Spatial Resolution of Reactant Species Consumption in Diesel Oxidation Catalysts

Irani, Karishma; Epling, William S.; Blint, Richard J.

doi:10.1007/s11244-009-9349-3

Cited by 13 publications

(7 citation statements)

References 9 publications

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“…The plot of normalized reaction rates for the sequential 0.5 inch segments is another way of looking at the conversion plots for the spatially resolved data, and is included to provide a different view of the conversion plots. These data demonstrate that back to front lightoff was observed, as has been previously shown when relatively slow ramp rates are used [6,7]. This backtofront reaction propagation is due to a combination of the exothermic CO oxidation reaction and some oxidation occurring down the length of the channels, which leads to lower CO selfpoisoning at the outlet of the sample.…”

Section: Spatially Resolved Co and Propylene Oxidation In The Absencesupporting

confidence: 79%

“…Typically, studies that included the oxidation of CO and hydrocarbon mixtures over DOCs have used lower total concentrations of CO and hydrocarbons; or in situations with high CO concentrations (on the order of 1 vol%) very low hydrocarbon concentrations were used (100 ppm) [4,5]. On the other hand, where comparable hydrocarbon concentrations were tested, the CO concentrations were nearly an order of magnitude lower than RCCI emissions [6]. Since CO strongly inhibits hydrocarbon oxidation and vice versa, it is important to consider situations where both concentration levels are high in order to select appropriate DOCs to treat LTC emissions.…”

Section: Ltc Technologies Include Premixed Charge Compression Ignitiomentioning

confidence: 99%

“…Both mass spectrometry (MS) and Fourier transform infrared spectroscopy (FTIR) have been used for analysis of gasphase concentrations along diesel oxidation catalysts, as well as other aftertreatment catalysts [6][7][8][9][10]. Regardless of the analyzer used, the concept of these experiments remains the same.…”

Section: Ltc Technologies Include Premixed Charge Compression Ignitiomentioning

confidence: 99%

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Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model oxidation catalyst

Hazlett

Epling

2016

Catalysis Today

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Spatially resolved Fourier transform infrared spectroscopy (SpaciIR) was used to measure gas phase concentration profiles during CO and C 3 H 6 oxidation reactions over a Pt/Al 2 O 3 monolith supported catalyst. The reaction conditions were selected as representative of certain low temperature combustion (LTC) engine exhaust conditions, where in this study higher concentrations of CO, C 3 H 6 and lower concentrations of NO x were used relative to standard engine exhaust. CO and C 3 H 6 oxidation and NO X reduction reactions were examined individually and in combination via temperature programmed oxidation (TPO) experiments. Significant NO X reduction occurred right at CO and C 3 H 6 light off, and NO oxidation only occurred after the oxidation of CO and C 3 H 6. C 3 H 6 oxidation was not observed until after most of the CO oxidized, as CO was more strongly adsorbed to the active site surface at low temperature. During the TPO of CO and C 3 H 6 , the conversion versus temperature profiles did not monotonically increase; two inflections were observed where the rate of conversion change as a function of temperature slowed over a small temperature range before again accelerating with temperature. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used in order to characterize intermediates that were present on the surface at the temperatures where these steps were noted. Surface ethylene and formate species were present during the first step, with acetate and formate in the second step. The inhibition steps were therefore attributed to the partial oxidation of propylene to ethylene, and then the subsequent partial oxidation of ethylene to acetate.

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Section: Spatially Resolved Co and Propylene Oxidation In The Absencesupporting

confidence: 79%

Section: Ltc Technologies Include Premixed Charge Compression Ignitiomentioning

confidence: 99%

Section: Ltc Technologies Include Premixed Charge Compression Ignitiomentioning

confidence: 99%

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Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model oxidation catalyst

Hazlett

Epling

2016

Catalysis Today

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“…One possibility is to introduce a capillary at different positions in the catalyst bed. This approach has been used to study millisecond partial oxidation processes,28 the oxidation of propylene,29 cycling over NO x ‐storage‐reduction catalysts30 and diesel oxidation catalysts 31. Bitsch‐Larsen et al 32.…”

Section: Imaging Catalytic Reactors and Catalyst Bodies: Catalyst mentioning

confidence: 99%

Imaging Catalysts at Work: A Hierarchical Approach from the Macro‐ to the Meso‐ and Nano‐scale

