Abstract
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.