Hydrogen generation by ethanol steam reforming over Rh/Al2O3 and Rh/CeZrO2 catalysts: A comparative study

Abstract

Rhodium (Rh) catalysts supported over Al2O3 and CeZrO2 were developed and their activity towards hydrogen generation through ethanol steam reforming (ESR) was compared. Reforming reactions were performed over a range of temperatures (450 °C–600 °C) and feed flow rates (0.1, 0.2 and 0.3 mL min−1) at a constant ethanol-to-water molar ration of 1:6. Although complete ethanol conversion could be effected, the H2 selectivity was found to be higher for Rh/CeZrO2 catalyst (62.9%) as compared to Rh/Al2O3 (59.3%) under optimized reaction conditions. The average exit flow rate was relatively higher for Rh/CeZrO2 catalyst (263 mL min−1) as compared to Rh/Al2O3 catalyst (236 mL min−1). In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) revealed the underlying mechanism responsible for better performance of Rh/CeZrO2 catalyst over Rh/Al2O3 catalyst. Rh/CeZrO2 catalyst was found to facilitate the decomposition of acetate intermediates, through carbonates at lower temperatures. On the other hand, over Rh/Al2O3, reaction proceeds through formation of both acetate as well as formate species both of which decompose at much higher temperatures. The amount of coke deposited was also lower in case of Rh/CeZrO2 catalyst (6.75 mmol gcatalyst−1) than over Rh/CeZrO2 catalyst (10.57 mmol gcatalyst−1).