Search

Lean gasoline engines offer greater fuel economy than common stoichiometric gasoline engines. However, excess oxygen prevents the use of the current three-way catalyst (TWC) to control nitrogen oxide (NOX) emissions in lean exhaust. A passive SCR concept, introduced by General Motors Global RD however, the rich operation necessary for NH3 production results in a fuel consumption penalty. The fuel penalty can be minimized by adjusting spark timing to increase rich-phase engine out NOX emissions and, thereby, NH3 levels. Additionally, higher engine out NOX during engine load increase to simulate acceleration resulted in additional fuel savings. A 10% fuel consumption benefit was achieved with the passive SCR approach by optimizing rich air-fuel equivalence ratio and spark timing while also utilizing acceleration load conditions.

The effect of CO 2 and H 2 O on the NO/O 2 storage over a Pt-Ba/Al 2 O 3 LNT catalyst was investigated in the temperature range 150–350 °C by combining FT-IR spectroscopy and microreactor flow experiments. It is found that the presence of water shows negligible effect on the NO x storage at all the temperatures studied. Otherwise, the presence of CO 2 inhibits the “nitrite route” (initial formation of surface nitrites and their subsequent evolution to nitrates), whereas the “nitrate route” (involving NO oxidation to NO 2 over Pt and its subsequent adsorption on Ba in the form of nitrates) proceeds as in the absence of CO 2 . The inhibition effect of CO 2 on nitrite formation increases on increasing the temperature. This behavior is likely related to the different thermal stability of nitrites and carbonates and, in particular, to the decreasing ability of nitrites to displace carbonates on increasing temperature. Simultaneously, the presence of CO 2 in the feed significantly shortens or eliminates the dead time in the NO x breakthrough at the reactor outlet. As a consequence, the presence of dead time in the absence of CO 2 has been correlated to the occurrence of the nitrite route.

This study demonstrated that a plasma–catalyst system using Pt catalyst provides high performance for NO decomposition under a humidified condition. In this work, we optimized the catalyst using various supported metals, oxides, and investigated the effects of the loading amount of metal and imposed voltage of plasma for highly efficient NO conversion. Results show that Pt is the most active metal and that it promotes formation of N 2 and N 2 O from NO, and that N 2 O was an intermediate of N 2 formation from NO over Pt. Regarding the effect of support, Pt catalysts supported on SiO 2 and Al 2 O 3 , showed higher activity. We investigated the effects of metallic surface area of Pt and imposed voltage. Results show that both the energy input and metallic surface area of Pt plays important roles for NO decomposition to N 2 in the plasma–catalyst system. The maximum peak current in plasma is extremely important.

This study was performed to develop a DME SR catalyst with high H2 selectivity using a heat source and water in the exhaust emissions of vehicles. The final goal of the research is to develop a combined system of SR + LNT for improving the de-NOx performance of the catalyst system in a DME engine. The scope of this research encompasses the optimization of the Cu concentration for the SR catalyst, evaluation of the NOx conversion efficiency of the LNT catalyst according to the kind of reductant (H2, CO, and DME), and evaluation of the de-NOx performance of the LNT catalyst and a combined system of SR + LNT. As a result of experiments concerning DME SR catalysts manufactured through the sol–gel method, the Cu20%/γ-Al2O3 catalyst showed the highest DME conversion and H2 selectivity. The combined system of SR + LNT using a Cu20%/γ-Al2O3 SR catalyst increased the NOx conversion by about 20% compared to the LNT catalyst alone at temperatures over 300 °C. In the combined system of SR + LNT, a supply of 1% of DME results in a higher NOx conversion than a supply of 0.75%, but results in NH3 slip and higher fuel consumption; therefore, supplying 0.75% of DME is favorable.

This paper aims to evaluate the de-NO x performance of a combined system of LNT + SCR catalysts according to the durability of hydrothermal aging and sulfur poisoning. NO x conversion, NH 3 production, and N 2 O emission from the LNT and the combined system of LNT and SCR were evaluated according to the conditions of hydrothermal aging (750–900 °C) and sulfur poisoning (1.0–1.48 g/L). Regarding the NO x -TPD characteristics, it was found that the amount of NO x desorption decreased due to hydrothermal aging and sulfur poisoning. The NO x conversion of the combined system of LNT and SCR (aged at 750 °C and 900 °C) was 10–30% higher than that of the LNT system. During this time, the maximum (NH 3 ) produced /(H 2 ) inlet ratio of the LNT catalyst was 0.81%, which the produced NH 3 reacted with NO x as a reductant at the downstream SCR catalyst. These characteristics are some merits that compensate the reduction in catalyst activity due to hydrothermal aging. The NO x conversion of the 1.48 g/L sulfur-poisoned LNT + SCR system was 20% lower after poisoning than before poisoning, and the NO x conversion of the LNT + SCR system did not recover due to excessive sulfur poisoning even after desulfation. The N 2 O emission of the hydrothermally aged catalyst was small because the NO x quantity stored on the LNT was reduced. The combined system of LNT and SCR catalysts had the merit of compensating the de-NO x performance, and reducing the NH 3 slip and the N 2 O emission, even though the catalysts were aged hydrothermally.

