Interface Promoted ZnO-LSCO Core-shell Nano-array Monolithic Catalysts For High Efficient Methane Catalytic Combustion

As a cleaner energy source, the efficient utilization of natural gas can not only reduce the energy shortage, but also the pollution problems associated with huge consumption of coal and oil. Currently, there is still a lot of energy waste and atmospheric pollution in the processes of natural gas production, transport and use.Therefore, developing efficient natural gas utilization technology has been a major challenge in both academia and industry.Recently, in order to reduce energy waste and environmental pollution from traditional methane flame combustion process, scientists have proposed that combination of gas phase free radical reaction and catalytic oxidation process could achieve catalytic combustion of methane at a relatively low temperature with high efficiency. Based on its excellent activity and thermal stability, perovskite LaxSr1-xCoO3 ( LSCO ) is the most potential substitute of precious metal for methane catalytic combustion. Researchers found that the integration of perovskite oxide nanoparticles with nano-array structure can greatly improve the catalytic activity for hydrocarbon combustion at low temperature compared with the ordinary perovskite powder catalyst. In this thesis, ZnO-La0.8Sr0.2CoO3 (LSCO) core-shell nano-array catalyst and LSCO nanotube array catalysts were fabricated via a low temperature hydrothermal process. ZnO-LSCO showed better catalytic performance than LSCO on methane catalytic combustion. In order to explore the origin of ZnO-LSCO catalytic activity, we have carried out the following work:(1) We have prepared uniform and dense ZnO nanorod arrays on the honeycomb ceramic substrate by a simple hydrothermal method. The diameter of ZnO nanorods is about 200-300nm, and the length of ZnO nanorods is around 1.5um. The ZnO nano-array structure is used as a template of nano-array catalyst.(2) Based on the synthesized ZnO nanorod arrays, we have loaded (La,Sr)CoO3 nanoparticle on ZnO nanorod arrays to obtain ZnO-LSCO core-shell nano-catalyst. Then LSCO nanotube arrays catalyst was obtained by reducing the ZnO-LSCO nanorod array at H2 atmosphere at high temperature. SEM and XRD proved that the nano-array catalysts had been synthesized successfully. Finally, the catalytic activity test for methane combustion shows that ZnO-LSCO core-shell catalyst has higher catalytic activity than LSCO nanotube arrays catalyst.(3) To investigate the origin of high catalytic activity for methane combustion of ZnO-LSCO core-shell catalyst, we have conducted a series of basic characterization:TEM and BET indicate that surface area is not the key factor for catalytic performance of methane combustion; and XPS, CO-TPR and O2-TPD demonstrate that the high catalytic acti’vity of ZnO-LSCO core-shell catalyst originates from the presence of ZnO and LSCO interface, which reduces the binding energy of O and La, Sr, Co atom in perovskite lattice. Therefore, surface lattice oxygens become more active, which contributes to the high catalytic activity of ZnO-LSCO nano-array.