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

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 g(cat) h/mol(CH4) and 600 degrees 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 H-2 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. (C) 2016 Elsevier B.V. All rights reserved.