Quantification of Gaseous Urea by FT-IR Spectroscopy and Its Application in Catalytic Urea Thermolysis

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

doi:10.1007/s11244-013-9941-4

Cited by 15 publications

(29 citation statements)

References 19 publications

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“…The materials were washcoated on cordierite monoliths (~2.5 g L -1 ) and tested in a dedicated setup under spray conditions [30]. The gaseous reaction products at the reactor outlet were quantified by FTIR spectroscopy (Antaris, Thermo Nicolet gas cell) [6]. The total flow rate was set at 750 L h -1 , and the contact time was varied by changing the number of monolith pieces stacked along the length of the reactor while keeping constant the total catalyst concentration per unit volume.…”

Section: Methodsmentioning

confidence: 99%

“…However, the application of urea is, in practice, impeded by several problems [3,4]. Alternative ammonia precursors, such as concentrated guanidinium formate, ammonium formate (AmFo), and methanamide solutions, have been proposed to replace urea because they are more thermally stable, freeze at lower temperatures, have a higher ammonia storage capacity, and decompose more selectively [4][5][6][7]. These precursors undergo thermolysis in the hot exhaust to produce formic acid in the gas phase [3].…”

Section: Introductionmentioning

confidence: 99%

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Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Sridhar

Ferri

Bokhoven

et al. 2017

Journal of Catalysis

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Owing to the problems associated with the usage of urea as the ammonia precursor compound in the selective catalytic reduction (SCR) process in automobiles, alternative compounds such as ammonium formate, methanamide and guanidinium formate have been suggested as more efficient and cleaner candidates. For the application of such formate-based ammonia precursors, a fundamental understanding of catalytic formic acid decomposition in the presence of the diesel exhaust components water and oxygen is required. Oxygen activation is a reaction step common to many catalytic processes. We observed that oxygen activation over titania and base-modified titania-supported gold catalysts is greatly enhanced in the presence of water, resulting in a significant increase in carbon dioxide production from the decomposition of formic acid. Unlike the supports, gold catalyzed the selective production of carbon dioxide. Monodentate and bidentate formates are the kinetically relevant surface species for carbon monoxide and carbon dioxide production, respectively. The support acts as a reservoir, storing bidentate formates that do not react in the steady state when formic acid and oxygen (and water) are co-fed. However, during transient experiments, when the feed is switched from formic acid to oxygen (and water), they are reactivated upon reverse spillover to the active site associated with gold, where they decompose to carbon dioxide. In the presence of oxygen and water, carbon monoxide oxidation and the water gas shift reaction do not produce carbon dioxide. Instead, a direct oxidative-dehydrogenationtype (ODH) pathway proceeds, which strongly differs from stoichiometric formic acid decomposition. A kinetically consistent mechanism is proposed in which the hydroperoxy species facilitate the C-H bond cleavage of formates to release carbon dioxide and water in the rate-determining step.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Sridhar

Ferri

Bokhoven

et al. 2017

Journal of Catalysis

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“…Recently, Bernhard et al. confirmed the presence of these lower frequency bands and they attributed the band around 1560 cm −1 to the asymmetric Ti−OCN−Ti stretching mode of adsorbed urea on titania . However, in contrast with these results, no peaks at higher wavenumbers were detected in our analysis and, moreover, no N 1s peak was revealed in the XPS data in the BE region around 400 eV.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic Investigation of Titania‐Supported Gold Nanoparticles Prepared by a Modified Deposition/Precipitation Method for the Oxidation of CO

et al. 2016

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“…Previously, Bernhard et al [37] reported catalytic urea thermolysis as well as hydrolysis under steady-state conditions [42,56]. Figures 16.3 and 16.4 show a catalyst screening, using the data of Ref.…”

Section: Catalytic Urea Decompositionmentioning

confidence: 97%

“…Urea sublimation under vacuum has been known for decades and gaseous urea exists in monomolecular form [32,40,41]. Recent studies have shown that gaseous urea also exists in monomolecular form under atmospheric pressure and that diluted urea vapor is sufficiently stable to be measured by Fourier transform infrared (FTIR) spectroscopy in a gas cell heated to 180°C [39,42]. Comparing the saturation vapor pressure of urea [39,40] with raw NO x emissions of 200-300 ppm of a modern Diesel engine [14] reveals that a temperature of only about 120°C is sufficient for complete evaporation of the required urea (assuming quantitative urea decomposition and NO x reduction).…”

Section: Urea Thermolysis and Evaporationmentioning

confidence: 99%

Ammonia Storage and Release in SCR Systems for Mobile Applications

Peitz

Bernhard

Kröcher

2014

Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts

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The SCR reaction requires ammonia for the reduction of nitrogen oxides. While compressed or liquefied ammonia is used for the supply of ammonia in stationary applications, the odorous ammonia gas had to be replaced in mobile SCR applications by an ammonia precursor compound for the safe storage and reliable release of ammonia in the right quantities and right dynamics. Thus, significant innovation was needed before mobile SCR systems could be realized, even though commercial operation of ammonia SCR systems in coal power plants ([250 MW) started already around 1980 [1]. After the invention of HC-SCR for mobile NO x sources, to avoid handling NH 3 [2], and the discovery of cyanuric acid as a safe NH 3 storage compound, [3] urea was proposed as a storage material for NH 3 in 1988 [4]. By then, urea was already known to work as an NH 3 precursor for SCR in stationary applications for 3 years [5]. First results on mobile urea-based SCR were publically presented in 1990, already showing NO x conversions above 90 % from 250°C at gas hourly space velocities (GHSV) of 12,900 h -1 [6]. The first patented mobile applications of urea solutions for SCR were registered in 1990 [7].Due to the large-scale production of urea as a bulk commodity, it is readily available in large quantities. Since the involved reactants CO 2 and NH 3 needed for urea synthesis are bulk chemicals that are produced directly from air and natural gas, using the well-known industrial Haber-Bosch process, urea can be produced at a low price [8]. Also, urea is nontoxic, noncorrosive and can easily be handled as aqueous solutions, such as a 32.5 wt % solution with the trade name AdBlue

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Quantification of Gaseous Urea by FT-IR Spectroscopy and Its Application in Catalytic Urea Thermolysis

Cited by 15 publications

References 19 publications

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Spectroscopic Investigation of Titania‐Supported Gold Nanoparticles Prepared by a Modified Deposition/Precipitation Method for the Oxidation of CO

Ammonia Storage and Release in SCR Systems for Mobile Applications

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