Aftertreatment System Research Articles

경유 대체 합성연료로서 OME 혼합 사용시 예상되는 기본 연소 특성 변화 및 생성물 예측

Ignition delay times and counterflow diffusion flame products are predicted by blending oxymethylene ether-2 (OME-2) into a surrogate diesel. OME-2 is one of a promising e-diesel blendstock which is synthesized from carbon dioxide and hydrogen, thereby reducing net carbon emission from a carbon life-cycle perspective. Results show that OME-2 is more reactive in engine-relevant conditions and the formation of particulate matter from a diffusion flame could be suppressed, thanks to its higher oxygen content. However, potentially harmful intermediates, e.g., formaldehyde and methyl formate, could be formed in large quantity with the use of OME-2, therefore novel combustion strategy and proper exhaust after-treatment system shall be essential for its practical use.

Dimethyl ether low-temperature catalytic oxidation over Rh/Al2O3 in a stagnation-flow reactor

Dimethyl ether (DME) is a promising fuel for use in low-temperature portable hydrogen production, domestic applications, or diesel engines. It burns with less emissions than conventional fuels and has properties similar to LPG in terms of storage and transport, rendering it effective in many strategies for combating climate change. In this study we investigated the partial and total oxidation of DME over 5 wt% Rh/Al2O3 at low temperatures (215 to 320 °C), relevant to portable and domestic energy applications as well as the after-treatment systems of DME-powered engines. We captured the effects of temperature, flow rate, and inlet feed composition on the reactivity. For partial oxidation, we utilized the stagnation-flow reactor geometry to isolate the oxidation zone from the reforming zone. We discuss the reaction order with respect to DME and O2 and provide activation energy values under kinetics control. We also provide data where internal and external mass transfer limitations are present to examine the diffusive-convective transport near the catalyst surface, not easily done in three-dimensional environments such as packed beds. The experimental data we provide here pave the way for accurate kinetic modeling of DME partial and total oxidation on Rh/Al2O3, for reactor design and optimization as well as rational catalyst design.

Ducted fuel injection with Low-Net-Carbon fuels as a solution for meeting future emissions regulations

Several studies have proven how ducted fuel injection (DFI) reduces soot emissions for compression-ignition engines. Nevertheless, no comprehensive study has investigated how DFI performs over a load range in combination with low-net-carbon fuels. In this study, optical-engine experiments were performed with four different fuels—conventional diesel and three low-net-carbon fuels—at low and moderate load, to measure emissions levels and performance. The 1.7-liter single-cylinder optical engine was equipped with a high-speed camera to capture natural luminosity images of the combustion event. Conventional diesel and DFI combustion were investigated at four different dilution levels (to simulate exhaust-gas recirculation effects), from 14 to 21 mol% oxygen in the intake. At a given dilution level, with commercial diesel fuel, DFI reduced soot by 82 % at medium load, and 75 % at low load without increasing NOx. The results further show how DFI with dilution reduces soot and NOx without compromising engine performance or other emission types, especially when combined with low-net-carbon fuels. DFI with the oxygenated low-net-carbon blend HEA67 simultaneously reduced soot and NOx by as much as 93 % and 82 %, respectively, relative to conventional diesel combustion with commercial diesel fuel. These soot and NOx reductions occurred while lifecycle CO2 was reduced by at least 70 % when using low-net-carbon fuels instead of conventional diesel. All emissions changes were compared with future emissions regulations for different vehicle sectors to investigate how DFI can be used to facilitate achievement of the regulations. The results show how the DFI cases fall below several future emissions regulation levels, rendering less need for aftertreatment systems and giving a possible lower cost of ownership.

