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Ag/ALUMİNA KATALİZÖRLERİ ÜZERİNDE ÜRENİN BOZUNMASININ İNCELENMESİ

THE INVESTIGATION OF UREA DECOMPOSITION OVER Ag/ALUMINA CATALYSTS

Journal Name:

  • Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi

Publication Year:

  • 2013

Key Words:

Keywords (Original Language):

Author NameUniversity of AuthorFaculty of Author
Abstract (2. Language): 
The NOx gases which are released from diesel vehicles can be reduced to N2 gas with selective catalytic reduction (SCR) reactions. The yield of these reactions are majorly related to the reducing agent. Both urea and its’ decomposition/hydrolysis compounds which are isocyanic asid (HNCO) and ammonia (NH3) can be used SCR reactions. Therefore, urea is an attractive reducing agent recently. Ag/Al2O3 catalysts have an important role for NOx reduction. The decomposion and hydrolysis compounds of urea on the %1 Ag/Al2O3 and %2 Ag/Al2O3 catalysts which are prepared by sol-gel method were investigated by using FTIR. The experimental studies were carried out between 100-400°C temperature in the presence of helium. As a result of the analyses of FTIR spectra, NH3, NH4 +, -CNO, melamine and CO2 were dedected as the decomposition and hydrolysis compounds of urea on the catalysts. Besides that, OH, CH, NH and C=O stretching vibration bands were also observed. NH4 + compound was not observed at any temperature on the %1 Ag/Al2O3 catalyst however, it was observed at the temperatures of 100 and 250 °C on the %2 Ag/Al2O3 catalyst. Ammonia, which is a decompositon and hydrolysis compound of urea, was observed on both catalysts at all temperatures and times. Isocyanate (-CNO), which is a decompositon compound of urea, gave its most intensive peak at the temperature of 200°C on %1 Ag/Al2O3 catalyst and at the temperature of 250°C on %2 Ag/Al2O3 catalyst.
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Abstract (Original Language): 
Dizel araçlardan çevreye salınan zararlı NOx gazları, seçici katalitik indirgeme (SCR) reaksiyonları ile N2 gazına dönüştürülebilmektedir. Bu reaksiyonların verimi, kullanılan indirgen maddeye önemli ölçüde bağlıdır. Ürenin hem kendisi hem de bozunma/hidroliz bileşikleri olan izosiyanik asit (HNCO) ve amonyak (NH3) SCR reaksiyonlarında kullanılabilmektedir. Bundan dolayı, üre son zamanlarda ilgi çeken bir indirgen maddedir. NOx indirgenmesinde Ag/Al2O3 katalizörleri önemli bir yere sahiptir. Sol-jel yöntemi kullanılarak hazırlanan %1 Ag/Al2O3 ve %2 Ag/Al2O3 katalizörü üzerinde ürenin bozunma ve hidroliz bileşikleri FTIR cihazı kullanılarak incelenmiştir. Deneysel çalışmalar, helyum ortamında 100–400°C sıcaklık aralığında gerçekleştirilmiştir. FTIR spektrumlarının analizi sonucunda katalizörler üzerinde ürenin bozunma ve hidroliz bileşikleri olarak NH3, NH4 +, -CNO, melamin ve CO2 tespit edilmiştir. Bunun yanı sıra OH, CH, NH ve C=O gerilme titreşim bantları da gözlenmiştir. NH4 + bileşiği %2 Ag/Al2O3 katalizörü üzerinde 100 ve 250 °C sıcaklıklarda gözlenirken, %1 Ag/Al2O3 katalizörü üzerinde hiçbir sıcaklıkta tespit edilmemiştir. Ürenin bozunma ve hidroliz bileşiği olan amonyak her iki katalizör üzerinde de çalışılan bütün sıcaklık ve zamanlarda gözlenmiştir. Ürenin bozunma bileşiği olan izosiyanat (-CNO), %1 Ag/Al2O3 katalizörü üzerinde en şiddetli pikini 200°C sıcaklıkta, %2 Ag/Al2O3 katalizörü üzerinde 250°C sıcaklıkta vermiştir.
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