(702f) Nickel-Based Catalysts for Aqueous-Phase Reforming of Short-Chain Alcohols

Aqueous-phase reforming (APR) is a technology to convert organic compounds in aqueous medium primarily to hydrogen and carbon dioxide. Because of the energetic efficiency of the process, APR has been considered as a promising route to upgrade the organic residue found in biorefinery water fractions to value added products. APR of oxygenated hydrocarbons to produce hydrogen requires catalysts that promote C-C bond cleavage and water-gas-shift (WGS) reaction. The highest activity and hydrogen selectivity in reforming reactions have typically been achieved over Pt-based catalysts. However, comparable activities were achieved over cheaper Ni catalysts¹. However, the most tested nickel-based catalysts have been observed to deactivate rapidly².

The target of this work was to prepare and test suitable nickel modified catalysts using zirconium and cerium mixed oxides as supports. These supports have been chosen because of their good hydrothermal stability which is the main issue to be considered in APR studies.

Nickel was introduced to CeO₂-ZrO₂ supports by incipient wetness impregnation method. Reduction of the catalyst was done in-situ in APR reactor before the reaction. Successful modification of all tested oxide supports by nickel was proven by various characterization methods (AAS, N₂ physisorption, TEM and XRD).

APR experiments were performed in a continuously operated stainless steel tubular reactor using downward flow. Reaction conditions of experiments were 230 °C, 32 bars and 5 wt% aq. solutions of short chain alcohols, namely methanol, ethanol, propan-1-ol and butan-1-ol, were used as a feedstock.

Deep characterization of prepared catalysts revealed differences in pore size, surface areas, and metal particle size.

The prepared catalysts showed very high activities in APR of short-chain alcohols and conversions over 50 % were achieved. In the case of methanol reforming, hydrogen, methane, CO and CO₂ were detected as the main gaseous products. In case of other alcohols APR, also significant formation of light alkanes and alkenes was detected in gaseous phase and of aldehydes in liquid phase products. Comparable conversions of longer alcohols were determined but lower hydrogen efficiency was achieved due to the significant formation of side products.

Furthermore, the possibility of the catalyst reuse (after their re-reduction) in the APR of methanol was tested and proven. However, some loss of activity, which was addressed to the Ni particles sintering, was observed.

References:

¹ Wikberg, H.; Grönberg, V.; Jermakka, J.; Kemppainen, K.; Kleen, M.; Laine, C.; et al. Tappi J. 2015, 14, 195-207.

² Coronado, I.; Stekrova, M.; Reinikainen, M.; Simell, P.; Lefferts, L.; Lehtonen, J. Int J Hydrogen Energy 2016, 41, 11003-11032.