Preparation And Characterization Of Zeolite Membrane Catalyst By Chemical Vapour Deposition For Catalytic Wet Peroxide Oxidation Of Phenol

Phenol-containing wastewater can not be conducted into open water without treatment because of the toxicity of phenol.With the development of industry in various countries,the total amount of phenolic wastewater is increasing,and it has become one of the most important toxic and harmful wastewater in water pollution.Therefore,the removal of phenol from wastewater is significant to ensure the human's health and water security.Catalytic wet peroxide oxidation?CWPO?takes advantage of employing H₂O₂ as liquid oxidant to overcome the gas–liquid mass transfer limitations,which has high efficiency,low cost and has attracted more and more attention of researchers.The catalyst plays an important role in improving efficiency and selectivity of CWPO processes.Therefore,it is necessary to develop novel microfiberous zeolite membrane catalysts for CWPO processes to improve catalytic activity and selectivity,enhance mass transfer and heat transfer,reduce the pressure in the bed,and improve the contact efficiency.In this work,Cu-ZSM-5 catalyst and microfiberous zeolite membrane catalysts Cu-ZSM-5/PSSF were prepared by chemical vapor deposition?CVD?.In addition,the characterization and their catalytic activity for CWPO of phenol in a fixed bed reactor were tested to probe the feasibility of CVD method in fabrication of catalysts and their application.Firstly,Cu-ZSM-5 catalysts were prepared by CVD for CWPO of phenol in a fixed bed reactor.Samples were characterized by XRD,N₂ adsorption–desorption,XPS,EDS and H₂-TPR respectively.The characterization results demonstrated that CuO was uniformly dispersed on ZSM-5 with slight effect on the structure properties of the support.Then,several variables such as the copper loading,reaction temperature,catalyst bed height and feed flow rate were discussed in the CWPO of phenol?1000 mg/L phenol and 5100 mg/L H₂O₂?.Based on the Cu-ZSM-5 catalyst with Cu loading of 6 wt.%,complete removal of phenol and a high TOC reduction?around 70%?have been achieved at the temperature of 80?,feed flow rate of 2 m L/min and catalyst bed height of 3 cm.Moreover,this catalyst maintained high catalytic activity after three runs with high phenol conversion?94%?under this optimum operating condition.Compared with the catalyst prepared by the impregnation method,the Cu-ZSM-5 prepared by CVD has a better capacity of further oxidizing the intermediate organic products into carbon dioxide and water with less metal loading.Oxalic acid can not be completely removed under various reaction conditions,which is the main reason for the loss of active component and deactivation of Cu-ZSM-5 catalysts.Meanwhile,the CuO over the ZSM-5 zeolite membrane was prepared by CVD.The microfibrous zeolite membrane catalysts Cu-ZSM-5/PSSF were applied for CWPO of phenol?1000 mg/L phenol and 5100 mg/L H₂O₂?in a fixed bed reactor.Samples were characterized by XRD,XPS,SEM,EDS,N₂ adsorption–desorption and TPR-H₂,respectively.The CuO of Cu-ZSM-5/PSSF ranged in shape from the needle-shape for a low copper loading to the spherical-shape for a high copper loading.Compared with the CuO deposited directly onto PSSF,the CuO supported on ZSM-5/PSSF tended to be more regular with smaller crystal size.Then,several parameters such as reaction temperature,Cu loading,catalyst bed height,feed flow rate as well as the different support were investigated in the CWPO of phenol.Experimental results revealed that a complete reduction of phenol and a high TOC removal around 60%had been achieved over Cu-ZSM-5/PSSF?6%?at the temperature of 80?,feed flow rate of 2 m L/min and catalyst bed height of 4 cm.This catalyst had a high stability during the continuous reaction for 14 h at the reaction condition above,and its catalytic efficiency was significantly higher than CuO/PSSF with the same Cu loading at temperature of 30?⁸0?.The possible oxidation pathway of phenol shows that phenol was firstly converted into hydroquinone and catechol,then oxidized to quinone,then gradually oxidized to form organic acids?mainly acetic acid and oxalic acid?,and finally mineralized to CO₂ and H₂O.