Modification of CuCl2·2H2O by dielectric barrier discharge and its application in the hydroxylation of benzene

Abstract

CuCl₂·2H₂O powder was modified by a dielectric barrier discharge (DBD) plasma at room temperature and atmospheric pressure (CuCl₂–DBD). And the catalytic activity for the benzene hydroxylation reaction using CuCl₂–DBD as a catalyst was investigated. The CuCl₂–DBD samples were characterized by XRD, SEM, TEM, BET, XPS, FT-IR, and TG-DTA. The results demonstrate that after DBD plasma treatment, crystal H₂O and about 50% of Cl in CuCl₂·2H₂O were removed, and the amounts of Cu and O increased on the surface of CuCl₂–DBD. CuCl₂·2H₂O with a large flat regular geometric shape was changed into small particles with the average particle diameter less than 50 nm; the specific surface area decreased from 16.1 m² g⁻¹ to 9.4 m² g⁻¹, and the pore volume increased approximately 45 times. However, the crystal structure and the H3 type mesoporous structure of CuCl₂·2H₂O were still retained after plasma treatment. The DBD plasma modified or etched the surface of CuCl₂·2H₂O, and changed the amounts of elements on the surface. This surface change makes CuCl₂–DBD insoluble in polar solvents. For the benzene hydroxylation reaction, CuCl₂–DBD exhibits a higher activity and selectivity than CuCl₂, in particular CuCl₂–DBD can be recycled and reused. Under the optimized conditions, the yield and the selectivity of phenol were 19.1% and 95.6%, respectively. The activity of the CuCl₂–DBD catalyst remained basically unchanged after repeated use four times.