Ammonia Storage Capacity Research Articles

Multi-objective optimization of chemical reaction characteristics of selective catalytic reduction in denitrification of diesel engine using ELM-MOPSO methodology

This study systematically investigated the effects of structural parameters in a two-stage selective catalytic reduction (SCR) catalyst on ammonia storage, NO conversion efficiency, and ammonia slip using computational fluid dynamics (CFD) simulations. The rank ordering of the correlations between structural parameters and performance metrics was determined by gray relational analysis (GRA). Both the catalyst diameter and the upstream catalyst porosity had correlations exceeding 0.9, making them key parameters affecting SCR performance. An extreme learning machine (ELM) prediction model was trained using data obtained from CFD simulations. The prediction performance of this ELM model was then evaluated using statistical metrics. Finally, the optimized Pareto frontier diagram was obtained through the multi-objective particle swarm optimization (MOPSO) algorithm, and the optimal results were selected for further CFD modeling analysis. The results showed that the upstream NO conversion efficiency of the SCR system was improved by 7.7 %, the downstream NO conversion efficiency was improved by 18.67 %, the ammonia slip was reduced by 71.97 %, and the upstream ammonia storage capacity was improved by 6.83 % compared with the original model.

Safety of ammonia as a hydrogen energy carrier

The safety of ammonia was divided into a fire hazard (flammability) and a health hazard. The flammability of ammonia decreased compared to other hydrogen energy carriers and carbon-based fuels because of the high flash point. The health hazard (frostbite and toxicity) of ammonia was large (3) and same as those of liquid hydrogen, LNG and carbon monoxide. Tolerance concentration in ACGIH was used as a ranking of toxicity. The tolerance concentration increased with decreasing the vapor concentration and the fuel content in water. The insoluble ammonia-absorbed zirconium phosphate has a large ammonia storage capacity of 10 wt%, a small vapor concentration in the presence of water and a small ammonia content in water below 1 ppm. It will be a candidate to reduce the toxicity of the leaked ammonia in a closed space.

Model-based simultaneous diagnosis of ammonia injection failure and catalyst ageing in [formula omitted] engine after-treatment systems

After-treatment systems (ATS) in vehicle powertrains are developed to achieve maximum pollutant abatement efficiency under design operating conditions. However, anomalies in the ATS may appear during real operation, such as reducing agent supply failure and catalyst ageing. As in the case of an ATS composed of a selective catalytic reduction (SCR) system plus an ammonia slip catalyst (ASC), injection failure leads to insufficient ammonia levels to reduce nitrogen oxide (NOx), and ageing decreases the ammonia storage capacity and NOx conversion efficiency, these drawbacks drive both pollutants to levels above those expected and allowed by governmental regulations. To address this problem, a novel methodology was proposed that simultaneously estimates the operational state of the ATS in terms of ammonia injection failure and ASC catalyst ageing. The approach through control-oriented models based on an artificial neural network (ANN) and sensor signal analysis (SSA), as well as an extended Kalman filter (EKF) observer, compares the current emission levels estimated by the observer in a two-dimensional probabilistic plan and a variable time-window, with those expected if the ATS were operating under normal conditions. The proposed methodology was evaluated in real driving cycles with the ATS subjected to several undesired operating conditions. As a result, the model was able to accurately estimate the levels of ammonia injection failure and catalyst ageing state. Therefore, enabling the control system to modify the ammonia injection strategy to achieve desired levels of NOx and NH3 emissions.

High Gravimetric and Volumetric Ammonia Capacities in Robust Metal-Organic Frameworks Prepared via Double Postsynthetic Modification.

