Effect of B and Sn on Ni catalysts supported on pure- and on WO3/MoO3-modified zirconias for direct CH4 conversion to H2

Methane cracking for hydrogen production was studied over monometallic/bimetallic Ni catalysts supported on pure or WO3/MoO3-modified zirconias. The catalysts were reduced easily with methane at 773 K, indicating that regeneration studies can be performed without using hydrogen. Ni–B and Ni–Sn bimetallic catalysts presented different behaviors when exposed to methane at 773 K. The former, because of its low thermal stability, behaved as a well dispersed phase with small nickel crystallites, while the latter behaved as a bimetallic catalyst. For all catalysts, except for Ni–Sn, the metallic particles, after 8 h of methane exposure at 773 K, were mostly concentrated at the tip of the carbon filaments, whereas zirconia surface was found to be free from these filaments. Additionally, our results suggest that the presence of Sn does not improve catalytic performance for hydrogen production by methane cracking, considering the catalytic systems under study. Rather, adding Sn seems to inhibit access to Ni sites, which are necessary for the C–H bond activation of methane and then for the nucleation of carbon species.

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► Hydrogen on Ni catalysts supported on pure or WO3/MoO3-modified zirconias.
► Ni–B and Ni–Sn bimetallic catalysts are different after exposed to methane at 773 K.
► All catalysts, except for Ni–Sn, after 8 h of methane exposure concentrated carbon filaments.
► MoO3 and WO3 modified zirconias led to different morphologies of graphite.
► Sn increased Ni dispersion and diminishing Ni ensemble inhibiting carbon deposition.