Low-temperature reforming of ethanol over CeO2-supported Ni-Rh bimetallic catalysts for hydrogen production

Abstract

A new series of Ni-Rh bimetallic catalysts with different Ni and Rh loadings on a high-surface-area CeO2 was developed for the reforming of bio-ethanol at low-temperature (below 450 °C) to produce H2-rich gas for on-site or on-board fuel cell applications. Oxidative steam reforming of ethanol (OSRE) over a Ni-Rh/CeO2 catalyst containing 5 wt% Ni and 1 wt% Rh was found to be more efficient offering about 100% ethanol conversion at 375 °C with high H2 and CO2 selectivity and low CO selectivity compared to the steam reforming of ethanol (SRE) reaction which required a higher temperature of about 450 °C to achieve 100% ethanol conversion. The high temperature SRE reaction favors the formation of large amount of CO, which would make the downsteam CO cleanup more complicated for polymer electrolyte membrane fuel cell (PEMFC). The presence of O2 in the feed gas was found to greatly enhance the conversion of ethanol to produce H2 and CO2 as major products. Increase in Ni content above 5 wt% in the catalyst formulation decreased the H2 selectivity while the selectivity of undesirable CH4 and acetaldehyde increased. The 1 wt% Rh/CeO2 catalyst was twice as active as 10 wt% Ni/CO2 catalyst in terms of ethanol conversion and acetaldehyde selectivity and this indicated that Rh was more effective in C–C bond cleavage than Ni. The reaction was found to proceed through the formation of acetaldehyde intermediate, which subsequently underwent decomposition to produce a mixture of CO and CH4 or reforming with H2O and O2 to produce CO, CO2 and H2. The role of Rh is mainly to cleave the C–C and C–H bonds of ethanol to produce H2 and COx while Ni addition helps converting CO into CO2 and H2 by WGS reaction under the conditions employed.