Investigation of the state of palladium in the potassium palladium-11-tungstosilicate/alumina system by diffuse-reflectance IR spectroscopy

Preferential catalytic hydrogenation of aromatic compounds versus ketones with a palladium substituted polyoxometalate as pre-catalyst

“…9 This is not especially surprising since true framework substitution of Pd(II) into the polyoxometalate would require a less or non-preferred octahedral coordination for Pd(II), which generally adopts a square planar coordination. The lability of the palladium center was also verified by addition of cyclooctadiene to the [PPdW 11 O 39 ] 5À compound, which resulted in the demetalation of the polyoxometalate and formation of [PW 11 O 39 ] 7À .…”

“…The palladium-substituted Keggin-type polyoxometalate formulated by elemental analysis as K 5 PPd(H 2 O)W 11 O 39 Á12H 2 O was prepared in a manner similar to the published literature procedure for the preparation of [(C 4 H 9 ) 4 N] 5 -PPd(H 2 O)W 11 O 39 . 7 The 31 P NMR spectrum (85% H 3 PO 4 as external standard) revealed a major peak at À15.17 ppm (95%) attributable to [PPd(H 2 O)W 11 O 39 ] 5À and=or possibly its dimer, 8 [PW 11 O 39 Pd-O-PdPW 11 O 39 ], and a small peak at À13.32 ppm (5%) attributable, from an authentic sample, to an impurity of the starting material, [PW 11 O 39 ] 7À . The IR spectrum showed peaks at 1100, 1046, 950, 851, 805 cm À1 .…”

“…Thus, an XPS measurement of the isolated '' active '' catalyst from the (Pd-POM)=Al 2 O 3 precursor revealed Pd in zero oxidation state only. 11 On the other hand trituration of the active catalyst with water at 90 C showed by 31 P NMR the extraction of the lacunary species, PW 11 O 39 7À , into solution (peak at À13.25 ppm) and the absence of dissolved palladium…”

Studying the Stability of Supported Heteropoly Compounds Using Data from Diffuse Reflectance Infrared Spectroscopy

“…Mixed heteropoly compounds (HPCs) with Keggin structure containing Ni and Co heteroatoms, which occupied the position of a tungsten atom in a W 3 O 13 fragment [9], were prepared according to the standard procedure [1,13]. Our samples were prepared by impregnating ZrO 2 -Al 2 O 3 double oxide or Al 2 O 3 with aqueous solutions of the corresponding HPCs [12,13]. IK-GO-…”

“…The synthesis of supported catalytic systems in which mixed heteropoly complexes containing Co, Ni, Pt, and any other transition metals in the inner coordination sphere (partially replacing W or Mo in the conventional Keggin structure) are used as active components, is a fundamentally new approach to obtaining highly dispersed metal particles on a support's surface. High dispersion of Pt and Pd in HPA/Al 2 O 3 supported systems (or preparations of atomically dispersed metal centers) was observed in [12,13].…”