Commercial Diesel Oxidation Catalyst Research Articles

Manganese-substituted strontium ferrite catalyst on honeycomb structured cordierite support for oxidation of diesel particulate matter

Perovskite-based catalysts have been explored as low-cost substitutes for platinum (Pt)- based catalysts for diesel particulate matter (DPM) oxidation. In this work, manganese (Mn)-substituted strontium ferrite (SrFeMnO3-δ) (SFM) as a catalyst was coated on the honeycomb structure of cordierite support and tested for its catalytic performance for DPM oxidation using a real-world engine. The characteristic diffraction peaks due to the presence of the perovskite structure of SFM were observed for the cordierite-supported SFM. Mn was substituted in the lattice of un-substituted strontium ferrite and no other impurities were formed upon the Mn-substitution. Highly agglomerated SFM particles were formed solely due to the perovskite phase formation temperature (900 °C). The SFM catalyst enhanced catalytic Printex-V oxidation performance compared to its oxidation without the catalyst, where Printex V was used as the model DPM. The SFM catalyst showed high CO2 selectivity upon the oxidation of DPM. These results infer that the SFM catalyst possesses promise as an alternative to commercially available DOC catalysts based on PGM for DPM oxidation. SFM-coated cordierite support performed much better in terms of particle number, mass and surface area than commercial diesel oxidation catalyst (DOC) or without DOC at no engine load. The performance is substantially higher even at moderate engine loads of up to 40% and comparable at very high engine loads of 100%. Detailed investigations on a real engine exhaust and measurement of crucial parameters like particle number, mass and surface area suggest convincing and relatively rare evidence for its potential as a catalyst for diesel exhaust emission control catalyst.

Short Pulse Reductive Activation of Pt/ceria for the Low-Temperature CO Abatement in Vehicles Operated with the Synthetic Diesel Fuel OME

The synthetic Diesel fuel oxymethylene ether (OME) is sulfur-free by nature, and due to the low soot formation, no active filter regeneration events are required, limiting the maximum temperatures seen by the exhaust catalysts to ~ 450 °C. These OME-specific ageing requirements will enable the application of new types of catalysts that cannot be used in conventional Diesel vehicles. Such new catalytic solutions will allow ultra-low emissions at a much-reduced cost and will hence contribute to the overall efficiency of the OME approach. In this contribution, we focus on CO abatement from OME exhaust. To enable an efficient evaluation of new catalysts under practically relevant conditions, a test bench was set up that can reproduce the transient temperature-, mass flow- and concentration profiles measured during real driving tests. In a first step, the transient test bench was used to compare CO oxidation over a commercial Diesel oxidation catalyst for OME- and conventional Diesel conditions. The same low-load cold-start drive cycle run with OME showed slightly lower raw emissions, but the CO emissions downstream of the catalyst increased by a factor of ~ 2. The main reason for the lower CO conversion is the lower temperature of the OME exhaust. In a second step, we investigated short-pulse reductive activation of Pt/ceria as a promising new technology that benefits from the OME-specific low ageing requirements. A Pt/ceria catalyst activated by a short 5–10 s reductive pulse achieved virtually 100% conversion even at exhaust temperatures below 80 °C. With one 5 s reductive activation pulse per 30-minute drive cycle, a CO conversion of > 99.9% is demonstrated over the low-load cold-start OME drive cycle, compared to 59% obtained with a standard commercial Diesel oxidation catalyst. To our knowledge, this is the first published demonstration of short pulse reductive activation of Pt/ceria for CO oxidation using realistic transient drive cycles.

