Effect of Pd salt precursor on the stability of structured foam catalysts for low-temperature methanol steam reforming

In this study, OB-SiC foams were used as carriers for Pd-Cu/CeO2-Al2O3 catalysts during low-temperature (200-350°C) methanol steam reforming. The structured catalysts were prepared by the dip-coating procedure followed by the sequential impregnation of CeO2 (30 wt% on Al2O3), Cu (20 wt%) and Pd (2 wt%); nitrate (N), acetylacetonate (AA) and acetate (A) were selected as palladium salt precursors. During activity tests performed at WHSV = 2 h- 1 and S/C = 1.5, the foam catalysts, independently from the selected precursor, displayed complete conversion above 250 degrees C; for lower temperatures, the best results also in terms of H2 yield, were recorded over the AA structured catalyst, which, according to the indirect BET and TPR measurements, appears to exhibit the highest active phase dispersion and consequently the best reducibility. Interestingly, the N catalyst enhanced CO2 selectivity in the low temperature range. The effect of space velocity change was also investigated, and very similar results were observed over the N, A and AA samples for WHSV increase from 1 to 2 h- 1, while, for a reaction temperature below 250°C at 2 h- 1, a quite higher conversion and hydrogen yield was recorded for the catalyst prepared from acetylacetonate. All three catalysts exhibited excellent stability, with constant activity and nearly zero coke selectivity during 24-h tests at 250°C under WHSV = 1 h- 1. However, the highest mean methanol conversion (99%) and hydrogen yield (94%) were recorded by choosing acetylacetonate as precursor. The latter stability results are very encouraging when compared with the few studies found in the recent literature over Cu-based foams for low-temperature methanol steam reforming.