The NOx storage and reduction (NSR) performance of low platinum (0.5 wt%) 0.5Pt–CoOx–15BaO/Al2O3 catalysts with varied Co loadings and calcination temperatures was studied to investigate the promotional effect of CoOx on the NSR catalysis. The NSR performance was tested under cyclic lean–rich conditions, and was evaluated in terms of NOx storage capacity (NSC) under the lean condition, the N2 selectivity and the amount of nitrogen-containing products (namely, the NOx reduction capacity (NRC)) under the rich condition. For the catalysts calcined at 800 °C, addition of CoOx to the 0.5Pt–15BaO/Al2O3 catalyst enhanced the NSC but lowered significantly the NRC, which made the NRC/NSC ratios dropped significantly from 0.82 for the reference 0.5Pt–15BaO/Al2O3 catalyst to around 0.50 for the catalysts containing 1 and 5 wt% Co, and to 0.37 for the catalyst containing 10 wt% Co. Moreover, the N2 selectivity remained at around 50% for the 0.5Pt–CoOx–15BaO/Al2O3 catalysts when the Co loading was kept low (0–5 wt%), and decreased significantly to 30% when the Co loading was 10 wt%. The calcination temperature of the 0.5Pt–CoOx–15BaO/Al2O3 sample containing 5 wt% Co was varied in the range of 350–800 °C to improve the NSR performance. The catalyst calcined at 550 °C was found to produce the highest NRC/NSC ratio (0.80) and N2 selectivity (76.1%) under the rich condition. The maximum efficiency for NSR catalysis of this catalyst seemed to be associated with the amount of binary Pt–Co oxides.

A highly active catalyst (La 0.7 Ag 0.3 MnO 3 ) for simultaneous removal of nitrogen oxides (NOx) and diesel soot is synthesized by solid state method and the catalyst is characterized by XRD, FT-IR, H 2 -TPR, and O 2 -TPD. The results indicate that metallic Ag appears in the La 0.7 Ag 0.3 MnO 3 catalyst. The concentration of oxygen vacancy and the over-stoichiometry oxygen content also remarkably increase as the substitution increase of Ag + for La 3+ at A-site ions. The simultaneous removal of soot particulates and NOx activities are evaluated by a temperature-programmed reaction (TPRe) technique. The superior performance of the La 0.7 Ag 0.3 Mn0 3 catalyst for the reaction is probably due to lots of oxygen vacancy and over-stoichiometry oxygen in the perovskite lattice along with the zero-valence silver.

In the CATHLEAN project (an EU Framework 5 project performed between 2003 and 2006) a consortium of researchers investigated the development of an advanced, ultra-low NOx, hybrid burner for heavy-duty gas turbines that combines catalytic and lean-premix combustion components. Catalytic elements were developed that preheat the incoming lean fuel/air mixture up to temperature of ca. 1100 K at the required high (20–30 m/s) operating velocities and inlet temperatures (670–690 K). High-pressure aging of a highly active Pd-based catalyst at 10 bars indicated that the catalyst activity decreases significantly in the first 200 h of operation, and that an optimal catalyst design should contain different regions (in the axial direction) to allow optimization of catalyst activity and material stability, e.g. higher activity at the flow entrance, greater thermal stability at the reactor outlet where temperatures are high. Full-scale burner investigations demonstrated the feasibility of the CATHLEAN hybrid catalytic burner concept, and provided an indication of performance enhancement due to catalytic conversion. Both NOx emissions and lean stability limit were improved (25% reduction in NOx emissions and reduction of lean blow-out limit of ca. 200 K).

The adsorption–reduction by H 2 of NO x stored on a model LNT Pt–Ba/Al 2 O 3 catalyst sample and on a combined LNT + Fe-ZSM5 SCR catalyst is investigated in this work. The storage of NO x over the LNT Pt–Ba/Al 2 O 3 catalyst leads to nitrite formation at low temperatures, and to nitrate at high temperatures (above 300 °C). The stored NO x are reduced mainly to NH 3 at low temperatures, and to N 2 at high temperatures. In line with previous data and according to experiments carried out with H 2 and NH 3 , a two-step in-series pathway for nitrogen formation is proposed involving at first the fast formation of ammonia upon reaction of NO x with H 2 , followed by the slower reaction of the so-formed ammonia with the stored NO x leading to N 2 . This two-step in-series pathway together with the integral behaviour of the reactor accounts for the temporal evolution of the products which is observed during regeneration of LNT catalysts. A Fe-ZSM5 SCR placed downstream the LNT catalyst stores NH 3 released during the rich phase from the LNT sample. The stored ammonia is effectively converted to N 2 during the subsequent lean phase, due to the occurrence of the SCR reaction over the Fe-ZSM5 catalyst bed. Hence the presence of a SCR catalyst layer placed downstream a LNT sample leads to the twofold benefit of reducing the NH 3 slip and to increase the NO x removal efficiency. These advantages are most important at low temperatures, and tend to vanish at high temperatures where the NH 3 slip is less important.