Exhaust Gas After-Treatment Systems for Gasoline and Diesel Vehicles

Review Exhaust Gas After-Treatment Systems for Gasoline and Diesel Vehicles Liye Bao 1, Jihua Wang 2, Lihui Shi 2, and Haijun Chen 1, * 1 College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300350, China 2 Valiant Co., Ltd., Yantai 264006, China * Correspondence: chenhj@nankai.edu.cn Received: 5 October 2022 Accepted: 10 November 2022 Published: 25 December 2022 Abstract: Exhaust gases released from vehicle engines have been a major cause of air pollution, and the emission limits have become much stricter in recent years due to a worldwide concern about the impact of air pollution on public health. These regulations have been complied to minimize the emissions of carbon monoxide (CO), hydrocarbons (HCs), nitrogen oxides (NO x) and particulate matter (PM) from gasoline and diesel vehicles engines. Different after-treatment systems (ATS) have been developed for the treatment of exhaust gases from gasoline and diesel engines, respectively. The ATS for gasoline engine based on the three-way catalysts (TWCs), as well as the ATS for diesel engines including diesel oxidation catalysts (DOC), selective catalytic reduction (SCR), diesel particulate filters (DPF) and ammonia slip catalysts (ASC), are summarized in this mini-review.

An Experimental and Computational Study on Triple Injection Strategies to Reduce Cold Start Diesel Engine Emissions

Abstract The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions.

Thermodynamic analysis of power recovery of marine diesel engine under high exhaust backpressure by additional electrically driven compressor

Marine diesel engines can be exposed to high backpressure conditions, because various aftertreatment systems and waste heat recovery devices have been applied to reduce emissions and some exhaust outlets are below sea level. The engine performance deteriorates sharply under high backpressure. This paper aims to study power recovery method under high backpressure based on thermodynamic analysis. Firstly, thermodynamic model is established and validated by experimental data. Next, effects of turbocharger efficiency and turbine area on power recovery are studied. The results show that feasible turbine performance are limitations for power recovery. If energy of compressor can be increased without changing turbine area, limitations can be overcome. Thirdly, additional electrically driven compressor as a solution is proposed to recover engine power. A comparative study of different electrically driven compressor schemes is carried out. The most suitable scheme is the series scheme at low-pressure stage because operating points for original compressor and electrically driven compressor are within a reasonable range. Finally, research on power recovery is carried out on optimal electric compressor scheme. The results show that when backpressure is 0.65 bar, engine net power can be increased by 49.4% and exhaust temperature drops by about 77 K, which largely reduces turbine thermal load.

Impact of hydrogen substitution for stable lean operation on spark ignition engines fueled by compressed natural gas

Compressed Natural Gas (CNG) appears as a midterm solution to conventional fuels, such as gasoline and diesel. The low carbon content and the possibility of being obtained from renewable sources (animal or agriculture waste, landfills, waste of the industry food or aquatic biomass) make CNG an attractive option to reduce Greenhouse Gases (GHG) emission. Applying lean combustion strategies on CNG improves efficiency levels while reducing pollutant emissions. In these conditions, heat transfer losses are reduced, and the thermal efficiency increased, especially at partial loads where increasing air dilution is one of the main strategies to reduce pumping losses. Hydrogen (H2) addition helps to enhance combustion in these diluted conditions and to reduce the combustion instability. This combustion concept has been widely studied over the last years, however further research is still needed. This investigation focuses on how hydrogen substitution affects the performance and emissions (both CO2 and pollutant) of a port fuel injection (PFI) spark ignition (SI) engine fueled by CNG. Thus, the main objective of this investigation is to contribute to the existent knowledge about dual-fuel combustion strategies based on CNG and H2 blends. Results demonstrated that hydrogen substitution helps to reduce the CO2 emissions by two ways: improving the engine efficiency and substituting part of the main carbon-based fuel. Despite of this advantage, NOx emissions are not reduced, and they will require after-treatment systems to deal with current pollutant regulations.

