BaO/TiO2/Al2O3 yapısındaki NOx depolama malzemelerinin optimum yüzey kimyasının belirlenmesi

Titania promoted NOx storage materials in the form of BaO/TiO2/Al2O3 weresynthesized via two different sol-gel preparation techniques, with varying surfacecompositions and morphologies [1, 2]. The influence of the TiO2 units on the NOxstorage component (8 - 20 wt. % BaO), the nature of the crystallographic phases,thermal stabilities and the dispersion of the surface oxide/nitrate domains wereinvestigated.The structural characterization of the synthesized NOx storage materials wereanalyzed by means of BET surface area analysis, X-ray diffraction (XRD), ex-situRaman spectroscopy, scanning electron microscopy (SEM), energy dispersive X- ray(EDX) and transmission electron microscopy (TEM). Comparative analysis of theresults showed that the TiO2/Al2O3 support material derived by the co-precipitationof the corresponding hydroxides via the sol-gel technique, exhibited distinctivelymore homogenous distribution of TiO2 domains.The functionality/performance of these materials upon NOx and SOxadsorptions were monitored by temperature programmed desorption (TPD) and insituFourier transform infrared (FTIR) spectroscopy. An improved Ba surfacedispersion was observed for the BaO/TiO2/Al2O3 materials synthesized via the coprecipitationof alkoxide precursors which was found to originate mostly from theincreased fraction of accessible TiO2/TiOx sites on the surface. These TiO2/TiOx sitesfunctioned as strong anchoring sites for surface BaO domains and were tailored toenhance surface dispersion of BaO. The relative stability of the NOx speciesadsorbed on the BaO/TiO2/Al2O3 system was found to increase in the followingorder: NO+/N2O3 on alumina << nitrates on alumina < surface nitrates on BaO 1073 K. SOx adsorption directly altered stability of the nitratespecies on the Ti/Al (Protocol 1, Protocol 2) samples. SOx uptake properties of theBaO/TiO2/Al2O3 materials were found to be strongly influenced by the morphologyof the TiO2/TiOx domains and the BaO loadings (8/20 wt% BaO). Consequently, thepresence of titania domains was seen to decrease the SOx desorption temperaturesand enhance the sulfur-tolerance of these materials by destabilizing the accumulatedsulfate species. SOx exposure on the synthesized materials led to a significantdecrease in the NOx adsorption capacities. The results obtained from FT-IR spectrashowed that the sulfur deposition on the NOx storage materials promoted by TiO2were more readily removed with respect to the conventional 8(20)Ba/Al samples.