An experimental investigation of the urea-water decomposition and selective catalytic reduction (SCR) of nitric oxides with urea using V2O5-WO3-TiO2 catalyst.

摘要

Two flow reactor studies, using an electrically heated laminar flow reactor overVanadia based (V2O5-WO3/TiO2) honeycomb catalyst, were performed at 1 atm pressureand various temperatures. The experiments were conducted using simulated exhaust gascompositions for different exhaust gases. A quartz tube was used in order to establishinert conditions inside the reactor. The experiments utilized a Fourier transform infrared(FTIR) spectrometer in order to perform both qualitative and quantitative analysis of thereaction products.Urea-water solution decomposition was investigated over V2O5-WO3/TiO2 catalystover the entire SCR temperature range using the temperature controlled flow reactor.The solution was preheated and then injected into pure nitrogen (N2) stream. The decompositionexperiments were conducted with a number of oxygen (O2) compositions (0,1, 10, and 15%) over the temperature range of 227oC to 477oC. The study showed ammonia(NH3), carbon-dioxide (CO2) and nitric oxide (NO) as the major products of decompositionalong with other products such as nitrous oxide (N2O) and nitrogen dioxide(NO2).The selective catalytic reduction (SCR) of nitric oxide (NO) with urea-water solutionover V2O5-WO3/TiO2 catalyst using a laboratory laminar-flow reactor was investigated.Urea-water solution was injected at a temperature higher than the vaporizationtemperature of water and the flow reactor temperature was varied from 127oC to 477oC.A FTIR spectrometer was used to determine the concentrations of the product species. The major products of SCR reduction were NH3, NO and CO2 along with the presenceof other minor products NO2 and N2O. NO removal of up to 87% was observed.The aim of the urea-water decomposition experiments was to study the decompositionprocess as close to the SCR configuration as possible. The aim of the SCR experimentswas to delineate the effect of various parameters including reaction temperatureand O2 concentration on the reduction process. The SCR investigation showed thatchanging parameter values significantly affected the NO removal, the residual NH3 concentration,the temperature of the maximum NO reduction, and the temperature of completeNH3 conversion. In the presence of O2, the reaction temperature for maximum NOreduction was 377?C for ratio of 1.0.