Comperative study of low temperature water gas shift reaction over partıculate and monolithic catalysts

Abstract

Low temperature water gas shift (LTWGS) performance of supported Pt-ceria catalysts was investigated over particulate and monolithic structures using both pure and mixed realistic feed compositions in the 225-300oC range. WGS reaction was carried out using three different catalysts, 1.4wt.%Pt-5wt.%CeOx/γ-Al2O3 and 1.4wt.%Pt-10wt.%CeOx/γ-Al2O3 in particulate form and 1.4wt.%Pt-5wt.%CeOx/γ-Al2O3 in monolithic form. The experimental work involved a parametric study of the effects on CO conversion of steam to CO ratio, H2 or CO2 addition to the feed, simultaneous addition of H2 and CO2 to the feed, and cerium oxide loading. H2O/CO ratios of 1, 2, 3, 5 and 7 were used over the particulate 1.4wt.%Pt-5wt.%CeOx/γ-Al2O3 catalyst at 225°C with 5 mol% CO in inert N2; increasing values of this ratio shifted the WGS reaction to the product side and increased CO conversion. H2 and CO2 addition effects were tested solely at the H2O/CO ratio of 3 with feed containing 5 mol% CO, 15 mol% H2O, 25 mol% H2, and 10 mol% CO2 in inert N2. The existence of H2 or CO2 in feed suppressed CO conversion according to Le Cheatelier’s Principle. A more drastic decrease was observed in conversion when H2 and CO2 co-existed in the feed at 225°C. Experiments with both H2 and CO2 in the feed were repeated at 250 and 275°C to cover the temperature range of LTWGS. Catalyst performance under mixed feed conditions was also tested by doubling the ceria in particulate catalyst 1.4wt.%Pt-10wt.%CeOx/γ-Al2O3; and no significant change was observed in CO conversion. Catalytic activity of monolithic Pt-ceria catalysts were examined by loading precursor having the same metal and promoter amounts (1.4wt.%Pt-5wt.%CeOx) as the particulate catalyst onto a cordierite monolith structure; results of mixed feed experiments at 250-300oC showed that monoliths require higher temperatures for reaching the CO conversion levels of particulate catalysts with similar composition.Önsan.