Facile synthesis of highly active Rh/Al2O3 steam reforming catalysts with preformed support by flame spray pyrolysis

• Rh catalysts supported on preformed Al2O3 are made by single flame spray pyrolysis.
• Rh supported on preformed Al2O3 shows enhanced activity for methane steam reforming.
• The use of preformed support particles inhibits the incorporation of Rh into Al2O3.
• The preformed Al2O3 support has a promoting effect on Rh reduction and H2 spillover.

A highly active catalyst is a necessity for a compact microchannel membrane reactor for methane steam reforming (MSR) due to the limitation of catalyst loading per membrane area and the deliberately reduced working temperature compared to a conventional reformer. Two series of Rh/Al2O3 catalysts with nominal Rh loadings in the range of 0.2–5 wt.% were prepared by flame spray pyrolysis (FSP) using flame made and preformed support particles. For the flame made support, Rh and Al precursors were premixed and sprayed simultaneously. In the other case, the Rh precursor was mixed with a preformed boehmite particle suspension and then sprayed into the flame. Their catalytic activity was investigated for MSR in a fix-bed reactor. The nominal 1 wt.% Rh catalyst supported on preformed Al2O3 exhibited the highest CH4 conversion of all catalysts at W/F = 0.374 gcat h/molCH4 and 600 °C. The turnover frequency (TOF) over both types of catalysts was much higher than the values of reported Rh reforming catalysts in that temperature range. In addition, the TOF values of catalysts based on preformed Al2O3 particles exceeded those over the ones with in situ formed Al2O3 by 29–39%. It is proposed that the preformed Al2O3 support promotes the catalytic activity, possibly enhancing H2 spillover which is considered to facilitate the rate determining steps in MSR. The successful synthesis of catalysts supported by preformed materials opens new possibilities for preparation of nano-structured catalysts from a multitude of support materials via flame spray pyrolysis.

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