Investigation into the behaviour of a wash-coated PGM-based catalyst layer onto micro-channel reactors for the steam reforming of methane

Master Thesis


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University of Cape Town

A wash-coating method which had originally been used for wash-coating a Rh/Al₂O₃ catalyst onto stainless steel micro-channels (MC) for the reforming of propane [24] was tested in the steam reforming of methane. The robustness of this method was unknown and was therefore tested for its possible application in methane steam reforming, which has far harsher reaction conditions. A 1 wt% Rh/Al₂O₃ catalyst was wash-coated onto heat treated MC reactor plates and tested at 700 °C with steam to carbon ratio of 3 at a number of catalyst mass specific space velocities (scc᛫(gcat᛫h)⁻¹). The MC tests yielded conflicting results with some tests having stable catalysts and the majority have unstable catalysts due to poor wash-coat adhesion. The unsuccessful cases were due to a loss of catalyst. The change in catalyst stability was postulated to be the result of the wash-coating suspension size being reduced too much. In the cases where catalyst instability due to poor adhesion and ultimately loss of the catalyst the suspension batch size was reduced such that the surface tension of the viscous suspension now exceeded the intermolecular forces in the liquid. This resulted bubble formation and due to the high viscosity of the suspension due to the presence of the polyvinyl alcohol (PVA) binder the bubbles remained during the wash-coating process which is thought to have adversely affected the wash-coats adhesion. Another possible cause which is thought to have amplified the poor adhesion of the unstable catalyst runs is the thermal expansion of the stainless-steel reactor plates. The results of this study could not give outright and straightforward conclusions as to why there were 2 stable runs and unstable runs due to a loss of catalyst. As a result, further work is required to confirm the postulations and trends seen in this study. Future work should concentrate on using a larger batch of suspension to mitigate bubble formation, adding an alumina primer layer before wash-coating the catalyst to aid adhesion through additional oxide bond formation and the use of a more thermally stable stainless steel reactor plate to mitigate thermal expansion.