Characterization of dispersed indium species obtained by thermal treatment of In–NH 4-zeolites and their impact on the SCR of NO x

Abstract

Indium species dispersed on zeolites by high temperature treatment in air of indium-impregnated NH 4-zeolites were characterized and related to the catalytic behavior of the solids in the selective catalytic reduction of NO x . NO-TPD, H 2-TPR and CO-TPR experimental results show that higher temperatures increase the fraction of dispersed InO + and In x O y phases. These species can oxidize nitric oxide to NO 2 and are in greater amounts on the mordenite framework. X-ray indium mapping and TEM observations show a heterogeneous distribution of In 2O 3 particles in solids with higher indium content. These oxides have smaller crystal size and a larger interaction in the framework of ZSM5. TGA–SDTA results point out that the thermal treatment simultaneously produces a solid-state indium exchange and a zeolite dehydroxylation, the exchange level being higher at larger indium contents. The catalytic behavior of the In–zeolites studied can be explained in terms of the type and proportion of indium species present according to the indium loading, thermal treatment and type of zeolite framework. For both zeolites, a higher temperature treatment extends the NO x conversion windows because there are larger amounts of active InO +. But the maximum deNO x activity is lower for In–mordenite due to the larger amounts of In x O y in this zeolite. This non-selective phase increases the methane conversion level. When the indium content is higher, the deNO x activity further increases, in line with a larger fraction of active InO + species. Besides, the catalytic activity of the solids does not decrease despite the excess of indium in these samples under the form of In 2O 3 crystals.