Ammonia is a promising energy vector that can store the high energy density of hydrogen. For this reason, numerous adsorbents have been investigated as ammonia storage materials, but ammonia adsorbents with a high gravimetric/volumetric ammonia capacity that can be simultaneously regenerated in an energy-efficient manner remain underdeveloped, which hampers their practical implementation. Herein, we report Ni_acryl_TMA (TMA = thiomallic acid), an acidic group-functionalized metal-organic framework prepared via successive postsynthetic modifications of mesoporous Ni2Cl2BTDD (BTDD = bis(1H-1,2,3,-triazolo [4,5-b],-[4',5'-i]) dibenzo[1,4]dioxin). By virtue of the densely located acid groups, Ni_acryl_TMA exhibited a top-tier gravimetric ammonia capacity of 23.5 mmol g-1 and the highest ammonia storage of 0.39 g cm-3 at 1 bar and 298 K. The structural integrity and ammonia storage capacity of Ni_acryl_TMA were maintained after ammonia adsorption-desorption tests over five cycles. Temperature-programmed desorption analysis revealed that the moderate strength of the interaction between the functional groups and ammonia significantly reduced the desorption temperature compared to that of the pristine framework with open metal sites. The structures of the postsynthetic modified analogues were elucidated based on Pawley/Rietveld refinement of the synchrotron powder X-ray diffraction patterns and van der Waals (vdW)-corrected density functional theory (DFT) calculations. Furthermore, the ammonia adsorption mechanism was investigated via in situ infrared and vdW-corrected DFT calculations, revealing an atypical guest-induced binding mode transformation of the integrated carboxylate. Dynamic breakthrough tests showed that Ni_acryl_TMA can selectively capture traces of ammonia under both dry and wet conditions (80% relative humidity). These results demonstrate that Ni_acryl_TMA is a superior ammonia storage/capture material.

Dual-layer AdSCR monolith catalysts: A new solution for NOx emissions control in cold start applications

A new dual layer monolithic AdSCR system (adsorption + selective catalytic reduction) constituted by Cu/CHA (top) and BaO/Al2O3 (bottom) was prepared and studied as a potential solution to improve the low-T performances of NH3-SCR catalysts. Two washcoat formulations were considered. The samples were characterized through optical microscopy and SEM-EDX; the ammonia storage capacity and the catalytic activity in the standard NH3-SCR reaction were also studied. When using water as solvent during the deposition, migration of Ba into the Cu-zeolite layer was observed, resulting in a decay of both ammonia storage capacity and NH3-SCR activity. On the other hand, when water was replaced by n-butanol, the two layers were well segregated, and no loss of SCR performances was noted. The butanol-based formulation exhibited promising performances in the NOx abatement during cold-start transients, with a NO removal efficiency of 31%, prior to ammonia injection, and of 52% after ammonia injection.

Research on NH3-SCR reductant technology progress for diesel vehicles

This paper describes the technical principle, research status and application status of four reducing agents (aqueous urea solution, solid ammonium salt, solid ammonia compound and liquid ammonia) which supply NH3 for SCR of diesel vehicles, introduces the replacement methods of solid ammonia, and analyzes the application feasibility of liquid ammonia. A comprehensive comparative study of the four reducing agents is carried out in terms of storage and validity requirements, low temperature performance, ammonia storage capacity, replacement mode, replacement frequency, safety, cost and future application prospect. It is found that the ammonia storage density of solid ammonia and liquid ammonia is 2.5 ~ 3.5 times of that of aqueous urea solution. And there is no significant difference in the theoretical use cost of several reducing agents, however, the actual use cost of aqueous urea solution is higher than the theoretical value on account of its actual decomposition rate less than 100%. The analysis shows that the requirements for NH3-SCR reductant technology in the future are excellent low temperature supply capacity, small space occupation, convenient use, low cost and guaranteed quality, and etc. As a traditional technology, aqueous urea solution is easy to crystallize at low temperature and can not meet the requirements of low temperature performance. Solid ammonium salt also has the problem of crystallization at low temperature. Solid ammonia compounds meet the above requirements, and the market application is gradually mature. If liquid ammonia wants to be applied in large-scale engineering, its safety problem of storage tank should be solved.

Measurement and Modeling of the effects of exhaust composition and hydrothermal aging on the ammonia storage capacity of a commercial Cu-SSZ-13 catalyst

Copper exchanged chabazites are among the state-of-the-art catalyst materials being studied for selective catalytic reduction of NOx, however, there is still a need to understand how these materials store ammonia after aging. In this work, studies are performed to assess the ammonia storage capacity of Cu-SSZ-13 as a function of concentration, temperature, and extent of hydrothermal aging. Ammonia binds at three difference sites: (i) a Cu site bound at 1 framework Al (Z1Cu site), (ii) a Cu site bound at 2 framework Al (Z2Cu site), and (iii) a Brønsted acid site (ZH site). Results show that a 3-site model can accurately capture ammonia storage across all conditions. Impacts for hydrothermal aging are considered via 3 aging reactions that change the site densities of each identified adsorption site. Model assessment shows that during aging there is a significant loss in Brønsted acid sites.

