Preparation and Properties of Copper-Containing Hydrotalcite-like Compounds

CuZnAl-hydrotalcite-like compounds (CuZnAl-HTLcs) were prepared by coprecipitation with Cu(NO 3) 2, Zn(NO 3) 2, Al(NO 3) 3, and NaOH. Based on the titration of the mixed salt solutions with different Cu/Zn/Al molar ratios, the effects of pH, precipitation way, Cu/Zn/Al molar ratio, temperature and time of the hydrothermal treatment on the preparation of CuZnAl-HTLcs were studied. The samples were characterized by XRD, ICP, and measurement of specific surface area, and used to catalyze phenol hydroxylation. The results showed that unique CuZnAl-HTLcs with high crystallinity can be prepared by precipitating a solution of (Cu+Zn)/Al molar ratio of 2.0 and Cu/Zn molar ratio ≤1.0 at pH=5.0～6.2 and then hydrothermal treatment at 100 ℃ for 3 h. The relative crystallinity of the sample obtained in the way of variable pH method is 100%, and those of the samples prepared by precipitation at low supersaturation and at high supersaturation are 76.5% and 75.9%, respectively. The Cu content in CuZnAl-HTLcs was higher than that in the mixed salt solution. This is because Cu 2+ has a greater ability to replace Al 3+ in Al(OH) 3 than Zn 2+. CuZnAl-HTLcs with high Cu content showed higher catalytic activity for the phenol hydroxylation, which implied that the Cu-Zn collaboration in the catalysis process is important.