The Study Of Mayenite's Application To The Catalysis Of Carbon Dioxide Methanation

Nowadays,the increasing of global economy mainly relies on non-renewable fossil fuels,which leads to the gradual increase of CO₂ concentration in the atmosphere.and several serious consequences.The task of CO₂ emission reduction is becoming more and more urgent.CO₂ methanation is an efficient way to utilize the overfull CO₂and easing the dependence of human being on fossil fuels.CO₂ methanation has great strategic significance for improving the energy consumption structure,reducing environmental pollution and ensuring energy security.The core of CO₂ methanation process is the preparation of catalysts.There,Ru catalysts were prepared by mayenite/mayenite electride and their catalytic performances and methanation mechanism were studied in depth.The main research contents and conclusions are shown as follow:OH^-groups occupies dominantly the cages in the framework of hydrothermally prepared C12A7 samples,the crystalline structure of the mayenite plays an important role in the catalysis of CO₂ methanation over Ru supported on C12A7:OH^-catalysts.The CO₂ conversion at 325?(GHSV=13000 h^-1)over Ru/500C12A7 is 78%.The TOF of Ru/500C12A7 at 250?is 4.53?10^-2 s^-1(E_a=85.0 kJ mol^-1),which is higher than the value of Ru/?-Al₂O₃(TOF at 250?=1.04?10^-2 s^-1,E_a=110.9 kJ mol^-1).And the time cause of CO₂ conversion over Ru/500C12A7 catalyst confirmed that the500C12A7 is a stable catalyst support.C12A7:e^-was achieved by reducing the resultant C12A7:OH^-powder with CaH₂,the encaged OH^-groups are completely removed and electrons are injected into the cages of C12A7.The electron density of C12A7:e^-decreases as raising the reduction temperature from 700 to 900?,and reaches the maximum value of 1.12×10²¹ cm^-3when the sample was reduced at 1000?.The catalytic activity of Ru/C12A7:e^-increases with the increasing of electron density of the electride substrates.Although the surface areas of 1000C12A7:e^-is only 1 m² g^-1,the CO₂ conversion at 350?(GHSV=13000 h^-1)over Ru/1000C12A7:e^-reaches 75%and the TOF at 250?is 4.18?10^-2 s^-1(E_a=91.7 kJ mol^-1)CO₂-TPD experiments confirm that 500C12A7 and 1000C12A7:e^-are capable of decomposing*CO₂ into*CO and*O,and the supporting Ru motivates the activation and decomposing of CO₂.The In-situ DRIFT spectra illustrates that*CO on Ru particles is the reaction intermediate of CO₂ methanation over Ru/500C12A7 and Ru/1000C12A7:e^-catalysts.The different anions?OH^-or e^-?contained in the cages of mayenite substrates influences drastically the ionization potential of Ru.Electrons encaged in C12A7:e^-are transferred to Ru metal over Ru/1000C12A7:e^-catalyst.As a result,the dissociation of*CO intermediate into*C and subsequent into deposition of carbons when the CO partial pressure above a certain value.And that's the reason why Ru/1000C12A7:e^-dose not catalyze CO methanation under 500?.