Rate constants of surface reactions in methanation over ruthenium/alumina catalyst as determined by pulse surface reaction rate analysis

Abstract

By use of a new PSRA (pulse surface reaction rate analysis) apparatus equipped with an emissionless infrared diffuse reflectance spectrometer (EDR) and a flame ionization detector (FID), the dynamics of both adsorbed CO and produced CH/sub 4/ were simultaneously measured in the CO hydrogenation over Ru/Al/sub 2/O/sub 3/ catalyst. When a CO pulse was introduced to the catalyst via the H/sub 2/ at temperatures above 405 K, an IR absorption band assignable to a linearly adsorbed CO appeared at 2040 cm/sup -1/. At the same time an FID response of CH/sub 4/ quickly increased. It was found that k/sub CH/sub x// is more than 50 times larger than k/sub CO/, indicating that on the Ru/Al/sub 2/O/sub 3/ catalyst the formation of (CH/sub x/)/sub ad/ from adsorbed CO is much slower than its hydrogenation to CH/sub 4/. Furthermore, an H/sub 2/-D/sub 2/ inverse isotope effect was observed for k/sub CO/, suggesting that hydrogen atoms play an important role in the C-O bond dissociation in the CO hydrogenation. A mechanism of the C-O bond dissociation was also discussed on the basis of these results for k/sub CO/. 7 references, 17 figures, 2 tables.