Doping Manganese Oxides with Ceria and Ceria Zirconia Using a One-Pot Sol\u2013Gel Method for Low Temperature Diesel Oxidation Catalysts

Octahedral molecular sieves (OMS-2) are an interesting form of manganese oxide with a 2 × 2 edge sharing tunnel structure and a cation positioned inside. Cryptomelane is an OMS-2 material with K+ cations within the crystalline tunnel and has been widely used in catalytic oxidation reactions, due to a mixed valency of Mn3+ and Mn4+ cations. Cryptomelane (K-OMS-2) can be modified by structural incorporation of various dopants and tunnel cations which can enhance the catalytic activity of the material. It also offers to be a promising alternative material for the low temperature emission control of combustion vehicles; particularly during cold start and low temperature conditions of diesel vehicles. In this work we used a one-pot sol–gel route to synthesize a range of manganese oxide based supports doped with Ce and CeZrO2, as alternative low temperature diesel oxidation catalysts. We have investigated the combination of manganese, ceria and zirconia in mixed oxide catalyst supports. The synthesized samples were loaded with 1 wt% Pt and their activity in the oxidation reactions of CO and C3H6, were compared with a commercial diesel oxidation catalyst with the same metal loading. The reductions in CO and C3H6 oxidation temperature T50 of 109 K and 81 K respectively was achieved compared to a commercial diesel oxidation catalyst.

Applied Catalysis in the Automotive Industry: Development of a Commercial Diesel Oxidation Catalyst Simulation Model Balanced for the Requirements of an Original Engine Manufacturer. Part 2, CO and HC Chemistry

Applied Catalysis in the Automotive Industry: Development of a Commercial Diesel Oxidation Catalyst Simulation Model Balanced for the Requirements of an Original Engine Manufacturer. Part 2, CO and HC Chemistry

Applied Catalysis in the Automotive Industry: Development of a Commercial Diesel Oxidation Catalyst Simulation Model Balanced for the Requirements of an Original Engine Manufacturer. Part 1, NOx Chemistry

Driven by a need for simulations in exhaust aftertreatment system R&D, a simulation model of a commercial diesel oxidation catalyst has been developed. Considering near future legislation demands in which cold starts will be of high importance, focus has been to develop a model which can be used to simulate as many engine operating points as possible and not just those at normal driving conditions. In order to emulate as many operating points as possible, the model has been calibrated and validated against synthetic gas bench tests in which inlet composition, temperature, and space velocity were varied. The model, which is of Langmuir-Hinshelwood type, incorporates three catalytic sites: one representing the precious metal, one NO/NO2 storage site, and one site with a high affinity to oxidation by NO2 with a concomitant NO production. The oxidation of the latter site by NO2 and simultaneous production of NO was found in the experimental data and contradicts the equilibrium thermodynamics of the NO + ½O2 ⇌ NO2 reaction, commonly used to describe the activity of diesel oxidation catalysts. The attitude in most of industry towards simulation models is that they represent a means to an ultimate objective, which is to understand the complete exhaust aftertreatment system. In this paper we present and discuss the performance of our diesel oxidation catalyst simulation model, developed solely using synthetic gas bench data, with this objective in mind.

Effect of Hydrothermal Aging over a Commercial DOC on NO2 Production and Subsequent SCR Efficiency

In this study, the effect of hydrothermal aging over a commercial diesel oxidation catalyst (DOC) on deterioration in nitrogen dioxide (NO2) production activity has been experimentally investigated based on a micro-reactor DOC experiment. Through this experimental result, the NO2 to nitrogen oxides (NOx) ratio at DOC outlet has been mathematically expressed as a function of DOC temperature according to various aging conditions. The current study reveals that the catalyst aging temperature is a more dominant factor than the aging duration in terms of the decrease in NO2 production performance through DOC. The DOC sample hydrothermally aged for 25 h at 750 °C has displayed the lowest NO2 to NOx ratio compared to the samples aged for 25 ~ 100 h at 650 °C. Also, in this study, the impact of hydrothermal aging of a DOC on the selective catalytic reduction (SCR) efficiency in a ‘DOC + SCR’ aftertreatment system was predicted by using transient SCR simulations. To validate the SCR simulation, this study has conducted a dynamometer test of a non-road heavy-duty diesel engine with employing a commercial ‘DOC + SCR’ system on the exhaust line. The current study has quantitatively estimated the effect of the variation in NO2 to NOx ratio due to the hydrothermal aging of DOC on the NOx removal efficiency of SCR.

