Al/Fe-, Al/Cu- and Al/(Fe-Cu)-pillared clays: Structural features at low Atomic Active Metal Ratios (AMR)

摘要: A set of Al/Fe-, Al/Cu- and Al/(Fe-Cu)-pillared clays were prepared from a Colombian bentonite in sodium or natural (Ca/Mg) form as starting materials. The effect the loading second metal(s) (Fe and/or Cu) related to Al (AMR) intercalating solutions at low range values ≤ 10%, on main physicochemical properties was investigated. insertion active metals rose almost linearly with AMR for both binary, Al/Fe- mixed metal systems. For three-metal Al/(Fe-Cu)- system, stabilization copper behaved randomly function AMR, while Fe not affected by presence Cu. On basis ionic radii involved, possible competition two octahedral sites available Al13 polycationic structure is proposed system (ionic values: Al3+ = 0.68 A; Fe3+ 0.67 Cu2+ 0.73 A), but also good explanation efficiency iron around 15 times higher than binary clear dependence compensation cationic exchange capacity polycations value found only which explained terms opposite changes final pH obtained solutions, induced Keggin-like polycations. change basal spacings XRD patterns oriented glasses interpreted expected molecular size amounts Cu would isomorphically substitute into framework, allowing propose that both, are able carry out such substitution, although different extent. hydrogen consumption H2-TPR analysis materials mainly distributed between broad peaks: one about 250oC 580oC, 750oC 950oC. Despite several oxide species form, first signal samples modified may correspond sequential overlapped reduction Fe2O3 up three steps: (1) → Fe3O4; (2) Fe3O4 FeO; (3) FeO Fe, effects 210-260 oC Cu2+→ Cu+ Cu+→ Cu0 temperatures ca. 400 700 oC. In shoulders observed 600oC 850oC, whose intensity grow increases, seem be kinds repeatedly claimed literature responsible high catalytic activity displayed these Fenton-like reactions; “decorating” pillars true Al/Fe pillars, respectively. textural suggest below 5.0 %, discrete maximum exist systems over sorption starts significantly affected. Simultaneous thermal (DSC/TGA) demonstrated addition enhanced more fraction physisorbed water decreased temperature event intercalation simple Al- SEM micrographs showed significant morphology particles increased 2.0 5.0%; amount added increased, greater tiny deposited clay surface seen, corresponding external aggregates. Likewise, ratio Fe/Al semi-quantitative chemical EDX indicated increasing leads inserted represented intercalated, possibly less aggregated Acknowledgements: Financial support MEC FEDER funds (Ref. MAT2007-66439-C02).