Fuel cells based on the oxidation of processed hydrogen containing small amounts of CO, as well as those based on direct methanol oxidation, suffer from severe poisoning by carbon monoxide. Hence, there is much interest in developing an anode electrocatalyst that either adsorbs very small amounts of CO while still able to oxidize hydrogen at an acceptable rate, or that oxidizes CO at a significantly reduced overpotential. The hydroxyl species OH is used here as a model for the oxygen-containing surface species with which CO is supposed to react under electrochemical conditions. However, the general issue of catalyst separation and recycling is not solved satisfactory so far. Solutions to this question will result in very efficient technology saving energy, investment and operational costs.
Membrane separation can even intensify a process in unifying catalyst and product separation steps.
The use of soluble molecularly enlarged supports for homogeneous catalysts prevents encountering new problems through mass transport limitations or catalyst entanglement in a solid support, while still enabling a filtration of the catalyst by nano- or ultrafiltration membranes. Another but also remarkable effect is that by decoupling the residence times of substrates and catalyst, it becomes possible to run a homogeneously catalyzed reaction in a continuous fashion. This provides the additional opportunity to control the reaction also in a reaction engineering way. The support used in this work is a polyphenylene dendrimer. This type of dendrimers forms shape persistent, inert and rather stable nanoparticles, which makes it a perfect support for the use in a nanofiltration membrane reactor.