On the scope of mechanochemical activation: The case of Cu/ZnO catalytic systems

ZnO was submitted to different conditions of high-energy ball milling to thoroughly study the outcome of mechanochemical activation. Structural modifications led to a decrease in crystallite size and an increase in micro-strain and specific surface area (SBET) with milling time. Different copper amounts were added on pristine (reference) and activated support by incipient wetness impregnation. Cu deposited over activated support showed an enhanced metal-support interaction since part of Cu2+ could be introduced into milled ZnO lattice, replacing Zn2+ ions and/or locating in lattice interstitials. Moreover, further analyses suggested an electron transfer from activated support to metal, generating a mixture of Cu2O-CuO species, particularly at the interface between metal and support. N2O chemisorption studies gave Cu particle sizes of 1.3, 1.9 and 3.5 nm (for 0.2, 0.5 and 1 wt% Cu, respectively) and thus a good metal dispersion over ZnO was achieved. Hence, support's activation by milling process showed to be an excellent approach to improve both metal-support interaction and metal dispersion of supported catalysts.