytically active Ir-WO x sites during the reaction. [ABSTRACT FROM AUTHOR]

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 catalysts in the selective catalytic reduction (SCR) of nitrogen oxides by ammonia was investigated. Focusing on the deactivation by calcium, phosphate, and potassium, the DeNO x activity followed the order K ? Ca >PO4. This trend was investigated on the structural level of the catalyst by means of temperature programmed desorption of ammonia (NH3-TPD) and a DRIFT characterization of the adsorbed ammonia species. The results suggest that the studied elements strongly reduce the acidity of the SCR catalyst in the order K ? Ca >PO4 by mainly affecting the Brønsted acidity of the surface. [ABSTRACT FROM AUTHOR]

A Pd catalyst is particularly effective for the oxidation of CO and C3H6 at low temperatures, while the Pt/Rh/Ce catalyst is active for NO reduction. The TWC activity of both catalysts generally decreased as the catalyst mileage increased. However, the NO reduction activity was less affected by catalyst aging compared to the oxidation reactions. The selectivity of the catalysts in favor of the CO–O2 reaction (vs. C3H6–O2 reaction) in the O2 partitioning experiments became less pronounced as the catalyst aged. The NO partitioning experiments reveal the superior capability of H2 in NO reduction to the other reductants (CO and C3H6) examined in the present study. The reactivities of NO with both H2 and CO were found to decrease upon catalyst aging, resulting in decreased overall NO removal activity. [ABSTRACT FROM AUTHOR]

In order to elucidate the effect of support in the catalytic performance, two selected potassium-promoted catalysts (K1Cu/beta and KCu2/Al2O3) were tested for the simultaneous NO x /soot removal from a simulated diesel exhaust. For comparative purpose, the behaviour of a platinum catalyst (Pt/beta) was also studied. Isothermal experiments revealed that the potassium-promoted catalysts show a high activity for NO x /soot removal in the 350–450 °C temperature range. In addition, the catalysts present the advantage that the main reaction products are N2 and CO2. Among the catalysts tested, KCu2/Al2O3 presents the best global performance at 450 °C: the highest soot consumption rate, even higher than the platinum catalysts, and a high NO x reduction. [ABSTRACT FROM AUTHOR]

Isothermal storage of NO2 and subsequent reduction with different reducing agents (H2, CO or H2 + CO) in a lean NO x trap catalyst was tested by Temperature Programmed Desorption (TPD) and Temperature Programmed Reduction (TPR) experiments at temperatures representative of automotive “cold-start” conditions (<200 °C) using a commercial NO x trap catalyst. Results from the TPR experiments revealed that no reduction of stored NO2 to N2 was observed at 100–180 °C, and at 200 °C 10% reduction only of NO2 to N2 was measured. A special affinity of H2 to form NH3 was observed during the reduction of stored NO2. The formation of NH3 increases with increasing amount of stored NO2 and decreases with increasing storage temperature. Direct relation exists between the amount of adsorbed and/or stored NO2 and the formation of H2O and NH3. [ABSTRACT FROM AUTHOR]

Abstract: A series of Pt–Ba/MO2 (MO2 =CeO2, SiO2, ZrO2) catalysts, containing 1wt.% Pt and different Ba-loadings (4.5–28wt.%), was investigated concerning NO x storage and reduction of the stored NO x species by propene using pulse thermal analysis combined with mass spectrometry and temperature-programmed reaction-desorption (TPRD). Well-characterized standard Pt/Al2O3 and Pt–Ba/Al2O3 catalysts were used as references. Exposure of the catalysts to NO/O2 pulses showed that the NO x storage capacity of the Ba-free as well as Ba-loaded catalysts was strongly affected by the nature of the support. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption on the Ba-free catalysts revealed that the distribution of CO chemisorbing sites also depends on the nature of the support. Among the Ba-free catalysts Pt/CeO2 exhibited the highest NO x uptake. No NO x uptake was observed with Pt/SiO2. With all supports the NO x storage capacity increased with the Ba-loading, but differently depending on the support. TPRD of catalysts after exposure to NO x pulses revealed that the thermal stability of the stored NO x species is affected by the nature of the support and the Ba-loading. Up to ca. 10wt.% of Ba, Pt–Ba/CeO2 showed the highest NO x uptake, whereas at the highest Ba-loading (28wt.%) Pt–Ba/Al2O3 and Pt–Ba/ZrO2 afforded highest NO x storage. The NO x storage capacity depended strongly on the relative abundance of the differently stable BaCO3 phases. To test the storage-reduction behavior, the catalysts were subjected to alternating pulses of NO/O2 and propene at 300°C. Depending on the support different reduction behavior was observed. While reduction occurred rapidly on Pt–Ba(16.7)/Al2O3 and Pt–Ba(16.7)/CeO2, it was relatively slow and incomplete on Pt–Ba(16.7)/ZrO2. This behavior was attributed to the low surface area of the ZrO2 support which at higher Ba-loading seems to result in partial blocking of active Pt sites. [Copyright &y& Elsevier]

