Effects of support and additives on Ni-based catalysts
Steam reforming (SR) of oxygenated species like bio-oil or ethanol can be used to produce hydrogen or synthesis gas from renewable resources. However, deactivation due to carbon deposition is a major challenge for these processes. In this study, different strategies to minimize carbon deposition on Ni-based catalysts during SR of ethanol were investigated in a flow reactor. Four different supports for Ni were tested and Ce0.6Zr0.4O2 showed the highest activity, but also suffered from severe carbon deposition at 600 °C or below. Operation at 600 °C or above were needed for full conversion of ethanol over the most active catalysts at the applied conditions. At these temperatures the offgas composition was close to the thermodynamical equilibrium. Operation at high temperatures, 700 °C and 750 °C, gave the lowest carbon deposition corresponding to 30–60 ppm of the carbon in the feed ending as solid carbon over Ni/MgAl2O4 and Ni/Ce0.6Zr0.4O2. Promotion of Ni/MgAl2O4 with K, CeO2, and ZrO2 increased conversion, decreased carbon deposition, or both. Promoting Ni/MgAl2O4 with both K and CeO2 showed particularly promising results with high degrees of conversion and carbon deposition of less than 400 ppm of the carbon in the feed at approx. 600 °C. The different promoters did not influence the product distribution to any significant extent. Selective poisoning with small amounts of K2SO4 on Ni–CeO2/MgAl2O4 at 600 °C decreased carbon deposition from 900 to 200 ppm of the carbon in the feed. However, the yield of H2 decreased from 80% to 64% and the yield of hydrocarbons increased from 3.5% to 12.7% when increasing the amount of K2SO4 on the catalyst from 0 wt% to 0.65 wt% indicating that the catalyst activity to hydrocarbon reforming decreased.
International Journal of Hydrogen Energy, 2013, Vol 38, Issue 35, p. 15105-15118