Synthesis of Pt pillared clay nanocomposite catalysts from [PtII(NH3)4]Cl2 precursor

Abstract

Pt-containing nanocomposite catalysts were synthesized by deposition of [Pt(NH₃)₄]²⁺ complex ions on several samples of Al pillared clays, differing in the nature of the parent clay and in the pillaring procedure. In particular, we compared classical Keggin-Al₁₃ pillared clays, with a rather open microporous network, with the new “Al₁₃-heidi” pillared clays, containing bulkier polycations. In Keggin-Al₁₃ pillared clays, Pt deposition occurred by grafting of the precursor complex ions on specific sites of the pillars. Upon subsequent H₂ reduction, mobile Pt species were formed that grew into large raft-like Pt⁰ particles located between the clay layers, causing substantial disruption of the microporous network. In Al₁₃-heidi pillared clays, on the other hand, diffusion of the [Pt(NH₃)₄]²⁺ was strongly hindered, and Pt⁰ particles were probably formed chiefly outside the clay layers. These structural differences translated into different activities for the reaction of benzene hydrogenation: Pt catalysts supported on Keggin-Al₁₃ pillared clays were much more active than a reference Pt/Al₂O₃ or than Pt/Al₁₃-heidi pillared clays, probably due to the existence of specific bifunctional sites at the interface between interlayer Pt⁰ particles and Brönsted acidic Al-containing pillars.