New silica/alumina-clay heterostructures: Properties as acid catalysts

New delaminated porous silica/alumina–clay heterostructures have been prepared by an innovative approach involving the use of the Cloisite 30B commercial organoclay as starting material. The presence of alkylchains was liable for the controlled hydrolysis and polycondensation of a mixture of silicon and aluminum alkoxides previously incorporated within the interlayer space of clay. This soft chemical route was based on a spontaneous gelation in which the heterocoagulation process gives rise to exfoliation of the clay layers. Handling the synthetic parameters was possible to attain organoclay delamination by the inclusion of different silica/alumina compositions. The structural modification induced the creation of micro and mesoporous clay-based solids with high specific surface areas (ca. 650 m2/g). The textural behavior of the clay changes noteworthy as the stack silicate layers were renewed into dispersed layers surrounded by well-dispersed nanoparticles of silica/alumina. These new porous silica/alumina solids can be described as “delaminated porous clay heterostructures (DPCHs)”, constituting a novel class of acid catalysts that compared to pillared-clays exhibit advantages such as the possibility of tuning of acidity by varying the Si/Al ratio. Their acid catalytic activity was evaluated for the synthesis of p-cymene from limonene, showing optimum conversion and efficient selectivity values.The authors acknowledge financial support from the CICYT (Spain; Project MAT2009-09960). C.B. is indebted to the MICINN for a Ramon y Cajal postdoctoral contract