Non-thermal Plasma Combined With Co-Ce Binary Metal Oxide Catalysts For Toluene Decomposition

Volatile organic compounds?VOCs?have extensive sources,which can be detrimental to the environment and human health.Developing efficient VOC decomposition technology is imminent.Non-thermal plasma has exhibited unique advantages for VOC decomposition,such as room temperature/pressure,quick response,high reactive activity and easy operation.In order to enhance the decoposition efficiency,energy efficiency and product selectivity,plasma catalysis comes into being.Reasonable selection and directional preparation of the catalysts is the key of efficient VOC decomposition.In recent years,binary metal oxide catalysts attract tremendous interest because of the synergistic effects between different different components.Considering the unique superiority of cobalt oxide and cerium oxide as well as the possible synergistic effect between Co and Ce,Co-Ce binary metal oxide catalysts have great potential in the plasma-catalytic decomposition of VOCs.In this work,toluene is selected as the target VOC.Co-Ce binary metal oxide catalysts are synthesized by the citric acid sol-gel method and applied to toluene decomposition.The main contents and conclusions are as follows:?1?The performance of toluene decomposition by non-thermal plasma and the influence of defferent experimental operating conditions are investigated.Results show that the specific input energy improves the toluene decomposition efficiency and CO₂selectivity,but decreases the energy efficiency.The gas flow and the initial concentration of toluene have opposite effects on the performance of toluene decomposition.Moreover,the toluene decomposition efficiency,CO₂ selectivity and energy efficiency are all advanced with the increase of discharge length and then dereased.40 mm is the optimum value for discharge length.?2?The performance of toluene decomposition by non-thermal plasma combined with Co-Ce binary metal oxide catalysts is invesgated.The introduction of catalysts enhanced toluene decomposition significantly.The performance of different Co-Ce catalysts is ranked as follows:Co_0.75Ce_0.25O_x>Co_0.5Ce_0.5O_x>Co_0.25Ce_0.75O_x,all of which are superior to monometallic counterparts.Co_0.75Ce_0.25O_x catalyst ows the highest toluene decoposition performance.The toluene decomposition efficiency,energy efficiency,CO₂ seletivity and carbon balance are 98.5%,7.12 g kWh^–1,87.3%and 97.8%,respectively.The durability and reusability measurements illustrate the excellent stability of the catalyst.?3?The influence of different Co/Ce ratios on the synergistic effects between Co and Ce is investigated.Results show that the incorporation of Co cations into CeO₂fluorite lattice leads to the the deformation of lattice framework and the generation of defects.The crystallite sizes decrease while the specific surface area as well as the contents of Ce³⁺and surface absorbed oxygen increase,yeilding more oxygen vacancies and active oxygen species for toluene decomposition.Co_0.75Ce_0.25O_x catalyst owns the smallest crystallite size and the largest specific surface area as well as the contents of Ce³⁺and surface absorbed oxygen.Moreover,Co-Ce catalysts have higher reducibility and oxygen mobility than monometallic counterparts.?4?The mechanism of the toluene decomposition by non-thermal plasma combined with Co-Ce binary metal oxide catalysts is invesgated.A simplified reaction kinetic model is established to describe the plasma catalysis process.The packed catalysts change the discharge mode from the filamentary discharge to the combined filamentary discharge and surface discharge,meanwhile the electric field strength is enhanced,providing more highly energetic electrons to boost the plasma catalysis reactions.The physicochemical properties of the catalysts keep invariant after the utilization of catalysts.The reaction pathway of toluene decomposition can be identified into gas-phase plasma reactions and catalytic reactions on catalyst surface.The redox cycle between Ce³⁺/Ce⁴⁺and Co²⁺/Co³⁺promotes the generation and mobility of active surface oxygen species of catalysts.