Preparation Of Manganese Oxide Supported Noble Metal Catalysts And Study On Catalytic Performance Of VOCs

Volatile organic compounds（VOCs）,particularly chlorine-containing volatile organic compounds（CVOCs）,are one of the most hazardous and hardest to degrade air pollutants,posing a serious threat to human health and social environment.As a result,removing VOCs is crucial.Catalytic combustion is the most appropriate approach due to its numerous advantages,such as ease of use,lower reaction temperature and no secondary emissions and so on.Catalysts with high activity and anti-chlorination performance become the major priority.In this paper,manganese oxide octahedral molecular sieve（OMS-2）supported noble metal catalysts were produced.The interaction between valence states of Mn,oxygen species and noble metals and the change of valence state of elements on the catalytic activity of the catalyst were investigated using toluene as the reaction substrate.In addition,1,2-Dichloroethane（1,2-DCE）was used as the reaction substrate to evaluate the anti-chlorination and anti-thermal aging characteristics of the catalyst.The structural stability of OMS-2 was improved by adding the additive Ce O₂,thereby improving the thermal aging resistance of the catalyst.The following are among the most crucial details and conclusions:When the loading of Pt was 0.15 wt.%,the ratio of raw materials(Mn O₄^-:Mn²⁺)was 2:3,and the calcination temperature was 300°C,the catalytic effect of Pt/OMS-2 which was synthesized in one step by the in-situ hydrothermal method was the best and toluene was entirely converted at 220°C.According to the characterization data,the addition of Pt species can promote the increase in the number of adsorbed oxygen（O_β+O_γ）and high-valence manganese(Mn⁴⁺),forming more active sites and accelerating the migration of oxygen,and ultimately greater catalytic activity.Furthermore,when the ratio of（O_β+O_γ）/O_αis less than 1,but near to 1,the catalysis of toluene is more favorable,showing that lattice oxygen and adsorbed oxygen play similarly important roles in the process of catalytic combustion of toluene by Pt/OMS-2.Pt/OMS-2 catalyst has a long service life and is ideal for catalysis of toluene at low temperatures,large fluxes,and high concentrations.The anti-chlorination performance of OMS-2 supported noble metal catalysts was examined using 1,2-DCE as the reaction substrate.Ru/OMS-2 has the best catalytic activity,outperforming typical Ru/Al₂O₃,thanks to chemical reduction with a loading of 0.2 wt.%and a calcination temperature of 300℃.The activity test reveals that the presence of Cl in the catalyst has no influence on its catalytic activity.However,Ru O₂ with bigger particles can increase the catalytic process,suggesting that the catalyst has stronger anti-chlorine poisoning capability.XPS characterization results show that the amounts of lattice oxygen（O）and low-valence manganese(Mn³⁺,Mn²⁺)both rise after loading Ru on OMS-2,and more intermediate-valence(Mn³⁺)creates more lattice oxygen defects,which speeds up the oxygen transfer rate.The Ru/OMS-2 is well suitable for the treatment of 1,2-DCE exhaust gases at low temperatures,high fluxes,and low concentrations.In order to improve the thermal aging resistance of Ru/OMS-2,the rare earth material Ce O₂ was wrapped on the surface of the catalyst for composite modification.When Ce-MOF was employed as a precursor,the raw material ratio（mass ratio of Ce O₂ to Ru/OMS-2）was0.18,and the calcination temperature was 500°C,the catalyst synthesized at 600°C for 4 h did not display the characteristic peak of Mn₂O₃.Through the activity test,the addition of Ce O₂may effectively improve the thermal aging resistance of the Ru/OMS-2.A part of Ce O₂generates by utilizing Ce-MOF as a precursor is connected to the cross section of OMS-2 with more lattice defects and expands to form a Ce-O-Mn bond,as observed by the morphology and structure of the catalyst.The excess Ce O₂ attaches to the rod body of OMS-2 to form a loose bird’s nest structure that does not obstruct access to other active sites.During the catalytic combustion of 1,2-DCE by Ru/OMS-2@Ce O₂,lattice oxygen dominates,which is first activated and migrates to the active site to participate in the oxidation reaction,and then gaseous oxygen is adsorbed on the catalyst surface and rapidly replenished Oxygen vacancies,thereby realizing the oxidation-reduction cycle process.The Ru/OMS-2@Ce O₂ has a long service life and is suited for 1,2-DCE exhaust gas treatment at high temperatures,large fluxes,and medium and low concentrations.