Experimental investigation on the influence of the presence of alkali compounds on the performance of a commercial Pt–Pd/Al2O3 diesel oxidation catalyst

Experimental investigation was conducted on the influence of the presence of alkali compounds such as K and Na present in biofuels on catalytic behaviors of a commercial diesel oxidation catalyst (Pt/Pd/Al2O3) in the monolith form. Doping of different alkali metal components on carrots of monolith was performed. These carrots were physicochemically characterized, and the catalytic tests consisted of series of temperature-programmed surface reactions with representative exhaust gas mixtures from diesel combustion. The aim of the present study is to reveal the effect of the alkali metal on overall catalytic activity of diesel oxidation catalyst (DOC) and more particularly to show their influence on the reactions involving CO, hydrocarbons, NO, and NO2. Potassium and sodium lead to different catalytic properties. A promotion effect was found in the presence of K, whereas an inhibiting effect was evidenced in the presence of Na or when both Na and K were doped onto the DOC.

A qualitative correlation between engine exhaust particulate number and mass emissions

Diesel particulate are designated as ‘carcinogenic’. In this study, a novel approach has been adopted to determine the relationship between particle mass and particle number emissions from a four-cylinder naturally aspired water-cooled transport diesel engine, which is fuelled by mineral diesel and 20% (v/v) Karanja biodiesel blend (B20) under different engine operating conditions. This approach involves establishing a relationship between particle number-mass emissions by mapping the inclination of identified particulate size concentrations for their dominating contribution towards either particle number or particulate mass. Established relationship is found to be dependent on engine operating condition. Experiment were performed on (i) raw engine exhaust, (ii) exhaust from a commercial diesel oxidation catalyst (DOC1) and (iii) exhaust from two in-house prepared DOCs (named as DOC2 and DOC3). Prepared DOCs were coated with Co-Ce mixed oxide and lanthanum perovskite based catalysts. Results obtained by applying this approach exhibited nearly similar particulate emission characteristics for test fuels, mineral diesel and B20. This technique can therefore be successfully adopted for particulate characterization.

Effectiveness of non-noble metal based diesel oxidation catalysts on particle number emissions from diesel and biodiesel exhaust

Two new formulations of non-noble metal based diesel oxidation catalysts based on CoCe based mixed oxide (DOC2) and perovskite catalysts (DOC3) were prepared and retrofitted in a 4-cylinder diesel engine fueled by diesel and Karanja biodiesel blend (KB20). In this study, their effectiveness in reducing raw exhaust particulate emissions vis-à-vis a commercial diesel oxidation catalyst (DOC1) was evaluated. Emission characteristics such as particle number-size distribution, mass-size distribution, and surface area-size distribution, total particle number concentration and count mean diameter as a function of engine load at constant engine speed were evaluated. Variations in total particle number concentration as a function of engine speed were also determined. The prepared DOCs and the commercial DOC showed varying degrees of performance as a function of engine operating conditions. Overall, effectiveness of the prepared DOC's appeared to be more fuel specific. For diesel exhaust, overall performance of DOC1 was more effective compared to both prepared DOCs, with DOC2 being superior to DOC3. In case of KB20 exhaust, the overall performance of DOC2 was either more effective or nearly comparable to DOC1, while DOC3 being not so effective. This showed that the DOCs based on CoCe based mixed oxide catalysts have potential to replace commercial noble metal based DOC's, especially in engines fueled by biodiesel.

Aging of Commercial Diesel Oxidation Catalysts: A preliminary Structure/Reactivity Study

This study focuses on the catalytic behavior of the diesel oxidation catalyst using different aging characteristics of road mileage in order to improve the efficiency of an ammonia SCR system on an after-treatment line composed by a DOC + DPF + SCR. The studied catalyst is a commercial diesel oxidation catalyst (Pt/Pd/Al2O3) provided by Continental. Hydrothermal aging were performed on carrots of monolith in varying the temperature of treatment. These carrots were characterized, X-ray diffraction, transmission electron microscopy coupled by EDS and specific surface measurement (SBET). The catalytic measurements consisted of series of temperature programmed surface reactions. To be close to real driving conditions, our experimental setup comprised a pre-heater in which the gases were heated up to 500 °C. The goal of this study is to understand the evolution of the active phase with the aging and to correlate these aging results with the corresponding overall catalytic activity and their impact on the reactions involved in the DOC with respect to CO, hydrocarbons and NO.

