Direct N₂O Decomposition Over Zeolites And Mixed Oxides

The catalytic N₂O decomposition reaction to nitrogen and oxygen is an efficient technologies for reducing nitrous oxide emissions from chemical processes,and consequently it has become of increasing attention in recent years.In order to control the emission of N₂O from chemical processes,various types of catalysts have been investigated such as ion-exchanges zeolites,supported systems and pure or mixed oxides.First part:Prepared a series of dip-coating M?Fe,Co?-BEA monolith catalyst using honeycomb cordierite as the substrate for N₂O direct decomposition.The M?Fe,Co?-BEA?M = 1 wt%?powder zeolites were prepared by the ion exchange method,which were then washcoated on the cordierite substrate by silica-gel or alumina-gel as a binder?5 and 10 wt%?.The morphologies of the prepared monolithic samples were analyzed by the scanning electron microscopy?SEM?,suggesting that the powder of M?Fe,Co?-BEA zeolites can be well dip-coated on the cordierite support by silica-gel or alumina-gel with a relatively lower content?5 wt%?.Through the catalytic activity evaluations,it is interestingly found that?I?the alumina-gel has an obvious promotion effect on N₂O decomposition for the Fe-BEA monolith samples,while silica-gel can improve the decomposition activity of the Co-BEA monolith samples;???the low binder content?5 wt%?is more preferable to the high binder content?10 wt%?for preparation of the monolith catalysts.Computational fluid dynamics?CFD?was also employed to simulate the N₂O direct decomposition over M?Fe,Co?-BEA monolith,wherein the fluid dynamics?mass distribution,pressure drop?were thereafter analyzed.Second part:A series of NiCe mixed metal oxides have been investigated for direct N₂O decomposition in absence of oxygen.Characterizations of XRD,BET,TEM,and H₂-TPR were applied to correlate their physiochemical properties with the corresponding catalytic efficiency.The catalyst Ni90Ce10 synthesized by hydrothermal method showed the optimum catalytic activity among the mixed metal oxides,which could totally dissociate N₂O at 360 ? in the absence of oxygen.The introduction of CeO₂ could hinder the aggregation of NiO molecules and preserve high surface area.A strong interaction was observed between NiO and CeO₂ molecules in the mixed metal oxides;the interaction improved oxygen mobility and created active site on the surface of the catalyst.Third part:A series of NiM?Rh,Ce?mixed oxides catalysts with different molar proportions have been investigated for the catalytic N₂O decomposition.Characterizations of XRD,BET,TEM,XPS and H₂-TPR were applied to correlate the structure/texture properties of the catalytically active component with the corresponding catalytic behavior.High surface area of mixed oxide catalysts were synthesized through hydrothermal method.The doping of certain amount of rhodium to NiO oxide strongly varies its catalytic performance.Through the catalytic activity evaluations,we found that the Ni98Rh02 has superior catalytic activity at relatively low temperature,which could completely decompose N₂O at 330 ? in the absence of oxygen.This high activity has related to high surface area of the catalyst,high reducibility of NiO.The addition of 10%Ce to the best sample Ni98Rh02 leads to enhance the catalytic efficiency of the catalyst,which reached 100%of conversion at 310 ?.