Accommodation of Mn II, Mn III–N, O, O, O-donor Schiff base complexes in zeolite-Y: Synthesis, structural studies and CO adsorption

Abstract

Manganese (II)-, (III)-complexes with NO 3 Schiff base ligand (SPAB) derived from salicylaldehyde and p-aminobenzoic acid have been synthesized and immobilized in the zeolite-Y supercages by a flexible ligand method. The synthesized new host/guest materials have been characterized by various physicochemical techniques, in addition to surface area measurements and nitrogen adsorption studies. Investigation of the stereochemistry of these incorporated chelates elucidated that, Mn(II) complex is tetrahedral with involvement of zeolite oxygen in coordination meanwhile Mn(III) complex has octahedral configuration with Jahn–Teller distortion but without contribution of the lattice oxygen. The intrazeolitic Schiff base complexes are thermally stable up to ≅600 °C without any decomposition. Catalytic activity towards CO adsorption for zeolite-encapsulated complexes has been investigated and compared with Mn II–Y using in situ FT-IR spectroscopy. The results pointed out that, encapsulation of manganese (II, III) complexes in zeolites enhances remarkably the selectivity towards the formation of unionized carboxyl (–COOH) species which is considered a characteristic property of the zeolite encapsulated Mn(II,III)–SPAB complexes over Mn II–Y. On the other hand, the in situ FT-IR data demonstrate that Mn II(SPAB)/Y and Mn III(SPAB)/Y can be used as reactive catalysts in water gas shift reaction (WGSR).