Study On Synthesis Of P-Chlorobenzaldehyde By Catalytic Partial Oxidation Of P-Chlorotoluene

p-Chlorobenzaldehyde is an important intermediate in the synthesis of a variety of fine chemicals such as dyes, pharmaceuticals and agrochemicals. Traditionally, p-chlorobenzaldehyde was mainly prepared by acid hydrolysis of p-chlorobenzal chloride formed in p-chlorotoluene chlorination. However, this production processes are tedious, heavily erosive, and caused seriously environmental problems. In recent years, as an oxidant, oxygen has attracted growing attention in the field of oxidation of methyl aromatics to their corresponding aldehydes. Moreover, it is desirable to develop a high-activity and reusable catalyst. In this paper, we tried to develop a highly efficient heterogeneous catalyst for oxidation of p-chlorotoluene to p-chlorobenzaldehyde. Besides, we investigated the relationship between the performance and physicochemical properties.As a redox catalyst, octahedral manganese oxide molecular sieves (OMS-2) has been tested for the partial oxidation of p-chlorotoluene to p-chlorobenzaldehyde for the first time. The effects of reaction conditions (amount of catalyst, initial water amount, reaction temperature, reaction time) on the yield of p-chlorobenzaldehyde were investigated systematically. Under optimal conditions (catalyst0.05g, water2g,100℃,10h),p-chlorobenzaldehyde selectivity and yield were68.7%and59.1%, respectively. Moreover, the catalyst can be reused for four cycles without any appreciable loss in activity, showing good stability and reusability. By combining the characterization results (e.g., XRD, SEM, BET, O2-TPD, H2-TPD) with the catalytic performance of the catalyst, it was deduced that p-chlorotoluene conversion depended on the abundance and mobility of lattice oxygen.In order to obtain more efficient catalysts, doped OMS-2was investigated for p-chlorotoluene reaction. It was observed that OMS-2modified with Zr (Zr-OMS-2) performed much higher catalytic activities than undoped OMS-2under equal reaction conditions. The yield of p-chlorobenzaldehyde reaches maximum at6wt%Zr loading (ca.79.6%yield,92.5%p-chlorotoluene conversion, and86%p-chlorobenzaldehyde selectivity). Different techniques, including XRD, SEM, EDXS, FTIR, NH3-TPD and N2adsorption-desorption were employed to clarify the relationship between the structure and catalyst performance. It was found that the Zr species are well-dispersed, and its catalytic performance is closely related to the proper acidity and higher special surface area of the Zr-OMS-2catalyst in p-chlorotoluene oxidation.