Study On The Thermal Shock Resistance Of Metal Monolithic Catalysts

Metal monolithic catalysts are mainly applied in the field of environmental treatment because of their good catalytic performances.However,during the process of industrial application,thermal stress caused by thermal shock will adversely affect the mechanical stability and the catalytic activity of metal monolith catalysts.In this paper,the thermal shock resistance of the metal monolith catalysts was studied.The monolithic catalysts based on FeCrAl alloy foil substrates and the monolithic catalysts based on FeNi foam substrates were prepared.The influence of thermal shock cycle number,time and temperature on the metal monolithic catalysts was explored.The effect of the material and shape on the thermal shock resistance of the metal monolith catalysts was also explored.Furthermore,the method of preparing the washcoat was examined to obtain metal monolithic catalysts with high thermal shock resistance and good mechanical stability.After subjected to the thermal shock,the defects of the washcoat extend and expand into cracks under the action of thermal stress;furthermore,the washcoat will peel off.The weight loss data are discrete,indicating that the fatigue damage process caused by thermal stress is random,and this phenomenon is also a manifestation of the monolithic catalyst non-uniformity.The increase of the thermal shocks cycle number will lead to an increase of the washcoat weight loss indicating that the washcoat adhesion become worse.As the thermal shock temperature increases,the washcoat weight loss increases first and then decreases,indicating that the destructive effect caused by thermal shock increases first and then weakens.The long-term high-temperature thermal shock will cause a crystal phase change of the active material,further make the specific surface area of the washcoat decrease,and the washcoat performance is deteriorated.In addition,the characteristics and geometry of the metal matrix itself have an important influence on the thermal shock effect.Therefore,in order to resist the effect of the thermal shock,it is necessary to select a suitable metal,reduce the thermal shock temperature and reduce the thermal shock turns.To obtain metal monolithic catalysts with high mechanical stability,a modified method is chosen: A primer is introduced first and an alumina slurry coating is further washcoated on FeCrAl alloy foils.The coating conditions with the best adhesion performance are: for aluminum sol,21 wt.% solid content and 2wt.% PEG are used as additives;for alumina slurry,30 wt.% solid content and 2wt.% PEG are used as additives.The additive affects the viscosity of the coating liquid and the washcoat morphology,which in turn has a significant effect on the washcoat adhesion.The calcination of the primer makes it smooth and tight,reducing the "contact" of the slurry layer,which will generate a gap between the two layers,thus adversely affects the washcoat adhesion property.The influence mechanism on the mechanical stability was further explored in the paper.