Ammonia Slip Estimation Based on Ammonia Slip Catalyst Control-Oriented Modeling and On-Board Diagnostics NOX Sensor Cross-Sensitivity Analysis

Abstract The incoming emission regulations for internal combustion engines are gradually introducing new pollutant species, which require greater complexity of the aftertreatment systems concerning layout, control, and diagnostics. This is the case of ammonia, which is injected into the exhaust gas through urea injections for NOx abatement in selective catalytic reduction (SCR) systems and can also be generated in three-way catalysts. However, ammonia slip requires its oxidation on a dedicated ammonia slip catalyst (ASC). The set composed of the urea injection system, SCR, and ASC requires control tools to ensure high NOx conversion efficiency and compliant ammonia slip under real driving conditions. These tasks are based on the use of NOx sensors ZrO2 pumping cell-based, which has the disadvantage of high cross-sensitivity to ammonia that can affect the measurement of NOx and compromise the SCR-ASC control strategies. The present work proposes a methodology to predict ammonia and NOx tailpipe emissions. For this purpose, a control-oriented ASC model was developed to use its ammonia slip prediction to determine the cross-sensitivity correction of the tailpipe NOx sensor. The model is based on a simplified solution of the transport equations of the species involved in the ASC reaction mechanism. The model was calibrated using steady- and quasi-steady-state tests performed in a Euro 6c engine. Finally, the performance of the proposed methodology to predict NOx and ammonia emissions was evaluated against experimental data corresponding to worldwide harmonized light vehicles test cycles (WLTC) applying different urea dosing strategies.

Emissions from a Euro 6 engine using polyoxymethylene dimethyl ethers: Chemical effects vs mapping strategy

New fuel technologies, such as electrofuels, are an attractive alternative to meet the energy demand and emission regulations, with sustainable electricity being the primary source of energy. Recently, there is increasing interest in using polyoxymethylene dimethyl ether (OME) as a diesel substitute. This study investigated the effect of a diesel fuel blend with 20% of OME (OME20) with 3–5 oxymethylene groups, on the performance, combustion characteristics, regulated emissions, particle number (PN), and particle size distribution in a compression ignition Euro 6 engine following the Worldwide harmonized Light vehicle Test Cycle (WLTC). Regulated emissions were measured downstream of the aftertreatment system, while PN emissions were measured upstream of the particulate filter. The results showed that OME20 increased the peaks of pressure and heat released rate, causing an increase in the combustion speed compared to diesel. OME20 reduced CO and THC accumulated emissions by 52% and 17%, respectively, and the PN exhibited a dramatic reduction close to 61%. Such reductions were influenced by both the fuel formulation and the engine settings induced by the fuel. With OME20, the engine requires higher fueling to maintain the same power output. Therefore, the accelerator pedal position was higher compared to diesel, leading a decrease in exhaust gas recirculation (EGR) rate to increase the air mass flow. Consequently, PN, CO and THC emissions were reduced, and conversely, accumulated NOx emissions increased up to 42%. OME20 decreased the peak number concentrations of accumulation-mode particles at all driving cycle phases and caused a slight shift of the particles toward smaller size compared to diesel fuel. From the results, it can be concluded that PN and regulated emissions, despite being strongly affected by the fuel properties, are very sensitive to the EGR rate and the equivalence ratio, which are established in the engine mapping.

CFD investigation of the radiative heat transfer effects on the adoption of an electrical heated catalyst to increase the abatement efficiency

The thermal transient of the after-treatment system (ATS) during the cold start and the typical urban drive low load engine operations is a crucial point for the conversion efficiency. In this context, the adoption of electrical heating is regarded as an effective solution to promote the catalytic activity and the pollutants abatement. This paper focuses on the evaluation of the radiative heat transfer affecting the operation of an electrical heated catalyst employed to increase the abatement efficiency of a standard catalyst. The modeling methodology relies on a CFD framework based on a Conjugate Heat Transfer (CHT) approach in OpenFOAM, so that a detailed characterization of the thermal transient of the different components of the exhaust line can be achieved. The electrical heating device under investigation is based on a metallic support and it is heated by the Joule effect. The distribution of the heat and its subsequent interaction with the gas flow significantly influence the catalyst operations. In this context, the CFD modeling framework has been further developed so that it is possible to accurately evaluate the radiative heat transfer in correspondence of the porous regions. The description of such features is mandatory for an accurate prediction of the maximum electrical heating device temperatures, resulting in a reliable estimation of the gas flow temperature and its subsequent interaction with the catalyst. The simulation methodology has been applied at first excluding the radiative heat transfer. Then, the developed radiation modeling is applied, so that its influence on the ATS performance can be fully evaluated.

