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Investigation of the perfluorinated polymer NAFION as a catalyst support

posted on 2023-05-27, 15:43 authored by Seen, AJ
This thesis reports on investigations into the potential uses of the perfluorinated ionexchange polymer NAFION as a catalyst support and as a Bronsted acid co-catalyst. Research has been undertaken with the aim of supporting complexes which are active homogeneous catalysts as well as investigating the formation of metal particle catalysts within NAFION. Four methods of immobilizing potential catalysts based on ionic interactions or physicalli entrapment have been tested and found successful. These were: (i) immobilization of Pd(N N) 2 2+ species by simple ion-exchange, (ii) activation of Ni[P(OEt)3]4 with NAFION-H+ to yield the cationic hydride species HNi[P(0E0 3]4+, (iii) replacement of Br and a PPh3 in Ni(o-toly1)Br(PPh3)2 with pyridine to produce the cationic Ni(o-toly1)(py) 2PPh3+ species, and (iv) immobilization of metallic Pt within NAFION by in-situ reduction of Pt(NH3 )42+. Complexes of the type Pd(N N)2X2, where N N is a chelating nitrogen donor ligand, e.g. 1,10-phenanthroline, and X is a non-coordinating anion, have previously been found to dimerize ethene. Such Pd complexes are easily supported within NAFION by ion-exchange. Attempts to use the supported Pd complexes as ethene dimerization catalysts initially met with limited success with activities being about 10 % of similar homogeneous catalyst activities. However, after undertaking further studies it was found that activities comparable with the homogeneous catalyst could be obtained by decreasing the catalyst loading in NAFION. The effects of ligand, solvent, temperature and pressure on catalytic activity have also been studied. The use of acid-NAFION as a Bronsted acid co-catalyst and support has been investigated. The Ni[P(OEt) 3]4complex was previously reported to isomerize 1-butene when activated with a BrOnsted acid. The proposed catalytic species is the HNi[P(OEt)3] 3+ cation. Experiments were undertaken in which 1-octene and 1-butene were isomerized by acid-NAFION / Ni[P(OEt)3]4systems. The NAFION not only functioned as the co-catalyst, but also supported the active catalyst. Diffusion restrictions were found to severely limit the 1-octene isomerization rate using the NAFION supported catalyst. The use of organonickel species activated by alkylaluminiums as oligomerization catalysts is an area which has received much attention in the past. It is however possible to activate organonickel species containing halides by treatment with Ag+ or T1+ salts to remove the halide anion. The replacement of the halide anion in such species by a neutral ligand, e.g. pyridine, has also produced a cationic Ni species. Immobilization of a cationic organonickel species using this method was successfully achieved. Catalytic testing was undertaken but the use of chlorobenzene as solvent prevented the NAFION from swelling and resulted in the activity of the supported catalyst being much less than the homogeneous species. Platinum particles have been immobilized in NAFION and have shown activity as hydrogenation catalysts. Characterization of the particles was difficult as determination of the metal dispersion was not possible using techniques such as chemisorption of CO, adsorption of r from solution or using cyclic voltammetry. TEM and X-ray line broadening analysis did however indicate that the Pt was distributed as a thin layer along the NAFION edge with the average particle size ca. 40 A. A plot of cyclohexene hydrogenation rate vs Pt loading in NAFION suggested that above 2.5 % wt/wt Pt the additional Pt was inaccessible.


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Includes bibliographical references. Thesis (PhD)--University of Tasmania, 1993

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