Thermal solid–solid interaction and catalytic properties of CuO/Al2O3 system treated with ZnO and MoO3

The effect of ZnO (1.70–12.13 wt.%) and MoO3 (2.96–19.63 wt.%) treatment on thermal solid–solid interaction and physicochemical properties of 0.20CuO/Al2O3 system was investigated. The pure and treated mixed solids were subjected to heat treatment at 400–1000 °C. The thermal behavior of these solids was studied by TG and DTA techniques. The thermal products were characterized using X-ray diffraction (XRD) analysis. The catalytic behavior of all solids was tested in hydrogen peroxide (H2O2) decomposition reaction at 30–50 °C. The results revealed that crystalline γ-Al2O3 phase were detected in all solids preheated at 400–800 °C with no diffraction lines from the CuO phase. Crystalline CuAl2O4 phase formed as a result of solid–solid interaction between CuO and Al2O3 at 800 °C. The treatment of pure solids with MoO3 hindered the formation of CuAl2O4 phase because of the formation of copper molybdate phase while the treatment with ZnO had the opposite effect and might form solid solutions of formula (ZnxCu1−x)Al2O4 at 800 and 1000 °C. Furthermore, MoO3 enhanced the crystallization of γ-Al2O3 into α-Al2O3 at 1000 °C. The catalytic activity of pure solids treated with MoO3 or ZnO and preheated at 400 and 600 °C increased up to 10.88 wt.% MoO3 and up to 3.34 wt.% ZnO. The observed increase in activity is attributed to increasing concentration of catalytically active constituents and/or formation of new active sites. The activity progressively decreased with increasing treatment temperature up to 1000 °C and with increasing concentration of MoO3 and ZnO up to 19.63 and 12.13 wt.%, respectively. The decreasing in activity is due to the formation of inactive compounds such as (ZnxCu1−x)Al2O4, MoO3, α-Al2O3 and/or sintering processes.