2012

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This review highlights the importance of developing multi‐scale characterisation techniques for analysing operating catalysts in their working environment. We emphasise that a hierarchy of in situ techniques that provides macro‐, meso‐ and nano‐scale information is required to elucidate and optimise catalyst performance fully. This combined methodology should ideally embrace spatially resolved and spatio‐temporal monitoring of a) the structure, catalytic activity, temperature and heat/mass transfer pattern in axial and radial directions in real reactors, b) the structure and temperature/heat/mass transport gradients in shaped catalysts and catalyst grains and c) meso‐ and nano‐scale information about particles and clusters, whose physical and electronic properties are linked directly to the micro‐kinetic behaviour of the catalysts. Techniques such as X‐ray diffraction (XRD), infrared (IR), Raman, X‐ray photoelectron spectroscopy (XPS), UV/Vis, and X‐ray absorption spectroscopy (XAS), which have mainly provided global atomic scale information, are being developed to provide the same information on a more local scale, often with sub‐second time resolution. X‐ray microscopy, both in the soft and more recently in the hard X‐ray regime, allows two‐ and three‐dimensional information to be collected down to 10 nm spatial resolution in a gas atmosphere or liquid, although this improvement is at the expense of temporal resolution. Electron microscopy, which provides excellent local atomic scale structural and spectroscopic information, is being developed towards tomographic imaging and realistic conditions, allowing gaps to be bridged in pressure, reaction conditions and length scales, up to the meso‐ and macro‐scale. In addition, new techniques such as single molecule fluorescence spectroscopy and non‐linear spectroscopic techniques are emerging. In this review, we discuss prospects for the development and combined application of both existing and new techniques for in situ catalyst characterisation.

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“…We speculate that the inflection at 200 °C is due to C 6 H 14 oxidation in the upstream 1:5 Pt:Pd portion versus that in the downstream monometallic Pt portion. This argument is based on the following; for the DZ sample, CO oxidation occurs in the very upstream length of the catalyst, followed by C 2 H 4 and C 7 H 8 , likely in that order. ,,, Therefore, CO oxidation is followed by C 2 H 4 , which is followed by C 7 H 8 , which is followed by C 6 H 14 along the catalyst length. There is likely some remaining portion of the 1:5 Pt:Pd upstream catalyst in the DZ sample that oxidized the C 6 H 14 , without C 2 H 4 inhibition influence.…”

Section: Results and Discussionmentioning

confidence: 99%

Zoning and Trapping Effects on CO and Hydrocarbon Light-Off in Diesel Oxidation Catalysts

Kang

Kalamaras

Balakotaiah

et al. 2017

Ind. Eng. Chem. Res.

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Monometallic Pt and bimetallic Pt/Pd oxidation catalysts, as model diesel oxidation catalysts, were tested in the oxidation of CO, C2H4, C2H6, C7H8, and C6H14. These single monolith catalysts were then compared to a dual-zoned system, where two monoliths were placed in series and the zones were comprised of different Pt/Pd ratios. Finally, a dual-layered system was also evaluated, where the added layer was made of Ag/BEA as a hydrocarbon trap. In terms of trends observed, for the single-zoned system, increasing the Pd content led to increased CO oxidation activity, while the best hydrocarbon oxidation was observed with increasing Pt content, except in the case of C2H6. An improvement in overall oxidation performance was achieved with the dual-zoned system, where a catalyst with a 1:5 Pt:Pd ratio upstream and monometallic Pt downstream proved best of those tested. This is attributed to a combination of relatively high CO oxidation in the upstream high-Pd content piece and the relatively high hydrocarbon oxidation with decreased CO inhibition in the high-Pt content downstream piece. Moreover, the addition of Ag-BEA as a top layer of the dual-zoned oxidation catalyst did result in hydrocarbon trapping, particularly toluene, in the low-temperature region. These results provide useful insight into system-level designs that might be applied to improve low-temperature oxidation performance especially.

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Spatial Resolution of Reactant Species Consumption in Diesel Oxidation Catalysts

Cited by 13 publications

References 9 publications

Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model oxidation catalyst

Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model oxidation catalyst

Imaging Catalysts at Work: A Hierarchical Approach from the Macro‐ to the Meso‐ and Nano‐scale

Zoning and Trapping Effects on CO and Hydrocarbon Light-Off in Diesel Oxidation Catalysts

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