Abstract
The inethanation activity of Ru/Al 2O 3 and its deactivation by carbon during reaction were studied in a Berty recycle reactor at 690 kPa and 510 to 610 K. The methanation activity of ruthenium is highly temperature-dependent from 510 to 610 K with an apparent activation energy of 113kJ/g-mol. Catalyst deactivation due to carbon deposition is minimal at low reaction temperatures (i.e., below 570 K); however, above 570 K the deactivation is rapid. The deactivation process is first-order in CO concentration and first-order in active site concentration; the activation energy for deactivation is 40kJ/g-mol. Two forms of carbon are observed in temperature-programmed surface reaction of hydrogen with the carbonaceous deposit formed during reaction. The deactivation kinetics and TPSR results are consistent with a process involving dissociation of CO to active carbon, followed by transformation of active carbon to an inactive carbon species. Carbon deposits can cause severe loss of activity at high reaction temperatures and will disguise the true kinetics of CO hydrogenation unless precautions are taken to avoid carbon formation.
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