Study On Catalytic Oxidation Of VOCs On Shaped Catalyst At Room Temperature

The serious harm of volatile organic pollutants（VOCs）to the ecological environment and human health has attracted wide attention all over the world.At present,the most promising VOCs treatment technology is catalytic oxidation technology,but there are still problems such as poor formability of catalysts,high reaction temperature,and easy inactivation of catalysts at high temperature.This study analyzed the feasibility of VOCs catalytic oxidation at room temperature from the perspective of thermodynamics and kinetics.The widely used ethyl acetate was used as VOCs model molecule to construct Ni/NAC shaped catalyst supported by nitrogen-doped activated carbon for its catalytic oxidation at ambient temperature.The structure-activity relationship and degradation mechanism of ethyl acetate at room temperature were investigated by correlating the microstructure and catalytic oxidation activity of the catalysts.The optimum catalyst Ni/NAC-900 was prepared by impregnating one pot method.The active metal sites,pyrolysis process,preparation method,nitrogen source,content of each component,and annealing temperature were optimized.Ni/NAC-900 can maintain over 90%removal of ethyl acetate within 56.5 h under the conditions of reaction temperature 25℃,initial concentration of ethyl acetate 540 mg·m^-3,relative humidity 18%,and volumetric space velocity 5000 h^-1.Raman,FTIR,and O 1s high-resolution XPS spectra showed that Ni/NAC-900had abundant defects and surface adsorbed oxygen species.XRD,SEM,TEM,and AC-HAADF-STEM confirmed the coexistence of Ni single atoms and NPs.The C 1s,N 1s,and Ni 2p high-resolution XPS spectra showed that most Ni species existed in the single atom form of Ni-NC coordination（1.38 wt%）and very few existed in the form of Ni NPs（0.12 wt%）.Combined with the characterization results and performance evaluation,it can be concluded that the well-developed pore structure,abundant defects,surface adsorbed oxygen species,and Ni-NC sites were favorable for the catalytic oxidation of ethyl acetate at room temperature.Poisoning and dissolution experiments showed that Ni-NC single atom sites were the active sites for catalytic oxidation of ethyl acetate at room temperature.Gas chromatographic result of the tail gas showed that the CO₂ selectivity of the reaction was 67.15%,and the reaction intermediates were detected by In-situ FTIR.The·OH and R·were detected in the gas reaction system by EPR.All the above,the reaction mechanism of catalytic oxidation of ethyl acetate on Ni/NAC-900 at room temperature was speculated:O₂ and H₂O in the air adsorbed on the surface of Ni/NAC-900 and were activated to produce·OH.Under the strong oxidation of·OH,ethyl acetate was eventually oxidized to CO₂ and H₂O.What’s more,·OH would also attack the C-H bond of alkyl group to form R·,and the generated R·can further combine with O₂ in the air to form·OH.The adsorbed oxygen on the surface of the catalyst also participated in the catalytic oxidation reaction of ethyl acetate at room temperature,which was supplemented by H₂O and O₂ in the air under the activation of defects on the surface of catalyst.