Influence of Aging Time on the Properties of Precursors of CuO/ZnO Catalysts for Methanol Synthesis

摘要

The aging process of pure copper precursors and copper-zinc binary precursors were studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnO were tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cu species were characterized with N_2 adsorption and N_2O passivation method, respectively. For the Cu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80℃, the initial phase was a mixture of copper nitrate hydroxide Cu_2(NO_3)(OH)_3, georgeite and hydrozincite Zn_5(CO_3)_2(OH)_6. By increasing the duration of its aging time, the phase of Cu_2(NO_3)(OH)_2 first transited to georgeite, and then interdiffused into Zn_5(CO_3)_2(OH)_6 and resulted in two new phases: rosasite (Cu,Zn)_2CO_3(OH)_2 and au-richalcite (Zn,Cu)_5(CO_3)_2(OH)_6. The former phase was much easier to be formed than the latter one, while the latter phase was more responsible for the activity of methanol synthesis than the former one. It is found that the composition and structure of the precursors altered obviously after the colour transition point. The experimental results showed that methanol synthesis is a structure-sensitive catalytic reaction.