Effect of preparation conditions on the catalytic performance of Cu–Fe/ZrO2 for the synthesis of DPU from aniline and CO2

• Cu–Fe/ZrO2 can effectively catalyze DPU synthesis reaction starting from CO2.
• Cu and CuO are major active components while Fe and Fe2O3 play the role of promoter.
• Acid–base properties of ZrO2 and dispersed state of metal affect catalytic activity.

Diphenyl urea (DPU) is an important chemical intermediate. The synthesis of DPU from aniline and CO2 is a green route and the studies on the catalyst for this route are of significance. The effect of preparation conditions on the catalytic performance of Cu–Fe/ZrO2 was investigated by means of XRD, H2-TPR, and BET in combination with activity test. Cu–Fe/ZrO2 was prepared by the following process: firstly an incipient wetness impregnation using cupric nitrate and ferric nitrate as the precursors and then calcination after being dried and finally reduction. The suitable conditions were as follows: metal loading based on metal oxide = 10% (wt.), molar ratio of Cu to Fe = 3:1, aging at ambient temperature for 24 h, drying at 110 °C for 10 h, calcinating at 450 °C for 6 h, and reducing at 300 °C for 3 h using a mixture of H2/N2 with 20% (vol.) of H2. It is concluded that (1) copper and cupric oxide are the main active species while iron and ferric oxide are the promoters; (2) the reduction properties of cupric oxide and ferric oxide play important roles in the catalysis of Cu–Fe/ZrO2; (3) both Lewis acid sites and Lewis base sites existed on the surface of ZrO2 promote the catalytic performance of Cu–Fe/ZrO2. In addition, the catalytic mechanism of Cu–Fe/ZrO2 in the reaction of aniline and CO2 to DPU was proposed.