Investigating carbon monoxide and propene oxidation on a platinum diesel oxidation catalyst

This paper presents a detailed analysis of global kinetic models for the oxidation of carbon monoxide and propene, in the presence of water, hydrogen, carbon dioxide, excess oxygen and nitrogen. The context is the automotive catalytic converter for a lean burn engine. Experimental results are presented for a commercial platinum diesel oxidation catalyst used in the form of a 400 CPSI washcoated monolith. Models are developed based on the classical LHHW format presented by Voltz et al., Ind. Eng. Chem. Prod. Res. Dev. 1973;12:294. The models are developed stepwise for experiments for each reactant alone and the predictive ability of the results is examined. It is found that it is necessary to use experiments with both reactants present to develop a reliable model.

Plasma-Assisted Diesel Oxidation Catalyst on Bench Scale: Focus on Light-off Temperature and NOx Behavior

The effect of a non-thermal plasma reactor over a commercial Diesel oxidation catalyst (DOC) was investigated. Studies have been focused on the gas treatment efficiency together with lowering light-off temperature when a DOC catalyst was connected downstream to plasma reactor in test bench scale. Experiments have been conducted using multi-DBDs (dielectric barrier discharge) reactor in planar configuration driven by a HV AC generator (11 kV–15 kHz). The specific input energy was set to 57 and 85 J/L. Experiments were performed in gas composition simulating Diesel exhaust. Commercial DOC, monolith-supported Pt–Pd/Al2O3, was used at gas hourly space velocities of about 55,000 and 82,000 h−1. CO and hydrocarbons light-off curves were determined for DOC, plasma, and plasma-DOC systems by temperature programmed surface reaction from 80 to 400 °C. Particular attention has been paid to the gas temperature between the plasma reactor and the DOC. Results show that the plasma-catalyst system provides the lowest light-off temperatures for CO and HCs. Under conditions of this study, light-off temperature improvement by about 57 °C was obtained and the plasma reactor totally oxidized NO to NO2 at low temperature.

Hysteresis effect study on diesel oxidation catalyst for a better efficiency of SCR systems

This study focuses on the behaviour of the diesel oxidation catalyst in order to improve the efficiency of an ammonia SCR system on an after-treatment line composed by a DOC+DPF+SCR. The studied catalyst is a commercial diesel oxidation catalyst (Pt/Pd/Al2O3) provided by Renault. For this study, the catalytic phase was extracted from a monolith and different ageings in temperature were performed. The catalysts were characterized by elementary analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled by EDS and X-ray photoelectrons spectroscopy (XPS). The specific surface area was also calculated using a specific apparatus. Main physicochemical properties and elementary analysis of the catalysts were performed in order to determine the noble metal contents. The catalytic measurements consisted on temperature programmed surface reaction (TPSR). The heating rate was chosen equal to 10°Cmin−1. The TPSR were used to determine light off temperature of each pollutant present in the exhaust gases. To be close to industrial conditions, our experimental setup is composed by a heater where the gases are heated up to 500°C. The goal of this study is to study the hysteresis effect with different gas composition and with different catalysts state (ageing, sample/powder).

