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Hydrolysis and thermolysis of urea and its decomposition byproducts biuret, cyanuric acid and melamine over anatase TiO2

Paper ID Volume ID Publish Year Pages File Format Full-Text
46414 46439 2012 9 PDF Available
Title
Hydrolysis and thermolysis of urea and its decomposition byproducts biuret, cyanuric acid and melamine over anatase TiO2
Abstract

A major problem in the selective catalytic reduction of NOx with urea (urea-SCR) is the formation of urea decomposition byproducts, which can be suppressed by the use of TiO2 as a hydrolysis catalyst. Temperature programmed desorption and reaction (TPD/R) experiments with urea, biuret, triuret, cyanuric acid and melamine on TiO2-coated and inert cordierite monoliths were used to investigate the reaction network of urea byproduct formation and decomposition over anatase TiO2. All investigated compounds were found to be catalytically hydrolyzed over TiO2. Biuret was directly hydrolyzed to urea in one step, whereas melamine hydrolyzed step-wise via ammeline and ammelide to cyanuric acid. Finally, cyanuric acid completely hydrolyzed to ammonia and carbon dioxide. The formation of byproducts was strongly favored in the absence of water. A reaction network was developed for the uncatalyzed and catalytic decomposition of urea, showing the most important reactions of urea, isocyanic acid, biuret, triuret, cyanuric acid, ammelide, ammeline and melamine under low-temperature operating conditions in SCR systems. Our results support the approach of using a special hydrolysis catalyst for urea decomposition or of catalytic coatings on exhaust pipes to avoid byproduct formation.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Anatase TiO2 as hydrolysis catalyst for urea decomposition byproducts. ► Biuret is directly hydrolyzed in one step to urea over TiO2 at only 100 °C. ► Melamine is hydrolyzed in a multi-step reaction, starting at substituting the amine groups. ►Stability against hydrolysis over TiO2: cyanuric acid > ammeline > ammelide ≈ melamine.

Keywords
cpsi, cells per square inch; CYA, cyanuric acid; DSC, differential scanning calorimetry; FTIR, Fourier transform infrared; GHSV, gas hourly space velocity; SCR, selective catalytic reduction of NOx; STP, standard pressure and temperature for gases (T = 0 
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Hydrolysis and thermolysis of urea and its decomposition byproducts biuret, cyanuric acid and melamine over anatase TiO2
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volumes 115–116, 5 April 2012, Pages 129–137
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us