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

Abstract

• 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 RuCl 3 · nH 2 O and RhCl 3 · 4H 2 O 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 13 C NMR analyses and by analogy with previous structural investigations of metal binding modes on these composite materials.

Effect of the coupling agent on the properties of poly(acrylic acid)−Al2O3 interpenetrating hybrids and sorption of metal ions

“…We used an AA/APS mole ratio of 10 and an excess of initiator, and the low solubility in 2‐butanol provides excellent conditions for reactivating the polymerization reaction during the sol‐gel treatment . The polymer backbone shows CH − and CH 2 − at 43 and 28 ppm, typical chemical shifts for PAA . PAA/Al 2 O 3 ‐TMPM( x ) with x = 0.125 − 0.50 showed new signals at 68 and 9.0 ppm.…”

Nanocatalysts for Hydrogenation Reactions

“…7 Metal loadings of 0.4-1.2 mmol/g have been achieved for many of the transition metal salts except that for the rhodium-based salt a loading of only 0.1 mmol/g has been achieved. These composites are screened as hydrogenation catalysts for 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. It was found that all 12 combinations of the silica polyamine composites and transition metal compound were active for the reduction of terminal olefins, but isomerization to internal alkenes was competitive in all cases.…”

Alkyne hydrogenation using Pd–Ag hybrid nanocatalysts in surface‐immobilized dendrimers

“…Catalytic hydrogenation is one of the most important processes in the modern petrochemical industry. Selective hydrogenation of the acetylenic and dienic fragments in C 2 –C 5 hydrocarbons to their corresponding olefins avoids further polymerization and oxidation of these petroleum components . The selective hydrogenation of phenylacetylene, which poisons polymerization catalysts, is more efficient than its separation from the feedstocks…”

“…Therefore, the synthesis of hybrid hydrogenation catalysts, which combine the merits of both homogeneous (high activity and selectivity) and heterogeneous (stability, recyclability) catalysts, is of current interest in the petrochemical industry. One approach to this type of system is the immobilization of metal complexes and/or metal nanoparticles in soluble polymers, bound to an inorganic carrier …”