Alternative SILP-SCR Catalysts based on Guanidinium Chromates

There is an increasing global concern about human caused emissions of pollutants like sulfur and nitrogen oxides to the atmosphere leading to, e.g. smog and acid rain damaging to the human health and the environment. Selective catalytic reduction (SCR) of NOx with ammonia as reductant is the most efficient method to eliminate NOx from flue gases in stationary sources via the reaction: 4NH3 + 4NO + O2 → 4N2 + 6H2O.

The traditionally used heterogeneous SCR catalyst, V2O5-WO3/TiO2, suffers significant deactivation with time due to the presence of relatively large amounts of potassium in the fly ash from bio-fuels. Some of the alkali particles reach the SCR catalyst and deactivate the catalyst both by physical pore blocking as well as by chemically deactivating the oxo vanadium sites.

Furthermore, the catalyst operates around 375ºC and thus has to be placed in a certain position in the flue gas duct. There is therefore a demand for alkali-resistant SCR catalysts more flexible regarding temperature of operation and position in the duct. Supported ionic liquid phase (SILP) catalysts with 1,1,3,3-Tetramethylguanidinium (TMGH+) and a chromium oxide anion supported on anatase have exhibited promising low-temperature SCR activity1 and may possess increased resistance towards potassium poisoning.

However, possible drawbacks of applying [TMGH]2Cr2O7 is a reduction in selectivity to N2 in the SCR reaction since the compound is known as an oxidant2 and may thus contribute to unwanted ammonia oxidation. [TMGH]2Cr2O7 is a solid at ambient conditions, which have allowed X-ray diffraction studies. In this work we present our latest findings regarding the characterization of [TMGH]2Cr2O7 and performance in the SCR reaction.