Study On The Spalling Resistance Of Active Materials Of Monolithic Catalysts

As well known, monolithic catalysts are widely used in the treatment of automotive exhaust gases, purification of industrial organic waste gases, etc. Recently, monolithic catalysts are also found to be attractive replacements for conventional bead catalysts in heterogeneous reactions. However, in use the active materials of monolithic catalysts may spall off from their substrate surfaces; therefore, the mechanical stability problem directly affects the industrial application of monolithic catalysts. In this study, a cordierite monolith-supported Cu-Mn mixed-oxide catalyst is used as a model to examine the mechanical stability of monolithic catalysts. The effects of the number and volume of the tested monolithic specimens on the reliability of the mechanical testing results are analyzed using a numerical simulation method. Moreover, the destructive effects of thermal shock parameters during application are researched by experiments.Numerical simulation analyses show that, when the number or the volume of the specimens increases, the statistical results of defects inside the specimens become more similar, and the overall difference of fatigue damage decreases. These lead to the markedly reduction of the scattering of the spalling resistance and the improvement of test precision. In addition, the relationships between the test precision and the volume/number of specimens are the same and are both in accord with a power function model.Thermal shock experiments indicate that the number of thermal shock cycles, thermal shock mode, thermal shock time, and temperature all have great impacts on the spalling of active material. With the increase of the number of thermal shock cycles and thermal shock temperature, the weight loss of active material after thermal shock increases, so does the weight loss after ultrasonic treatment. And the rapid cooling and rapid heating lead to the most serious damage to the mechanical stability. When the thermal shock time is extremely short or very long, the damage degree of mechanical stability and the weight loss of active material will be decreased. What’s more, the process of thermal shock has a tremendous impact on the adhesive and cohesive failures of active material and the size effect on material fatigue can be ignored.