Continuous lean NO_x reduction with hydrocarbons over dual pore system catalysts

摘要

In order to reduce CO_2 emissions there is a trend towards an increased use of more fuel-efficient lean burn combustion engines and thus an increased need for deNO_x catalysts for such engines.In this study a mechanical mixture of CoFER and HZSM-5 zeolites was studied as a dual pore system catalyst for the continuous lean reduction of NO_x with isobutane as reducing agent.The degree of NO_x conversion was found to be strongly dependent on the oxygen concentration in the gas mixture,and the highest degree of reduction was achieved with 10% O_2.This optimum is explained by the need for NO_2 as an intermediate for the catalyst to work efficiently,and that above a certain oxygen concentration O_2 oxidises the hydrocarbon resulting in a lower reduction potential for NO_x.At an operating temperature of 350degC the conversion of NO_x to N_2 was 52% under steady-state conditions,but the efficiency can be improved further by optimisation of the oxidising zeolite and of the mixing ratio of the two zeolites.