Application of two morphologies of Mn 2 O 3 for efficient catalytic ortho -methylation of 4-chlorophenol.

Vapor phase ortho -methylation of 4-chlorophenol with methanol was studied over Mn 2 O 3 catalyst with two kinds of morphologies. Here, Mn 2 O 3 was prepared by a precipitation and hydrothermal method, and showed the morphology of nanoparticles and nanowires, respectively. XRD characterization and BET results showed that, with the increase of calcination temperature, Mn 2 O 3 had a higher crystallinity and a smaller specific surface area. N 2 adsorption/desorption and TPD measurements indicated that Mn 2 O 3 nanowires possessed larger external surface areas and more abundant acid and base sites. Simultaneously, in the fixed bed reactor, methanol was used as the methylation reagent for the ortho -methylation reaction of 4-chlorophenol. XRD, XPS, TG-MS and other characterizations made it clear that methanol reduced 4-chlorophenol and its methide, which were the main side-reactions. And Mn 3+ was reduced to Mn 2+ under the reaction conditions. Changing the carrier gas N 2 to a H 2 /Ar mixture further verified that the hydrogen generated by the decomposition of methanol was not the reason for dechlorination of 4-chlorophenol compounds. Here we summarized the progress of 4-chlorophenol methylation based on the methylation of phenol. Also, we proposed a mechanism of the 4-chlorophenol dechlorination effect which was similar to the Meerwein-Ponndorf-Verley-type (MPV) reaction. The crystal phase and carbon deposition were investigated in different reaction periods by XRD and TG-DTA. The reaction conditions for the two kinds of morphologies of the Mn 2 O 3 catalyst such as calcination temperature, reaction temperature, phenol-methanol ratio and reaction space velocity were optimized.