Sepiolite-carbon nanocomposites doped with Pd as improving catalysts for hydrodechlorination processes

The present work introduces a new type of improved catalysts based on sepiolite-carbon nanocomposites anchoring Pd nanoparticles. The nanocomposites are prepared by assembly in aqueous media of graphene nano platelets (GNP) and the nanofibrous sepiolite under a sonomechanical treatment. The methodology allows the co-assembly of other nanomaterials such as multiwall carbon nanotubes (MWCNT) and Pd nanoparticles, these last ones in situ generated from PdCl2 and further treatment with NaBH4. The presence of silanol groups at the external surface of sepiolite favors the growth and assembly of Pd NP which exhibit a quite narrow size distribution independently of the composition of the prepared sepiolite-carbon nanocomposite. The electrical conductivity of the prepared sepiolite-carbon/Pd materials depends of the composition, being lower in materials with higher content in sepiolite. However, the presence of the clay mineral improves textural properties of the resulting materials. The prepared sepiolite-carbon/Pd nanocomposites were tested as catalysts in the hydrodechlorination (HDC) of 4-chlorophenol (4-CPh) under H-2 flux, showing all of them an exclusive selectivity towards phenol, though their catalytic activity depends on their composition. Sepiolite is able to neutralize the evolved MCI, favoring the catalytic process. In addition, the good balance between textural and electrical properties achieved in some of the prepared materials enhances the contact between the catalyst surface and the reagents and also favors the electronic transfer, making this new type of sepiolite-carbon/Pd systems very promising. In fact, the concept here reported could be extended to other catalytic applications where the supported metal acting as active center requires the presence of heat and water resistant conductive supports.