Hydrogen Production Via Ethanol Steam Reforming Reaction Over Modified Ni-base Catalysts

Producing hydrogen from ethanol steam reforming reaction is still a current highlight for fuel cell technique, and exploring high active catalysts with high hydrogen selectivity and good stability at low temperature is one of important issues to the utilization of hydrogen energy.In this article Ni-based bimetallic catalysts supported onγ-Al₂O₃·(amorphous)SiO₂ were prepared using deposition-precipitation methods and effects of second metal species of La, Co, Cu, Zr or Y on the catalytic performance were investigated in the steam reforming reaction of ethanol by using characterization of XPS, XRD, TPR, and NH3-TPD. Activity tests showed that the second metal species of Cu,Co,La or Y can efficiently promote the catalyst performance of hydrogen production at low temperatures. TPR patterns indicate that addition of La, Y, or Zr enhances the incorporation of metal catalytic component into the support. XPS results show that addition of La, Co significantly increases the metallic nickel content in the reduced catalysts surface. XRD results suggest that addition of La greatly decrease crystal sizes of metallic nickel. NH3-TPD profiles reflect that addition of La, Co can decrease the acid strength of catalysts. TGA results prove that addition of La or Co reduces significantly the amount of graphitic coke deposited on the catalysts. Over Ni-Co/γ-Al₂O₃·(amorphous)SiO₂ and Ni-La/γ-Al₂O₃·(amorphous)SiO₂ catalyst hydrogen selectivity increased with the increase of temperature and the water/ethanol molar ratio, and decreased with the increase of LHSV. Over Ni-La/γ-Al₂O₃·(amorphous)SiO₂ catalyst,hydrogen selectivity was 55.0% at 400℃and increased to 99.0% at 650℃, in particularly CO selectivity was as low as 0.67% at 400℃.Effects of calcination temperature and Cu metal content on the catalytic performance of Ni-Cu catalysts was investigated, and found that the hydrogen selectivity is the highest over the catalyst calcined at 650℃and catalytic components of Ni, Cu were highly dispersed in the supports. When the content of catalytic components Cu is 5%, the hydrogen selectivity is the highest over the catalyst. MgO modified Ni-Cu/γ-Al₂O₃ catalysts has higher hydrogen selectivity and lower the methane selectivity. Characterization of XRD validated that MgAl2O4 phase existed in the catalyst, which can prevented the aggregation and the growth of catalytic Cu, Ni species during the calcinations and reduction treatment.Effect of Co metal content and different supports on the catalytic performance of Ni-Co catalysts was investigated, and found that when the content of catalytic components Co was 5%, the hydrogen selectivity was higher over the catalyst. characterization of XRD validated that crystal grain sizes of NiO and Co3O4 were smaller and dispersed well in the catalyst with 5% Co. Activity tests indicate thatγ-Al₂O₃·(amorphous)SiO₂ supported Ni-Co catalyst has good catalytic performance at low temperature for the ethanol reforming reactions.Finally, The stability of the Ni-La catalysts with different supports(SiO₂,γ-Al₂O₃,γ-Al₂O₃·(amorphous)SiO₂) with time-on-stream was examined, and found that no ethylene was detected and the hydrogen selectivity remained about 67.0% at the reaction time of 100h overγ-Al₂O₃·(amorphous)SiO₂ supported Ni-La catalyst. TGA and XPS results were used to detect the carbon deposited on the stability examined Ni-La catalysts and found that the deposition carbon over theγ-Al₂O₃·(amorphous)SiO₂ supported Ni-La catalyst was only 0.86 g C g-1cat, among which graphite carbon was about 42.81%. Therefore,the addition of Si in theγ-Al₂O₃ support can decrease the amounts of deposition carbon on Ni based catalysts and enhanced the stability of Ni based catalysts.