(679g) Monodisperse Au-FeCx Bimetallic Catalysts for Selective Synthesis of Higher Alcohols from Syngas

Monodisperse Au-FeC_x
Bimetallic Catalysts for Selective Synthesis of Higher Alcohols from Syngas

Zhuang
Zeng, Yue Wang and Xinbin Ma*

Key
Laboratory for Green Chemical Technology of Ministry of Education,
Collaborative Innovation Center of Chemical Science and Engineering, School of
Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People¡¯s
Republic of China

Abstract

Higher alcohols (HA), referring to
primary alcohols with two or more carbon atoms, have attracted great attentions
owing to their wide applications as fuel, fuel additives as well as
intermediates for chemicals production. Selective synthesis of higher alcohols
directly from syngas (HAS) is quite promising but still challenging due to the
low HA selectivity and space time yield. Fe-based catalysts have been extensively
studied due to their unique advantages, such as relatively low cost, abundant
reserve and tolerance of a wide H₂/CO ratio. Bimetallic systems, especially
CuFe catalysts, are widely studied to enhance the catalytic performance and
selectivity to oxygenates, in which Cu species are responsible for
non-dissociative CO adsorption and insertion, while iron carbides are for CO dissociation
and C-C couple. Consequently, ensuring the spatial proximity of the dual sites
to maximize their synergistic effects has the top priority for catalyst design.

Herein, we presented an effective and
facile strategy for higher alcohols synthesis from syngas (H₂/CO=1)
by using Au-FeC_x bimetallic catalysts supported on ¦Á-Al₂O₃,
which were derived from monodisperse dumbbell-like Au (6 nm)-Fe₃O₄
(12 nm) nanoparticles. The dumbbell-like structure could be preserved after
pretreatment, which may boost the synergistic effects between Au and FeC_x.
Considering the impressive capacity for molecularly CO adsorption of Au catalysts,
we here use Au species for non-dissociative CO adsorption, which may effectively
improve the selectivity to alcohols.

To illustrate the superiority of the
dumbbell-like structure of Au-Fe catalysts in HAS, we use the Au+Fe catalyst
(in which most of Au and Fe₃O₄ NPs located separately) as
well as monometallic Au and monometallic Fe catalysts as contrast samples. As
expected, Au-Fe catalyst achieved the total oxygenates selectivity as high as
52.5 % while it is only 36.6 % for the Au+Fe catalyst. More importantly, the higher
alcohols of the Au-Fe catalyst took up a much higher proportion (72.8 wt%) than
other catalysts in the total oxygenates. It is demonstrated that intimate
contact and sufficient interface between Au and FeC_x in
dumbbell-like Au-Fe catalyst maximizes the synergy of the dual sites, which
suppressed the undesired CO₂ and hydrocarbons and significantly
enhanced the formation of higher alcohols. We further adjusted the Fe/Au molar
ratio to modulate the proximity of Au and FeC_x sites and found that Au-Fe
(Fe/Au=10) was also the most suitable candidate for HAS. Moreover, the role of
Au species was explored as well using the combination of H₂-TPR, XPS
and CO-TPD/MS. It is demonstrated that Au species not only served as an
electron donator to promote reduction and subsequent carburization of Fe
species, forming more iron carbides, but also
boosted CO adsorbtion and insertion to promote the oxygenates formation.
This research may supply a potential route for the rational design of effective
bimetallic catalysts focusing on the maximization of synergistic effect of the
dual sites.

Key words:
Au, iron carbides,
bimetallic catalysts, syngas, higher alcohols

AUTHOR
INFORMATION

Corresponding Author

*E-mail: xbma@tju.edu.cn.