H. Goto et al.
AppliedCatalysisA,Generalxxx(xxxx)xxx–xxx
nitride (h-BN) were chosen as supports because silica is widely known
as an inert support and h-BN is also recognized as inert but recently was
found to be active itself for hydrogenation of alkenes [17].
was examined by Fourier transform infrared (FTIR) spectroscopy.
About 20 mg of samples was pressed into a disk with 20 mm diameter,
and set in the center of a cell. The cell was heated from room tem-
perature to 350 °C at a rate of 10 °C min−1 in vacuum and then kept at
this temperature for 1 h in vacuum (below 0.003 Torr). After the cell
was cooled to 50 °C, 2,5-dimethylfuran (ca. 5 Torr) was introduced to
the cell. After 30 min, the cell was evacuated at 50 °C for 30 min and
heated to 300 °C in vacuum. The IR spectra were recorded by using the
spectrometer (Jasco FT/IR-6100) equipped with mercury cadmium
telluride (MCT) detector at 4 cm−1 resolution.
2. Experimental
2.1. Materials
The chemicals hexachloroplatinic acid (H2PtCl6, > 99.9%, Sigma-
Aldrich), boron nitride (Wako) and SiO2 (CAB-O-SIL EH-5, Cabot) were
used as received. The chemicals as reactants were 2,5-dimethylfuran
(2,5-DMF, 99.88%, Apollo Scientific), 2,5-dimethyltetrahydrofuran
(2,5-DMTHF, > 98%, TCI) and toluene (> 99.5%, Wako).
The solid acid property was examined by temperature-programmed
desorption of ammonia (NH3-TPD)(TPD-1-AT, Microtrac BEL).
Quantities of 20 mg of sample were heated from room temperature to
350 °C in He (50 cm3 min−1) at a rate of 10 min−1 and kept at this
temperature for 1 h. After the samples was cooled to 100 °C and held at
2.2. Catalyst preparation
this temperature for 30 min, a 10% NH3/He stream (50 cm3 min−1
)
The supported platinum catalysts were prepared by incipient wet-
ness impregnation and subsequent reduction. A quantity of 1 wt% of
hexachloroplatinic acid dissolved in distilled water was impregnated
drop-wise to the incipient wetness point on supports (boron nitride and
SiO2) which were dried beforehand at 100 °C overnight. Quantities of
1 g of the precursor-support mixtures were dried at 100 °C for 24 h and
reduced under a hydrogen flow of 50 mL min−1 at 350 °C for 1 h with a
heating rate of 5 °C min−1 before the measurements. The commercial
boron nitride was ball-milled at 400 rpm for 12 h using a planetary ball
mill (Pulverisette 7, Fritsch, zirconia balls (10 mm diameter)) to make
the support.
was introduced for 0.5 h. The saturated sample was flushed with He
(50 cm3 min−1) for 30 min, and then the temperature was increased
from 100 to 600 °C at a heating rate of 10 °C min−1. Masses 16 and 17
were monitored during the desorption by a mass spectrometer. As a
comparison, H-ZSM5 (Si/Al = 15) zeolite with 1.0 mmol g−1 of acid
sites was used.
2.4. Hydrogenation of 2,5-Dimethylfuran
The activity tests of hydrogenation of 2,5-dimethylfuran (2,5-DMF)
were carried out in a fixed-bed flow reactor in the gas phase at ambient
pressure and a temperature range of 150–350 °C. Amounts of catalysts
equivalent to 0.87 μmol of active sites as determined by CO chemi-
sorption were used. Before the activity testing, the catalysts were pre-
treated in the reactor in hydrogen flow (200 cm3(NTP) min−1) at
350 °C for 1 h. The inlet concentration of 2,5-DMF was 10 mol% in a
flow of hydrogen of 50 cm3(NTP) min−1 (34 μmol s−1). The reactant
also contained 5 vol% of toluene as an internal standard and was de-
livered through a bubbler maintained at 35 °C to obtain a ratio of H2/
2,5-DMF of 10/1. In the experiments, the contact time was kept con-
stant at 0.26 s. Contact time is defined as follows.
