Selective catalytic reduction of NO with NH3 on wire mesh honeycomb

Abstract

Wire mesh honeycomb has not only the excellent mass transfer of powder but also the moderate pressure drop of ceramic honeycomb owing to its high porosity structure. It also has the following advantages: high thermal shock resistance, geometric flexibility, simplicity in the catalyst recovery, excellent thermal response, high mechanical strength, axial dispersion and low cost. This research concentrated on selective catalytic reduction of NO with ammonia on wire mesh honeycomb. Preparation methods of wire mesh honeycomb were investigated. The result showed that the pretreatment of wire mesh has an obvious effect on catalytic performance of wire mesh honeycomb. Acid etching can remove grease or oil on the surface of wire mesh. Acid can also react with metal oxide on the surface or metal in the bulk. Calcination has been done inside the muffle furnace. The effects of pretreatment were studied by SEM, BET, XRD and activity measurement. After calcination, an even microcrystalline substrate can be obtained. This substrate can not only increase the strength of wash coat, but also improve the mass transfer of the catalyst. Because this substrate is mainly composed of gamma-Fe3O4, ammonia oxidation at high temperature can be inhibited. At low temperature (theta<200&DEG;C), the reaction is mainly controlled by chemical kinetics. Because of the same component and loading amount, the activity of catalyst samples pretreated by different methods is almost the same. At higher temperature (260&DEG;C<theta<320&DEG;C), the reaction is controlled by mass transfer, so the pretreatment can affect the activity significantly. Among the catalyst samples pretreated by different methods, wire mesh honeycomb with &gamma;-Fe3O4 layer has the highest activity. When &phi;(O-2) = 21%, V(NO) = V (NH3) = 500 &mu;l/L, GHSV=5000 h(-1) and &theta;=340&DEG;C, NO conversion is above 90%. Ammonia oxidation begins at &theta; = 340&DEG;C. When &theta; > 380degreesC, the reaction is completely controlled by ammonia oxidation. Compared with alpha-Fe2O3, gamma-Fe3O4 is an inert material which can inhibit the ammonia oxidation. The best preparation method is etching wire mesh with dilute acid, then calcining it at 500degreesC for 20 h.