Journal
CARBON
Volume 40, Issue 7, Pages 1063-1070Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0008-6223(01)00243-3
Keywords
catalytically grown carbon; catalyst support, doping; transmission electron microscopy
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The structure and morphology of carbon species generated under dry reforming of methane (DRM) at 650 and 800degreesC on 'bare' and 'K-doped' Ni/MgO catalysts have been comparatively investigated by Transmission Electron Microscopy (TEM) analyses of 'used' samples. K-addition (K-at/Ni-at, 0.125) strongly improves the resistance of the Ni/MgO catalyst to coking and sintering phenomena at any temperature. At 650degreesC, an extensive formation of filamentous (whisker carbon) carbon species on bare Ni/MgO catalyst causes the detachment of a large number of Ni particles from the support with a consequent destruction of the structure and remarkable sintering phenomena of the active phase. Considerably lower amounts of carbon deposits with a shell-like (encapsulating carbon) morphology, forming at 800degreesC on both catalysts, point to the Bouduard reaction as the main route of carbon deposition on Ni-based catalysts during DRM. The electronic effect induced by potassium on the active phase of the Ni/MgO system, timely monitored by a rise in E-app of DRM from 50 to 70 kJ/mol, markedly hinders the rate of coking also affecting the morphology of carbon whiskers, by inhibiting the processes of C diffusion and nucleation across Ni particles under steady-state conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.
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