Synthesis of Fe-SSZ-13 using a ferrocene-based structure directing agent for the NH3 -SCR reaction

Abstract

Nitrogen oxide (NOX) emissions from industrial processes and transportation continues to cause harm to both the environment and human health through the production of acid rain, depleting the ozone layer and causing cardiovascular and respiratory problems in humans. Over the past 50 years selective catalytic reduction of NOX by ammonia (NH3-SCR) has been successfully used to limit NOx emissions. Iron and copper zeolite catalysts have been extensively used for NH3-SCR due to their high activity, high selectivity to N2 and low N2O formation. While Cu-based zeolites are favoured for NH3-SCR application due to their excellent activity and stability at lower temperatures, Fe-zeolites have shown greater stability at higher temperatures typical of diesel exhausts and produce less N2O. Improving the lower temperature activity of Fe-Zeolites is of great interest to industry.

This thesis outlines the use of (Ferrocenylmethyl)trimethylammonium hydroxide (FMTMA OH) as a template in a one-pot method to produce a chabazite with homogenously distributed Fe species. The original idea for the use of (Ferrocenylmethyl)trimethylammonium hydroxide (FMTMA OH) as a template came from Raul Lobo during a previous Johnson Matthey sponsored project. This thesis details the development work done to find suitable conditions for the synthesis of FMTMA OH, evaluation of calcination conditions on the Fe species in the final material and finally testing of fresh and aged catalysts under standard NH3-SCR conditions against a benchmark material made using incipient wetness impregnation.

Analysis of the fresh Fe chabazite synthesised with FMTMA OH (Fc-SSZ-13) samples showed they contained homogenously distributed Fe, mainly isolated and dimeric species, regardless of the calcination conditions. Conversely, the fresh benchmark sample contained a wide range of Fe species and significant agglomeration of Fe was seen in these samples. Catalytic testing of the Fc-SSZ-13 showed comparable NOx conversion to the benchmark sample although, aged samples showed much greater deactivation compared the benchmark. Analysis of the aged samples showed significantly more Fe clusters seen in Fc-SSZ-13 than in the benchmark sample, indicating that sintering of the Fe in Fc-SSZ-13 was much more prevalent.