Energy & Fuels, Vol.27, No.8, 4739-4747, 2013
Stability and Performance of Ruthenium Catalysts Based on Refractory Oxide Supports in Supercritical Water Conditions
Eleven commercial stabilized and unstabilized zirconia and titania samples have been tested for stability as potential catalyst supports for supercritical water gasification at 400 degrees C and 28.5 MPa. Samples based on monoclinic zirconia and rutile as well as one sample based on stabilized tetragonal zirconia showed good physical stability. Most samples showed a loss of surface area during the first 20 h of hydrothermal treatment, leveling out at longer exposure times. In a continuous fixed-bed reactor setup, a performance and stability test of the samples loaded with 2 wt % ruthenium gave good results for three samples, of which the sample based on stabilized tetragonal zirconia showed the best performance. For those samples, the surface area decreased only to a minor extent, which we attribute to an aging step that has been performed prior to impregnation with ruthenium. The metal surface area showed a minor decrease for all samples. The reason for this decrease is probably the build-up of a layer of carbon deposit on top of the active sites.