Synthetic and catalytic studies of inorganically pillared and organically pillared layered double hydroxides

By using freshly prepared or thoroughtly wet layered double hydroxides (LDHs), or by coprecipitating the LDHs in the presence of the pillaring anions, we have synthesized and performed a catalytic study on a large number of pillared HT anionic clays. The metal cations used in the layers include A13+, Cr3+, Fe3+, Mg2+, Ni2+, Zn2+, Co2+, Fe2+, Cue2+, Ba2+, and Ca2+. ing was achieved with an extensive variety of heteropolyoxometalates having the Keggin structure, as well as some other larger heteropolyoxometalate anions. The product was usually a mixture of one phase with an ideally pillared structure and another phase containing defects in the layers; defects that were created during the pillaring reaction. Hexacyanoferrate(111) was also used as a pillaring anion in a clean reaction that provides an example of LDHs pillared with organometallic species. The organic pillars, [O3PC6H4PO3]4-, [O3PC6H4C6H4Po3]−4, and [O3PC6H4 C6HC6H4PO3]4−, first formed intercalates with d-spacings exactly equal to the sum of the height of the pillar and the thickness of the LDH layer. These intercalates, in turn, dehydrate easily to yield lower d-spacing compounds in which the organic pillars are, presumably, fixed onto the layers through POM bonds. talysis tests of polyoxometalate-pillared LDHs on isopropanol showed high levels of conversion, generally enhanced acid activity, and a gradual change in selectivity with respect to dehydrogenation versus dehydration. The selectivity data are presented in correlation with the composition of the LDH layers.