Study On The Directed Regulation Of Co/Cu Oxides And Their Catalytic Oxidation Mechanism For Simulation VOCs Produced During Granulation Process Of Waste Plastics

The science and technology have made enormous progress with large consumption of fossil energy.The resulting haze,photochemical smog,acid rain,ozone layer destruction and other environmental problems produce negative infulence on the orderly production and life of human benings.The acid rain in most areas has been sloved in china in recent years and the government focus on the O₃ problem.Besides,it will focus on alleviating the problem of volatile organic compounds(VOCs)pollution emissions.VOCs,as a kind of pollutants with abandunt variety,complex composition and wide distribution,has gone unheeded in the past years.Studies in recent years have shown that VOCs are not only the main component of photochemical smog and urban haze,but also an important precursor of PM_2.5,and an important source of greenhouse gases.Ozone may produce resuting from VOCs oxidized with nitrogen under light and heat,which is harm to human health.Therefore,alleviating the problem of VOCs pollution will effectively improve human habitation and living environment.The widely using of plastic products produes a large number of waste plastics.The recycling of waste plastics is an effective programme that can obtain a double harvest of economic and environmental benefits.However,VOCs will be generated during the process of recycling,processing and pelletizing of waste plastics,which poses a serious threat to the atmospheric environment.Among various VOCs treatment technologies,the catalytic oxidation strategy has received extensive attention due to its wide application range,high treatment efficiency,low treatment energy consumption.One of the most important key issues of catalytic oxidation methods is the development and preparation of high-efficiency,stable and cost-effective catalysts.In recent years,transition metal oxide catalysts have attracted much attention because of their low cost and strong controllability of chemical properties.On the other hand,its performance can be further improved because the catalysts are easily poisoned and have poor stability.Therefore,considering the advantages of composite transition metal oxide catalysts,such strategies in the article are aim to prepare transition metal composite oxide catalysts with strong weather resistance,stable performance,excellent catalytic performance and acceptable cost via synergistic effects of binary or ternary.Thus a series of Co-based and Cu-based catalysts were prepared through biomass template method,hydrothermal method and electrospinning technology,using X-ray diffraction(XRD),Scanning electron microscope(SEM),Transmission electron microscope(TEM),N₂ adsorption-desorption technology,H₂ temperature programmed reduction(H₂-TPR),O₂ temperature programmed desorption(O₂-TPD),C₃H₈temperature programmed surface reaction(C₃H₈-TPSR),NH₃ temperature programmed desorption(NH₃-TPD),elemental analysis,original Infrared diffuse reflectance Fourier transform spectroscopy(In situ DRIFTs),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy(Raman)and inductively coupled atomic emission spectrometry(ICP-AES)and other technologies to performed the structure of the catalyst.The catalytic performance for VOCs(toluene,vinyl chloride and propane as model molecules)produced during the plastic recycling process and granulation process was studied.The specific contents are as follows.(1)Three-dimensional network ESM-Co O_x catalyst was synthesized through the self-adsorption of the egg shell membrane in the solution by using stearic acid-treated egg shell membrane as a template,and its catalytic activity for toluene gas was investigated.ESM-Co O_x exhibits excellent catalytic oxidation ability and stability for the degradation of toluene due to its abundant oxygen vacancies and a special three-dimensional network structure.The conversion rate can reach 96%at 300 ^oC and also stable near 96%during 36 h stability test.(2)The solubility of ammonium tungstate in the special hydrothermal condition is utilized to synthesize the uniform microspheres of Ce-Cu-W-O oxides.Compared to the W-undoped counterpart,it possesses larger amounts of Ce³⁺and oxygen vacancies,promoting the oxygen mobility.The formed rich surface WO₃ can effectively provide acid sites,which is helpful for adsorbing vinyl chloride and interrupting C–Cl bond.In addition,the presence of WO₃ induces the formation of fine Cu O nanoparticles with respect to the traditional coprecipitation method,resulting in a better reducibility.Benefiting from the enhanced both acidity and reducibility,the Ce-Cu-W-O microspheres deliver an excellent low temperature vinyl chloride oxidation activity(a reaction rate of2.01×10^-7 mol/(g_cat·s)at 250 ^oC)and a high HCl selectivity.Moreover,subtle deactivation occurs after the three cycling activity tests,and a stable vinyl chloride conversion as well as mineralization is found during the 72 h of durability test at 300 ^oC,demonstrating its good thermal stability.(3)A one-dimensional(1D)core-shell of Co-Ce oxide has been prepared by multifluidic coaxial electrospinning method and evaluated for the total oxidation of propane(C₃H₈).Activity and morphological characterizations show that the Ce O₂@Co₃O₄ nanofiber catalyst,of which the core is Ce O₂ and the shell is Co₃O₄,exhibits excellent oxidation activity.The exposed Co₃O₄ grown on the outside of the fibers can rapidly react with C₃H₈ while Ce O₂ with high oxygen storage capacity in the inside is conductive to the enhanced oxidation rate.Besides,the continuous grain boundary provides a fast mass transfer channel for lattice oxygen,and rich oxygen vacancies favor the mobility of active oxygen species.In situ DRIFTs confirms that the Ce O₂@Co₃O₄ catalyst have a faster rate of C₃H₈ adsorption and better oxidation activity with respect to the counterpart using a single-needle electrospinning method.Moreover,the Ce O₂@Co₃O₄ catalyst displays excellent thermal stability,and strong resistance against 5 vol%H₂O and 5 vol%CO₂ at both 300 ^oC and 400 ^oC.(4)Ternary catalysts Ce O₂-Cu O@Ce O₂-Co₃O₄ catalyst with good structural stability,balance acidity and redox as well as fast lattice oxygen mobility was prepared for the simultaneous catalytic oxidation of propane-vinyl chloride-toluene based on the three staregies mentioned in the aboved chapters.And catalytic performance of Ce O₂-Cu O@Ce O₂-Co₃O₄,Ce O₂-Co₃O₄@Ce O₂-Cu O and Ce O₂-Cu O-Co₃O₄ for single atmosphere,two atmospheres and three atmospheres were obtained.Ce O₂-Cu O@Ce O₂-Co₃O₄ shows the best catalytic oxidation performance under single atmosphere,most of two atmospheres(propane-vinyl chloride and toluene-vinyl chloride)and three atmospheres.In situ DRIFTs shows that toluene is dominant in the adsorption process of catalyst,while the adsorption of propane and vinyl chloride is competitive.