Efficient synthesis of p-chlorobenzaldehyde through liquid-phase oxidation of p-chlorotoluene using manganese-containing ZSM-5 as catalyst

Manganese-containing MFI-type Mn-ZSM-5 zeolites were prepared and characterized by XRD, UV-vis DRS, SEM, XPS, N₂ adsorption-desorption, NH₃-TPD and ICP-AES techniques. The zeolites show high catalytic activity and selectivity in the heterogeneous oxidation of p-chlorotoluene to p-chlorobenzaldehyde. The effects of catalyst concentration, water addition, HBr amount, as well as reaction time and temperature on product yield were investigated. Under the optimized conditions (catalyst 20 mg, p-chlorotoluene 1 mL, solvent (acetic acid) 10 mL, HBr (40 wt%) 30 mg, H₂O 3 g, oxygen flow rate 50 mL min^-1, time 8 h, temperature 100 °C), the Mn-ZSM-5 (Si/Mn = 48, Mn 1.7 wt%) catalyst shows p-chlorotoluene conversion of 93.8% and p-chlorobenzaldehyde selectivity of 90.5%. The excellent catalytic activity can be attributed to the distribution of Mn species and the mild acid sites.