Concerns about emissions of carbon dioxide have created a need to develop more fuel-efficient vehicles. Diesel engines are generally more efficient than gasoline engines but improvements in the latter can be achieved by operating under lean-burn conditions. With both diesel and lean-burn gasoline engines, the nitrogen oxides are emissted under oxidising conditions. It is scientifically very challenging to reduce nitrogen oxides under oxidising conditions. After a short survey of conventional three-way catalysts, and the associated fundamental aspects of NOx reduction under stoichoimetric conditions, this review focuses on the knowledge and know-how that has been developed for lean engine emission control. Early research on hydrocarbon selective catalytic reduction on zeolite, oxide, and metal-based systems is examined, and some of the key mechanistic models are described. Since none of these systems are of sufficient activity and stability to satisfy current legislation attention has turned to NOx storage and reduction systems. The basic principles of these are described, and the present state of knowledge regarding the mechanisms of storage and regeneration are discussed. The many apparent discrepancies are highlighted and an attempt is made to rationalise the current state of knowledge by taking into account the varying experimental conditions reported nit he literature. For diesel engines, NOx storage and reduction is not an ideal solution and so the final section of this review is concerned with silver-based catalysts and especially with the dramatic effect of small amounts of hydrogen on the efficiency of these catalysts for hydrocarbons selective catalytic reduction. [ABSTRACT FROM AUTHOR]

Isothermal storage and reduction of NO2 with CO, C3H6 and H2 as reducing agents on a lean NOx adsorber was investigated by temperature programmed desorption (TPD) and temperature programmed reduction (TPR) studies. The reduction of NOx was clearly favoured with H2 as reducing agent. Carbon monoxide and C3H6 showed fairly low reduction of NOx. The NOx reduction at low temperatures with H2 as reducing agent was found to be effective, clearly much more effective than for CO. [ABSTRACT FROM AUTHOR]

The H2/NO/O2 reaction under lean-burn conditions has been studied by means of in situ DRIFTS, reactor measurements and temperature-programmed desorption with the aim of understanding the very different behavior of Pd/TiO2 and Pd/Al2O3 catalysts. The former deliver very high NOx conversions (70-80%) with good N2 selectivity whereas the latter show very low activity. In addition, PdTiO2 exhibits two distinct NOx reduction pathways, thus greatly extending the useful temperature range. It is shown that the PdTiO2 low-temperature channel involves adsorption and subsequent dissociation of NO on reduced (Pd0) metal sites. The low activity of PdAl2O3 is a consequence of palladium remaining in an oxidized state under reaction conditions. The high-temperature NO reduction channel found with PdTiO2 is associated with the generation and subsequent reaction of NHx species. [ABSTRACT FROM AUTHOR]

Sn0.5Ti0.5O2 shows excellent catalytic performance both for the CO-SO2 reaction and the CO-SO2-NO reaction. At 350 ° C, 525 ppm SO2/520 ppm NO/2085 ppm CO, SV = 3000 h-1, the conversion of SO2 is nearly complete in the CO-SO2 reaction and above 89% in the CO-SO2-NO reaction; NO conversion is above 98% in the latter reaction. The selectivities of S and N2 are both close to 100%. SO2 shows a significant promoting effect on the activity of the Sn0.5Ti0.5O2 catalyst for NO reduction by CO. Combining transient response experiments, catalytic tests and TPD results, we propose a SO2-assisted NO-CO reaction concept. The existence of a surface sulfur species, which was formed during the CO-SO2 or CO-SO2-NO reaction, is proved by XPS analysis. It is the active site for NO reduction in the CO-SO2-NO reaction, and through which SO2 accomplishes its promoter role. On the basis of the results obtained, the SO2-assisted redox mechanism of simultaneous reduction of SO2 and NO by CO is proposed. [ABSTRACT FROM AUTHOR]

Fe-ZSM-5 catalysts were prepared by subliming FeCl3 into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl3 exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl3 into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl3 at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl3 at 700 °C were found to be more active for NO reduction with NH3 in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl3 at 320 °C. To determine the active sites, the catalysts were characterized by H2-TPR, in situ DRIFTS of NO adsorption, NH3-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH3 could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when γ positions in Fe-ZSM-5, corresponding to Fe2+(NO) band at 1877 cm-1 in DRIFTS, were preferentially occupied. [ABSTRACT FROM AUTHOR]