Study On The Catalytic Performance Of Toluene Over Novel Cobalt-based Metal Oxides

Toluene is the most common type of volatile organic pollutants?VOCs?,which causes great damage to human health and the environment.How to effectively reduce the concentration of toluene has attracted widespread attention.The research found that the temperature required for direct combustion to remove toluene is high and the secondary pollution is serious.Catalytic oxidation technology can remove toluene at a lower temperature,which has the lower cost and smaller secondary pollution.Catalyst is the core and key of technology in catalytic oxidation.Therefore,it is important to prepare an efficient catalyst to catalyze the oxidation of toluene at low temperature.As a member of a large family of metal-organic frameworks?MOFs?,Zeolitic Imidazolate Framework-67 is widely concerned because of its adjustable structure,morphology and high porosity.Moreover,Co₃O₄ can be directly obtained by thermal treatment,which would maintain the morphology and characteristics of ZIFs and is beneficial to catalytic oxidation.Therefore,it is worth investigating to design a kind of efficient ZIFs-derived metal oxides.In this paper,a novel core-shell type ZIFs-based catalyst was first prepared,then series of copper-cobalt composite oxides were developed by using ZIF-67 as the template,and the characterization techniques such as XRD,FT-IR,N₂adsorption-desorption,Raman,SEM,TEM,XPS,H₂-TPR and O₂-TPD reveal the effects of catalyst morphology,structure and synergistic on the catalytic oxidation performance of toluene.The main contents are as follows:Based on the liquid-phase diffusion method,we successfully prepared diamond dodecahedron structure ZIF-67,spheroid Co Ce-ZIF and spherical Ce-MOF material.And Co₃O₄,Ce O₂@Co₃O₄ and Ce O₂ metal oxides were obtained by calcining.Then,the catalytic oxidation activity of these samples towards toluene were evaluated.Results show that the core-shell structure Ce O₂@Co₃O₄ catalyst achieves 90%conversion of toluene at only 225 ^oC,which is much higher than that of pure Co₃O₄ and Ce O₂ samples,indicating that the core-shell Ce O₂@Co₃O₄ has good catalytic performance for toluene oxidation.In addition,Ce O₂@Co₃O₄ was found to have a lower activation energy?E_a=82.0 k J/mol?than pure oxides,indicating that oxidation reactions are more likely to occur.According to the series characterization,which suggested that the superior performance of Ce O₂@Co₃O₄ catalyst depends on its unique core-shell structure,rich active oxygen species and higher concentration of oxygen vacancies.In addition,the synergistic effect of Co-Ce greatly enhanced the activity and reduction performance of the catalyst.Using ZIF-67 as a sacrifice template to obtain a series of layered copper-cobalt double hydroxides with controllable surface states by etching the template through water bath reflow,denoted as x Cu Co-LDH?x=1,2,3,4?.In addition,we directly combine 2-methylimidazole and the copper nitrate solution for comparison,Cu-LDH was obtained with the same method.After calcination,the copper-containing LDHs were transformed into the corresponding layered bimetal oxide?denoted as Cu Co-LDO?,and the catalytic performance of these samples were also investigated.The results show that when the actual Cu content reaches 20.14 wt.%,a flower-like 3Cu Co-LDO sample was obtained,which exhibited the most excellent catalytic activity for toluene oxidation(T₉₀=232 ^oC)and high reaction rate(r=14.77×10⁵ mol·g^-1·s^-1).Many characterization techniques show that the incorporation of different Cu content has a crucial role on the morphology and structure change of Cu Co-LDH,and the Cu content significantly affects the surface state and catalytic activity of the Cu-Co double oxide.It can be concluded that the excellent catalytic performance of ZIF-67-derived flower-like Cu Co-LDO is mainly related to its specific structural,rich reactive oxygen species,surface Co³⁺/Co²⁺ratio and the synergistic effect of Cu-Co.