Diesel Particulate Filter Regeneration Strategies: Study of Hydrogen Addition on Biodiesel Fuelled Engines

The diesel particulate filter (DPF) has attracted considerable attention for the reduction of particulate emissions to meet strict forthcoming emission regulations. The advantages associated with the current commercial diesel oxidation catalyst (DOC) have been implemented and combined with that of the diesel particulate filter for overall improvement in filtration and oxidation efficiencies. This study has been extended to include regeneration of the DPF, with the main focus being on the impact of hydrogen on the DOC performance by means of actual exhaust gas from a diesel engine operating on diesel, biodiesel (RME), and low temperature Fischer–Tropsch (LTFT) synthetic diesel (GTL). This technique is a key element for continuous DPF regeneration at low temperatures. A DOC has the ability to effectively oxidize hydrocarbon and carbon monoxide, as well as enhance the NO2 concentration with increased hydrogen concentration from 0 to 3000 ppm. However, hydrogen addition without the use of a DOC had no significant benefit for DPF regeneration. The combustion of different fuels illustrated in terms of NO2 formation (specifically NO2/NO ratio) over the DOC followed the order RME > GTL > diesel, which represented the ability of DPF regeneration activity in the presence of hydrogen (3000 ppm).

The influence of chemical and thermal aging on the catalytic activity of a monolithic diesel oxidation catalyst

Chemical and thermal aging effects and their influence on the catalytic activity were analyzed for a commercial engine aged diesel oxidation catalyst (DOC). Samples were taken from the inlet (DOCin), the middle (DOCmid) and the outlet (DOCout) area of the ceramic monolith and were compared with a new (DOCnew) and thermal aged (DOC800°C) diesel oxidation catalyst. In all aged DOCs the platinum particles were sintered with particle diameters typically ranging between 10 and 20nm. DOCmid, DOCout and DOC800°C exhibited platinum particle morphology with edges and facets. Round platinum particles without discernable edges and facets were detected in the case of DOCin. DOCin showed two types of continuous, μm-thick contaminant deposits (up to 5 and 20μm) with differing elemental compositions covering the washcoat. Catalytic activity towards the abatement of CO, propene and NO did not show any substantial difference between the different engine aged DOC samples. Thermal aging seems to be the primary cause for the observed loss in catalytic activity compared to DOCnew. However, NO2 production above 275°C was increasing along the monolith in the order of DOCin<DOCmid<DOCout revealing a possible influence of the type of aging on activity towards NO oxidation.

Re-evaluation and Modeling of a Commercial Diesel Oxidation Catalyst

A modeling approach to predict the performance of a commercial diesel oxidation catalyst (DOC) under actual vehicle operating conditions is presented in this study. Prior to completing this prediction, the performance characteristics of DOCs, as previously published, are examined to validate the currently developed in-house computational code. Steady-state experiments with DOCs mounted on a light-duty four-cylinder 2.0-L turbocharged diesel engine then are performed, using an engine-dynamometer system to calibrate the kinetic parameters such as activation energies and pre-exponential factors of heterogeneous reactions. The reaction rates for CO, HC, and NO oxidations over a fresh Pt/Al2O3 catalyst are determined in conjunction with a transient one-dimensional (1D) heterogeneous plug-flow reactor (PFR) model with diesel exhaust gas temperatures in the range of 150−450 °C and space velocities in the range of (1−5) × 105 h−1. To determine the kinetic parameters that best fit the experimental data, a two-step...

Hydrocarbon storage modeling for diesel oxidation catalysts

A simple hydrocarbon (HC) storage model was proposed which represents the adsorption–desorption processes in zeolites incorporated in a diesel oxidation catalyst (DOC). Using four experiments in which the HC was stepped up and the reactor run until steady state, a Langmuir isotherm was generated that was sufficient to represent the equilibrium data, and the remaining rate constant capturing the adsorption time scale was obtained by fitting. The model thus developed was validated using reactor data which was obtained by stepping the inlet HC concentration to zero after outlet reached equilibrium. A typical DOC which contained both a storage component (zeolite) and noble metal component (for oxidation) was studied using a full scale 1D reactor model which includes the storage kinetics developed here with the oxidation kinetics developed in our previous work [ Sampara et al., 2008. Global kinetics for a commercial diesel oxidation catalyst with two exhaust hydrocarbons. Industrial & Engineering Chemistry Research 47, 311–322]. Simulations of a simplified warm-up process indicated that the zeolite storage component reduces the overall cold start HC emissions by at least a factor of two if the warm-up rate achieves 45 – 65 ∘ C min - 1 , a range commonly observed during start-up. Modeling results also showed that the HC oxidation for these reactors commonly starts at the rear end of the reactor due to reduced CO inhibition. The rates of the individual processes during cold start were analyzed in detail and compared with the rate of inlet temperature increase provided from the exhaust.

