Insertion of lithium into the jarosite hydroxysulfate NaFe3­(SO4)2(OH)6 leads to an amorphous phase Li2+x NaFe3­(SO4)2(OH)6 (with 0 < x<0.5), through a biphasic mechanism. The latter phase exhibits reversible electrochemical lithium intercalation/deintercalation through a solid-solution-like process, leading back to the oxidized jarosite Li x NaFe3­(SO4)2(OH)6 (with 0.3 < x < 0.6), with redox cycling at 2.82 V and a capacity of 110 mAh/g at C/20. This unique topotactic reaction between an amorphous and a well-crystallized phase is interpreted on the basis of the formation of an inorganic polymer.

Operando-IR was used to study the photocatalytic oxidation of methanol in gas phase using a new *BEA zeolite supported TiO 2 (*BEA-Ti) photocatalyst. Following the photocatalytic reaction with time resolved IR spectroscopy coupled to mass spectrometry allowed a quantitative and mechanistic study. The surface species and the parameters affecting the reactivity and selectivity of the reaction were identified and a mechanism was proposed. For comparison, *BEA zeolite and TiO 2 (P25) compounds have been examined as photocatalysts. The effect of the temperature on the reactivity and selectivity of the photooxidation was investigated by TPD measurements (from RT to 473K). The new *BEA-Ti material showed high reactivity, despite its low content in TiO 2 (~10%).