Catalytic combustion offers improved combustion stability extending the lean flame temperature limit to allow ultra-low NO x emissions. Instead of replacing the entire lean-premixed (LP) injector with a catalytic injector, advanced Rich Catalytic/Lean-burn (RCL ® ) technology is developed and integrated to replace only the pilot portion of the injector. The pre-reaction within the pilot provides enhanced reactivity reducing the need to use higher temperature flames to stabilize the combustor primary zone. This concept synergistically combines the best features of catalytic combustion and conventional aerodynamically stabilized combustion technology. The present paper discusses the development and engine testing of a set of Taurus 70 injectors equipped with RCL ® pilots for natural gas applications. Testing showed engine NO x emissions of ∼2.5 ppmv corrected to 15% O 2 were achieved at baseload conditions. Engine CO emissions were less than 2 ppm. Combustor acoustics were low (at or below 0.1 psi RMS) during testing. The RCL ® catalytic pilot supported the engine startup and shutdown process without major modification of existing engine controls. These initial results are promising. Further development work is needed to establish long term catalyst durability, engine transient behavior, and advancing the pilot technology to production status.

The technology of methane combustion in small gas turbine catalytic combustors on alternative granulated catalysts with a low content of noble metals has been developed and studied. The operations of catalyst packages for environmentally clean combustion consisting of one-, two- or three catalysts with different chemical composition, shape and size of granules have been analyzed. The optimized design of a three-stage catalyst package with total height of 340 mm includes 40mm of highly active Pd-Ce-Al 2 O 3 at the entrance of the combustion chamber in the form of 7.5 mm x 7.5 mm x 2.5 mm rings; 240mm of a basic catalyst based on Mn-hexaaluminate with the granules of the same form and size; and 60mm of Pd―Mn―La―Al 2 O 3 catalyst as 4-5 mm spherical granules at the exit of the combustion chamber. Such optimal design yielded methane combustion over 99.97% at T inlet =470―580 °C and oxygen excess coefficient 5.2-7.0. The emission levels were NO x < 1 ppm, CO < 10 ppm, HC < 10 ppm. The pressure drop across the catalyst package was less than 4% of the total pressure (1 bar).

The characteristics of low platinum Pt–BaO catalysts for NOx storage and reduction (NSR) were studied over three series of samples that have similar barium loadings (ca. 15 wt% Ba), namely, Pt–BaO/Al2O3, CoOx promoted Pt–BaO/Al2O3 and Pt–BaO/ZrO2–Al2O3 catalysts. The catalysts were calcined at 800 °C and their NSR performances were evaluated under cyclic lean (1000 ppm NO and 10 vol% O2 in Ar)/rich (1 vol% H2 in Ar) conditions with particular attention paid to detect the possible harmful by-products, i.e., NH3 and N2O, during the reduction of the stored NOx under the rich condition. Lowering the Pt loading in the Pt–BaO/Al2O3 catalyst from 1.0 to 0.5 wt% resulted in a 15% decrease in the NOx storage capacity (NSC) under the lean condition but the N2 selectivity under the rich condition declined dramatically (from 85% to 53%), indicating that the NOx reduction performance under the rich condition is the key to low platinum NSR catalysts. The cobalt oxides was identified as an unsuitable promoter for lowering the Pt loading; its addition into Pt–BaO/Al2O3 at the Pt loading of 0.5 wt% further reduced the N2 selectivity under the rich condition although significant improvement in the NSC under lean condition could be observed. It was found instead that the use of ZrO2–Al2O3 as an alternative of the Al2O3 support was effective in lowering the dependence on Pt loading of the Pt–BaO for the NSR catalysis since the ZrO2–Al2O3 support could make the catalyst highly selective for the formation of N2 under the rich condition, at a lower Pt loading. The overall NSR performance of a Pt–BaO/ZrO2–Al2O3 catalyst with 0.5 wt% Pt was found comparable to that of its counterpart Pt–BaO/Al2O3 catalyst with 1.0 wt% Pt, demonstrating a viable way for developing low platinum NSR catalysts.

Catalytic removal of NO x under lean-burn conditions is challenging to attain the future stringent NO x emission standards. Selective catalytic reduction (SCR) of NO x with different reducing agents and NO x storage-reduction (NSR) are viewed as the two most promising technologies for NO x removal. Although a variety of catalytic systems have been developed for these processes, their practical applications remain difficult due to catalyst deactivation caused by SO 2 in the exhaust gases. Therefore, improving catalyst tolerance against SO 2 is one of the most important targets in the deNO x catalyst development. This review focuses on the knowledge and know-how that have been developed in improving the sulfur tolerance of deNO x catalysts. Ag/Al 2 O 3 is the most promising catalyst for the HC-SCR of NO x . Support modification, H 2 co-feeding and some other strategies to improve the sulfur tolerance of Ag/Al 2 O 3 are discussed. Some novel catalyst systems with high sulfur tolerance for NH 3 -SCR, H 2 -SCR and NSR are addressed, respectively. For NSR catalysts, developing novel sulfur resistant NO x storage systems and effective desulfation processes seem to be two avenues to improve their sulfur resistance.

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 16 s with 4, 2, and 1% H 2 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 H 2 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.