2.3. Catalyst characterization
The crystal structure of the catalysts was determined by X-ray dif-
fraction (XRD, RINT-2700, Rigaku) with Cu Kα radiation
(λ = 0.1548 nm) at a voltage of 40 kV and a current of 100 mA. Scans
were obtained at a speed of 2° min−1 with step width of 0.02° for 2θ
values from 20° to 60°. The surface area of the catalysts was measured
by nitrogen adsorption (BELSORP-mini II, Microtrac-BEL) using the
Brunauer-Emmett-Teller (BET) method. Prior to the measurement,
samples were evacuated at 200 °C for 2 h. The amount of active sites on
the catalysts was estimated by carbon monoxide (CO) chemisorption.
Quantities of 0.5 g of samples were placed in a quartz reactor and were
reduced in hydrogen flow at 350 °C for 1 h and then cooled to 50 °C in
helium flow. Pulses of 3% CO/He were introduced over the pretreated
catalysts for 21 cycles at 50 °C. The diminished peak areas of the mass
spectrometer signal at m/z = 28 were used to calculate the amount of
adsorbed CO. About 10% experimental errors should be considered
because the measurement using mass spectrometer involved some short
intervals for detection of CO signals.
CO uptake[μmol/g] × Catalyst weight[g]
Contact time[s]=
Reactant molar flow rate[μmol/s]
After introduction of the reactant the temperature was varied in the
following
order,
350 °C → 250 °C → 150 °C → 200 °C → 300 °C.
Product gas mixtures were analyzed using an on-line gas chromato-
graph (GC; GC-2014, Shimadzu) equipped with a flame ionization de-
tector (FID) and a commercial HP-1 capitally column. The contact time
study was carried out in the same manner, except at a fixed temperature
of 175 °C and various contact times from 0.06 to 0.43 s. The contact
time was controlled by changing the hydrogen flow rate from 25 to
190 cm3(NTP) min−1 using the same amount of the catalyst. GC-FID
and GC–MS analysis confirmed that toluene was not hydrogenated
under the reaction conditions. The equilibrium constant for toluene
The particle size distribution of supported Pt nanoparticles was
evaluated by transmission electron microscopy (TEM) (Hitachi H-7650)
at 100 kV. A carbon-coated copper grid was used as a substrate and the
catalyst was dispersed in water and put on the grid.
The local structure of supported Pt nanoparticles was estimated by
X-ray absorption fine structure (XAFS) spectroscopy at beamline BL-9C
of the Photon Factory of the Institute of Material Structure Science,
High Energy Accelerator Research Organization (KEK) in Japan. The
synchrotron ring operated at 2.5 GeV and 430 mA. About 80 mg of
sample was pressed into a pellet 10 mm in diameter, and set in the
center of an in situ XAFS cell. Hydrogen was introduced at a flow rate of
50 mL(NTP) min−1 and the cell was heated from room temperature to
350 °C at a rate of 10 °C min−1 and then kept at 350 °C for 1 h. After in
situ reduction, the measurements were performed at 350 °C under hy-
drogen flow in transmission mode. The collected data were analyzed by
the software program REX 2000 (Rigaku Co.). The parameters for the
curve fitting analysis were obtained with FEFF. The curve-fitting was
1
1
650
hydrogenation is reported as Keq = 3.60 × 109kPa3 × e−26179
−
(
[18]. Under the reaction conditions in this study, the equTilibrium
conversion of toluene is negligible (< 0.1%) at a higher temperature
than 200 °C. Although the equilibrium conversion of toluene is 98% at
150 °C, no formation of methylcyclohexane was observed in this ex-
periment. This is probably due to low activity of platinum for the hy-
drogenation and competitive adsorption of 2,5-dimethylfuran.
3. Results and discussion
Fig. 1 shows XRD patterns of 1 wt% Pt/BN, 1 wt% Pt/SiO2 and their
supports. The Pt/BN catalyst showed four peaks at 26.6°, 41.6°, 39.5°
and 46.4°. The former two peaks are derived from h-BN support, cor-
responding to the (002) interlayer reflection and the (100) in-plane
conducted in the range of k = 0.25–1.4 nm−1
The adsorption behavior of 2,5-dimethylfuran on Pt/BN and Pt/SiO2
.
2