Download STRUCTURED SUPPORTED IONIC LIQUID PHASE (SSILP

STRUCTURED SUPPORTED IONIC LIQUID PHASE (SSILP)
CATALYSTS FOR CONTINIOUS-FLOW HYDROGENATIONS
LIOUBOV Kiwi-Minsker and MARINA Ruta
Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne
(GGRC-ISIC-EPFL), Station 6, CH-1015 Lausanne, Switzerland
[email protected]
Structured Supported Ionic Liquid Phase (SSILP) catalysis is a new concept with the advantages
of ionic liquids (IL) used as solvent for nano-metals or homogeneous catalyst deposited on
structured catalytic supports. This is achieved by confining the IL with the active phase to the
surface of a structured support consisting of sintered metal fibers (SMF) coated by a layer of
carbon nanofibers (CNF). The IL thin film immobilized on CNF/SMF supports presents a high
interface area ensuring efficient use of the catalytic active phase. The regular structure of the
support with high porosity (> 0.8) allows a low pressure drop and even gas-flow distribution in a
fixed-bed reactor. This parameter is very important for complex reactions with an intermediate as
a target product. It allows attaining a high selectivity leading to process intensification and
favorable environmental impact. The high thermo-conductivity of the CNF/SMF support
suppresses the formation hot spots during exothermic hydrogenation reactions. The feasibility of
the SSILP catalysis for gas-phase continuous flow reactions has tested in the hydrogenation of
1,3-cyclohexadiene to cyclohexene and acetylene to ethylene as model reactions.
The 1,3-cyclohexadiene hydrogenation was carried out using structured catalyst containing a
homogeneous Rh-based complex immobilized in IL confined on CNF/SMF. In order to elucidate
the influence of the support nature on the catalyst activity/selectivity, the SMF were also coated
by a thin zeolite (ZSM-5) film on which the IL phase containing Rh catalyst was deposited. The
catalyst [Rh(H)2Cl(PPh3)3/IL/CNF/SMF] showed turnover frequency of 150-250 h-1 and
selectivity of > 96%.
The selective hydrogenation of acetylene to ethylene was tested with monodispersed Pdnanoparticles of 5 and 10 nm obtained in [bmim][PF6] or [bmimOH][Tf2N], respectively, and
showed excellent long-term stability. The IL cation-anion network surrounding the nanoparticles
suppressed the formation of active-site ensembles known to catalyze oligomerization of acetylene
responsible for the catalyst deactivation. The catalytic system developed also demonstrated high
efficiency and long-term stability without any deactivation in ethylene-rich feed, being promising
for industrial application.
Catalysts were characterized by SEM, TEM, XRD and a high pressure 1H NMR and 1H{31P} to
provide insight into the nature of the active catalytic species.