چكيده به لاتين
Due to the harmful effects of greenhouses which are mainly attributed to volatile organic compounds (VOCs) and hydrocarbons, environmental laws are very important. That's why, the catalytic oxidation of hydrocarbons, especially methane, is of great importance. The use of perovskite-type catalysts due to their high activity and stability under the oxidation-reduction cycle, are good replacement for nobel metals in oxidation reactions.
In this project, mechanochemical method which is a new, simple and cost-effective synthesis method has been used to prepare nanocatalysts. To improve the performance of the LaCuO3 catalyst, metals such as Fe, Ni, Al and Y were studied at first. Among them, Ni metal showed better catalytic performance than other metals. Then the substitution of different Ni values (x= 0, 0.1, 0.3, 0.5, 0.7) were studied, which LaCu0.5Ni0.5O3 showed the best catalytic performance. So that, adding Ni to the value of x = 0.5 ,conversion percentage of methane increases from 7.83% to 73.83% at 500 °C.
In the next step, cobalt and manganese metals were used to improve the catalytic performance of LaCu0.5Ni0.5O3, that substitution of copper by manganese significantly improved catalytic activity especially at 450°C. The results showed that catalytic activity and specific surface area increased with the addition of manganese metal. So that, catalysts containing Mn have reached conversion percentage above 60%. For this reason, LaCu0.2Mn0.3Ni0.5O3 catalyst was chosen as the best catalyst.
The stability of the optimal catalysts LaCu0.5Ni0.5O3 and LaCu0.2Mn0.3Ni0.5O3 were investigated at 11 hours and 700°C, that both of them showed high stability. Furthermore, the effects of calcination temperature, GHSV and feed ratio on optimal catalysts were investigated. The results showed that with decreasing of calcination temperature, the average crystal size decreases, the specific surface area increases and also catalyst activity improves. Calcined catalysts at 500°C have the best catalytic performance. Increasing of the amount of GHSV and the feed ratio (CH4/O2) leads to increase in the conversion percentage of methane.
In the following, mechanochemical synthesis method was compared with pechini and sol-gel on catalyst activity of LaCu0.5Ni0.5O3. According to the results, mechanochemical synthesis method showed better performance than pechini and sol-gel.