The ammonia storage and ammonia species reactivity within Cu-ZSM-5 with different copper electronic states

Three Cu-ZSM-5 catalysts having different copper species: 1) the isolated Cu2+ ions, 2) the structures of Cu2+ ions with extra-lattice oxygen (ELO), and 3) the CuO-like nanoparticles, were comparatively studied for their ammonia storage capacity under NH3-Ar, NH3-O2-Ar, and NH3-NO-O2-Ar (SCR-like) feeds. EPR, DR UV–vis, DRIFT techniques and TPD modes were used to evaluate the effect of Cu-state in the O2-activated catalysts on their ammonia storage capacity and conversion of the adsorbed ammonia under Ar, O2-Ar, or NO-O2-Ar feeds. Several types of NH3-species were generated in the NH3-saturated and SCR-treated catalysts. It was shown that NH3-species within the NH3-saturated catalysts, which contained the Cu-structures with ELO or CuO-like nanoparticles, were more reactive compared with the catalyst with isolated Cu2+ ions. For the first two samples, the ammonia sorption capacity determined from the sorption-desorption dynamics at given temperature (25, 200, 300 °C) was higher than amount of the TPD(Ar)-desorbed ammonia under Ar. It is due to selective oxidation of some amount from the coordinated NH3-species, for which ELO of Cu-structures is consumed, the process is accompanied by reduction of Cu2+ to Cu+. The total quantity of the TPD-desorbed ammonia as well as the amount of ammonia coordinated in [Cu(NH3)n]2+ complex decreased with increasing sorption temperature and under O2-Ar or NO-O2-Ar feeds used for TPD mode. Regardless of Cu-states in the catalysts, the molar ratio of the ammonia storage capacity to copper loading was shown by the sorption-desorption dynamics to be ca. 2 at 200 °C, versus 4 typical of the catalyst saturated at 25 °C. These values are consistent with DR UV–vis data, showing a.b. at 14100-14500 cm−1 and 15700−15800 cm−1, respectively. The NH3-TPD(Ar) mode with the NH3-saturated catalysts showed the molar ratio of the TPD-desorbed ammonia to copper loading (ν(NH3)/ν(Cu) equal to 2 for the sample with isolated Cu2+ions; but for two others, the ν(NH3)/ν(Cu) was < 1. Finally, this work is trying to manifest the role of isolated Cu2+ ions and Cu-structures with ELO for SCR-activity.

Thermodynamic and Spectroscopic Analyses of Zirconium Phosphate-Absorbed Ammonia

Zirconium phosphate is insoluble in water and has a large ammonia storage capacity with a low ammonia plateau concentration in water. In this study, the thermodynamics of ammonia on zirconium phosp...

Simulation Study of Ammonia Storage Characteristics of Selective Catalytic Reduction for Diesel Engines

Non-road machinery is very important, but non-road machinery has problems such as working under complex operating conditions. Agricultural machinery is an important type of non-road machinery, which mainly relies on diesel engines due to their high fuel efficiencies. The exhaust temperature of agricultural machinery changes drastically under different working conditions. This article aims to research on pollution control of non-road machinery. Among the exhaust after treatment technologies, selective catalytic reduction (SCR) technology is a very important method to reduce NOx. In this study, a series of tests was conducted to investigate the effects of temperature and exhaust gas mass flow on the NOx conversion and dynamic ammonia storage space distribution characteristics in simulation models. The genetic algorithm, a kind of global optimization algorithm that can avoid local optimization, was used in the parameter identification process. The simulation results showed that the ammonia storage capacity of SCR catalyst decreases as the temperature of SCR increases. With the decrease in temperature, the NH3 desorption rate gradually decreased. An uneven distribution of ammonia storage similar to the shape of ɛ was observed in the simulation and this kind of uneven distribution is obvious at low temperature. The effective area of the catalyst is near the inlet of the catalyst. This work presents an approach to help figure out the details in the ammonia storage process. This work provides information about the dynamic ammonia storage characteristics and guide for better SCR design.

