Pd-Ru/TiO2 catalyst - An active and selective catalyst for furfural hydrogenation

Article abstract of DOI:10.1039/c5cy01650a

The selective hydrogenation of furfural at ambient temperature has been investigated using a Pd/TiO₂ catalyst. The effect of the solvent was studied and high activity and selectivity to 2-methylfuran and furfuryl alcohol was observed using octane as solvent but a number of byproducts were observed. The addition of Ru to the PdTiO₂ catalyst decreased the catalytic activity but improved the selectivity towards 2-methylfuran and furfuryl alcohol with decreased byproduct formation. Variation of the Ru/Pd ratio has shown an interesting effect on the selectivity. The addition of a small amount of Ru (1 wt%) shifted the selectivity towards furfuryl alcohol and 2-methylrofuran. Further increasing the Ru ratio decreased the catalytic activity and also showed a very poor selectivity to 2-methylfuran.

Full text of DOI:10.1039/c5cy01650a

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Pd-Ru/TiO2 catalyst – an active and selective catalyst for furfural hydrogenation
Obaid F. Aldosari, Sarwat Iqbal, Peter J. Miedziak, Gemma L. Brett, Daniel R. Jones, Xi Liu,
Jennifer K. Edwards, David J. Morgan, David K. Knight, and Graham J. Hutchings*
*hutch@cardiff.ac.uk
Cardiff Catalysis Institute, Main Building Park Place, Cardiff, UK, CF10 3AT
1

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Abstract
The selective hydrogenation of furfural at ambient temperature has been investigated using a
Pd/TiO2 catalyst. The effect of the solvent was studied and high activity and selectivity to 2ꢀ
methylfuran and furfuryl alcohol was observed using octane as solvent but a number of
byproducts were observed. The addition of Ru to the PdTiO2 catalyst decreased the catalytic
activity but improved the selectivity towards 2ꢀmethylfuran and furfuryl alcohol with
decreased byproduct formation. Variation of the Ru/Pd ratio has shown an interesting effect
on the selectivity. The addition of a small amount of Ru (1 wt. %) shifted the selectivity
towards furfuryl alcohol and 2ꢀmethylrofuran. Further increasing the Ru ratio decreased the
catalytic activity and also showed a very poor selectivity to 2ꢀmethylfuran.
Key words: Furfural, Pd/Ru catalysts, room temperature, 2ꢀmethylfuyran, furfuryl alcohol,
hydrogenation, alternative fuel derivatives
2

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Introduction
Biomass is considered as one of the most important resources of renewable energy,
yet the development of efficient technologies which can utilize biomass represents a major
challenge.1 The utilization of chemical intermediates like furfural (FFR), furfuryl alcohol
(FA), together with attractive biofuels like 2ꢀmethylfuran (2ꢀMF) and 2ꢀ
methyltetrahydrofuran (2ꢀMTHF) is the main focus of much current research.2ꢀ4 FFR, a
product from xylose conversion is an important bioꢀderivative.1 It is considered to be a
platform chemical for the upgrading of fuels through the formation of FA and 2ꢀMF by
hydrogenation.5 FA and 2ꢀMF have a range of applications in the chemical industry; FA is
mainly used in the manufacturing of resins,6 and as a starting material for the synthesis of
1,5ꢀpentanediol,7, 8 2ꢀMF9 and tetrahydrofurfuryl alcohol (THFA).10 2ꢀMF is obtained from
the hydrogenation of FFR and FA. The main applications of 2ꢀMF are in the synthesis of
perfume intermediates, and chloroquine lateral chains in medical applications.
Copperꢀbased catalysts have received considerable attention for the hydrogenation of
FFR. Dongxia et al. have reported FFR hydrogenation in the liquid phase at a temperature of
180 °C and 69ꢀ104 barg pressure of pure hydrogen with the utilization of a copper chromite
catalyst.11 The catalyst was found to be very active for the synthesis of 2ꢀFA. Copper in
combination with other metals supported on oxides e.g., Cu/Cr,12 Cu/Fe,13, 14 Cu/Zn/Al,15
Cu/TiO2,5 Cu/SiO2,16ꢀ18 Cu/Ni/Mg/Al,19 Cu/Pd,20, 21 has been reported to be active for the
hydrogenation of FFR forming 2ꢀMF, 2ꢀMTHF, and 2ꢀFA. A number of other metal oxide
catalysts have also been studied and found to be suitable candidates for this reaction. e.g.,
Ru,22, 23 Ni,24 Fe,24ꢀ26 supported catalysts. Almost all of these studies have been performed
under very harsh reaction conditions, both in terms of the temperature and the hydrogen
pressure required to observe activity. Therefore, a process for the selective synthesis of 2ꢀMF
and 2ꢀFA from FFR under milder reaction conditions is highly desirable. We have recently
9
10
reported that Pd/TiO2 and Pd/Sn/TiO2 catalysts can be used very effectively for the
conversion of FA into 2ꢀmethyfuran at room temperature. Medlin et al. have recently
reported an application of selfꢀassembled layers used to block the Pd active sites which can
minimize the decarbonylation reaction and the corresponding side product formation during
furfural hydrogenation.27In the present study we report the hydrogenation of FFR using the
previously reported Pd/TiO2 catalyst in 1,2ꢀdichloroethane, toluene, methanol and octane.
Variation of the solvent has shown an interesting effect on the selectivity pattern.
Furthermore, we have studied the addition of a second metal component, namely Ru, and
3

