INTERMEDIATE SPECIES ON ZIRCONIA SUPPORTED METHANOL AEROGEL CATALYSTS .1. STATE OF THE CATALYST SURFACE BEFORE AND AFTER THE ADSORPTION OF HYDROGEN

Four aerogel catalysts: ZrO2; ZnO/ZrO2; CuO/ZrO2 and CuO/ZnO/ZrO2, for methanol synthesis were studied by IR spectroscopy and by temperature-programmed desorption of hydrogen in order to detect any synergy in the adsorption of hydrogen by zirconia as a result of addition of ZnO, CuO or both ZnO and CuO. Whereas pure ZrO2 hardlY adsorbs any hydrogen, the addition of ZnO or CuO, or still better of ZnO and CuO, in small amounts (5%), makes ZrO2 a reservoir of hydrogen. This enhanced adsorption of hydrogen by ZrO2 is interpreted by the spillover of hydrogen from the donor oxide (ZnO, CuO) to the acceptor oxide (ZrO2). This spilled over hydrogen is stored in the form of hydroxyl groups (band at 3680 cm-1) which cannot be distinguished from those formed by the rehydroxylation of the surface of ZrO2 (bands at 3680 and 3780 cm-1). An interconversion between these species seems very probable.