The adsorbed methyl carbonate species has been detected by the
FT-IR observation.33,41,44 It has been reported that the adsorbed
methyl carbonate species is formed from the dissociative adsorp-
tion of dimethyl carbonate44 as well as methanol and CO2.41 The
high ratio of methyl benzylcarbamate to dibenzylurea can be
related to high coverage of methyl carbonate and low coverage
of C6H5CH2NHCOO(a) species.
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Conclusions
(1) The synthesis of methyl benzylcarbamate from benzylamine,
CO2 and methanol is catalyzed by CeO2 as a heterogeneous
catalyst.
(2) In the reaction of C6H5CH2NH2 + CO2 + CH3OH using
CeO2, dibenzylurea, N-benzylidenebenzylamine, N-methyl ben-
zylamine and dimethyl carbonate were formed as by-products.
The formation of dibenzylurea, N-methyl benzylamine and
dimethyl carbonate is catalyzed by CeO2, and that of N-
benzylidenebenzylamine proceeds in the liquid phase without
CeO2.
(3) Theyieldof methylbenzylcarbamate reached 92% at >99%
benzylamine conversion and 92% benzylamine-based selectivity
under C6H5CH2NH2 : CH3OH = 900 mmol: 5 mmol, 5 MPa
CO2, 423 K, 12 h.
(4) CeO2 catalyzed the carbamate formation from the amines
(benzylamine, aminomethylcyclohexane and methylamine) +
CO2 + alcohols (methanol, ethanol, 1-propanol and 2-propanol)
with good yield and high selectivity.
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(5) The CeO2 catalyst is deactivated by the poisonous adsorp-
tion of the products. It was verified that the CeO2 catalyst was
reusable after the calcination at 873 K.
(6) The main formation route of methyl benzylcarbamate
is suggested to be the catalytic reaction of benzylamine with
dimethyl carbonate or the precursor of dimethyl carbonate
formed from CH3OH and CO2 on CeO2.
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Acknowledgements
A part of this research is funded by the Cabinet Office,
Government of Japan through its “Funding Program for Next
Generation World-leading Researchers”.
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