Study On The Preparation Of Supported Pd Catalyst And Their Catalytic Activity For Hydrodechlorination And Reductive Alkylation

It is significant to investigate the methods for the synthesis of 4,6-diaminoresocinol (DAR) that is the indispensable monomer used in preparing the high-performance fiber PBO. In this paper, DAR was synthesized by catalytic HDC and nitro reduction of 2-chloro-4,6-dinitroresorcinol over 10 wt.% Pd/C catalyst. The solvent effect on the yield of DAR and the content of 2-Cl-DAR byproduct was studied, and the ethanol-water mixture was considered as the most appropriate reaction media. The operation conditions of catalytic reaction were optimized, and the optimum operation conditions were obtained:2.5 g of 10 wt.% Pd/C catalyst,60.0 g of 2-chloro-4,6-dinitroresorcinon and 20.0 g of ammonium acetate, 600 ml of 80% ethanol-water solution, a stir of 1300 rpm, hydrogen atmosphere of 2.2 MPa. At the initial reaction temperature of 40℃,37.8 g of DAR was obtained with 0.37% 2-Cl-DAR byproduct.4,6-bis(isopropylamino)resorcinol (BPAR) was catalytically synthesized from 2-Chloro-4,6-dinitroresorcinol by an one-pot reaction including reductive mono-N-alkylation and HDC over 10 wt.% Pd/C catalyst, in which acetone was used as alkyl source and hydrogen as reducing reagent. The effects of reaction conditions, such as the amount of acetic acid, reaction time, solvent, hydrogen pressure and catalyst amount, on the yield of BPAR were investigated. The optimum operation conditions were obtained as follows:2.0 g of 10 wt.% Pd/C catalyst,20 ml of acetic acid,40.0 g of 2-chloro-4,6-dinitroresorcinon 320 ml of 1:1 (v/v) acetone/2-propanol mixtures,50 ml of water,13.3 g of ammonium acetate, hydrogen atmosphere of 2.2 MPa, a stir of 1300 rpm. In the reaction condition above the synthesis reaction was carried out for 90 min,91% of BPAR yield was obtained.When various nitrophenol derivatives were used as the reactant and ketone as alkyl reagent, the corresponding secondary alkyl aminophenols with the high yield were achieved by a one-pot catalytic synthesis method in above operation condition over 10 wt.% Pd/C catalyst. When aldehyde was used as the alkyl reagent, the corresponding tertiary amine as a sole N-alkylation product was obtained.Liquid phase HDC catalyzed by supported Pd catalyst is considered as an economical and environmentally benign method in the synthesization of organic compounds as well as the nondestructive disposal of chlorinated arene. It is significant to investigate the correlations between the structure of Pd active sites and the performance of Pd catalyst for the HDC of chlorinated arene.Three different carriers, mesoporous silica-carbon nanocomposites (MSC), mesoporous SiO2 (SBA-15) and active carbon (AC) were employed as the supports of Pd catalyst (noted as Pd/MSC, Pd/SBA-15 and Pd/AC, respectively). The textural properties of the supports and catalysts have been determined by the low temperature N2 adsorption/desorption, XRD, H2-TPR, H2-TPD, XPS, HR-TEM. The results show the nano-sized Pd particles with the saw-edged grain boundaries formed on Pd/MSC due to the unique hybrid nature of carbon and silica. The mainly isolated Pd particles with terrace formed on Pd/SBA-15 and Pd/AC were observed, and a small quantity of Pd defect existed on Pd/AC.In the HDC of chlorophenols at low temperature (-15℃), the activity of catalyst depends on the content of Pd defect. Pd/MSC with a high concentration of defective surface Pd atoms exhibited the very high catalytic activity, and Pd/SBA-15 with a high concentration of plane surface Pd atoms exhibited the lower catalytic activity.The ab initio Density Functional Theory (DFT) was used to calculate the adsorption energies of Et3N,4-CP and 2,4-DCP by formingπ-orσ-complex on the terrace site of Pd (111) and the step edge of Pd (211), which are to simulate the plane and defective surface Pd atoms. The results show that 4-CP was activated via the formation ofπ-complex with aromatic ring on Pd (111) and Pd (211). It is evident that HDC of 2,4-DCP with steric hindrance over Pd/MSC isn't similar to the situations over other two catalysts, in which 2,4-DCP adsorbed on the Pd atoms by formingσ-complex with C-Cl bond at 4-position, resulting in the only intermediate specie of 2-CP. The intermediate species of 2-CP and 4-CP were detected simultaneously in the HDC of 2,4-DCP on Pd/AC and Pd/SBA-15 in which 2,4-DCP was adsorbed flatly by the formation ofπ-complex with the aromatic ring.The inhibition of Et3N occurs mainly on Pd/MSC and Pd/AC, because of the competition adsorption with substrates on the defective surface Pd atoms. Reducing the concentration of can relieve the inhibitory effect evidently.