Active and stable supported Rh nanoparticles in steam methane reforming at high flow rate

PEM fuel cells are ideal for stationary and mobile applications, like remote electricity generators or vehicle power source, and are considered twice as efficient as internal combustion engines (ICE) [1]. Although infrastructure for hydrogen is still lacking (high capital costs, specifically for remote areas), hydrogen production/distribution should ideally make use of existing infrastructure. Fossil fuels, like LNG, LPG, diesel, are widely available and can be used as a source of hydrogen. Even though it produces CO2, a fuel processor with fuel cell still produces 'cleaner' electricity than ICE, while being cost-effective [2]. For distributed H2 production the key requirements for a fuel processor include rapid startup, good dynamic response to follow the change in hydrogen demand and high fuel conversion at high flow rate in small size reactors. Much work has been reported on initial performances of catalysts for steam reforming (SR), but much less their long-term stability at high space velocity. Rh has been demonstrated to be a highly active metal for SR [3,4]. High surface area CeO2 has high oxygen storage capacity, providing oxygen to the oxidation reaction step [5]. In this study, a series of supported Rh catalysts were prepared on CeO2 and CeO2-Al2O3 supports. CeO2 supports with different surface areas (SA) were obtained through various preparation methods (combustion, surfactant-assisted precipitation), ranging SA from 60 to 160 m2/g. Also, one commercial CeO2 (SA = 20 m2/g) was used for comparison. CeO2-Al2O3 supports were synthesised by surfactant-assisted coprecipitation method, ranging SA from 160 to 320 m2/g. Rhodium catalysts (0.5 wt%) were prepared by wet impregnation of the prepared supports. The physico-chemical characteristics of the catalysts were determined by XRD, H2-TPR, COchemisorption, CO2-TPD and SEM measurements. The catalysts were evaluated for their steam methane reforming (SMR) performance over lifetimes up to 200 hours of time-on-stream at high space velocities. The results show that the catalytic activity (Figure 1) is strictly connected with morphological and structural properties of the obtained materials. The surfactant-assisted precipitation method allows obtaining very high SA materials with increased metal phase dispersion [6], resulting in stable conversions at typical fuel processing conditions (after line-in of the catalysts). However, under more severe conditions (800°C and 300,000 h-1) the catalysts deactivated, probably due to SA loses and Rh sinters. Al2O3 addiction helps to prevent loss in active sites, ensuring high and stable catalytic activity towards SMR reaction.