“…[ 33 ] The synergistic effects between Cu and other transition metals, such as Fe, Co, and Ni, during catalytic CO oxidation have been widely studied. [ 34 ] Thus, in this study, we examined the CO oxidation activities of Cu‐based metal oxide catalysts derived from 15 different bimetal HDSs containing relatively large secondary metal cations (Bi, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Tm, Y, or Yb). Since the NO 3 − and OH − anions in the Cu‐based HDSs were fully decomposed and disappeared at temperatures below 400 °C, regardless of the type of metal cation used (Figure S17, Supporting Information), the possibility of any influence from surface anion impurities derived from the precursor, such as nitrates, on catalytic activities, was ruled out after calcination at temperatures above 400 °C.…”