The deposition of coke from methane on a Ni/MgAl2O4 catalyst

Temperature-programmed reaction techniques and Raman spectroscopy were used to characterize coke species deposited on a 5% Ni/ MgAl2O4 catalyst for dry reforming of methane. The CH4 temperature-programmed decomposition profiles showed that the ignited decomposition temperatures of CH4 increased from 273 to 378 degrees C when MgAl2O4 replaced the catalyst support gamma-Al2O3. The temperature-programmed oxidation, temperature-programmed hydrogenation and temperature-programmed CO2 reaction profiles showed that there were three carbon species (i.e. C-alpha, C beta and C-gamma) on the catalyst surface. Raman spectroscopy showed that C-gamma was graphite-like carbon species, which was responsible for catalyst deactivation. The C gamma species was the most inactive species toward H-2 and O-2, while it was unexpectedly more active toward CO2. The unique reactivity of CO2 with different coke specie could be ascribed to the carbonate, bidentate and formate species formation on MgAl2O4 surface. These surface species enhanced the oxidation of C gamma species and thus contributed to the high stability of Ni/MgAl2O4 catalyst. (C) 2007 Elsevier Ltd. All rights reserved.