Res. Chem. Intermed.
, Vol. 32, No. 3–4, pp. 279–290 (2006)
Also available online - www.vsppub.com
Infrared spectroscopic study on the reaction mechanism
of CO hydrogenation over Pd/CeO
, SHIGERU AIDA, TOSHIKI KASAHARA
and TOSHIHIRO MIYAO
Department of Applied Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1,
Rokkakubashi, Kanagawa, Yokohama, 221-8686, Japan
Received 22 January 2005; accepted 14 June 2005
Abstract—In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO
hydrogenation over Pd/CeO
. Instead of direct dissociation of CO, a new reaction pathway is proposed
for methane formation, involving geminal dicarbonyl intermediates and (HCO)
which may be located on the surface of Pd covered with thin layers of reduced ceria (SMSI effect).
Transformation of methane formation sites into methanol formation ones by the oxidation with water
vapor formed during the CO
reaction is proposed, which may be located on the Pd (111) planes
adjacent to ceria support.
Keywords: Infrared spectroscopy; in situ; ceria support; CO hydrogenation; SMSI effect.
It is well known that palladium is a good catalyst for methanol formation at
elevated pressures of the CO
reaction, although methane is the sole product
under ambient pressure. Many studies have been reported concerning the activity
and selectivity controlling factors in the CO
reaction over supported Pd
catalysts. So far, three factors have been proposed: particle size [1, 2], addition of
promoters [3, 4] and support effects [5, 6]. As for the particle size of Pd, there is still
some discrepancy whether smaller or larger particles are favorable for methane and
methanol formation, respectively. The important role of promoters is recognized
to be the stabilization of cationic Pd, as well as formyl or formate intermediates
for methanol formation, whereas the assistance of CO dissociation seems to be the
important role for methane formation.
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