Enhancing ammonia storage by tailoring zeolite doping

Abstract

Selective catalytic reduction with NH3 as a reducing agent (NH3-SCR) is currently the most widely used technology to reduce NOx emissions from automotive diesel engines. One of the most prevalent types of catalysts for this purpose is zeolites. The technology requires storage of NH3 in the zeolites over a large temperature range. NH3 is stored by adsorption to H+ Brønsted acid sites and other counter ions. In this thesis, adsorption of NH3 in the zeolites CHA, BEA and MFI and the zeolite like structure AlPO have been investigated using density functional theory (DFT). In all cases, the effect of doping the zeolite framework was explored. Calculations were performed for four different dopant atoms and the counter ions H+, Cu(I), Cu(II) and Cu(II) with (OH)− adsorbed. It was found that the type of dopant atom has a clear effect on the adsorption energies of NH3 on H+ and Cu(II), while the effect is less noticeable in the cases of Cu(I) and Cu(II) with (OH)− adsorbed. The type of zeolite was also found to largely influence the results. The effect of different Al dopant distributions in CHA was also explored. It was found that the relative positions of the dopant atoms have a considerable impact on the adsorption energies.