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Y. Li et al. / Materials Research Bulletin 39 (2004) 195–203
molybdenum so far. For example, Robert et al. [12] prepared nanocrystalline metallic alloy powders,
e.g. the nanocrystals that is made of an alloy of nickel and molybdenum, by high energy mechanical
alloying. They found the electrodes produced from these powders presented an excellent chemical,
electrochemical, and mechanical stability, and had an electrocatalytic activity for the hydrogen
evolution which is comparable or higher than the electrodes which are presently used in the
electrochemical industry. Zach et al. [13,14] prepared metallic molybdenum nanowire by a two-step
procedure of electro-deposition and reduction, and made investigation into the electronic and
mechanical properties. Cheng and Zhao [11] synthesized nanosized metallic molybdenum from
carbonyl molybdenum by microwave plasma. Therefore, it is of interest and significance to make
investigation into the preparation and physico-chemical properties of nanosized metallic molybdenum.
Herein, we presented a novel route to the synthesis of nanosized metallic molybdenum by thermo-
synthesis method from MoO3 and KBH4 at moderate temperature, and applied as-synthesized
nanosized metallic molybdenum in the selective hydrogenation of longer chain linear alkadienes, and
made a comparison with noble metal catalysts (Pd/Al2O3). It was discovered that the as-synthesized
metallic molybdenum exhibited better catalytic activity and selectivity for the selective hydrogenation
of longer chain linear alkadienes than noble metal catalysts (Pd/Al2O3). To our best knowledge, there
have been no similar reports up to now.
2. Experimental
MoO3 (7.2 g) was mixed with KBH4 according to 1:3 of molar ratio of MoO3 and KBH4, and
comminuted in mortar. Then, the mixture of MoO3 and KBH4 was transferred into a 1 l autoclave, and
Ar purged the autoclave. The autoclave was heated from room temperature to 300 8C, and kept at
300 8C for 2 h. After the reaction, the produced gases were let out, and the autoclave was cooled to
room temperature. The product mixture was passivated by allowing a mixture of 1% O2/Ar to diffuse
into the autoclave at flow rate of 100 ml/min for 4 h to prevent the product from violently oxidizing if
exposed to air immediately following the reaction. The final product is obtained by dissolving the
above-mentioned mixture in distilled water, thoroughly washing, filtering, exchanging with acetone for
several times, and drying at room temperature.
Powder X-ray diffraction analysis was performed with Ni-filtered Cu Ka radiation with Shimadzu
XD-3A X-ray diffractometer. The working voltage of 35 KV and the electronic current of 25 mA were
employed. Transmission electron microscopy (TEM) images were obtained on a JEM-200 CX
transmission electron microscope, using an accelerating voltage of 200 kV. The composition of as-
synthesized samples was determined by using induced coupled plasma (ICP) on TJA1100. The surface
species of the as-synthesized sample were analyzed by a ESCALab MK2 X-Ray Photoelectron
Spectrometer. Mg Ka radiation was selected as X-ray source. The sample was pressed into self-
supported wafer and fixed on a holder, then, the catalyst was out-gassed. The residual pressure in the
analysis chamber was maintained below 10À9 Torr. The spectra of sample were collected and corrected
by referencing the binding energy to carbon (C1s ¼ 284:6 eV).
To evaluate the catalytic properties of the as-synthesized nanosized metallic molybdenum catalyst, we
tested its catalytic activity for the liquid selective hydrogenation of longer chain alkadienes (C10–C13),
which is an important petrochemical industrial reaction for production of alkyl benzene. The
measurement of reaction of catalysts for selective hydrogenation of long chain alkadienes were