Various silica-supported rare earth oxides were examined for photocatalytic methane conversion around room
temperature. Among them, silica-supported cerium oxide with low loading amount showed the highest
photoactivity for nonoxidative coupling of methane (NOCM) to produce both ethane and hydrogen. XANES,
DR UV−vis, and phosphorescence spectra of silica-supported cerium oxide revealed that the main species
on the low loading samples were highly dispersed Ce(III) oxides, suggesting that they were the photocatalytic
active sites for the reaction. The highly dispersed Ce(III) oxides could be formed also on alumina, which
enhanced the photoactivity of alumina for the NOCM.
Highly dispersed cerium oxide species on silica and alumina, which mainly exist as Ce(III) species, promote non-oxidative direct methane coupling photocatalytically around room temperature, while Ce(IV) species as CeO2 particles do not behave as a catalyst for this reaction.
A series of silica-supported cerium oxide samples having various cerium content were prepared by conventional impregnation method, followed by calcination in air. Ce L III -edge XANES study revealed that highly dispersed cerium oxide species on silica surface were predominantly in trivalent oxidation state and cerium oxide nano-particles on silica contain mainly tetravalent cation like as CeO 2 bulk oxide. This elucidated that UV absorption band at 265 nm is assignable to Ce(III) species dispersed on silica.
This paper proposes new identification laws of an adaptive flux observer for speed sensorless vector controls. In speed sensorless vector controls of an induction motor with the adaptive observer, the speed identification system is known to be unstable in a part of regenerating region. In addition, it is pointed out that the stator resistance variation interferes with the speed identification. Thus it is necessary to find an adaptive scheme which can stabilize the identification system.In this paper, firstly, the stability on the parameter identification is discussed from the viewpoint of Popov's hyper stability. Secondly, identification laws for the speed and the stator resistance are proposed based on the new identification system which is derived by using the augmented error. Finally, effectiveness of the proposed method is shown by experiments.
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