744
Chemistry Letters 2002
Selective Dimerization of Ethene over Lanthanide Catalysts Deposited from Eu or Yb Metal
Solutions in Liquid Ammonia
Hayao Imamura,Ã Takumi Kuhara, Masataka Furutachi, Takahiko Sakamoto, and Yoshihisa Sakata
Department of Advanced Materials Science and Engineering, Faculty of Engineering, Yamaguchi University,
2-16-1 Tokiwadai, Ube 755-8611
(Received March 25, 2002; CL-020269)
Europium and ytterbium catalysts obtained by impregnation
highly dispersed, but the reason why the catalysis of Yb systems
was superior to that of Eu systems is unknown.
of active carbon with lanthanide metal (Eu and Yb) solutions in
liquid ammonia were found to be active for the dimerization of
ethene. Ethene was selectively dimerized at 423–473 K to yield
butene isomers with selectivity of 10–62%. The active catalysts
were characterized as lanthanide nitride formed by the thermal
decomposition of its amide.
The dimerization of ethene on Yb/ACbegan from reaction
temperatures near 373 K. Time courses of 10% Yb/AC-catalyzed
ethene dimerization at 473 K were shown in Figure 1. The
consumption of the ethene reactant did not necessarily agree with
the amounts of the butene products. No products other than
butenes were detected by gas chromatography; thus the
oligomerization to products with higher molecular weights
occurs at the same time. Accumulation of such oligomerized
deposits on the catalysts would probably result in gradual
deactivation of Yb/ACwith reaction time as shown in Figure 1.
In the range where the steady formation of butenes was observed,
the butene selectivity evaluated by percentage of the amounts of
actually formed butenes to the amounts of butenes calculated
from ethene consumed remained unchanged at approximately
62% during the reaction. Yb/ACpreferentially yielded but-2-ene
(90%) with a trans/cis ratio of about 2, being close to equilibrium
composition of butenes at 473 K. The initial rates of Ln/AC-
catalyzed dimerization were proportional to the first power of the
ethene pressure (10–200 Torr; 1 Torr=133.322 Pa).
Recently there has been a growing interest in lanthanides and
their derivatives for potential synthetic and catalytic activity. It
has been shown that the use of dissolution of lanthanide metals
(Ln: Eu and Yb) in liquid ammonia enables the preparation of
novel lanthanide-containing catalysts which exhibit specific
properties for various reactions.1 In this study, we report that
the catalysts prepared by impregnation of active carbon with
solutions of Eu or Yb metals dissolved in liquid ammonia are
active for the highly selective dimerization of ethene. There have
been few studies published of catalytic dimerization of ethene to
butenes on lanthanides to the best of our knowledge. Selective
dimerization of alkenes is also of great potential synthetic and
industrial importance.2
Ammonia gas was purified through a calcium oxide column
and subsequently through a sodium hydroxide column. Active
carbon (designated hereafter as AC) obtained from Nacalai
Tesque Inc. was evacuated at 873 K for 18 h and subsequently
treated with hydrogen at 673 K. In a typical preparation of AC-
supported lanthanide catalysts (Ln/AC) with Ln loading of 10–
20 wt%, in a 50 cm3 stainless steel reactor were placed Eu or Yb
metals (0.12–0.24 g; 99.9%; Santoku Co.) and AC (1.2 g) under
an atmosphere of dry nitrogen. The reactor was briefly evacuated,
cooled by a dry ice/methanol bath, and then, about 3000 cm3 of
purified ammonia gas was liquefied. The Eu and Yb metal readily
dissolved in liquid ammonia to yield a homogeneous solution
containing the ammoniated electrons,3 with which ACwas
impregnated. Upon stirring at 293 K for 6–10 h, the dissolved
lanthanide was deposited in the form of amide on AC. Ammonia
was subsequently removed from the reactor leaving Ln/AC. Ln/
MnO, Ln/TiO2 and Ln/ZrO2 were similarly prepared. The
catalytic reactions were carried out in a gas-recirculation reactor
with a fixed volume of ca. 364 cm3.
Figure 1. Time courses of 10% Yb/AC-catalyzed
ethene dimerization at 473 K.
Ethene was effectively dimerized into mixed n-butene
isomers when brought into contact with various lanthanide
catalysts (Ln/AC, Ln/MnO, Ln/TiO2 and Ln/ZrO2) at 473 K. The
lanthanide catalysts exhibited activity for ethene oligomerization
with selectivity toward butene formation. Yb/ACand Eu/AC
showed similar catalytic behavior, and especially Yb/ACwas
excellent in activity and selectivity for butene formation
compared to other catalysts. The lanthanide for Ln/ACwas
The catalytic properties of 20% Eu/ACand 15% Yb/ACfor
the dimerization strongly depended upon thermal pretreatment
with evacuation (Figure 2). The activity and selectivity for Yb/
AC-catalyzed ethene dimerization increased with increasing
evacuation temperatures and passed through a maximum around
973 K. As shown in Figure 2, Eu/ACshowed a maximal activity
when evacuated around 673 K. In XRD of 20% Eu/ACand 15%
Copyright Ó 2002 The Chemical Society of Japan