We present a new result on positron annihilation spectroscopy on phase transition and reactivity (towards positronium) of confined liquids in the pores of ZSM-5 zeolite using Doppler broadened annihilation radiation measurement and lifetime spectroscopy. Benzene confined in intergranular spaces (mesopores) and micropores in ZSM-5 shows two distinct freezing points. While the freezing temperature of benzene in mesopore is close to the bulk value, a 5-6 K depression is observed for benzene inside micropores (size similar to 5 angstrom). The reactivity of nitrobenzene towards positronium is studied in nitrobenzene-benzene mixture incorporated in ZSM-5 pores. An anomalous enhancement in the reactivity is observed as compared to measurements in the bulk liquid. The results are discussed. (c) 2006 Elsevier B.V. All rights reserved.