Reduction of Diesel Engine’s Particulate Matters using Retrofit CeO2 Diesel Oxidative Catalyst and Partial Flow Diesel Particulate Filter System

In this research, CeO2 was chosen for the DOC catalyst. Moreover, a partial-flow DPF was installed after DOC. The exhaust gas experiment was conducted at 20% - 50% engine load varying 1000,1500, and 2000 rpm of engine speed. The research results show that NOx reduced around 25% with CeO2 DOC and DPF systems at higher engine load. On the other hand, particulate matters decrease around 65% after CeO2 DOC and DPF systems. Furthermore, CO and HC amount were substantially reduced after applying after-treatment systems. According to fuel consumption, BSFC, and BTE results, the after-treatment system has no significant impact on engine performance.

Real driving emissions of Euro 6 electric/gasoline hybrid and natural gas vehicles

Electric hybrid powertrain and natural gas fuel for spark-ignition engines are among the much promising technologies to reduce the fossil fuel use for road transportation and the emissions of harmful and greenhouse gases. This paper investigated gas and particulate real emissions of hybrid and natural gas passenger cars. On road testing were carried out along urban, rural and motorway routes in Napoli (Italy), by using portable emissions measurement systems. Hybrid vehicle has the main advantage of fuel saving in urban environment due to large use of pure electric mode operation at low speed and load. On the other hand, continuous engine restarting causes peak emissions due to a longer light-off time of aftertreatment systems. By analysing the Vehicle Specific Power, it was observed that at same positive values of power, natural gas vehicle is characterized by lower emission and fuel/energy consumption rates compared to the hybrid vehicle.

A preliminary computational analysis towards the use of Electrically Heated Mixing Catalyst for innovative SCR after-treatment systems

This work aims at investigating the possible advantages of substituting the mixer in traditional SCR systems with an Electrically Heated Catalytic structure (EHC). First of all, EHC technology is being widely investigated in literature because it offers a concrete solution for catalyst thermal activation and film formation reduction in engine cold start conditions; however, its adoption as a mixer can also guarantee other important improvements in reducing pollutant emissions. In this work, a low-pressure injection of Ad-Blue impacts an electrically heated structure and a complete analysis of liquid droplets and film evaporation is carried out. A hybrid Eulerian-Lagrangian model has been adopted on a multi-region configuration, accounting for fluid-solid conjugate heat transfer (CHT), which plays a key role in the conversion strategy: it has been demonstrated that the heated structure can be exploited to significantly increase the exhaust gas enthalpy in the cold start, which represents an important improvement for pollutant conversion. Different heating strategies are analysed, with the objective of maximising the spray evaporation and the uniformity of the ammonia distribution downstream of the mixer. The objectives of this work are emphasizing the improvements that an electrically heated mixing catalyst can bring to the traditional SCR configuration, laying the foundation for other following studies.

Numerical assessment of fuel physical properties on high-dilution diesel advanced compression ignition combustion

Using traditional lean air-fuel mixture aftertreatment technologies to reduce NOx at low exhaust temperatures is limited below 175°C. Recent low engine load NOx emission regulations encouraged researchers to explore the potential of fuel physical properties to enable low-temperature, low-NOx combustion under challenging conditions in which the selective catalytic reduction device might be unable to treat engine-out NOx. Three diesel range fuels were developed to explore how the distillation profile affects and may enable low-load diesel advanced-compression ignition. The least volatile fuel is a conventional, commercially available diesel #2 fuel with a cetane number of 45.3. The second-most volatile fuel is diesel #1 fuel, which can also be found commercially. The last fuel, which is the most volatile, is a new formulation designed to target a final boiling point approximately 50 K below diesel #1 fuel and was termed diesel #0 fuel. A computational fluid dynamics model was developed and validated against experimental data to investigate the underlying effects of each of the developed fuels in the combustion process. Finally, each fuel physical property (e.g., density, viscosity, etc.) was changed independently to assess its effect under the same operating conditions and identify potential directions for fuel formulation that may enable improved NOx emissions and reduce the reliance on aftertreatment systems for NOx control. The results showed that although changes in the fuel distillation curve and other physical properties affect the air-fuel mixtures substantially, changes were not sufficient to result in a large impact to low-load NOx formation. The maximum predicted NOx reduction was 11% uncorrected by combustion phasing. The results suggest that further research efforts should focus on changing the chemical properties of the fuel, like the cetane number, to allow higher EGR dilution and stable combustion.

