Encapsulation of palladium in polyurea microcapsules

Abstract

An interfacial polymerisation approach is adopted to encapsulate palladium(II) acetate and palladium nanoparticles in polyurea microcapsules for use in catalysis.

Effect of retained chlorine in ENCAT™ 30 catalysts on the development of encapsulated Pd: insights from in situ Pd K, L3 and Cl K-edge XAS

“…These are most clearly seen in the spectra of the ENCAT™ 30 sample at 2.827, 2.83, and 2.836 keV. The latter of these can also be seen to become more prominent after heating in ethanol/water to 350 K. These features correspond closely to Cl bound to Na on ClO 4 , ClO 3 , and ClO 2 forms, [34] implying that some of the chlorine retained is associated with residual levels of Na (arising from the use of sodium lignosulphate in polymer encapsulation process [1]) and that as a function of catalyst treatment the levels of these species can augment within the catalyst.…”

“…It seems these Cl containing species may become encapsulated with the Pd and are not reliably removed by subsequent washing procedures. EDX (see supplemental data) also shows that Na and S (from sodium lignosulfonate used in the original preparation [1]) may also be trapped and, in the former case, the Cl K-edge XANES provides evidence that this can also subsequently form NaClO x species though reaction with some of the retained Cl.…”

“…Congruent with both the Pd K-edge spectra (Figure 1), and the Cl K-edge data (Figure 2), the Pd L 3 -edge white line of the ENCAT30™ NP has only a marginally lower energy maximum and is broadened only slightly to lower bindging energies, compared to ENCAT™ 30. Subsequent reaction in ethanol-water is observed to cause further reduction The source of the chlorine in the ENCAT™ cases is deemed to lies in the chlorinated solvents (dichloroethane or chloroform [1][2][3][4][5][6][7][8]) used to solubilise the Pd(acetate) precursor prior to encapsulation. It seems these Cl containing species may become encapsulated with the Pd and are not reliably removed by subsequent washing procedures.…”

“…Separation of organometallic Pd catalysts from reaction products and leaching of Pd in heterogeneous Pd catalysts are two major considerations for the successful and large scale application of Pd by the pharmaceutical industry. In order to ameliorate these issues the encapsulation of either Pd organometallic species (such as palladium acetate -ENCAT™ 30-or palladium phosphines) or small palladium nanoparticles (reduced ENCAT™ 30 = ENCAT™ 30 NP) using polymer matrices has proved very successful [1][2][3][4][5][6][7][8], and for some years now a range of polyurea encapsulated catalysts (ENCAT™) have been commercially available and shown to be efficient and recyclable catalysts for a range of important conversions [9,10].…”

Palladium Nanoscale Catalysts in Ionic Liquids: Coupling and Hydrogenation Reactions

“…Today, rather few works have been published using Pd-NPs in ILs as catalyst in this reaction. (Pathak et al, 2000;Ramarao et al, 2002;Gopidas et al, 2003;Narayanan & ElSayed, 2003;Pittelkow et al, 2003;Kim et al, 2004;Liu et al, 2004;Fernandez et al, 2007;Durand et al, 2008) For example, Calo and Nacci reported on Pd-NPs in tetraalkylammonium ILs, starting from Pd(OAc) 2 in the presence of TBAA at 90 °C, which were used as precursor for the coupling of aryl halides (Scheme 5; entry 6, Table 1 Interestingly, with tetrabutylammonium hydroxide as base, the catalytic efficiency increased significantly, thus, the reaction was performed even under milder conditions. This can be explained by the elevated concentration of tetraalkylammonium in water, contributing through partitioning equilibrium, keeping the concentration of the cations in the IL constant.…”