Discrete Polyoxopalladates as Molecular Precursors for Supported Palladium Metal Nanoparticles as Hydrogenation Catalysts

Abstract

We have used discrete polyoxopalladates­(II) (POPs) of the MPd12X8 nanocube- and Pd15X10 nanostar-types (M = central metal ion, X = capping group) as molecular precursors (diameter ca. 1 nm) for the formation of supported (SBA-15) metallic nanoparticles. These materials proved to be highly active in the hydrogenation of o-xylene. The characterization of such hydrogenation catalysts revealed that the average size of the resulting alloy particles is quite uniform with diameters ranging from 1 to 3 nm (indicating little to no agglomeration). The central transition-metal ion M n+ (MnII, FeIII, CoII, NiII, CuII, ZnII, PdII) in the POP structure and also the nature of the capping group (AsO4 3–, SeO3 2–, PO4 3–, phenyl-AsO3 2–) influence the resulting catalytic performance.

Polyoxometalates: Tailoring metal oxides in molecular dimension toward energy applications

“…Polyoxopalladates have been employed for catalysts and hydrogen uptake . For instance, Pd 12 ‐based polyoxopalladates have been studied for the hydrogenation catalyst, which is tuned by the central metal ion and capping groups . The formation of polyoxopalladates with various sizes including Pd 15 , Pd 22 , Pd 72 , and Pd 84 has been achieved .…”

“…6,337 For instance, Pd 12 -based polyoxopalladates have been studied for the hydrogenation catalyst, which is tuned by the central metal ion and capping groups. 338 The formation of polyoxopalladates with various sizes including Pd 15 , Pd 22 , Pd 72 , and Pd 84 has been achieved. [339][340][341][342][343][344] In addition, the supramolecular properties and self-assembly of novel polyoxopalladates based on Pd 12 functionalized by organic ligands and Pd 13 have been investigated, 345,346 and the host-guest chemistry of Pd 13 -based polyoxopalladate is identified to exhibit non-covalent interactions between the polyoxopalladate and cyclodextrins.…”

Towards Size‐Controlled Deposition of Palladium Nanoparticles from Polyoxometalate Precursors: An Electrochemical Scanning Tunneling Microscopy Study

“…Examples for such an approach are the impregnation of a support by platinum octanethiolate [7] or polyoxopalladates(II) (POPs) and the subsequent calcination and reduction towards the active metallic state. [8] POPs have also been investigated as molecular precursors for heterogeneous catalysts through incorporation into metal organic frameworks (MOFs). [9] POP-based heterogeneous catalysts with a well-defined size distribution show promising catalytic properties ranging from cross-coupling reactions [10,11] to hydrogenations.…”

“…The family of discrete POPs shows distinct stoichiometries -POPs with n = 12 up to 84 could be prepared [16] and are sufficiently labile to be decomposed electrochemically, or alternatively by pH changes or contact with molecular hydrogen. [8,17,18,19,20,21] We decided to study in particular the POP with an "open-shell" structure, [SrPd 12 O 6 (OH) 3 (PhAsO 3 ) 6 (OAc) 3 ] 4À (SrPd 12 , structure see Figure S1), which we reduced directly at the solid-liquid interface, obtaining well-defined palladium(0) cluster sizes. Synthesis and structural details can be found in Yang et al [17] This "open-shell" polyanion SrPd 12 was selected due to its presence of acetate and phenylarsonate ligands, the former being sterically less demanding than the latter.…”

Robust alkyl‐bridged bis(N‐heterocyclic carbene)palladium(II) complexes anchored on Merrifield's resin as active catalysts for the selective synthesis of flavones and alkynones

“…[ 13,18–20 ] Apart from the easy separation of the catalyst from the coupling products, the supported catalyst is effectively recyclable and can be reused, [ 20,21 ] which makes it an economically viable alternative in the industry. [ 22–24 ] Taking into consideration the intrinsic advantages of the improved supported catalysts, there are increasing interests in immobilizing the palladium catalysts onto different solid supports such as functionalized silica, [ 25 ] functionalized organic polymers, [ 26,27 ] clay, [ 13,20 ] magnetic nanoparticles, [ 28 ] ZIF‐, [ 29 ] MOF‐, [ 30 ] and Pd/C. [ 31–35 ]…”