Catalytic properties of transition metal salts immobilized on nanoporous silica polyamine composites II: hydrogenation

The transition metal compounds Pd(OAc)2, RhCl3·4H2O and RuCl3 · nH2O were adsorbed onto the nanoporous silica polyamine composite (SPC) particles (150–250 µm), WP‐1 [poly(ethyleneimine) on amorphous silica], BP‐1 [poly(allylamine) on amorphous silica], WP‐2 (WP‐1 modified with chloroacetic acid) and...

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Published in:Applied organometallic chemistry 2011-04, Vol.25 (4), p.245-254
Main Authors: Allen, Jesse, Rosenberg, Edward, Karakhanov, Eduard, Kardashev, Sergey V., Maximov, Anton, Zolotukhina, Anna
Format: Article
Language:English
Subjects:
Catalysis
Catalysts
composite materials
Hydrogenation
Nanocomposites
Nanomaterials
Nanostructure
Polyamines
Silicon dioxide
transition metal
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Summary:The transition metal compounds Pd(OAc)2, RhCl3·4H2O and RuCl3 · nH2O were adsorbed onto the nanoporous silica polyamine composite (SPC) particles (150–250 µm), WP‐1 [poly(ethyleneimine) on amorphous silica], BP‐1 [poly(allylamine) on amorphous silica], WP‐2 (WP‐1 modified with chloroacetic acid) and BP‐2 (BP‐1 modified with chloroacetic acid). Inductively coupled plasma‐atomic emission spectrometry analysis of the dried samples after digestion indicated metal loadings of 0.4–1.2 mmol g−1 except for RhCl3·4H2O on BP‐2 which showed a metal loading of only 0.1 mmol g−1. The metal loaded composites were then screened as hydrogenation catalysts for the reduction of 1‐octene, 1‐decene, 1‐hexene and 1, 3‐cyclohexadiene at a hydrogen pressure of 5 atm in the temperature range of 50–90 °C. All 12 combinations of SPC and transition metal compound proved active for the reduction of the terminal olefins, but isomerization to internal alkenes was competitive in all cases. Under these conditions, selective hydrogenation of 1,3‐cyclohexadiene to cyclohexene was observed with some of the catalysts. Turnover frequencies were estimated for the hydrogenation reactions based on the metal loading and were in some cases comparable to more conventional heterogeneous hydrogenation catalysts. Examination of the catalysts before and after reaction with X‐ray photoelectron spectroscopy and transmission electron microscopy revealed that, in the cases of Pd(OAc)2 on WP‐2, BP‐1 and BP‐2, conversion of the surface‐ligand bound metal ions to metal nano‐particles occurs. This was not the case for Pd(OAc)2 on WP‐1 or for RuCl3 · nH2O and RhCl3· 4H2O on all four composites. The overall results are discussed in terms of differences in metal ion coordination modes for the composite transition‐metal combinations. Suggested ligand interactions are supported by solid state CPMAS 13C NMR analyses and by analogy with previous structural investigations of metal binding modes on these composite materials. Copyright © 2011 John Wiley & Sons, Ltd. The silica polyamine composites made from poly(allylamine) (PAA) and poly(ethyleneimine) (PEI) were loaded with salts of Pd2+, Ru3+ and Rh3+ and the resulting materials were tested as hydrogenation catalysts. All were active catalysts under mild conditions with the Rh3+ and Ru3+ containing composites showing good selectivity for the reduction of cyclohexadiene to cyclohexene. The nature of the metal sites has been partially elucidated by SSNMR, XPS and TEM.
ISSN:0268-2605
1099-0739
1099-0739
DOI:10.1002/aoc.1749