Preparation Of Rare Earth Tourmaline Composite And Its Catalytic Oxidation Of Methane

The methane catalytic oxidation technology has a wide application prospect in pollution control, like natural gas vehicle and industrial exhaust. Among the various methane catalysts, perovskite LaCoO3 and LaMnO3 possess unique structure and good stability, but its methane catalytic activity still remains to be improved.In this study, LaCoO3/tourmaline composites and LaMnO3/tourmaline composites were prepared by sol-gel method and hydrothermal process. The influence of tourmaline on precursor formation, crystallization process and methane catalytic activity were studied. The microstructure and surface performance of rare earth tourmaline composites were characterized by XRD, BET, SEM, H2-TPR and XPS. The results indicated that the micro electric field of tourmaline could reduce the size of gel particles and agglomeration in sol-gel method. The BET surface area, surface oxygen content and low temperature redox ability were enhanced when tourmaline addition was 2%. In hydrothermal process, the filling degree, hydrothermal temperature and tourmaline addition all had great impact on microstructure and catalytic performance of rare earth tourmaline composites. The tourmaline addition has accelerated the dissolution of rare earth perovskite, and reduced the crystal growth rate, obtained stick or coral like morphology. The addition of tourmaline in hydrothermal process also exist an optimal value of 2%, by this time the surface area of LaCoO3/tourmaline composite reached 40.450 m2/g, almost four times compared that of the LaCoO3 prepared by sol-gel method, and 23.392 m2/g for LaMn O3/tourmaline composite, almost two times compared that of the LaMnO3 prepared by sol-gel method. The surface of rare earth tourmaline composites exposed a large number of oxygen vacancies, while surface oxygen content and low temperature redox ability greatly increased.The methane catalytic oxidation on rare earth tourmaline composites were conforms to the Rideal-Eley mechanism. The molecular thermal motion of methane was accelerated by the infrared radiation of tourmaline, then active methane molecules adsorbed on the surface of composites and react with the high content surface oxygen, gradually formed products and new oxygen vacancies, at last, the products desorbed and the vacancies reform to new surface oxygen. The methane catalytic activity test and long term stability test of composites indicated that, the activity showed the best result when 2% tourmaline added in the composites. The ignition temperature of 2% tourmaline added LaCoO3 prepared by sol-gel method was reduced 18℃, and 34℃ for 2% tourmaline added LaMnO3; The ignition temperature of 2% tourmaline added LaCoO3 prepared by hydrothermal process was reduced 65℃, and 28℃ for 2% tourmaline added LaMnO3. The long term stability test showed that both 2% tourmaline additive and hydrothermal could enhance the stability of composites.