Sustained release catalysis: Dynamic copper releasing from stoichiometric spinel CuAl2O4 during methanol steam reforming

Dynamic copper releasing from a stoichiometric CuAl2O4 catalyst in methanol steam reforming (MSR) is investigated via detailed characterizations of six samples that are collected after testing for different time (TOS). It reveals that Cu can be liberated from spinel structure under the MSR conditions, serving as the active species. The Cu releasing rate increases first and then decreases with TOS, and the released Cu atoms agglomerate into nano entities. Consequently, the number of these Cu nanoparticles increases quasi-linearly with TOS, suggesting at least part of newly released Cu do not coalesce with the former nanoparticles but form new entities anchored on the surfaces of remnant defective Cu-Al spinel, which retains a small portion of Cu2+ (5.8%) in spinel lattice even at a prolonged TOS of 300 h. The findings evidence the dynamic changes of both active Cu metal and local surface structures, which are essentially different from conventional catalysis.