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observed lower catalytic activity, but high selectivity to 2ꢀMF and FA with less byproduct
formation compared to the unmodified Pd/TiO2 catalysts.
Experimental
Materials
FFR (98%), 1,2ꢀdichloroethane (98%), methanol (99.8%), octane (98%), toluene
(99%) and all reaction intermediates were purchased from Sigma Aldrich and used as
received. Palladium (II) chloride and ruthenium (III) chloride metal precursors were also
purchased from Sigma Aldrich. TiO2 was purchased from Degussa (P25). Pure hydrogen
(99.9%) and nitrogen (99.9%) were obtained from BOC.
Catalyst preparation
All the monometallic catalysts supported on TiO2 were prepared by a standard wet
impregnation method reported previously.10 In a typical synthesis the PdCl2 was added to 2ml
deionised water and stirred for approximately 15 min at 80 °C until the Pd dissolved
completely. The TiO2 support was added to the solution and stirred to form a paste. The paste
o
was subsequently dried at 110 °C for 16 h, and calcined in static air (400 °C, 3 h, 20 C minꢀ
1).
Bimetallic catalysts were prepared in the same manner, with the concomitant heating
and stirring of the PdCl2 and RuCl3 precursors together.
Characterization
X-ray diffraction (XRD). Powder XRD was carried out using a PANalytical X'Pert Pro
with a CuKα Xꢀray source run at 40 kV and 40 mA fitted with an X'Celerator detector. Each
sample was scanned from 2θ = 10 to 80 for 30 min. The catalysts were ground into fine
powder form and loaded on a silicon wafer. The results obtained were compared with the
information in ICDD library for each catalyst.
Temperature programmed reduction (TPR). Temperature programmed reduction/
oxidation was carried out using a TPDRO 1100 series analyser. Samples (80 mg) were preꢀ
treated for 1 h at 130 °C (20 °C/ min) in a flow of Argon (20 mL/ min). Following this the
gas flow was changed to 10% H2/Ar or 10%O2/He and the temperature was ramped to 800 °C
4

