Catalytic behavior of nickel loaded on acid-activated and pillared clay in total gas-phase oxidation of ethanol

Abstract

Layered and acid-activated clays, used as catalytic support, were synthesized from natural Algerian montmorillonite. All supports were prepared by (1) pillaring with aquo/hydroxo/oxo Al clusters, in particular Al13 that contains only octahedral Al-species, (2) an acidic H2SO4 treatment, and (3) combined pillaring + acid treatment. Five and 10 wt% of active Ni species are deposited by impregnation. The obtained catalysts are characterized by XRD, SAXS (structure), N2 sorption, SEM (texture), XRF (chemical composition), FTIR (to evidence Al13 clusters), and H2-TPR (to distinguish NiO and other Ni-containing species). The activity is measured for the gas-phase total oxidation of ethanol, which is a highly reactive volatile organic molecule. The acid activation pretreatment affects the clay (montmorillonite sheets) because of its delamination (exfoliation) associated with a decreased number of superposed sheets seen in XRD, SEM, and a decreased Si/Al ratio observed by XRF. The d001 spacing in XRD increases from 11.70 (before pillaring) to 18.24 A (after pillaring) evidencing the inclusion of hydroxylaluminic cations and water in the inter-sheets space. d001 = 17.50 A has already been reported with less dealuminated pillared clays. The 10% Ni-loaded pillared clay is the best catalyst (giving up to 100% of conversion) for ethanol total oxidation at relatively low temperatures (T ≤ 250 °C) and ambient pressure. Thus, pillaring, acidic treatments, and Ni amount are the main factors governing on the changing of textural, structural, and catalytic properties of montmorillonite for ethanol oxidative reaction.