The dc and ac conductivities as well as the dielectric constant (1
) were measured for different zeolites encapsulated gold (AuCl3) samples at different temperatures (300–500 K) and various frequencies (5 kHz–1 MHz).The conductivitywas found to change in the order Au/FSM-27 . Au/NaY . Au/FSM-47. Sorbed water contained inside zeolites assists greatly the proton mobility (zeolite protons) and the ionmobility (Naþ andAuþ) and hence enhance the electric conduction in the temperature range 300–373 K. Raising the temperature over 373 Kinduces dehydration effect that assists themetallic gold formation and thus a dramatic loss in conductivity was revealed. The conduction mechanism was expected to be partially ionic and partially electronic. The IR study showed that the exposure ofAu zeolites to COgas produced a characteristic band of Auþ–COat 2180 cm21 that tends to decreasewith temperatures and even vanishes at 376 K in favor of Au0–CO at 2128 cm21. Similarly, a phase transition at 338 K, that occurs in the range 300– 376 K,was confirmed byDTAto further emphasize the temperature regions of eitherAuþ cations (338 K) orAu0 (376 K) formation. q 2002 Elsevier Science Ltd. All rights reserved.