Hydrogen production via steam reforming of glycerol over Rh/γ-Al_2O_3 catalysts modified with CeO_2, MgO or La_2O_3

摘要

The glycerol steam reforming (GSR) reaction for hydrogen production was investigated over Rh-based catalysts supported on gamma-Al2O3 modified with CeO2, MgO or La2O3. High specific surface area mesoporous supports (Al2O3, CeO2-Al2O3, MgO-Al2O3 and La2O3-Al2O3) were synthesized by the surfactantassisted co-precipitation method using cetyltrimethylammonium bromide (CTAB) as template. Then, highly dispersed Rh-based catalysts were prepared by the wetness impregnation technique. The physicochemical properties of the as-prepared supports and catalysts were investigated by N-2-physisorption, XRD, ICP-AES, CO-chemisorption, TEM, H-2-TPR, CO2-TPD and NH3-TPD measurements. Performance test experiments were carried out in a continuous flow fixed-bed reactor at water-to-glycerol feed ratio (WGFR) of 20:1 (molar), temperatures from 400 degrees C to 750 degrees C, weight hourly space velocity of 50,000 ml g(-1) h(-1) and atmospheric pressure. The stability of all catalysts was also investigated through 12 h time-on-stream (TOS) experiments at 600 degrees C using a WGFR of 9:1. All catalysts were remarkably stable during TOS with total glycerol conversion of =90%, glycerol conversion into gaseous products of =45% and H-2 selectivity of = 78%. The final H-2 yield for all catalysts was 2.4-2.9 mol H-2/mol glycerol. TEM experiments showed that the carbon formed onto the spent catalysts was amorphous and that sintering was mostly avoided during TOS, helping explain the excellent catalytic stability observed. The unpromoted catalyst seems to be following a different reaction pathway than and the promoted ones that depends strongly on the population and kind of acid and basic sites over its surface. (c) 2020 Elsevier Ltd. All rights reserved.