An analysis of SCR reactor deactivation impact on NOx emissions from a compression ignition engine

Catalytic exhaust gas aftertreatment devices fitted to combustion engines are susceptible to partial deactivation as their operating time progresses. This includes selective catalytic reduction (SCR) reactors meant for NOx emission control. There are several known deactivation mechanisms of SCR reactors already analyzed in detail in the literature. This paper, however, approaches the analysis of reactor deactivation by comparison of exhaust gas characteristics over repeatable cycle for fresh and aged samples of a SCR reactor for non-road mobile machinery. The research aims to outline which parameters describing the SCR reactor’s performance are most affected by its ageing. In order to do that, fresh and aged samples of the reactor were tested under the Non Road Steady Cycle. The acquired emission results, including concentration traces of particular compounds were analyzed. The specific NOx emission of the aged reactor was significantly higher than that of the fresh one. The NOx conversion efficiency of both reactors was found similar at periods of steady engine operation. It was recognized that during transient conditions the NOx conversion efficiency of the aged reactor was decreased. It was found that the main factor contributing to that phenomenon is the drop in the ammonia storage capacity of the aged SCR sample.

Influence of CO2 and H2O co-feeding in the NOx abatement by SCR over an efficient Cu-CHA catalyst

Cu-SAPO-34 materials with 2 wt% of copper synthesized in one pot with all the copper inside the framework are hydrothermally stable. Copper oxide species were not detected by XRD after thermal and hydrothermal aging at 750 °C. CO2 and H2O molecules are retained on Cu-SAPO catalyst and are related to CO2 adsorption aided by water involving the Cu-species. Copper species coordination is modified by the reaction atmosphere and the species are directly involved in the SCR-process. A decrease in the ammonia storage capacity in the presence of water has been justified due to the cooperative competition between the ammonia and water adsorption and/or CO2 carbonation over the same sites. Higher coordinated Cu species localized inside of CHA-framework, up to a loading close to 4% with this methodology, are highly efficient in the removal of NOx by reaction with ammonia, in the presence of oxygen, water (1.5%) and CO2 (0.3%) as reaction atmosphere. The SCR mechanism is essentially the same as in dry conditions because the Cu2+/Cu+ ions, in equilibrium with H2O + CO2, are the active species in the SCR-reaction. Hydrated-carbonated Cu(II) and hydrated-carbonated Cu(I) species are associated with the redox-chemistry of NOx abatement as responsible for the improvement in the standard SCR; favoring the hindering of ammonia oxidation and nitrate decomposition. In the SCR temperature range, the conversion values registered for this catalyst are higher than 80% with total selectivity to N2.

An OBD strategy to estimate SCR ageing and detect urea injection faults

The most recent regulation for diesel engines with regards to NOx emissions and SCR systems considers stringent OBD requirements. In this paper, an observer of the ageing state is developed considering NO, NO2 and NH3 concentrations, the surface coverage ratio θNH3, and the ammonia storage capacity Ω as states. The observer is based on an extended Kalman filter and the SCR downstream NOx and NH3 measurements. Accuracy and convergence time are presented for the observer validation in simulation in a dynamic WHTC at warm starting conditions. As the ageing state estimation is based on the residual between a model and measurements, an additional indicator avoids associating an error inherent of urea injection faults to ageing. The performance of this indicator is independent from the ageing state of the SCR. The highly detailed, physics-based 1D SIMCAT model is used as the SCR plant for the ageing estimation and as the model to track the urea injected quality. Then, a control-oriented model is also used in simulation to allow the state-space representation required for the observer. Accuracy of both models is argued, showing the limitations and advantages of the control-oriented model.

Nox conversion efficiency optimization based on NSGA-II and state-feedback nonlinear model predictive control of selective catalytic reduction system in diesel engine

The selective catalytic reduction (SCR) technology is a promising diesel after-treatment technology due to its high NOx reduction potential. A nonlinear model predictive control (NMPC) approach was proposed based on the three-state SCR model here for control and optimization of SCR system to maximize NOx reduction while minimizing NH3 slip and urea consumption; moreover, the ammonia coverage ratio was designed to asa control target, whose desired range was obtained by means of the singular perturbation method, that is to say, the upper limit of ammonia coverage ratio was derived by 10ppm NH3 slip while the lower limit was calculated by maximum NOx conversion efficiency, which was obtained through a novel model based non-dominated sorting genetic algorithm (NSGA-II) according to an optimum tradeoff between NOx conversion and NH3 slip at each engine operating point. The state-feedback NMPC algorithm was applied to ensure the estimated ammonia coverage ratio falling in the desired range so that the SCR performance can be optimized over entire engine operating. The standard European steady-state cycle (ESC) was performed for data generation from a diesel engine equipped with a commercial SCR and to verify the effectiveness of the designed control strategy. Simulation results over the entire ESC indicated that the NOx conversion efficiency may be optimal in various engine operating modes and the NMPC controller ensures the most part of the cycle may conform to the NOx emissions requirements; moreover, the downstream NH3 concentration was less than the limit; especially, the whole mean NH3 slip was 9.7ppm which is basically close to the given limit (10ppm); furthermore, the ammonia storage capacity falls rapidly along with growth of the temperature but the NMPC still worked well for prevention of any unacceptably high NH3 slip. The experimental verification was carried out and the results showed that the designed strategy was effective and acceptable compared with the simulated results.

