Ag/Alumina Katalizörleri Üzerinde Ürenin Bozunmasının İncelenmesi

Öz

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.

Anahtar Kelimeler

• Ag/Alumina Katalizörler, Ürenin Bozunması, FTIR

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