Study Of Monolithic Catalysts For Catalyzing Xylene-containing Waste Gases

Catalytic combustion is one of the efficient and clean methods for purifying organic waste gas.The design and preparation of catalysts is the key to the catalytic combustion.Thus,in this paper,the MOx(M = Cu,Ni or Co)modified manganese-cerium mixed-oxide catalysts supported on ceramic monolith were prepared by citrate sol-gel method and examined for the catalytic combustion of o-xylene.On the one hand,the effects of the preparation parameters and the reaction conditions on the catalytic properties for the combustion of o-xylene were investigated comprehensively.And the catalytic stability of the optimum catalyst was also investigated.On the other hand,the mechanical stability of the prepared catalyst was systematically investigated from two aspects:the preparation parameters and the simulation of various conditions in the practical application.Results show that the monolithic catalyst prepared by pretreatment with acetic acid had better catalytic activity,and the activity of the monolithic catalyst prepared by pretreatment with nitric acid and hydrochloric acid was similar.The addition of CuOx could significantly enhance the catalytic properties of the monolithic catalysts.The activities of the MnCeNi/monolith and MnCeCo/monolith catalysts are similar.It is shown that the MnCeCu0.4Vmonolith catalyst with the active phase loading of 11.4 wt%and calcined at 500? for 3 h displays the highest catalytic activity.When the concentration of o-xylene is 1000 ppm and the space velocity is 10,000 h-1,the temperature at which 90%o-xylene conversion is reached is 277 ?.It is also seen that the optimum catalyst has a good catalytic stability and exhibits an excellent activity not only at a rather high space velocity but also within a wide range of o-xylene concentration.Furthermore,the optimum catalyst also show the high combustion performance for other hydrocarbons,e.g.,n-butanol and styrene.In addition,the mechanical stability of the monolithic catalysts prepared by acetic acid pretreatment to the cordierites was improved.It is possible that acetic acid pretreatment can effectively reduce the interface spalling.With the increase of the total amount of active phase,the mechanical stability of monolithic catalysts decreased and then increased.This may be because the ultrasonic vibration not only affects the interface spalling,but also affects the interior spalling.The effect of calcination temperature on the mechanical stability of the catalyst is the biggest,the calcination time is minimal.For the effect of atmosphere,the mechanical stability of the catalyst was reduced.Especially in the flow of O-xylene,the interface defects and internal defects of the active layer can be easily extended to failure,so the probability of interface spalling and interior spalling is increased.The catalytic combustion can improve the mechanical stability of the monolithic catalysts.For the effect of thermal shock,the mechanical stability of monolithic catalysts which slowly cooled in a muffle furnace was larger than that quickly cooled in air.This is due to the quickly cooled increases the thermal mismatch within the active layer and the thermal mismatch between the active layers.And the interface thermal mismatch can be intensified as the thermal shock time,so the mechanical stability reduced.