A comparative study of zirconia supported nickel and/or ruthenium catalysts for glycerol steam reforming

The physico-chemical properties of Ni, Ru, Ru-Ni monoclinic ZrO2 catalysts were studied and their catalytic activities in the glycerol steam reforming reaction (GSR) were compared. The cata-lysts were prepared by the wet impregnation method, calcined at 600 degrees C and characterized using XRD, BET, H2-TPR and CO2-TPD techniques. The XRD analyses revealed varying crystallite sizes depending on the active phase nature and composition. The H2-TPR analyses demonstrated that the reducibility of the active metal oxide species and its dispersion were affected by the active phase composition. The CO2-TPD analyses revealed that surface modification following impreg-nation modified the basic properties of the catalysts. The catalytic activity tests (T = 400-700 degrees C, WGFR 9:1, flow rate of 0.025 mL/min) showed that the nickel based catalysts were active while the ruthenium based catalyst was inactive. Combining ruthenium and nickel over zirconia led to smaller Ni particle sizes and a better metal dispersion both of which con-tributed to higher H2 yields and an increased coke resistance. During 24 h on stream, the com-bined Ru-Ni/ZrO2 catalyst maintained a higher total glycerol conversion compared to the Ni/ZrO2 catalyst. Only filamentous coke was identified on the spent catalysts after the stability tests. For a higher water to glycerol feed ratio (WGFR 46:1), encapsulating coke was formed over Ru-Ni/ZrO2 leading to the blockage of active sites and a more rapid catalyst deactivation.