Chemical quenching and inhibition of positronium in Cr2O3/Al2O3 catalysts

Abstract

The pore structure of Cr 2 O 3 /Al 2 O 3 catalysts and the surface chemical properties of these pores were characterized by positron lifetime and coincidence Doppler broadening (CDB) measurements. Four lifetime components could be resolved from the positron lifetime spectrum, with two long lifetime components and two short lifetime components. The two long lifetimes τ 4 and τ 3 are attributed to ortho-positronium (o-Ps) annihilation in large pores and microvoids, respectively. With increasing Cr 2 O 3 content, both τ 4 and its intensity I 4 show sharp decrease, while τ 3 and its intensity I 3 keep nearly unchanged. The Doppler broadening S parameters also show sharp decrease with increasing Cr 2 O 3 content. Detailed analysis of the CDB spectrum reveals that the parapositronium (p-Ps) intensity also decreases with increasing Cr 2 O 3 content. This indicates that the change of o-Ps lifetime τ 4 is due to

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