Influence of alkali metal modification and reaction conditions on the catalytic activity and stability of Ni containing smectite-type material for steam reforming of acetic acid

A Ni incorporated mesoporous smectite-like material, SM(Ni), was modified by various alkali metals, such as, Li, Na, K, Rb or Cs, and tested for the steam reforming of acetic acid as a model compound of aqueous phase of bio-oil derived from biomass pyrolysis. Initial conversion of acetic acid and concentration of H2 produced are drastically enhanced by the modification with these alkali metals. 1.0 wt% K-modified SM(Ni) catalyst exhibits the highest activity among the modified SM(Ni) materials tested. Addition of K promotes the reduction of Ni species incorporated in the smectite, yielding more metallic Ni species than in the original SM(Ni) sample. Therefore, the K-modified SM(Ni) catalyst gives higher initial activity compared with the original smectite catalyst. However, these modified materials lose their activities due to carbon deposition on their surface during the course of reaction, similar to the original SM(Ni). The influence of reaction conditions, such as O2 or H2 addition, steam to carbon ratio (S/C) and reaction temperature, was also investigated. Higher and more stable activity was obtained with unmodified SM(Ni) catalyst at a high reaction temperature of 973 K and at an S/C ratio of 3.3.