Effect Of Acid Treatment On Performance Of SmMnO₃/Cordierite Monolithic Catalysts

Nowadays,volatile organic compounds（VOCs）have seriously affected the global ecological environment and people’s health.Among various governance methods,the catalytic combustion has been considered as an efficient and widely used strategy for the complete elimination of VOCs due to its high energy efficiency,low operating cost and secondary pollution.The crucial step in VOCs catalytic combustion reaction is the selection of catalyst.In this paper,SmMnO₃/cordierite monolithic catalyst was obtained by loading SmMnO₃ on cordierite.The effect of acid treatment and calcination process on catalytic performance of catalysts in o-xylene catalytic combustion was investigated.The main work and results are as follows:1.SmMnO₃/cordierite monolithic catalysts were synthesized by a modified citric acid method and treated with dilute HNO₃,which was used to explore the effect of acid treatment on the catalytic performance and mechanical stability of the monolithic catalysts.The results show that acid treatment can significantly improve catalytic activity of catalyst in o-xylene oxidation,which is attributed to the increase of the specific surface area of the catalyst and the change of surface oxygen species.Secondly,a series of single factor experiments show that the SmMnO₃/cordierite monolithic catalyst treated by 1.0 mol/L HNO₃ for 6 h and calcined at 450°C for 1 h has high performance.Then,the mechanical stability test results show that too long acid treatment time and too high acid concentration will reduce the mechanical stability of the catalyst,and 1.0 mol/L HNO₃ treatment for 1 h is beneficial to improve the mechanical stability.And different calcination temperature and calcination time will also affect the mechanical stability of the catalyst.2.Response surface methodology（RSM）was used to establish a mathematical model for the catalytic activity of SmMnO₃/cordierite monolithic catalyst.The effects of different process factors and their interactions on catalyst properties were visualized by central composite rotation design（CCRD）.Experimental results verify the effectiveness of the proposed model.The results show that the acid treatment time is the most significant process factor affecting the catalytic combustion activity.In the experimental range,the catalytic activity increased with the increase of acid treatment time or acid concentration,increased first and then decreased with the increase of calcination temperature,and decreased with the increase of calcination time.Under the conditions of acid treatment time of 6 h,acid concentration of 1 mol/L,calcination temperature of 408.1℃,and calcination time of 1 h,the catalyst showed high catalytic performance.The reaction temperatures required for 50%and 90%conversion of o-xylene are 260.9°C and 284.0°C.