A combined Diesel exhaust gas aftertreatment system is studied, consisting of the NO x storage and reduction catalyst (NSRC, called also lean NO x trap, LNT) and the catalyst for selective catalytic reduction of NO x by NH 3 ( NH 3 -SCR). Most of the time the system is operated under prevailing fuel-lean conditions, enabling economical running of the engine. During this phase the NO x emissions are being adsorbed in the NSRC. However, short fuel enrichments need to be applied periodically for the NSRC regeneration (reduction of the stored NO x ). Ammonia produced in the NSRC as a by-product of the NO x reduction under controlled fuel-rich conditions is then adsorbed in the NH 3 -SCR reactor located downstream. The adsorbed NH 3 is consequently utilised in selective NO x reduction during the next fuel-lean period. The NSRC + SCR configuration thus eliminates the need for an external NH 3 source (e.g., periodically re-filled urea solution tank) that is necessary in the case of the stand-alone SCR. Development of effective mathematical models for the NSRC and SCR catalysts is discussed. Dynamic measurements in a lab mini-reactor are performed separately for the industrial NSRC (PtRh/Ba/Ce/ γ -Al 2 O 3 type) and SCR (Fe-ZSM type) catalyst samples. The experimental results are employed in the evaluation of rate parameters for the individual catalysts. Particular attention is given to the dynamic evolution of NH 3 during the NSRC regeneration and its dependence on temperature and length of the enrichment period. Trends in NH 3 selectivity with the NSRC ageing are discussed. Synergistic effects of the NSRC and NH 3 -SCR are then studied by simulations of defined lean/rich operation and engine test driving cycles. The combined NSRC + SCR system provides higher NO x conversions in comparison with the stand-alone NSRC and it prevents undesired NH 3 slip. The positive effects of the downstream SCR are most important at lower intermediate temperatures, and in the case of an aged NSRC that usually produces more NH 3 .

In order to study the effect of washcoat composition on lean NOx trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of La-stabilized CeO2 (5 wt% La2O3) or CeO2-ZrO2 (Ce:Zr = 70:30) were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that aging resulted in deterioration of the NOx storage, NOx release and NOx reduction functions, whereas the observation of lean phase NO2 slip for all of the aged catalysts indicated that LNT performance was not limited by the kinetics of NO oxidation. After aging, all of the catalysts showed increased selectivity to NH3 in the temperature range 250–450 °C. TEM, H2 chemisorption, XPS and elemental analysis data revealed two main changes which can explain the degradation in LNT performance. First, residual sulfur in the catalysts, present as BaSO4, decreased catalyst NOx storage capacity. Second, sintering of the precious metals in the washcoat was observed, which can be expected to decrease the rate of NOx reduction. Additionally, sintering is hypothesized to result in segregation of the precious metal and Ba phases, resulting in less efficient NOx spillover from Pt to Ba during NOx adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NOx spillover during catalyst regeneration. Spectacular improvement in LNT durability was observed for catalysts containing CeO2 or CeO2-ZrO2 relative to their non-ceria containing analog. This was attributed to (i) the ability of ceria to participate in NOx storage/reduction as a supplement to the main Ba NOx storage component; (ii) the fact that Pt and CeO2(-ZrO2) are not subject to phase segregation; and (iii) the ability of ceria to trap sulfur, resulting in decreased sulfur accumulation on the Ba component.

Using model powder catalysts and fully formulated monolithic lean NOx trap (LNT) catalysts, the effect of ceria on LNT desulfation behavior was investigated. TPR experiments performed on the model catalysts showed that each of the oxide phases present (BaO, CeO2, and Al2O3) is able to store sulfur and that they possess distinct behavior in terms of the temperatures at which desulfation occurs. For a Pt/BaO/Al2O3 catalyst, addition of ceria was found to reduce the degree of sulfur accumulation on the BaO phase, particularly at high sulfur loadings, by contributing to sulfur capture. The importance of maintaining the Pt and Ba phases in close proximity for efficient LNT desulfation was also demonstrated; physically separating the Pt and Ba sites resulted in a shift of the desulfation temperature of the surface BaSO4 by 20–40 °C towards higher temperature, i.e., towards the position characteristic of bulk BaSO4. From the monolith studies, it was found that relative to a sample containing no ceria, samples containing La-stabilized CeO2 or CeO2–ZrO2 showed a greater resistance to deactivation during sulfation (as reflected by the NOx storage efficiency), and required lower temperatures to restore the NOx storage efficiency to its pre-sulfation value. In addition to the ability of ceria to store sulfur and release it at relatively low temperatures under reducing conditions, these findings can be attributed to the high water–gas shift activity displayed Pt/CeO2, which result in increased intra-catalyst concentrations of H2 under rich conditions. The results also showed that precious metal loadings can significantly impact desulfation efficiency and that both high Rh and Pt loadings are beneficial for catalyst desulfation.

Selective catalytic reduction with NH3 (NH3-SCR technology), based on V2O5/WO3/TiO2 catalysts, has been previously commercialized for abating NOx emissions from various stationary and mobile lean-burn or diesel engines. However, meeting the uniquely stringent US EPA 2010 regulations for diesel engines required introduction of a new class of SCR catalysts, based on Cu- or Fe-exchanged zeolites. While remarkably active and stable, these new materials proved substantially more difficult than vanadia-based catalysts to operate transiently on the road, due to their much higher NH3 storage. The objective of this work was to develop a concise experimental protocol, elucidating multiple catalytic functions, steady-state and transient, of practical relevance to the mobile SCR applications. This paper provides a comprehensive overview of such functions, using select data from various representative Cu- and Fe-zeolite catalysts. While the bulk of the reported results originated directly from the developed protocol, additional experiments, validating the assumptions or clarifying unexpected experimental observations, are included.

