Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

Fe2O3/Al2O3 catalysts were prepared by solid state reaction method using image-Fe2O3 and image-Al2O3 nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes image and image are attributed to positronium annihilation in two types of pores distributed inside Al2O3 grain and between the grains, respectively. With increasing Fe2O3 content from 3 wt% to 40 wt%, the lifetime image keeps nearly unchanged, while the longest lifetime image shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe2O3 content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of image is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.