Effects of Pd–Rh Composition and CeZrO2-Modification of Al2O3 on Performance of Metal-Foam-Coated Pd–Rh/Al2O3 Catalyst for Steam Reforming of Model Biogas

Abstract

Catalysts prepared by coating 1.31 wt% (Pd–Rh)/alumina composites on metal foam substrate were tested for steam reforming of model biogas (SRB) at 1 atm pressure to study the effects of Pd–Rh composition and CeZrO2-modification of Al2O3. Among the catalysts supported on unmodified alumina, [Pd(7)–Rh(1)] catalyst performed slightly better with respect to CH4 conversion as well as H2 and CO yields, whereas [Pd(3)–Rh(1)] catalyst performed slightly better for suppression of coke formation. Modification of Al2O3 with 49 wt% CeZrO2 improved catalytic activity and metal dispersion of [Pd(7)–Rh(1)] catalyst, despite 25 % loss of BET surface area. For the biogas-reforming reaction at 998 K and GHSV 1,400 h−1 with steam/methane (S/C) ratio of 1.50 in the feed, [Pd(7)–Rh(1)]/(CeZrO2·Al2O3) exhibited 92 % CH4 conversion in a microchannel-structured heat exchanger platform reactor, 20 % more than the conversion obtained over [Pd(7)–Rh(1)]/Al2O3. H2 and CO yields were also enhanced by CeZrO2-modification of Al2O3, however, these enhancements were accompanied by H2/CO selectivity decrease and CO/(CO + CO2) selectivity increase. Variation of Pd–Rh composition and CeZrO2-modification of Al2O3 did not affect catalytic stability in the feed with S/C = 1.50 for 200 h at 1,023 K and GHSV 20,000 h−1 in a tubular packed-bed reactor, while CeZrO2-modification of Al2O3 improved resistance to deterioration of surface area, pore structure and metal dispersion.