A light-duty diesel engine has been operated in advanced combustion modes known generally as premixed charge compression ignition (PCCI). The emissions have been characterized for several load and speed combinations. Fewer NOx and particulate matter (PM) emissions are produced by PCCI, but higher CO and hydrocarbon (HC) emissions result. In addition, the nature of the PM differs from conventional combustion; the PM is smaller and has a much higher soluble organic fraction (SOF) content (68% vs. 30% for conventional combustion). Three catalyst technologies were studied to determine the affects of HECC on catalyst performance; the technologies were a lean NOx trap (LNT), diesel oxidation catalyst (DOC), and diesel particulate filter (DPF). The LNT benefited greatly from the reduced NOx emissions associated with PCCI. NOx capacity requirements are reduced as well as overall tailpipe NOx levels particularly at low load and temperature conditions where regeneration of the LNT is difficult. The DOC performance requirements for PCCI are more stringent due to the higher CO and HC emissions; however, the DOC was effective at controlling the higher CO and HC emissions at conditions above the light-off temperature. Below light-off, CO and HC emissions are problematic. The study of DPF technology focused on the fuel penalties associated with DPF regeneration or “desoot” due to the different PM loading rates from PCCI vs. conventional combustion. Less frequent desoot events were required from the lower PM from PCCI and, when used in conjunction with an LNT, the lower PM from less frequent LNT regeneration. The lower desoot frequency leads a ∼3% fuel penalty for a mixture of PCCI and conventional loads vs. ∼4% for conventional only combustion.

A detailed analysis of the catalytic behaviour in the storage/reduction of NO x of single Pt–Ba/Al 2 O 3 LNT and FeZSM-5 SCR systems and of combined LNT + SCR configurations is analyzed and compared in this work under clean conditions (i.e. in the absence of CO 2 and H 2 O in the feed stream). By working under dilute conditions (i.e. with low reductant concentrations) and with an inert purge between the lean and the rich phases, nearly ideal isothermal conditions could be attained and the chemical pathways operating in the each step of the NSR cycle could be analyzed for the investigated catalysts configurations. It is found that when the SCR catalyst is placed downstream the NSR catalyst bed (double-bed configuration), ammonia released from the LNT sample during the rich phase is stored on the SCR catalyst placed downstream and is then converted to N 2 in the subsequent lean phase according to the occurrence of a SCR reaction. This has a benefit on both the NO x removal efficiency and the N 2 selectivity. If the zeolite SCR catalyst is mixed with the LNT sample (physical mixture), during the rich phase the SCR catalyst traps ammonia which being intermediate in N 2 formation leads to a decrease in the evolution of nitrogen at the reactor outlet. Ammonia stored on the SCR catalyst then reacts with NO x during the subsequent lean phase, leading to a significant N 2 evolution: this increases the NO x removal efficiency and the N 2 selectivity if compared to the single Pt–Ba/Al 2 O 3 catalyst sample.

In this paper the reactivity of NOx stored at 350 °C onto Pt–Ba/Al2O3 LNT catalyst in the reduction by H2, CO and CO/H2O mixture is investigated by means of transient experiments and complementary FT-IR analyses. Hydrogen is found to be the best reductant, being characterized by the highest NOx removal efficiency in the range 150–350 °C. It is proposed that the reduction by hydrogen proceeds according to a dual-steps mechanism in which NOx are first reduced to ammonia, which in turn further reacts with other nitrate species leading selectively to N2. Conversely, when CO is used as reducing agent under dry conditions only a part of the initially stored NOx is removed as N2, the other fraction being reduced to adsorbed cyanates/isocyanates species. It is proposed that the cyanate/isocyanate ad-species lead to the formation of nitrogen by oxidation involving other nitrate species; this reaction is self-poisoned by CO. In the presence of water, CO reduced nitrates into cyanates/isocyanates ad-species that were readily hydrolyzed to ammonia; this species is hence precursor in N2 formation upon reaction with residual nitrate species. Alternatively, stored nitrates are reduced by H2 formed via the water gas shift (WGS) reaction.

A single-cylinder diesel engine with an emissions control system – diesel oxidation catalyst (DOC), Fe–zeolite selective catalytic reduction (SCR) catalyst, and diesel particulate filter (DPF) – was used to perform accelerated thermal aging of the SCR catalyst. Cyclic aging is performed at SCR inlet temperatures of 650, 750 and 850 °C for up to 50 aging cycles. To assess the validity of the implemented accelerated thermal aging protocol, a field-aged SCR catalyst of similar formulation was also evaluated. The monoliths were cut into sections and evaluated for NO x performance in a bench-flow reactor. While the rear section of both the field-aged and the accelerated engine-aged SCR catalysts maintained high NO x conversion, 75–80% at 400 °C, the front section exhibited a drastic decrease to only 20–35% at 400 °C. This two-tiered deactivation was also observed for field-aged samples that were analyzed in this study. To understand the observed performance changes, thorough materials characterization was performed which revealed two primary degradation mechanisms. The first mechanism is a general Fe–zeolite deterioration which led to surface area losses, dealumination of the zeolite, and Fe 2 O 3 crystal growth. This degradation accelerated above 750 °C, and the effects were generally more severe in the front of the catalyst. The second deactivation mechanism is linked to trace levels of Pt that are suspected to be volatizing from the DOC and depositing on the front section of the SCR catalyst. Chemical evidence of this can be seen in the high levels of NH 3 oxidation (80% conversion at 400 °C), which coincides with the decrease in performance.

