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Active oxygen center in oxidative coupling of methane on La_(2)O_(3) catalyst

Journal of Energy Chemistry 2021年第9期30卷 649-659页

作者： Xiaohong Zhou Yaoqi Pang Zebang Liu evgeny i.vovk Alexander Pvan Bavel Shenggang Li Yong Yang School of Physical Science and Technology Shanghai Tech UniversityShanghai 201210China Shanghai institute of Optics and Fine Mechanics Chinese Academy of SciencesShanghai 201800China University of Chinese Academy of Sciences Beijing 100049China Shell Technology Centre Amsterdam P.O.Box 380001030 BN AmsterdamNetherlands CAS Key Laboratory of Low-Carbon Conversion Science and Engineering Shanghai Advanced Research InstituteChinese Academy of SciencesShanghai 201210China

La_(2)O_(3) catalyzed oxidative coupling of methane(OCM) is a promising process that converts methane directly to valuable C_(2)(ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C_(2) products, and a lower light-off temperature as well. Further study is focused on carbonate-free La_(2)O_(3) catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 e V correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results,DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexacoordinate lattice oxygen sites, with energy 2.18 e V lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C_(2) products selectivity in OCM over La_(2)O_(3) catalyst.

关键词： in-situ XPS Online MS DFT Oxidative coupling of methane High C_(2)selectivity Active oxygen center La_(2)O_(3)catalyst

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Low-agglomerated yttria nanopowders via decomposition of sulfate-doped precursor with transient morphology

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Journal of Rare Earths 2014年第4期32卷 320-325页

作者： R.P.Yavetskiy D.Yu.Kosyanov V.N.Baumer A.G.Doroshenko A.i.Fedorov N.A.Matveevskaya A.V.Tolmachev O.M.vovk institute for Single Crystals of NAS of Ukraine State Scientific institution"institute for Single Crystals"of NAS of Ukraine

The fabrication peculiarities of low-agglomerated yttria （Y2O3） nanopowders via thermal decomposition of sulfate-doped precursor with transient morphology were studied. it was determined that Y2（OH）5（NO3）x（CO2）y（SO4）z·nH2O （n=1-2） crystalline precursor underwent fragmentation and decomposition into isolated quasi-spherical Y2O3 particles upon calcination. Effect was con-nected with minimizing the free energy of the plate-like crystallites via reducing the contact surface until to the moment of spheroidi-zation and attainment of isolation that occurred atТ=1100 °С. Residual sulfate ions slowed down the surface diffusion during heat treatment thus retaining quasy-spherical morphology and low aggregation degree of Y2O3 nanopowders. Sulfate-doped yttria nanopowders with medium particle size of 53±13 nm possessed improved sinterability in comparison with undoped ones arising from finer particle size, narrower particle distribution and lower agglomeration degree.

关键词： precursor transient morphology sulfate-ions yttria nanopowders particle size sinterability rare earths

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