Mechanistic study of hydrothermally aged Cu/SSZ-13 catalysts for ammonia-SCR

The impact of hydrothermal ageing on the copper sites, crystalline order and critical reactions of a Cu/SSZ-13 was studied. The investigated catalyst had a low Si/Al ratio of 3.7 and was underexchanged at 65%. We propose that this catalyst had nearly saturated ion exchange positions in the 6-membered ring units (6MR) with copper ions, but still contained a significant amount of protonic sites in the large cages (8MR units). Investigation of a broad range of ageing temperatures (550–850°C) allowed us to observe that no significant number of copper ions moved from the large cages into the 6MR units. Nevertheless, the Cu ions experienced a significant increase in reducibility above ageing temperatures of 700°C. However, these changes appeared not to have a large impact on catalyst activity, which was more significantly correlated with long and short-range loss of crystallinity. Thus dealumination occurred at all temperatures above 550°C and was correlated with significantly reduced ammonia storage capacity and ammonia oxidation ability. Low-temperature SCR activity was not much affected below 850°C, but decreased significantly when total collapse of the zeolite framework occurred at this temperature. At ageing temperatures above 750°C, formation of oxidic copper species was observed and correlated partially with increased high-temperature ammonia oxidation capacity, though it is possible that oxidation in parallel occurs on non-oxidic sites in ion-exchange positions. On the other hand, low-temperature ammonia oxidation was shown to occur on ionic copper sites (likely in the 6MR units) and decrease with increasing ageing temperature. We further found some evidence that low-temperature formation of N2O during standard SCR may occur on different sites or via different mechanisms.

The effect of soot on ammonium nitrate species and NO2 selective catalytic reduction over Cu-zeolite catalyst-coated particulate filter.

A selective catalytic reduction (SCR)-coated particulate filter was evaluated by means of dynamic tests performed using NH3, NO2, O2 and H2O. The reactions were examined both prior to and after soot removal in order to study the effect of soot on ammonium nitrate formation and decomposition, ammonia storage and NO2 SCR. A slightly larger ammonia storage capacity was observed when soot was present in the sample, which indicated that small amounts of ammonia can adsorb on the soot. Feeding of NO2 and NH3 in the presence of O2 and H2O at low temperature (150, 175 and 200°C) leads to a large formation of ammonium nitrate species and during the subsequent temperature ramp using H2O and argon, a production of nitrous oxides was observed. The N2O formation is often related to ammonium nitrate decomposition, and our results showed that the N2O formation was clearly decreased by the presence of soot. We therefore propose that in the presence of soot, there are fewer ammonium nitrate species on the surface due to the interactions with the soot. Indeed, we do observe CO2 production during the reaction conditions also at 150°C, which shows that there is a reaction with these species and soot. In addition, the conversion of NOx due to NO2 SCR was significantly enhanced in the presence of soot; we attribute this to the smaller amount of ammonium nitrate species present in the experiments where soot is available since it is well known that ammonium nitrate formation is a major problem at low temperature due to the blocking of the catalytic sites. Further, a scanning electron microscopy analysis of the soot particles shows that they are about 30-40 nm and are therefore too large to enter the pores of the zeolites. There are likely CuxOy or other copper species available on the outside of the zeolite crystallites, which could have been enhanced due to the hydrothermal treatment at 850°C of the SCR-coated filter prior to the soot loading. We therefore propose that soot is interacting with the ammonium nitrate species on the CuxOy or other copper species on the surface of the zeolite particles, which reduces the ammonium nitrate blocking of the catalyst and thereby results in higher NO2 SCR activity.