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(10 °C/ min) with a 5 min hold at the Tmax. H2/O2 uptake was monitored using a TCD
detector.
X-ray photoelectron spectroscopy (XPS). Samples were characterized using a Kratos
Axis UltraꢀDLD photoelectron spectrometer, using monochromatic Al Kα radiation, at 144 W
(12 mA × 12 kV) power. High resolution and survey scans were performed at pass energies
of 40 and 160 eV respectively. Spectra were calibrated to the C (1s) signal for adventitious
carbon at 284.8 eV and quantified using CasaXPS v2.3.17, utilizing sensitivity factors
supplied by the manufacturer.
Transmission electron microscopy (TEM). TEM was carried out using a Jeol 2100
with a LaB6 filament operating at 200 kV. Samples were prepared by dispersing the powder
catalyst in ethanol and dropping the suspension onto a lacey carbon film over a 300 mesh
copper grid.
FFR hydrogenation reaction.
The hydrogenation of FFR was carried out using a stainless steel stirred autoclave (50 ml,
Parr Instruments, Model 5500HP) equipped with a Teflon liner using catalyst (0.1 g), FFR (1
g) and solvent (15 ml). The sealed autoclave was purged three times with N2, and three times
with H2 before being pressurized to 3 barg with H2. The autoclave was stirred at 1000 rpm at
ambient temperature. When the reaction was completed, the mixture was cooled, filtered and
the postꢀreaction mixture was centrifuged prior to being analysed by GC (Bruker Sion 456ꢀ
GC fitted with a Brꢀ1ms capillary column). Products were identified by comparison with the
authentic samples. For the quantification of the amounts of reactant consumed and products
generated an external calibration method was used, with 1ꢀpropanol being the external
standard.
Results and Discussion
In our initial experiments we investigated a range of organic solvents with the
5%Pd/TiO2 catalyst to study the hydrogenation of FFR under mild reaction conditions (25 °C
and 3 barg H2). The products expected from the hydrogenation of FFR that can be used as
fuel derivatives are summarized in scheme 1.
The main target products we focused on in this study are 2ꢀMF, and FA. Table 1
shows the comparison of various organic solvents for the catalyzed reactions. Generally the
solvent is chosen in order to increase the concentration of dissolved hydrogen, and as a result
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enables an increase in the reaction rate.28 We have observed a high catalytic activity with
toluene and methanol but the selectivity observed was completely different between the two
solvents. The reaction in toluene showed a high selectivity of 2ꢀMF and THFA. The use of
methanol as the solvent led to a significantly increased selectivity of THFA alcohol along
with a large amount of side products. Formation of THFA requires the selective
hydrogenation of the furan double bonds with the hydrogenation of the alcohol so it follows a
different reaction pathway, as shown in scheme 1.
The reaction in 1,2ꢀdicholoroethane showed formation of a mixture of products and a
very small amount of the desirable products were produced, which is in contrast to our
previous observations on the hydrogenation of FA where we achieved a full conversion of FA
into 2ꢀMF in 1,2ꢀdichloroethane.9
Although, the catalytic activity was far higher with methanol, 1,2ꢀdichloroethane and
toluene but the amount of side products was also very high; therefore we chose octane for
further investigation of the reaction parameters. Interestingly, the selectivity observed with
octane was shifted more towards 2ꢀMF and FA with far lower amounts of side products
(mainly acetals and ketals) compared with the other solvents.
To further probe the reaction we varied the loading of the Pd from 1 to 5 wt% and the
data for FFR hydrogenation is provided in Table 2. Initially we performed the blank reactions
as well as reactions with the pure TiO2 and observed no activity. Increasing the loading of Pd
metal from 1% to 5% increased the catalytic activity, although not proportionally, and also
increased the selectivity of 2ꢀMF significantly.
We have previously reported the characterization of all these catalysts with the
variation of Pd metal loading.9 The particle size of Pd was found to be very low (<2nm) and
there was no major difference observed in the particle size distribution when the metal
loading was increased from 1% to 5% wt. Given the uniformity of the particle size
distribution we can link the increased catalytic activity to an increased concentration of active
metal sites.
A time on line study for FFR hydrogenation was performed using 5% Pd/TiO2
catalyst and the activity data is provided in Figure 1. As expected there was an increase in
conversion with an increase in the reaction time from 30 min to 180 min. In the initial 30 min
only 2ꢀMF and FA were formed with no side products being observed, an increase in the
amount of byproducts was observed, however, when the reaction was performed over longer
times. Small amounts of THFA were also observed which could be a hydrogenation product
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of FFR or FA. It is possible for side reactions from FA and 2ꢀMF to occur as shown in
scheme 1, which can further react to form various other molecules like acetals and ketals.
From the data in Figure 1 it is apparent that the monometallic 5%Pd/TiO2 catalyst
displays high activity for FFR hydrogenation and the selectivity of 2ꢀMF and FA was high
but there was still a significant number of side products. We have previously shown that the
addition of a second metal (Sn) into Pd/TiO2 catalyst can improve the selectivity pattern in
FA hydrogenation10 and changing the ratio of metals in a bimetallic catalyst can have a
significant effect on the reaction profile in benzyl alcohol and hexenol oxidation reactions.29,
30
Ru is one of the most studied metals for the hydrogenation reactions of furanꢀderived
compounds,31ꢀ35 therefore, we synthesized bimetallic catalysts with the different ratios of Ru
and Pd. The catalysts were tested for FFR hydrogenation reaction in octane at room
temperature under 3 barg pressure of hydrogen. The data is presented in Table 3.
Monometallic 5%Ru/TiO2 catalysts whilst exhibiting a lower catalytic activity
produced exclusively FA. The addition of a small amount of Pd showed a decrease in
selectivity towards FA and the formation of 2ꢀMF was obvious.
Furthermore increasing the Pd content, whilst maintaining an overall 5 wt% metal
loading, served to increase the catalytic activity and improved the selectivity towards FA
compared with 2ꢀMF. When both metals were present in a 1:1 ratio the conversion was high
and FA was the dominant product and lower amounts of 2ꢀMF (also a consecutive product of
FA) were observed. Interestingly, much lower amounts of side products was observed with
the 1% Ruꢀ4% Pd/TiO2 catalyst. This catalyst showed the highest selectivity to 2ꢀMF and FA
compared with the pure monometallic 5%Ru/TiO2 and 5%Ru/TiO2 catalysts. The small
amount of ruthenium metal may have prevented the side reaction pathways, allowing the
consecutive hydrogenation reaction to take place. Further increasing the amount of Pd from
4% to 4.5% showed no particular change in activity or selectivity to 2ꢀMF but the number of
side products increased from 2 to 7%. From these data we conclude that the addition of 1%
Ru into Pd/TiO2 is optimal composition required for the synthesis of 2ꢀMF and FA from FFR
under these reaction conditions. Luo et al. have reported the use of palladium ruthenium
alloyed catalysts for the hydrogenation, suggesting that the palladium dilutes and separates
the active ruthenium sites,36 it is possible that we are observing a similar effect for this case,
however, for this reaction the palladium is the active species being diluted and isolated by the
ruthenium.
Powder Xꢀray diffraction (XRD) patterns of monometallic unreduced Ru/TiO2,
Pd/TiO2 and Ru/Pd/TiO2 catalysts are shown in Figure 2. There was no significant difference
7

