Hydrogenation of cyclohexene with perfluorinated cation- and anion-exchange membranes supported platinum

摘要

A perfluorinated cation-exchange membrane (Nafion) and an anion-exchange membrane (Tosflex) supported platinum (Pt) were prepared by ion-exchanging with Pt(NH_3)_2~(2+) or K_2PtCl_4, respectively. They were then reduced either with a large excess of NaBH_4 or under hydrogen in a glass-lined stainless-steel bomb at 80℃ and 20.6 MPa for 3 h. UV visible spectra indicated that 70-80% of ion exchange was completed. The rate of hydrogenation of cyclo(c-)hexene in methanol with both platinised membranes showed similar trends, increasing with an increase in the Pt loading on the membrane. However, catalytic activity expressed as turnover frequency (TOF) reached a maximum(0.23 s~(-1)) at about a 0.5% Pt loading. When the Tosflex-Pt was reduced by H_2, partial Pt reduction was obtained, resulting in a low TOF. The rate of hydrogenation of c-hexene over a range of pressures indicated that the system was not diffusion limiting after