Estimation and adaptive nonlinear model predictive control of selective catalytic reduction systems in automotive applications

The demands of high NOx conversion efficiency and low tailpipe ammonia slip for urea-based selective catalytic reduction (SCR) systems have been substantially increased in the past decade, as NOx emission legislations for Diesel engines are becoming more stringent than ever before. Since catalyst aging has a significant impact on SCR performance, robust and adaptive SCR control has been preferred for degraded SCR systems to realize emission control objectives. The purpose of this paper is twofold. Firstly, a robust ammonia coverage ratio observer was designed for estimating the ammonia coverage ratio reference for catalysts with different aging levels. An ammonia storage capacity observer was developed for estimating the actual ammonia storage capacity which can be reduced due to catalyst aging. An adaptive ammonia coverage ratio reference design was then developed to estimate the desired ammonia coverage ratio ranges at each instantaneous engine operating point for both single-cell and two-cell SCR systems at different aging levels based on a singular perturbation method. Secondly, to ensure the estimated ammonia coverage ratio falls in the desired ranges for most of engine operating conditions, robust nonlinear model predictive control (NMPC) algorithms were designed for both single-cell and two-cell SCR systems. Experimental data over US06 cycle were collected from a Diesel engine and aftertreatment system platform for controller verification. Simulation results under US06 test cycle demonstrate that the proposed NMPC algorithms were capable of consistently achieving high NOx conversion efficiency (>95.6%) and constrained tailpipe ammonia slip (<10ppm on average and <12ppm on the peak) for both fresh catalyst and aged catalyst with 30% loss of ammonia storage capacity.

High-Throughput Screening as a Supplemental Tool for the Development of Advanced Emission Control Catalysts: Methodological Approaches and Data Processing

A high-throughput (HT) screening platform developed at hte with the application focus on automotive catalysis is described. hte HT units are configured for performing steady-state testing, as well as dynamic tests with fast feed switches, such as lean/rich excursions for the evaluation of NOx storage capacity and efficiency of lean NOx traps (LNT), ammonia storage capacity for selective catalytic reduction (SCR), evaluation of oxygen storage capacity (OSC), as well as lambda sweep tests for screening of three-way catalysts (TWC). Even though catalysts are screened on a rather small scale (~100 mg powder), experience showed that dosing rather complex gas mixtures in concentrations close to that found in real exhaust for the given application is mandatory to generate relevant data. The objective of this work is to give additional insight into HT technology. In the industrial research laboratory, HT screening has matured to become a reliable approach for rapid screening of both reaction parameter spaces, as well as material properties relevant for exhaust gas catalyst development. Due to the speed of optimized screening involving 48 parallel reactors, automated handling of primary data is an imported requirement. Software for data reduction, like estimation of light-off temperature, needs to be robust and handle results for diverse sample libraries in an unattended fashion. In combination with the statistical design of experiment and multivariate data analysis, HT testing has become a valuable enhancement to automotive catalyst development.

Chemical deactivation of H-BEA and Fe-BEA as NH3-SCR catalysts—effect of potassium

H-BEA and Fe-BEA were experimentally studied for selective catalytic reduction of NOX using ammonia (NH3-SCR) with a focus on the chemical deactivation caused by potassium exposure where cordierite-supported H-BEA and Fe-BEA samples were exposed to 10 or 50ppm KNO3 for 14, 24 and 48h in a continuous gas flow reactor at 350°C. The samples were catalytically evaluated and characterized using a flow-reactor system and X-ray photoelectron spectroscopy.The results show that new NOX storage sites are formed on the expense of Brønsted acid sites for ammonia storage for all potassium-exposed samples. The formation of new NOX storage sites results in increased NH3-SCR activity for the potassium-exposed H-BEA samples. However, for the potassium-exposed Fe-BEA samples, the results show a significant decrease in SCR activity.Deconvolution of the Fe 2p3/2 XPS peak shows a clear increase in the relative amount of Fe3+ for the potassium-exposed Fe-BEA samples, indicating that isolated iron species active for NH3-SCR are exchanged with potassium, forming smaller trivalent iron clusters inside the zeolite pores. Transient experiments during NH3-SCR show that the decrease in ammonia storage capacity due to potassium exposure results in a decreased period with improved NO reduction after NH3 cut-off.

Metal-decorated graphene oxide for ammonia adsorption

Based on the first-principles density functional theory, we have studied the stability, electronic structure and ammonia storage capacity of metal-decorated graphene oxide (GO). Metal atoms (Mg and Li) are bonded strongly to the epoxy oxygen atoms on the surface of the GO sheet, which can act as high-surface-area adsorbent for the ammonia uptake and release. Each metal atom can bind several ammonia molecules around itself with a reasonable binding energy. We find metal-decorated GO can store up to tens of moles of ammonia per kilogram, which is far better than the recently reported excellent ammonia adsorption by GO.