Nafion catalyst

Figure 9.24. SEM of top view (top) and cross section (bottom) of the Pt/Nafion catalyst used for electrochemical promotion of H2 oxidation.35 Reproduced by permission of The Electrochemical Society, Inc.

E. Smotkin The group of Professor Smotkin at Illinois (IIT) was first to demonstrate NEMCA for an isomerization reaction (1-butene to cis-and trans-2-butene) over a Pd/Nafion catalyst at room temperature. This important and spectacular discovery underlines the great potential ofNafion for inducing NEMCA at low temperatures for numerous important organic synthesis reactions. 

The results obtained in the reaction at 70°C are shown in Table 7.1. Even in the case of a small molecule of ethanol the specific rate (per functional group) with the grafted copolymer is seven times higher than the one with the Nafion catalyst, and this difference increases with the size of the alcohol molecule. This... 

Versus the Nafion catalyst (random copolymer) higher specific catalytic activity and surface area, relative simplicity of the synthetic method. 

Table 5.28. Activity of Nafion Catalysts in the Acylation of Anisole with Octanoic Acid376...

Ohsaka and co-workers658 have reported a new method to prepare peroxyacetic acid by oxidizing acetic acid with H202 in the presence of Nafion catalysts. Nafion-H proved to be superior to Nafion SAC-13 to give a conversion of 16% (5% of catalyst, initial reactant concentrations [CH3COOH] = 1.65 M, [H202] = 2.85 M, 17 h). 

Only two heterogeneous catalysts were evaluated Montmorillonite K-10 and SAC-13 (a Nafion catalyst), gave FFA conversions of 71% and 74% respectively after 4hrs at 180°C at a 2wt% loading, but suffered from the same issue of acrolein formation as the homogeneous acids. 

The use of Nafion/silica composites and zeolite catalysts in this kind of reaction has been studied. These composites containing different amounts of Nafion catalyst are compared with the original material and with Amberlyst 15, a well known macroreticular ion-exchange resin, which achieves remarkable results in several acid catalyzed reactions (81). 

Initial experiments performed at the INL compared different catalysts, fluids, and operating conditions to determine the effect of SCF on solid acid catalyst alkylation (5). Three sets of studies were performed a catalyst comparison using six different catalysts (i.e., two zeolites, two sulfated metal oxides, and two Nafion catalysts) with methane as a cosolvent an exploration of the effect of varying methane addition on alkylation using a USY zeolite catalyst and a study of the effect of seven cosolvents (i.e., three hydrocarbons, two fluorocarbons, carbon dioxide, and sulfur hexafluoride) at L, ML, NC-L, and SCF conditions on the USY catalyst performance. 

Substrate Nafion catalyst yield (%) Nafion/silica composite yield (%)... 

The goal of this work is to investigate temporal alkylation activity on unsupported and supported Nafion catalysts, both macroporous in nature, for isobutane/butene alkylation in supercritical reaction mixtures in the 358-378 K range, and to examine how the product... 

Temporal conversion and selectivity profiles obtained over a silica-supported Nafion catalyst in a stirred reactor operated at supercritical conditions are shown in Figure 2. The experiment was carried out at 80 bar, 368 K, and 0.05 h OWHSV, using a 5 1 isoparaf-fm/olefm (FO) ratio and 2.4 fold molar excess of CO2 [(C02+I)/0=19j. At these conditions, a steady butene conversion (80%) and product selectivity are demonstrated for 48 hours on stream. The alkylate selectivity (TMP+DMFI) and overall Cg selectivity are constant at 27% and 75% respectively. Clearly operation in the near-supercritical region facilitates superior alkylate production over other published results using Nafion catalysts in the liquid phase... 

Figure 4 shows the butene conversion over the silica-supported Nafion catalyst in both liquid and supercritical phases at 368 K, an OWHSV of 0.05 h and an I/O ratio of 10. The liquid phase was maintained at a pressure of 26 bar, while the supercritical phase was maintained at 95 bar, with a 2.4 fold molar excess of carbon dioxide ( 70% total mole fraction CO2). In both cases, a high steady butene conversion is observed. However, the alkylate selectivity continuously declines to zero after 45 hours on stream, at which point the catalyst is only active for butene oligomerization. At the supercritical condition, the acid sites responsible for alkylation are kept active, extending the production of the desired trimethylpentanes. Similar results comparing liquid and supercritical phase runs were also seen on unsupported Nafion . 

Ethyl acetate can be formed over a NAFION catalyst from acetic acid and ethylene in the vapor phase at 135°C. Conversions were 48Z based on acetic acid and after 100 hours, the activity of the catalyst was undimlnlshed (36). The reverse of the above reaction has been demonstrated by the pyrolysis of ethyl acetate to ethylene at 185 C with NAFION tubing (37). The conversion of ethyl acetate is 19.4%, and ethene is the only gaseous product. Without the polymeric catalyst, the pyrolysis... 

The polarization curves in Figure 19.9 show that incorporation of PTFE/C nanocomposite into the Pt/C/Nafion catalyst can significantly improve the mass transport property of the catalyst layer without any negative effect on the electrocatalytic activity of the Pt catalysts. 

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