Oxidative Steam Reforming Of Ethanol For The Production Of Hydrogen Over Metallic Nickel-based Monolithic Catalysts

Oxidative steam reforming (OSR) of ethanol, which is a combination of steam reforming and partial oxidation reactions, is proposed as the most effective process for the conversion of ethanol to hydrogen. OSR also possesses the advantages of rapid start-up and possibility of thermally neutral operation. In this work, Ni monolith based catalysts were used for the oxidative steam reforming of ethanol. The oxide promoters, CeO₂ and CeO₂-ZrO₂, were added to the Ni monolith to promote its catalytic capability and stability.A series of CeO₂, ZrO₂ or CeO₂-ZrO₂ promoted monolithic Ni catalysts were prepared by impregnating nickel sponge with Ce(NO3)3 and/or Zr(NO3)4 solutions. The catalysts were characterized with XRD, SEM, BET and ICP. The influences of several parameters on the catalytic activity and selectivity were examined including reaction temperature, GHSV, C/O and C2H5OH/H2O ratios. The results revealed that (1) in all the experiments of this work, the conversion of ethanol was complete and was not affected by the changes of the parameters investigated; (2) addition of CeO₂ promoted the WGS reaction, increased the selectivity to H2 while reduced the selectivities to undesirable products CH4, C2H4 and C2H6; the catalyst with the optimal CeO₂ loading of 7.33wt.% showed the selectivities to H2, CH4 and CO of 98.3%, 2.2% and 31.2%, respectively; trace amount of C2H6 and no C2H4 was observed during 170 min testing; (3) the optimal Ce/Zr loading molar ratio was 3.26; the catalyst Ce0.15Zr0.05Ni with the optimal loading ratio exhibited the highest selectivity to H2 and the best stability among the prepared series of CeZrNi catalysts; the XRD patterns revealed the existence of Ce-Zr interaction as a sign of the formation of the solid solution between CeO₂ and ZrO₂; it is supposed that the solid solution formation attributes to the enhancement of the redox property and thermal stability of the CeO₂-ZrO₂ and thus the improvement of its catalytic capability and stability; (4) the catalytic properties of Ce0.8Ni and Ce0.15Zr0.05Ni showed similar trends with the changes of reaction temperature, GHSV, C/O and C2H5OH/H2O ratios in the oxidative steam reforming: selectivity to H2 increased, while selectivities to CH4, C2H4 and C2H6 decreased with the increase of reaction temperature or the decrease of C2H5OH/H2O ratio; selectivity to H2 decreased, while selectivities to CH4, C₂H₄ and C₂H₆ increased with the increase of GHSV or C/O ratio.