A crystallite-scale model is incorporated into a reactor-scale model to study the effect of Pt dispersion and temperature during the regeneration of a lean NOx trap (LNT) comprising a Pt/BaO catalyst. The current study is based on a recent experimental study [R.D. Clayton, M.P. Harold, V. Balakotaiah, C.Z. Wan, Appl. Catal. B 90 (2009) 662]. The model shows that an increase in the Pt dispersion for a fixed Pt loading increases the interfacial perimeter between Pt and Ba, and has a significant effect on the regeneration kinetics. The transient product distribution displayed by three catalysts having varied Pt dispersions (3.2%, 8% and 50%) is explained by the localized stored NOx gradients in the Ba phase. A rate determining process during the regeneration is found to be the diffusion of stored NOx within the Ba phase towards the Pt/Ba interface. Temperature-dependent NOx diffusivities in the Ba phase are used to predict the breakthrough profiles of H2, N2 and NH3 over a range of catalyst temperatures. Finite gradients in the stored NOx concentration are predicted in the Ba phase, thus showing that the nitrate ions are not sufficiently mobile at lower temperatures for the low dispersion catalysts. The model predicts that the highest amount of NH3 is produced by the low dispersion catalyst (3.2% dispersion) at high temperatures, by the high dispersion catalyst (50% dispersion) at low temperatures, and by the intermediate dispersion catalyst (8% dispersion) at intermediate temperatures, consistent with the experimental data. It is found that the net NH3 generation is favored under conditions when NOx transport to the Pt/Ba interface is the rate determining process. The model considers the consumption of chemisorbed oxygen on Pt by H2, which is used to predict the low effluent N2 concentration for the 50% dispersion catalyst as compared to the 8% dispersion catalyst. Finally, a novel design is proposed to maximize the amount of NH3 in the effluent of a LNT, which can be used as a feed to a selective catalytic reduction (SCR) unit placed downstream of the LNT.

Reactor activity measurements and FTIR spectroscopy were applied to study the transient and steady state behavior of Cu and Fe exchanged zeolite catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 at 200 °C. Different surface NOx adsorption complexes were observed on the two catalysts. IR bands assigned to surface nitrate/nitrite groups were apparent on the Cu catalyst under most testing conditions. On the Fe catalyst, IR bands assigned to surface nitro groups were also observed, in addition to nitrate/nitrite groups. Both the nitrate/nitrite and the nitro group showed high reactivity with NH3, which explained similar initial transient SCR activity of the two catalysts. The presence of NH3 was found to block the Fe sites from catalyzing the oxidation of NO and severely inhibited the overall SCR activity when there was no NO2 in the gas mixture. Addition of NO2 improved the low temperature SCR activity of both catalysts. The higher SCR activity on the Fe catalyst at the optimum NO:NO2 = 1:1 was attributed to the high intrinsic activity of the nitro groups formed on the Fe catalyst.

NOx storage on Pt/BaO/γ-Al 2 O 3 Lean NOx Traps (LNTs) has been studied with a particular focus on the NOx storage capacity (NSC) of these traps for the time up to which 1% of the inlet [NOx] escapes the trap. This complete or ‘fast’ NOx sorption capability of LNTs for appreciable amounts of time is what makes these catalysts useful for automotive NOx emission abatement. The fast NSC for LNT formulations with combinations of a range of Pt (0.6–6.3 wt.%) and Ba (4–20 wt.%) loadings was measured under various lean feed compositions including NO, NO 2 and NO + NO 2 as the NOx sources and presence and absence of 7%CO 2 and 7%H 2 O. All the measurements were performed at 300 °C and at a space velocity of 30,000 h −1 . The complex trends in the fast NSC due to various Pt, Ba loading combinations are explained with the help of a phenomenological model. The model addresses the trends in fast NSC primarily through combinations of NOx storage contributions in parallel pathways on Ba vicinal to Pt and Ba uninfluenced by Pt. We attribute the influence of Pt to the spillover of dissociated oxygen atoms from Pt to the vicinal Ba sites. This Pt–Ba synergy was found to play a dominating role in governing the fast NSCs of all the LNT samples especially in presence of CO 2 , H 2 O and CO 2 + H 2 O in the lean feed. It was also found to be the prominent factor in limiting the fast NSC when NO and NO + NO 2 (with low NO 2 /NO) were the NOx sources rather than NO 2 . We propose that the NOx storage process on Ba vicinal to Pt involves a localized reaction front of NOx that travels through the catalyst bed with saturation of those sites. This process has no preference between NO and NO 2 as a precursor. CO 2 and H 2 O affect through competition for both types of Ba sites available for NOx storage.

