Catalytic urea hydrolysis in the selective catalytic reduction of NOx: catalyst screening and kinetics on anatase TiO2and ZrO2

Bernhard, Andreas M.; Peitz, Daniel; Elsener, Martin; Schildhauer, Tilman J.; Kröcher, Oliver

doi:10.1039/c2cy20668d

Cited by 67 publications

(70 citation statements)

References 31 publications

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“…In addition, it was likewise proposed that zirconium oxide works differently. A different reaction pathway is advanced in which water directly reacts with adsorbed urea rather than adsorbed HNCO, leading to a high urea hydrolysis activity of the ZrO2 catalyst, compared to its low urea thermolysis activity [23]. Conversely, these authors also report that anatase TiO2 presents higher efficiency than ZrO2 for urea thermolysis.…”

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 75%

“…It is reported that the urea thermolysis is much slower than HNCO hydrolysis and therefore that catalytic urea thermolysis into NH3 and HNCO is probably the rate-determining step in urea decomposition [22]. Recently, kinetic studies on the decomposition reactions of urea on TiO2 support this assumption [23]. In addition, it was likewise proposed that zirconium oxide works differently.…”

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 80%

“…These results clearly evidence that the rate determining step in catalytic urea decomposition depends on the composition of the solid. Finally, for the urea thermolysis into HNCO and NH3, the following activity order was observed: TiO2 > H-ZSM-5 ≈ Al2O3 > ZrO2 > SiO2; whereas for the HNCO hydrolysis, the ranking becomes ZrO2 > TiO2 > Al2O3 > H-ZSM-5 > SiO2 [23].…”

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 99%

“…According to the previously mentioned work [23], it is proposed that the decrease of the NOx conversion between tR = 5.2 s and tR = 4.0 s is mainly attributable to a limitation of the HNCO hydrolysis, impacting the NH3 availability.…”

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 99%

“…For instance, over anatase TiO2, Bernhard et al [23] observed that the hydrolysis was somewhat slower than thermolysis below 150 °C, whereas the hydrolysis was faster above 160 °C. Unfortunately, during the urea decomposition process, undesired reactions can also occur.…”

Section: Introductionmentioning

confidence: 99%

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Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

et al. 2015

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Abstract:The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype powdered catalysts, a specific synthetic gas bench adjusted to powdered material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis, OPEN ACCESSCatalysts 2015, 5 1536 which can be improved by addition upstream of an active solid for the hydrolysis reaction such as ZrO2. Thus, this µ-scale synthetic gas bench adjusted to powdered materials enables the specific behaviour of urea use for NOx reduction to be demonstrated.

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Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 75%

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 80%

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 99%

Section: Understanding Of the Loss Of Activity Observed For Tr = 40 Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

et al. 2015

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Urea Decomposition in Selective Catalytic Reduction on V₂O₅/WO₃/TiO₂ Catalyst in Diesel Exhaust

et al. 2017

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Selective catalytic reduction (SCR) of NO x by AdBlue and NH3 on monolithic V 2 O 5 /WO 3 /TiO 2 catalyst was studied under flow conditions realistic for diesel exhaust. The tests provided same standard and fast SCR for AdBlue and NH 3 from 150 to 350°C. For standard urea-SCR, axial concentration profiles were checked by monoliths with different lengths evidencing incomplete conversion of urea and isocyanic acid at low temperatures. But SCR was not clearly affected by under-stoichiometric NH 3 as substantiated by kinetic analysis. However, above 250°C, SCR was limited by internal mass transport indicated by Weisz-Prater criterion and lower activation barrier. Formation of deposits was investigated at 175°C and below showing some urea around the nozzle, whereas cyanuric acid and biuret additionally formed around the catalyst.

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Urea Conversion for Low‐Temperature Selective Catalytic Reduction in a Swirled Diesel Exhaust Gas Configuration

et al. 2022

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A novel design of an AdBlue mixing unit to reduce urea deposits at low temperatures in diesel exhaust is described. The main principle of the mixer includes the injection of AdBlue in an axisymmetric swirling flow, which is achieved by splitting the exhaust stream and off‐centred introduction of the sub‐flows. Crucial geometric parameters were analyzed by computational fluid dynamics (CFD) simulations towards pressure loss, flow field, and spray morphology. Deposit formation was experimentally investigated on three upscaling levels implying an optical test bench, a diesel engine test bench, and a hydraulic excavator. In particular, the studies with the hydraulic excavator showed neither deposits nor critical back pressure. Overall, the experiments substantiated the working principle of the AdBlue mixer.

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Catalytic urea hydrolysis in the selective catalytic reduction of NO_x: catalyst screening and kinetics on anatase TiO₂and ZrO₂

Cited by 67 publications

References 31 publications

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

Urea Decomposition in Selective Catalytic Reduction on V₂O₅/WO₃/TiO₂ Catalyst in Diesel Exhaust

Urea Conversion for Low‐Temperature Selective Catalytic Reduction in a Swirled Diesel Exhaust Gas Configuration

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Catalytic urea hydrolysis in the selective catalytic reduction of NOx: catalyst screening and kinetics on anatase TiO2and ZrO2

Cited by 67 publications

References 31 publications

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

Urea Decomposition in Selective Catalytic Reduction on V2O5/WO3/TiO2 Catalyst in Diesel Exhaust

Urea Conversion for Low‐Temperature Selective Catalytic Reduction in a Swirled Diesel Exhaust Gas Configuration

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Resources

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Catalytic urea hydrolysis in the selective catalytic reduction of NO_x: catalyst screening and kinetics on anatase TiO₂and ZrO₂

Urea Decomposition in Selective Catalytic Reduction on V₂O₅/WO₃/TiO₂ Catalyst in Diesel Exhaust