Insight Into The Performance Of Metal Oxide Monolithic Catalyst For Ozone Decomposition

Ground-level ozone is a pollutant that is very harmful to humans,but its concentration is gradually increasing currently.In order to reduce the concentration of ozone,the study of ozone decomposition has received extensive attentions in the academic community.Up to now,there are several methods for decomposing ozone,such as pharmaceutical method,decomposition method,diluted emission method,pre-ozonation method,thermal decomposition method,adsorption method,washing method,and so on.The catalytic decomposition method is widely used because of its low cost,safe operation,and high efficiency.At present,the most widely used catalysts in basic research and industrial applications fields mainly include the following three categories:?1?activated carbons;?2?precious metals;and?3?transition metals.However,the above various types of catalysts still have drawbacks,therefore,it is necessary to continue basic research on the catalyst for decomposing ozone.Although there have been many works about various catalysts for decomposing ozone,the system investigations on the catalytic decomposition of ozone by monolithic catalysts of transition metals and noble metals has been rarely reported.Therefore,this work mainly focuses on the transition metals and precious metals catalysts for decomposing ozone.The preparation of the catalyst and the performance of its decomposition of ozone were systematically studied.In this work,the different ratios metal oxides monolithic catalysts NiO/Mn₃O₄ were prepared.The nickel salt catalysts of different precursors and different ratios of Ag/CuO catalysts were also synthesized.To evaluate the ozone decomposition activity of the above catalysts,the catalytic reactions were investigated systematically.The specific surface,redox,surface active species status and ozone catalytic decomposition efficiency were investigated.The results of this work as following show:The Ni?NO₃?₂·6H₂O,Mn₃O₄ powder and pseudoboehmite were used as raw materials,preparate NiO/Mn₃O₄ catalysts.The obtained slurry was impregnated with cordierite and calcined to obtain different ratios of NiO/Mn₃O₄ catalyst.Through the decomposition test of ozone,it was found that the activity of 30NiO/Mn₃O₄ catalyst was the highest when the space velocity was 20000 h^-1,the decomposition rate of ozone reached 98%,and the catalyst deactivation was not obvious.When the space velocity is increased to 40000 h^-1,the activity of 50NiO/Mn₃O₄ catalyst is the highest,and the decomposition rate of ozone is about 90%,but deactivation occurs.The characterizations show that the specific surface area of Mn₃O₄and NiO composite catalysts is larger than that of single metal oxide catalysts,and Mn₃O₄interacts with NiO in Mn₃O₄ and NiO composite catalysts.The reduction temperature of the mixed catalyst of Mn₃O₄ and NiO is reduced.The above factors work together to enhance the catalytic decomposition of ozone efficience.Hence,the synergistic catalysis performance of Mn₃O₄ and NiO is improved.According to the above method,Ni?NO₃?₂·6H₂O,NiO and NiCl₂ were used as precursors to prepare catalysts and named as NiN,NiO and NiCl.Then,the three catalysts were used to evaluate the ozone decomposition activity,respectively.The NiN catalyst gives the highgest performance.The decomposition rate of ozone reaches 98%and the catalyst is not easy to deactivate.The NiCl catalyst shows the lowest activity.The ozone decomposition rate is only30%and the catalyst is easy to deactivate.The characterizations show that the catalyst prepared with Ni?NO₃?₂·6H₂O as the precursor has a smaller particle size,so it exposes more crystal defects,and the catalyst surface has more defects,which is benefit to ozone decomposition reaction.The catalyst with NiCl₂ as precursor is easy to deactivate,which is mainly because of the presence of Ni-Cl bond.Due to the large electronegativity of Cl,the electron binding energy of Ni is shifted,and electron is not easy to lose,therefore,the catalytic activity is low.The 1% Ag/CuO,5%Ag/CuO,9%Ag/CuO catalysts were prepared from Cu?NO₃?₂·3H₂O,AgNO₃ and pseudoboehmite as raw materials for catalytic activity evaluation.The relationship between activity and composition of catalysts were investigated..