A series of MnO 2 /ZrO 2 mixed oxides were prepared in reverse microemulsions for NOx adsorption and abatement. The results show that the amount of NOx adsorbed was increased with increasing MnO 2 content in various MnO 2 /ZrO 2 samples. The maximum uptake value of NOx was 27.66 mg NOx/g adsorbent on the 40% Mn–Zr sample at 200 °C with NOx initial adsorption rate as 2.63 mg/(g adsorbent min). TPD results show that the complete desorption of NOx was easily obtained by heating the sample to 450 °C, and the temperature for the complete desorption can be further decreased to 210 °C by adding carbon monoxide into the argon desorption streams. Furthermore, water vapor was found to reduce NOx adsorption capacity because of its stronger competitive adsorption with NOx species. It is noteworthy that a small amount of sulfur dioxide could significantly increase the initial rate of NOx adsorption although it slightly decreased the NOx adsorption capacity.

A monolithic cordierite-based CuO/Al2O3 catalyst showed industrial potential for simultaneous SO2 and NO removal from flue gases at 350–400 °C. However, it is still a challenge to prevent CuO from aggregation and to keep it in an active state during the removal and regeneration processes. This work shows that addition of V2O5 to the catalyst can significantly reduce CuO particle size and improve SO2 removal activity, and maintain a high selective catalytic reduction (SCR) activity for NO removal. Furthermore, V2O5 additive prevents aggregation of SiO2 in the cordierite with the coated Al2O3, and inhibits over reduction of the SO2 removal product, CuSO4, during the regeneration by NH3, which are important to the catalyst's stability. V2O5 additive changes the regeneration product from Cu3N to CuO and thus may avoid the temperature rise and NOx release in the subsequent removal process.

Heterogeneous 1D model with global kinetics is proposed for industrial NOx storage and reduction catalyst (NSRC) on the basis of lab experiments in a mini-reactor in the temperature range 100–500 ° C. The NOx reduction dynamics and selectivity towards N2 or NH3 are modelled for three main reducing components present in the rich exhaust gas: CO, H2, and unburned hydrocarbons (HCs). The following reactions are considered: CO, H2 and HC oxidation, NOx reduction, NO/NO2 transformation, NO and NO2 storage, oxygen storage effects, water gas shift and steam reforming, and reduction of the stored NOx by H2, CO and HC. Ammonia is formed mainly by the reaction of H2 with NOx, but also by the water-assisted reaction of CO with NOx (formation and consequent hydrolysis of isocyanates). Inclusion of the latter route is necessary to explain the NH3 formation in CO-rich mixtures without H2 at lower temperatures. At higher temperatures, water gas shift and steam reforming reactions enable in situ H2 production from CO, HC and H2O. The formed ammonia subsequently reacts with oxygen and NOx deposited on the catalyst surface downstream, which results in NH3 wave travelling along the catalytic monolith. The highest NH3 yield is obtained around 200 ° C, when the NH3 formation from the accumulated NOx is already ignited, while the ammonia consumption reactions are still relatively slow. At lower temperatures CO inhibits the NOx reduction by H2 (i.e., the NH3 production). At higher temperatures the ammonia oxidation reactions become fast enough to eliminate most of the NH3 produced locally from the stored NOx. However, ammonia can be still observed after the completion of the regeneration, when it is formed steadily from the rich inlet gas containing NOx. Model results are confronted with the lab data, and calculated evolution of concentration profiles inside the monolith is discussed. The developed model is validated by engine test driving cycle data.

In this work we present the results obtained with 3 catalysts (Pt, Rh and Ag on alumina) tested in ranges of temperatures and gas hourly space velocities typical of diesel engines in real trucks. N ...

This study summarizes the effect of the electrochemical promotion of catalysis (EPOC) by using potassium conductors in environmental catalytic reactions applied to the removal of several automotive pollutants, such us CO, C3H6 and nitrogen oxides (N2O and NOx). It has been shown the extraordinarily potential of using Pt/K–βAl2O3 in a wide variety of environmental reactions (oxidation, reduction), activating the catalyst at lower reaction temperatures and decreasing the inhibitory effect of poisons such as water in the reaction atmosphere. In addition, a new application of potassium conductors-based electrochemical catalysts has been developed for the NOx storage/reduction process (NSR). The idea of coupling catalysis and solid-state electrochemistry on this process would allow to improve and simplify the current NSR technology. Finally, the results have been obtained under reaction conditions compatible with the treatment of automotive exhaust emissions. This demonstrates the potential for the practical use of the phenomenon of electrochemical promotion by using potassium conductors on this kind of process.

The effect of temperature and transient addition of H2 on the NOx–SCR reaction was investigated over a 2-wt.% Ag/Al2O3 catalyst using isotopically labelled 15NO. The addition and removal of hydrogen had a marked effect on the nitrogen balance at temperatures ranging from 245 to 400 °C. At a low temperature (245 °C), the addition of hydrogen resulted in the storage of NOx, whereas, the reverse was true at 400 °C, where NOx was stored upon removal of hydrogen from the feed. The transient NOx storage effect could be harnessed to allow continuous high NOx conversion with intermittent hydrogen addition. In particular, an average NOx conversion of 79% could be achieved during transient experiments in which H2 was switched in and out of the feed in 6-s intervals at 300 °C.

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.

