Optimization of transition metal nanoparticle- phosphonium IL composite catalytic systems for deep hydrogenation and hydrodeoxygenation reactions
Scott, Robert WJ
PublisherRoyal Society of Chemistry
Peer Reviewed StatusPeer Reviewed
MetadataShow full item record
A variety of metal nanoparticle (NP)/tetraalkylphosphonium ionic liquid (IL) composite systems were evaluated as potential catalysts for the deep hydrogenation of aromatic molecules. Particles were synthesized by reducing appropriate metal salts by LiBH4 in a variety of ILs. Gold NPs were used as probes to investigate the effect of both chain lengths of the alkyl substituents on the phosphonium cation and the nature of anions, on the stability of NPs dispersed in the ILs. The presence of three medium-to-long alkyl chains (such as hexyl) along with one long alkyl chain (such as tetradecyl) in the IL, coupled with highly coordinating anions (such as halides, or to a smaller extent, bis-triflimides) produced the most stable dispersions. These ILs also showed maximum resistance to heat-induced sintering; for example, TEM studies of Pt NPs heated under hydrogen to 120 °C showed only moderate sintering in trihexyl(tetradecyl)phosphonium chloride and bis(triflimide) ILs. Finally, olefinic hydrogenations, aromatic hydrogenations, and hydrodeoxygenation of phenol were carried out with Ru, Pt, Rh and PtRh NPs using hydrogen at elevated pressures. From preliminary studies, Ru NPs dispersed in trihexyl(tetradecyl)phosphonium chloride emerged as the catalyst system of choice. The presence of borate Lewis-acid by-products in the reaction medium (from the borohydride reduction step) allowed for partial phenol hydrodeoxygenation.
CitationA. Banerjee, R. W. J. Scott, Green Chem., 2015, 17, 1597-1604.
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