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8
08C and then dried at 1108C for 16 h. The resulting powder was
constant integrated CO peak areas were measured by the thermal
conductivity detector (TCD, sensitivity 150 mA, attenuation 2).
ground and calcined in static air at 4008C for 3 h with a heating
rate of 58Cmin . This material was designated as Au-Pd/TiO
ꢀ1
IMP
.
2
Thermogravimetric analysis (TGA) was performed by using a Perki-
nElmer TGA 4000 apparatus under an atmosphere of flowing air
ꢀ1
(
30 mLmin ). The sample was first heated to 708C and kept at
Preparation of Au-Pd/TiO by physical mixing
2
this temperature for 1 h to remove the majority of the water, then
Palladium(II) acetate (Sigma Aldrich 99.9%) and gold(III) acetate
Alfa Aesar 99.9%) were added to the titania support, and the mix-
ture was ground manually in a pestle and mortar for 10 min. The
the temperature was increased from 70 to 6008C at a rate of
ꢀ1
(
5
8Cmin . The weight change was calculated based on the weight
of the dried sample at 708C.
resultant mixture was heat treated at 3508C for 2 h in a tubular
ꢀ
1
Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy
studies were performed by using a Bruker Tensor 27 spectrometer
fitted with a HgCdTe (MCT) detector and standard analysis cell.
furnace under flowing He (58Cmin ). This material was designated
PM
as Au-Pd/TiO2
.
ꢀ1
Spectra were collected at RT in the range of 4000–600 cm with
ꢀ1
Preparation of Au-Pd/TiO by deposition–precipitation
128 accumulation scans and a resolution of 2 cm . The spectrum
of KBr was used as the background so all species detected were as-
sociated with the catalyst. Before DRIFT analysis, samples were
dried for 3 h at 1208C.
2
Water (300 mL) was heated to 608C under stirring. Simultaneously,
PdCl (11.6 mg) was dissolved in a stirred and heated aqueous solu-
2
ꢀ1
tion (1.5 mL) of HAuCl ·3H O (0.44 mol L ). This solution and tita-
4
2
Au
The metal content of the catalysts was determined by using an
Agilent 4100 MP-AES. Catalysts were digested for 4 h in aqua regia
nia (1.98 g) were added to the water (300 mL) with the simultane-
ous addition of sodium carbonate solution to maintain the overall
pH at 9. The slurry was maintained at pH 9 for 1.5 h, and then the
solid was collected by filtration and washed with deionised water
(10 mL) and later diluted to 100 mL with deionised water. The Au
and Pd content was analysed with two emission lines for each
metal, l=242 and 267 nm for Au and l=340 and 363 nm for Pd.
The samples were introduced to the nitrogen plasma using
a single-pass spray chamber at a pressure of 120 kPa without air
injection. The instrument was calibrated with 2.5, 5 and 10 ppm Au
and Pd standards in 10% aqua regia along with a 10% aqua regia
blank. The samples were tested three times, and the average result
is presented.
(
1 L). The washed solid was dried (1108C for 16 h) and calcined in
1
ꢀ
static air at 4008C for 3 h with a heating rate of 58Cmin . This ma-
terial was designated as Au-Pd/TiO2
DP
.
Preparation of Au-Pd/TiO by sol immobilisation
2
[33]
Catalysts were prepared based on a previous method. An aque-
ous solution of PdCl and HAuCl ·3H O with the desired concentra-
2
4
2
tion was prepared and added to a 1 L glass beaker that contained
water (800 mL) with stirring. To this solution, PVA (weight-average
molecular mass=9000–10000 gmol ; 80% hydrolysed, Sigma–Al-
drich) was added such that the PVA to metal ratio was 0.65 by
mass. After 15 min of stirring, a freshly prepared solution of NaBH4
n-Butanol oxidation
ꢀ
1
Catalytic reactions were performed in a 50 mL glass reactor. Typi-
ꢀ
1
cally, aqueous butanol solution (10 mL, 0.54 molL ; 4 wt%) was
admitted into the reactor, and catalyst (150 mg) was suspended in
the solution (metal-to-substrate ratioꢁ550). The glass reactor was
purged three times with oxygen and adjusted to the desired pres-
sure of 3 bar. This pressure was maintained at a constant level
throughout the experiment; hence as the oxygen was consumed
in the reaction it was replenished continuously. The reaction mix-
ture was heated to the desired temperature (80–1208C) and stirred
for 6 h. The reactor vessel was then cooled in an ice bath. After
cooling for 10 min, the reactor was opened slowly, and an ethanol
solution (50 mL) that contained a known amount of 2-butanol (ex-
ternal standard) was added. The catalyst was separated by filtration
and centrifugation, and the liquid was analysed by GC with flame
ionisation detection (FID, Varian star 3400 cx with a 30 m CP-Wax
(
0.1m, > 96% purity, NaBH /metal mole fraction=5, Sigma–Al-
4
drich) was added to form a dark-brown sol. After 30 min of sol
generation, the colloid was immobilised by adding titania and
acidifying to pH 2 by sulfuric acid. After 2 h, the catalyst was col-
lected by filtration, washed thoroughly with distilled water and
dried at 1108C for 16 h. These catalysts were designated as Au-Pd/
SOL_PVA
TiO2
.
Catalyst characterisation
XPS spectra were recorded by using a Kratos Axis Ultra DLD spec-
trometer that employed a monochromatic AlKa X-ray source (75–
1
4
50 W) and analyser pass energies of 160 eV (for survey scans) or
0 eV (for detailed scans). Catalysts samples were mounted using
5
2 CB column). For product identification, GC–MS (Waters, GCT Pre-
mier) was employed. The selectivity to the products was calculated
by Equation (1):
double-sided adhesive tape, and binding energies were referenced
to the C1s binding energy of adventitious carbon (284.7 eV). TEM
was performed by using a Jeol 2100 instrument with a LaB6 fila-
ment that operated at 200 kV. Samples were prepared by dispers-
ing the powder catalyst in ethanol and dropping the suspension
onto a lacey carbon film over a 300 mesh copper grid.
Selectivity to product i ð%Þ ¼
C-based mol of product i
ð1Þ
1
00 ꢂ
Sum of C-based mol of all products
CO chemisorption experiments were performed by using a Quan-
tachrome Chembet. A known amount of catalyst was introduced
to the sample cell, secured between two layers of quartz wool and
The TOF was reported after 1 h reaction time and was based on
the amount of surface metal. From the size of Au-Pd nanoparticles,
if we assume a face-centred cubic (FCC) cub-octahedral shape, the
number of total atoms in the cluster and the number of surface
metal atoms were estimated using the method proposed by Mori
ꢀ1
ꢀ1
pre-treated at 1108C in H (30 mLmin , 30 min, 58Cmin ramp
2
rate) followed by purging with He at the same temperature
ꢀ1
(
30 mLmin , 15 min) and cooling under He to 278C. Subsequently,
[34]
CO pulses (70 mL) were introduced into the sample cell until four
et al. The average atom diameter for Au and Pd (0.281 nm) was
ChemSusChem 0000, 00, 0 – 0
7
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