High-throughput study of the effects of inorganic additives and poisons on NH3-SCR catalysts. Part II: Fe–zeolite catalysts

This study was carried out to identify potential deactivating effects of inorganic materials which are put through an aftertreatment system of a diesel engine as combustion products of lubricant oil additives (i.e. Ca, Mg, Zn, P, B, Mo), impurities of (bio-)diesel fuel, urea solution (K, Ca) and aerosol particulate from intake air (Na, Cl). The effects of adding inorganic additives to an industrial Fe–MFI-SCR catalyst (Fe-BEA) have been evaluated by means of high-throughput methods. The results indicate the impact of different inorganic additives and poisons to Fe–zeolite–NH3-SCR catalysts in case of addition to the catalyst after catalyst preparation by ion exchange and molding of a washcoat by dip-coating procedures. Results of high-throughput screening are supplemented by experiments in more realistic scale, using catalysts and conditions close to the industrial application. As the mechanism of the uptake of inorganic poisons into the catalytic washcoat of an aftertreatment system is not yet quantitatively understood, thereby the addition of the additive to the as-sold catalyst was conducted in different ways, i.e. by wet-chemical impregnation and by exposure to aerosols generated from thermal decomposition of aqueous precursor solutions of potential poisons. It was found that alkaline metals, which are severe poisons to the established vanadia-based catalysts (see Part I), also exhibit deactivating potential towards Fe–zeolite catalysts and induce the reduction of the ammonia storage capability. However, their effect to the catalytic activity is dependant on the operation mode of the catalyst, and is far less pronounced than the effect of alkaline metals to vanadia-based catalysts. The exposure of Fe–zeolite catalysts to phosphates leads to a strong deactivation of the catalyst.