Low temperature synthesis of Cu1−xAl2.5 spinel solid solution as sustained release catalyst for methanol to hydrogen

In order to find a method to synthesize spinel solid solution at low temperature, in this paper, pseudo-boehmite and copper nitrate were used as raw materials, and citric acid was used as accelerator for the first time, the Cu1−xAl2.5 spinel solid solutions were synthesized by ball milling treatment of the solid mixture and then calcined at elevated temperatures. The obtained materials were characterized by X-ray diffraction (XRD), Brunner−Emmett−Teller (BET) measurements, H2-temperature programmed reduction (H2-TPR), infrared (IR) and thermogravimetric methods (TG), and the mechanism of citric acid promoting the synthesis of the spinel solid solution was suggested. The results show that an optimal amount of citric acid can significantly promote the formation of the spinel structure, thus substantially decreasing the synthetic temperature from the above 900 °C–700 °C. At 700 °C, the preparation without the accelerator resulted in small amount of the spinel solid solution, while the use of accelerator gave rise to 82.96% spinel solid solution. Importantly, the Cu1−xAl2.5 spinel solid solution prepared at 700 °C demonstrates the best sustained release catalytic performance, and the catalytic activity reached more than 90% and remained stable within 50 h. The findings of this report might be provide guidance for the solid phase preparation of catalysts at relatively lower temperatures, thus facilitating the commercialization of the sustained release catalyst system.