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observed between these catalysts and the major component reflections were related with
titania (P25). We have used a mixture of anatase and rutile titania and both of these phases
remained stable. It suggested that either the particle size of Pd and Ru particles (metallic or
oxide) was too small to be detected by XRD or the metals were homogeneously dispersed on
the surface of TiO2.
To try to explain the differences observed in the catalytic performance for the
catalysts we analyzed them using TEM, and the representative images are shown in Figure 3
and the associated particle size distributions are shown in Figure 4. The most active catalyst
was the 5%Pd/TiO2 and we have previously reported the characterization of this catalyst9, it
had an average particle size of 1.1nm. The catalysts in general seem to have lower activity as
the ratio of palladium/ruthenium decreased. The 0.5%Ru:4.5%Pd/TiO2 and
1%Ru:4%Pd/TiO2 catalysts display identical conversions (39%), the TEM analysis of these
catalysts reveals that they also have a very small average particle sizes of 1.3 and 1.1 nm
respectively (Figures 3/4e and f). This is slightly larger than those reported for the
5%Pd/TiO2 catalyst. This suggests that there is an inverse relationship between the activity
and the particle size for this reaction system. There are, however, significant differences in
the selectivity of the two catalysts which suggests the reaction pathways are more related to
the composition of the catalysts than the particle size.
2%Ru:3%Pd/TiO2 has a slightly lower activity than that would be expected from the
pattern observed for the other catalysts. The TEM images and PSD are shown in Figure 3d.
The average particle size for this catalyst is larger than those with the lower amounts of
palladium at 2 nm, Figure 4d shows that the particles seem to be larger with some evidence of
clusters forming, interestingly the 2.5%Ruꢀ2.5%Pd/TiO2 catalyst (Figure 3c) has a smaller
average particle size, with some evidence of slightly larger particles seen but not as many as
the 2%Ruꢀ3%Pd/TiO2 catalyst. Again this may correlate directly with the conversion data
with the 2.5%Ruꢀ2.5%Pd/TiO2 catalysts slightly more active than the 2%Ru:3%Pd/TiO2
catalyst.
The catalysts with the lowest amount of palladium, 3%Ruꢀ2%Pd/TiO2 and 4%Ruꢀ
1%Pd/TiO2 (Figures 3b and 3a respectively), once again have a smaller particle size,
however, the activity of these catalysts is lower, suggesting that at low palladium content the
particle size is not the only factor that affects the activity. As the most active catalyst was the
palladium monometallic catalyst and the ruthenium monometallic catalyst was amongst the
least active catalyst it seems likely that the palladium is the active component in these
catalysts, we suggest that when the relative amount of ruthenium in the catalyst becomes too
8

