Study On Preparation Of CoAl₂O₄/Ceramic Honeycomb Catalyst And Catalytic Ozonation Performance Of Hydroquinone Wastewater

Hydroquinone is a kind of important chemical raw material which mainly from pesticides,pharmaceuticals,dyes and photosensitive materials.The wastewater produced during the hydroquinone production or utilization has toxic effects on the human body and harms human health,and it is urgent to treat it.Comparing with physical and biological methods,catalytic ozonation can catalyze ozone to produce more highly oxidizing substances by using metals or metal oxides as catalysts,which can accelerate the mineralization of hydroquinone.Heterogeneous catalytic ozonation utilizes solids as catalysts and the catalysts is easy to recycle and reuse without causing secondary pollution.CoAl₂O₄/ceramic honeycomb catalyst was prepared by coating method using Co?NO₃?₂·6H₂O and Al?OH?-3 as precursors and ceramics honeycomb as carrier.The structure and performance of the catalysts were analyzed by X-ray diffraction?XRD?,N₂ adsorption/desorption,field emission scanning electron microscope?FESEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?and compressive strength.The effects of coating times,roasting times,roasting temperatures and amounts of active ingredients on catalyst performance were investigated.The four factors and three levels of orthogonal test were used to determine the main factors affecting the catalytic ozonation of CoAl₂O₄/ceramic honeycomb catalyst.The preparation conditions was optimized and the catalytic ozonation mechanism was studied.The results showed that the crystal phase of CoAl₂O₄/ceramics honeycomb belonged to a typical spinel structure with a large specific surface area of 76.7 m²·g^-1,pore volume of 0.0017cm³·g^-1 and pore size of 3.9 nm,respectively.The surface of the CoAl₂O₄/ceramic honeycomb catalyst had a sponge-like microporous structure with a maximum compressive load of 7660 N and so the catalyst could resist hydraulic shock load.The catalytic ozonation system was established by using hydroquinone as a target contaminant.Based on orthogonal experiment,the coating number is the most important factor influencing the catalytic performance in the four factors of coating times,roasting time,roasting temperature and the addition amount of active ingredients.The optimal preparation conditions of CoAl₂O₄/ceramic honeycomb catalysts were as follows:coating 6 times,calcining at 500°C for 6 h and Co:Al molar ratio of 0.2:5.CoAl₂O₄/ceramic honeycomb catalyst showed the highest catalytic activity.CoAl₂O₄/ceramic honeycomb catalyst showed the highest catalytic performance,and the removal rate of hydroquinone the COD were 81.6%and 52.3%.When the CoAl₂O₄/ceramic honeycomb catalyst was repeatedly used 5 times,the removal rate of hydroquinone remained stable and it could be reused.The degradation efficiency of hydroquinone decreased significantly after the addition of tert-butanol,which showed that the degradation of hydroquinone by CoAl₂O₄/ceramic honeycomb catalyst follows the hydroxyl radical mechanism.In order to improve the activity and service life of the catalyst,a two-component metal catalysts were prepared to change the component of CoAl₂O₄/ceramic honeycomb catalyst.Four kinds of Mn-Co/ceramic honeycomb catalysts with different molar ratios of Mn and Co were prepared by coated method when cobalt nitrate hexahydrate?Co?NO3?2·6H2O?and manganese nitrate?Mn?NO₃?₂?were used as precursors and ceramic honeycomb were used as carrier,respectively.Compared with CoAl₂O₄/ceramic honeycomb catalyst?without Mn elements?,Mn₁Co₁/ceramic honeycomb catalyst?Mn:Co=1:1?had a dense lamellar structure with specific surface area of 98.2 m²·g^-1,pore volume of 0.025 cm³·g^-1 and pore size of 3.5 nm,respectively.The catalytic activity of Mn₁Co₁/honeycomb ceramic catalyst was the highest,and the removal rates of hydroquinone and COD were 98.6%and 61.3%,respectively.The catalytic ozonation reaction system established performed high ozone utilization rate and good treatment efficiency for refractory organic pollutants.The catalysts was easy to achieve industrialization due to its less consumption,excellent catalytic characteristics and long working life.