Research Progress on Sulfur Deactivation and Regeneration over Cu-CHA Zeolite Catalyst

Benefiting from the exceptional selective catalytic reduction of NOx with ammonia (NH3-SCR) activity, excellent N2 selectivity, and superior hydrothermal durability, the Cu2+-exchanged zeolite catalyst with a chabazite structure (Cu-CHA) has been considered the predominant SCR catalyst in nitrogen oxide (NOx) abatement. However, sulfur poisoning remains one of the most significant deterrents to the catalyst in real applications. This review summarizes the NH3-SCR reaction mechanism on Cu-CHA, including the active sites and the nature of hydrothermal aging resistance. On the basis of the NH3-SCR reaction mechanism, the review gives a comprehensive summary of sulfate species, sulfate loading, emitted gaseous composition, and the impact of exposure temperature/time on Cu-CHA. The nature of the regeneration of sulfated catalysts is also covered in this review. The review gives a valuable summary of new insights into the matching between the design of NH3-SCR activity and sulfur resistance, highlighting the opportunities and challenges presented by Cu-CHA. Guidance for future sulfur poisoning diagnosis, effective regeneration strategies, and a design for an efficient catalyst for the aftertreatment system (ATS) are proposed to minimize the deterioration of NOx abatement in the future. Finally, we call for more attention to be paid to the effects of PO43- and metal co-cations with sulfur in the ATS.

Real-Time Measurement of NOx Emissions from Modern Diesel Vehicles Using On-Board Sensors

In this work, the performance of on-board vehicle exhaust emission sensors is investigated and compared to reference laboratory and on-road instrumentation for two modern diesel light-duty commercial vehicles, type-approved as Euro 6d-TEMP-EVAP-ISC and Euro 6d-ISC-FCM. The first step of the analysis was to perform emissions tests in the laboratory and compare the NOx concentrations registered by the vehicle sensors available at the engine-out and tailpipe positions with those recorded by reference laboratory instrumentation. In a second step, tests were also conducted on road, comparing the performance of on-board sensors with those of Portable Emission Measurement System (PEMS) analysers, which were taken as references. The uncertainty related to exhaust flow measurements was also addressed. In particular, emissions factors calculated using the flow rates measured either in the laboratory or on-road were compared to those obtained by computing exhaust flows with on-board recorded data available from the vehicle electronic control unit. Results showed maximum deviations on the order of 34% in laboratory tests and of 21% during on-road measurements. Finally, measurements were also carried out during a diesel particulate filter regeneration event, showing the good performance of the on-board sensors even when high NOx concentrations were present. These conditions can be similar to those experienced in the case of an after-treatment system malfunction or of a high-emitting event, and can thus be of interest for real-time malfunction identification and monitoring.

Turbulent uniformity fluctuations in automotive catalysts – A RANS vs DES assessment

Attaining sufficient flow uniformity in catalytic aftertreatment systems is a major challenge for the automotive industry. Computational fluid dynamics (CFD) simulations offer means of analyzing and quantifying this flow uniformity in silico. In this work, predictions from numerical simulations of flow uniformity obtained using a conventional steady-state Reynolds-Averaged Navier-Stokes (RANS) approach are contrasted against comprehensive Detached Eddy Simulations (DES) where the large-scale turbulence is resolved in space and time. It is shown that the DES approach provides access to data on flow uniformity fluctuations that could be significant for the catalyst light-off behavior. However, the computational cost of the DES is approximately three orders of magnitude larger than that of the corresponding RANS simulation.

A negative emission internal combustion engine vehicle?