Kinetic Parameter Estimation of a Diesel Oxidation Catalyst under Actual Vehicle Operating Conditions

A realistic numerical model of a commercial diesel oxidation catalyst (DOC) was developed under an actual vehicle operating condition. To provide the material data as well as to examine the performance characteristics, conversion experiments through the DOC were performed with a 2.0 liter EGR-mounted diesel engine on a dynamometer test bench. Then, on the basis of the currently developed in-house computational code, kinetic parameters of the model reactions were calibrated through a numerical fit to the experimental data. To cover a wide range of operating temperatures, the experiments and modeling were conducted under low engine speeds (i.e., 1000 and 1500 rpm). Main objectives of this study are to develop not only a numerical model based on real-world experiments but also a methodology of how to construct it. Details of the procedure are described step-by-step in this article. Also, on the basis of the experimental results currently observed, it is proposed that additional models considering the NO2 reaction to produce NO are further required than the generally adopted DOC models to capture the negative efficiency behavior in NO oxidation at low temperatures. Because the present DOC model does not take these reactions into account, its prediction performance with experimental results at 1000 rpm is poor for NO and NO2 emissions at low temperatures but is fairly good for CO and HC emissions. On the other hand, the prediction performance at 1500 rpm is good for all of the species as well as over all of the operating temperature ranges.

Global Kinetics for a Commercial Diesel Oxidation Catalyst with Two Exhaust Hydrocarbons

Global kinetics for the oxidation of diesel fuel (DF), propylene (C3H6), CO, H2, and NO were determined over a commercial diesel oxidation catalyst (DOC) with simulated diesel exhaust between 200 and 415 °C over a wide concentration range intended to represent engine exhaust from both conventional and premixed compression ignition (PCI) combustion. Total hydrocarbons in the exhaust were represented as a combination of propylene, to represent partially oxidized fuel species, and diesel fuel, to represent unburned fuel. An integral reactor with high space velocity capability (up to 2 million h-1) was used to generate low and moderate conversion data for the rate-generation process. Mass transport properties of DF were determined based on the experimental data. First-order concentration dependency for all of the reactants involved in the DF, C3H6, CO, and H2 oxidation reactions adequately captured the experimental behavior. An overall inhibition term including only the effects of CO and NO was found to be adequate for these reactions over the range of conditions examined for this study. For the NO oxidation reaction, the rate was found to be first order with respect to NO and 0.5 with respect to O2. The inhibition term for this reaction was found to be a function of DF and NO. Modeling approaches and optimization strategies similar to our previous work1 were employed for the entire rate-generation process. These rate expressions were first validated against light-off curves generated with the same laboratory reactor operating at realistic space velocities and subsequently validated against light-off curves generated on a full-size DOC mounted on a 1.7 L Isuzu diesel engine using both conventional and PCI combustion strategies.

Reactivation of a Commercial Diesel Oxidation Catalyst by Acid Washing

The catalytic activity of samples taken from an oxidation catalyst mounted on diesel-driven automobiles and aged under road conditions was recovered to a significant extent by washing with a dilute solution of citric acid. The characterization of samples arising from a fresh, a vehicle-aged, and a regenerated catalyst was carried out by scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Relatively high levels of S and P, in the form of aluminum sulfate and phosphate, respectively, together with contaminant Si were detected in the used catalyst. Washing of the vehicle-aged catalytic oxidation converter revealed high efficiency in the extraction of the main contaminants detected (S and P) by this nondestructive methodology. The results of the experiments reported here should encourage the development of a technology based on this reactivation procedure for the rejuvenation of the catalytic device mounted on diesel exhaust pipes.