The potentiality of Ir-based catalysts for the simultaneous removal of soot and NOx in the presence of O 2 is investigated by using temperature programmed reaction (TPR) technique. The behaviors of the catalysts for the soot oxidation and the NOx reduction are also separately analyzed. The results show that soot plays an important role on the NOx reduction, the formed NO 2 promotes the soot oxidation, and soot and NOx can be removed simultaneously over Ir-based catalysts in the presence of O 2 . The simultaneous removal paths of soot and NOx over Ir catalyst are proposed that the NO 2 formation by the oxidation of NO oxidizes the soot and the CO formation by the soot oxidation reduces NO. Furthermore, the adsorbed-dissociation of NO 2 is a path of the NOx reduction. Comparing with Pt catalyst, Ir catalyst is a more effective catalyst for the simultaneous removal of soot and NOx. The Ir contents and support materials have some effects on the catalytic activity and 1 wt.% Ir/ZSM-5 exhibits a high level activity for the simultaneous removal of soot and NOx.

Exhaust gasses from small and medium stationary sources contain NO x that will be regulated by new European legislation in the coming years. Among all the processes the SCR-NH 3 seems to be the more promising one. However, the application of commercial catalysts to these new facilities presents some drawbacks such as the high and narrow operation temperature, its low withdraw to SO 2 or its high cost production. In order to improve this technology, in previous works, carbon-supported catalytic briquettes have shown a good kinetic performance under the above commented conditions. In this study, other aspects such as thermal stability, long-term performance, spatial velocity influence and mechanical resistance were evaluated. Finally, a simple economic assessment was carried out providing a three times lower cost production than commercial catalysts. From all the data collected, there are some evidences that these catalyst briquettes will have a good performance in small and medium facilities, being an interesting alternative to commercial ones.

Several nitrogen compounds can be produced during the regeneration phase in periodically operated NOx storage and reduction catalyst (NSRC) for conversion of automobile exhaust gases. Besides the main product N2, also NO, N2O, and NH3 can be formed, depending on the regeneration phase length, temperature, and gas composition. This contribution focuses on experimental evaluation of the NOx reduction dynamics and selectivity towards the main products (NO, N2 and NH3) within the short rich phase, and consequent development of the corresponding global reaction-kinetic model. An industrial NSRC monolith sample of PtRh/Ba/CeO2/ γ -Al2O3 type is employed in nearly isothermal laboratory micro-reactor. The oxygen and NOx storage/reduction experiments are performed in the temperature range 100–500 °C in the presence of CO2 and H2O, using H2, CO and C3H6 as the reducing agents. The spatially distributed NSRC model developed earlier is extended by the following reactions: NH3 is formed by the reaction of H2 with NOx and it can further react with oxygen and NOx deposited on the catalyst surface, producing N2. Considering this scheme with ammonia as an active intermediate of the NOx reduction, a good agreement with experiments is obtained in terms of the NOx reduction dynamics and selectivity. A reduction front travelling in the flow direction along the reactor is predicted, with the NH3 maximum on the moving boundary. When the front reaches the reactor outlet, the NH3 peak is observed in the exhaust gas. It is assumed that the ammonia formation during the NOx reduction by CO and HCs at higher temperatures proceed via the water gas shift and steam reforming reactions producing hydrogen. It is further demonstrated that oxygen storage effects influence the dynamics of the stored NOx reduction. The temperature dependences of the outlet ammonia peak delay and the selectivity towards NH3 are correlated with the effective oxygen and NOx storage capacity.

In a general model of “three-function deNO x ” catalyst, the partial oxidation of methane by NO 2 is an important step (CH 4 + NO 2 → C x H y O z + NO). To study the effect of the length and diameter, in the mesopores of SBA-15, we have synthesized catalysts with 3 wt.% cobalt supported on SBA-15, with differences in length and diameter of channels. Three different cobalt species were detected on all catalysts. We demonstrated by TPSR experiments that the activity of cobalt/SBA-15 catalysts is affected by the length, the diameter and connections between mesopores of the SBA-15 supports. We show that by changing textural properties of silica support the temperature of 100% conversion of NO 2 into NO can decrease by more than 100 °C.

Catalytic properties of active carbons treated with N-compounds and promoted with manganese oxides were studied in selective catalytic reduction of NO with ammonia. The following elements of the preparation had a beneficial effect on activity and selectivity of the catalysts: pre-oxidation of active carbon prior to the introduction of N-species, the choice of N-compound, together with the post-treatment procedure, and the optimisation of the amount of active material. Apart from the introduction of N-surface groups, it was important to control the amount of acidic surface species which in turn determined the distribution of MeOx and reducibility of the samples, thus influencing the formation of undesired by-product (N2O).

In this paper the mechanisms that rule the reduction by hydrogen of NOx species adsorbed at different temperatures were investigated over a model LNT Pt–Ba/Al2O3 catalyst and over the corresponding Ba/Al2O3 system to address the role of the noble metal component in such mechanisms. It was found that the reduction proceeds according to a dual-step mechanism in which hydrogen reacts fast and at low temperature with nitrates producing ammonia, which however is not a terminal product as it can further react with other nitrate species leading selectively to N2. The results collected in the analysis of each of the dual-step reactions showed that they both occur through a Pt-catalyzed pathway active at very low temperatures, which does not involve the thermal decomposition of the adsorbed NOx species as a preliminary step.