Modern internal combustion engine vehicles carry extensive exhaust aftertreatment systems that have the potential to reduce their tailpipe pollutant emissions to near-zero, or even within the zero levels of measurement equipment in real-world conditions. It has been reported, therefore, that such vehicles have the potential to have tailpipe pollutant levels lower than the air intake of the vehicle – that they are cleaning the ambient air. This study investigates this hypothesis using a range of internal combustion engines and real-world emissions data alongside pollutant (in this case nitrogen dioxide and particulate matter) data from around the world and the accuracy of the instrumentation typically used to measure tailpipe emissions. The results show that it is unlikely that a modern internal combustion engine vehicle will clean ambient air, even at extreme pollution levels, although it is possible. However, where a vehicle inlet is in the plume of a dirtier vehicle or the pollution measured is among the highest values recorded globally, the pollution reduction can be substantial.

Effects of waste-cooking-oil biodiesel blends on diesel vehicle emissions and their reducing characteristics with exhaust after-treatment system

The waste-cooking-oil biodiesel is proven to be a clean alternative fuel, its effect on the vehicle emissions at different driving conditions needs further quantitative evaluation, especially with the exhaust after-treatment. The objective of this study is to quantify the effect of waste-cooking-oil biodiesel on the gaseous and particulate emissions from an urban bus at different driving conditions, and with a combination of diesel oxidation catalyst (DOC) and a catalyzed diesel particulate filter (CDPF) after-treatment. Results showed that the emissions depended on the driving conditions, vehicle acceleration and high speed increased the emissions. The biodiesel blends produced a reduction in the carbon monoxide (CO), total hydrocarbon (THC), particle number (PN) and particle mass (PM) emissions, but an increase in the carbon dioxide (CO2) and nitrogen oxide (NOx) emission, and this changing trend increased with not only the biodiesel blending ratio but also the vehicle speed and acceleration. The particle size distribution remained bimodal logarithm distribution after using the biodiesel, and more accumulation mode particles reduced compared with nucleation mode ones, increasing the proportion of nucleation mode particles. The after-treatment system composed of DOC and CDPF could reduce 58.0% of the CO and 53.1% of the THC when using B10 (10% biodiesel and 90% diesel by volume), and the reduction effect was enhanced with the increase of the biodiesel blending ratio, also with the increase of speed and acceleration. The after-treatment system reduced more than 99% of the PN and 94% of the PM, achieving excellent reduction effects, independent of fuel type and driving conditions.

Decomposition of Heavy Diesel SCR Urea Fluid Adsorbed in Cu/HZSM-5 SCR Catalysts Studied by FTIR Spectroscopy at Ambient Conditions

A method is presented to study the decomposition of urea deposited on Cu/HZSM-5 SCR catalysts and therewith the ability of the Cu/HZSM-5 SCR catalyst to be regenerated when being overdosed with SCR urea fluids during operation. This straightforward laboratory method could speed up calibration of exhaust gas aftertreatment systems. As an example, the removal of adsorbed urea to the SCR substrate due to dosage malfunction is studied. To study the removal of adsorbed urea on the catalyst substrate, FTIR experiments have been conducted to investigate the state of the catalyst. Besides Cu/HZSM-5 also HZSM-5 and CuOx were studied as model compounds to provide more inside on the processes occurring at the Cu/HZSM-5 surface upon urea decomposition. To simulate exposure of the SCR catalyst to overdosing of the urea solution, samples were impregnated with a 32 wt% urea solution, which correlates to that of commercial heavy duty diesel urea solutions. After impregnation, the samples were heated at various temperatures in the 133–400 °C temperature region, typically the operation window of a SCR catalyst. After heating, the samples were cooled to room temperature and measured in FTIR. The obtained spectra were compared with various literature reports to correlate the observed absorption bands to urea, urea related compounds and decomposition compounds. The concentration of these adsorbed species decreases at increased thermolysis temperature and is no longer visible at temperatures >250 °C. Extended heat treatment at 200 °C revealed only minor loss of adsorbents after 6 h and were still observable in the FTIR spectra after 24 h. Urea derived adsorbents were completely removed when simulating catalyst regeneration under SCR operation conditions under continuous air flow with a humidity of 10% and at elevated temperatures (400 °C).