Autothermal Reforming of Acetic Acid to Hydrogen and Syngas on Ni and Rh Catalysts

The autothermal reforming (ATR) of acetic acid (HAc) as a model bio-oil compound is examined via bench scale experiments and equilibrium modelling to produce hydrogen and syngas. This study compares the performance of nickel (Ni-Al, Ni-CaAl) vs. rhodium (Rh-Al) for particulate packed bed (PPB), and of Rh-Al in PPB vs. Rh with and without Ceria for honeycomb monolith ('M') catalysts (R-M and RC-M). All PPB and M catalysts used Al2O3 as main support or washcoat, and when not pre-reduced, exhibited good performance with more than 90% of the HAc converted to C1-gases. The maximum H-2 yield (6.5 wt.% of feed HAc) was obtained with both the Rh-Al and Ni-CaAl catalysts used in PPB, compared to the equilibrium limit of 7.2 wt.%, although carbon deposition from Ni-CaAl at 13.9 mg g(cat)(-1) h(-1) was significantly larger than Rh-Al's (5.5 mg g(cat)(-1) h(-1)); close to maximum H-2 yields of 6.2 and 6.3 wt.% were obtained for R-M and RC-M respectively. The overall better performance of the Ni-CaAl catalyst over that of the Ni-Al was attributed to the added CaO reducing the acidity of the Al2O3 support, which provided a superior resistance to persistent coke formation. Unlike Rh-Al, the R-M and RC-M exhibited low steam conversions to H-2 and CH4, evidencing little activity in water gas shift and methanation. However, the monolith catalysts showed no significant loss of activity, unlike Ni-Al. Both catalytic PPB (small reactor volumes) and monolith structures (ease of flow, strength, and stability) offer different advantages, thus Rh and Ni catalysts with new supports and structures combining these advantages for their suitability to the scale of local biomass resources could help the future sustainable use of biomasses and their bio-oils as storage friendly and energy dense sources of green hydrogen.