No abstract

A partially fluorinated polyether ionomer from polycondensation of decafluorobiphenyl with 2,2‐bis(4‐hydroxyphenyl)hexafluoropropane, followed by sulphonation with H2SO4 (60% SO3), has been prepared and optimised in terms of molecular weight and sulphonation degree. The partially fluorinated ionomer has been blended with poly(2,2′‐m‐phenylene‐5,5′‐bibenzimidazole) (PBI), yielding base–acid blends with PBI in excess. The base–acid blend membranes have been characterised in terms of solubility in DMAc, water uptake and oxidative stability by immersion in aqueous 5 wt.‐% H2O2 solutions and Fenton's Reagent, respectively.

Due to an unfortunate mistake, the publishers regret that Fig. 7 on p.196 of the above article was incorrect. The correct figure is shown below. The editorial team apologizes for any inconvenience this may have caused. 0 0,2 0,4 0,6 0 50 100 150 200 Temperature / ° C Conductivity / Scm-1 100%H3PO4 PPA-membrane, ADL=32, RH=0% Nafion 117, RH=95% DMAc-membrane, ADL=5.7 TFA-membrane, ADL=6, RH=5% PBI-1b, ADL=11, RH=10% Fig.7 Proton conductivity of acid doped PBI and PBI-1b blend membranes as a function of temperature. As a comparison, data for 100% phosphoric acid and Nafion 117 are also included. The PPA-cast membrane was with an acid doping level of 32 and at relative humidity of 0% [20]; The DMAc-cast membrane was with an acid doping level of 5.7 and under atmosphere with a water-to-air ratio of about 0.7 [6]; The TFA membrane was with an acid doping level of 6.0 and at relative humidity of 5% [7].

We describe an improved temporal analysis of products (TAP) reactor design whose main new features in comparison to the recent TAP-2 design of Gleaves et al. [Appl. Catal. A 160, 55 (1997)] are the use of a turbomolecular pump, piezoelectrically driven pulse valves, and a newly designed, differentially pumped gate valve. The gate valve allows fast and simple changes between high pressure operation, in which in situ catalyst treatment can be performed, and the analytic mode with a direct line-of-sight connection to the analysis chamber and the mass spectrometer. The heating system and pulse valves are located outside the vacuum chamber, resulting in a system that is easy to operate and modify. The high stability and reproducibility of the pulse intensity allows for direct, quantitative evaluation of single-pulse and multipulse experiments. The performance of the system is demonstrated using the CO oxidation over a Au/TiO(2) catalyst as test reaction.

We describe an apparatus for spatially resolving scanning mass spectrometry which is able to measure the gas composition above catalytically active microstructures or arrays of these microstructures with a lateral resolution of better than 100 mum under reaction conditions and which allows us to quantitatively determine reaction rates on individual microstructures. Measurements of the three-dimensional gas composition at different vertical distances and separations between active structures allow the evaluation of gas phase mass transport effects. The system is based on a piezoelectrically driven positioning substage for controlled lateral and vertical positioning of the sample under a rigidly mounted capillary probe connecting to a mass spectrometer. Measurements can be performed at pressures in the range of <10(-2)-10 mbars and temperatures between room temperature and 450 degrees C. The performance of the setup is demonstrated using the CO oxidation reaction on Pt microstructures on Si with sizes between 100 and 300 mum and distances in the same order of magnitude, evaluating CO(2) formation and CO consumption above the microstructures. The rapidly decaying lateral resolution with increasing distance between sample and probe underlines the effects of (lateral) gas transport in the room between sample and probe. The reaction rates and apparent activation energy obtained from such measurements agree with previous data on extended surfaces, demonstrating the feasibility of determining absolute reaction rates on individual microstructures.