In Situ Formation of Wilkinson-Type Hydroformylation Catalysts: Insights into the Structure, Stability, and Kinetics of Triphenylphosphine- and Xantphos-Modified Rh/SiO2
journal contribution
posted on 2013-03-01, 00:00 authored by Sankaranarayanapillai Shylesh, David Hanna, Anton Mlinar, Xüé-Qia̅n Kǒng, Jeffrey A. Reimer, Alexis T. BellAn investigation has been carried out to identify the
effects of
catalyst preparation on the activity, selectivity, and stability of
phosphine-modified rhodium/silica catalysts (Rh/SiO2) for
propene hydroformylation. High selectivity to aldehydes was achieved,
without the formation of propane or butanol. Catalyst activity and
selectivity was found to depend strongly on the nature and concentration
of the phosphine ligands and the amount of rhodium dispersed on the
silica support. Screening of different ligands showed that a bidentate
xantphos (X) ligand was ∼2-fold more active than the monodentate
phosphine ligand (PPh3) screened at a ligand-to-rhodium
ratio of 15:1. Investigation of the effects of reaction temperature,
reactant partial pressures, and phosphine-to-rhodium ratio indicates
that the kinetics of propene hydroformylation over X-promoted Rh/SiO2 is nearly identical to those for sulfoxantphos-modified rhodium-containing
supported ionic liquid phase (SX-Rh SILP) catalysts. In-situ FTIR
and solid-state 31P MAS NMR characterization provide evidence
for the formation of HRh(CO)n(PPh3)4–n species on PPh3-modified Rh/SiO2, and HRh(CO)2(X) species
on xantphos-modified Rh/SiO2. The high catalytic activity
observed over rhodium-containing silica catalysts is attributed to
formation of Rh(I)(CO)2 species by the process
of corrosive chemisorption of Rh nanoparticles by CO and the subsequent
ligation of phosphine ligands to the dicarbonyl species. Evidence
is also presented suggesting that the active form of the catalyst
resides on the surface of the Rh nanoparticles.
