The structural stability of manganese titanate MnTiO3 at high pressure was investigated by X-ray diffraction and Raman spectroscopy with diamond anvil cells. Ilmenite-type MnTiO3 is stable at least to 26.6 GPa, and li...The structural stability of manganese titanate MnTiO3 at high pressure was investigated by X-ray diffraction and Raman spectroscopy with diamond anvil cells. Ilmenite-type MnTiO3 is stable at least to 26.6 GPa, and lithium niobate type MnTiO3 reversibly transforms at room temperature to perovskite at 2.0 GPa. Bulk moduli （K300） of ilmenite, lithium niobate and perovskite are 174（4） GPa, 179 （8） GPa, and 208（5） GPa, respectively （at fixed first pressure derivative K＇ = 4）. The Griineisen parameter T has been estimated to be 1.28 for ilmenite and 1.75 for perovskite. In ilmenite phase, TiO6 octahedra become more regular with increasing pressure. In perovskite phase structural distortion increases with pressure increase.展开更多
Mn_2O_3-Na_2WO_4/SiO_2 is considered as the most promising catalyst for the oxidative coupling of methane（OCM） process; however, it only has a better catalytic performance over 800 °C. To improve its low-temper...Mn_2O_3-Na_2WO_4/SiO_2 is considered as the most promising catalyst for the oxidative coupling of methane（OCM） process; however, it only has a better catalytic performance over 800 °C. To improve its low-temperature performance, an attempt has been made to modify the Mn_2O_3-Na_2WO_4/SiO_2 catalyst using TiO_2, MgO, Ga_2O_3, and ZrO_2. Among the synthesized catalysts, the TiO_2-modified Mn_2O_3-Na_2WO_4/SiO_2 catalyst shows markedly improved low-temperature OCM performance,achieving a high CH_4 conversion of ~23% and a good C_2-C_3 selectivity of ~73% at 700 °C（the catalyst bed temperature）, along with promising stability for at least 300 h without signs of deactivation.In comparison with the unmodified Mn_2O_3-Na_2WO_4/SiO_2 catalyst, the TiO_2 modification results in significant improvement in the low-temperature activity/selectivity, whereas the MgO modification has almost no impact and the Ga_2O_3 and ZrO_2 modifications have a negative effect. The X-ray diffraction（XRD） and Raman results reveal that the formation of a MnTiO_3 phase and a MnTiO_3-dominated catalyst surface is crucial for the improvement of the low-temperature activity/selectivity in the OCM process.展开更多
基金National Key Research and Development Program(2016YFB0901600)Science and Technology Commission of Shanghai(16ZR1440500,16JC1401700)+2 种基金National Science Foundation of China(51672301)Key Research Program of Chinese Academy of Sciences(QYZDJ-SSW-JSC013,KGZD-EW-T06)Youth Innovation Promotion Association CAS
基金supported by the Petro China Innovation Foundation(2016D-5007-0506)the “Strategic Priority Research Program” of the Chinese Academy of Sciences(XDA09030101)~~
基金an Alexander von Humboldt Fellowship in Germany and S.Qin acknowledges the financial support of the National Natural Science Foundation of China(Grant No. 40972029)
文摘The structural stability of manganese titanate MnTiO3 at high pressure was investigated by X-ray diffraction and Raman spectroscopy with diamond anvil cells. Ilmenite-type MnTiO3 is stable at least to 26.6 GPa, and lithium niobate type MnTiO3 reversibly transforms at room temperature to perovskite at 2.0 GPa. Bulk moduli （K300） of ilmenite, lithium niobate and perovskite are 174（4） GPa, 179 （8） GPa, and 208（5） GPa, respectively （at fixed first pressure derivative K＇ = 4）. The Griineisen parameter T has been estimated to be 1.28 for ilmenite and 1.75 for perovskite. In ilmenite phase, TiO6 octahedra become more regular with increasing pressure. In perovskite phase structural distortion increases with pressure increase.
文摘Mn_2O_3-Na_2WO_4/SiO_2 is considered as the most promising catalyst for the oxidative coupling of methane（OCM） process; however, it only has a better catalytic performance over 800 °C. To improve its low-temperature performance, an attempt has been made to modify the Mn_2O_3-Na_2WO_4/SiO_2 catalyst using TiO_2, MgO, Ga_2O_3, and ZrO_2. Among the synthesized catalysts, the TiO_2-modified Mn_2O_3-Na_2WO_4/SiO_2 catalyst shows markedly improved low-temperature OCM performance,achieving a high CH_4 conversion of ~23% and a good C_2-C_3 selectivity of ~73% at 700 °C（the catalyst bed temperature）, along with promising stability for at least 300 h without signs of deactivation.In comparison with the unmodified Mn_2O_3-Na_2WO_4/SiO_2 catalyst, the TiO_2 modification results in significant improvement in the low-temperature activity/selectivity, whereas the MgO modification has almost no impact and the Ga_2O_3 and ZrO_2 modifications have a negative effect. The X-ray diffraction（XRD） and Raman results reveal that the formation of a MnTiO_3 phase and a MnTiO_3-dominated catalyst surface is crucial for the improvement of the low-temperature activity/selectivity in the OCM process.