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large the catalysts loses activity as the substrate can no longer access the active palladium
sites. Interestingly the 3%Ruꢀ2%Pd/TiO2 catalyst has the smallest particle size of all the
catalysts studied in this work and also has a conversion that is relatively higher than would be
expected if the activity was solely related to the palladium content. Overall the TEM suggests
that to form an active catalyst for this reaction small particle are required, however a
significant amount of the metal component must be palladium but the amount of ruthenium
can be tuned to affect the reaction selectivity.
TPR measurements were performed with all the catalysts in order to investigate the
reducibility of metal oxide species. A combined TPR profile is presented in Figure 5.
Monometallic 5% Ru/TiO2 catalyst (a) showed a reduction peak above 150 °C which became
broader with an addition of Pd (bꢀe). On the other hand the monometallic 5% Pd/TiO2 (h)
catalyst showed a reduction peak at a temperature less than 100 °C. The catalysts with
1%Ru/4% Pd (f) and 0.5% Ru/4.5% Pd (g) showed a very different reduction behavior
compared with the other bimetallic catalysts. A feature was observed around 100 °C in both
of these catalysts which can be related to the emission of trapped hydrogen (Pd β hydride
species) above 90 °C. This feature of hydrogen evolution indicates that hydrogen can be
adsorbed on the surface of the catalyst at sub ambient temperatures and gets released in the
form of hydrogen molecules when the temperature is raised above 90 °C.37 To further probe
the nature of the metal particles we performed CO chemisorption studies with these catalysts
and normalized the metal surface area with the activity. We observed that the specific activity
was not a function of the metal surface area. As expected, the Pd dispersion increased with an
increase in the concentration of Pd.
XPS analysis of mono and bimetallic unreduced catalysts are presented in Figure 6. It
revealed multiple oxidation states for both Pd and Ru. For monometallic 5% Pd, the spectra
was dominated by a signal at 337.7 eV attributable to PdꢀCl bonds with a ratio of ca. 1:1 and
supported by the significant residual chlorine at 198.4 eV which is characteristic of metalꢀ
38
chlorine bonds and as observed for Pd deposited from solution on Fe3O4.
Additionally,
PdO was also evident at 336 eV. In contrast, the monometallic ruthenium catalyst was found
to be chloride free, but exhibited two species with binding energies of 280.1 and 280.8 eV
attributable to Ru(0) 39and RuO2 respectively40 in a 1:1 ratio suggesting the metallic
ruthenium was covered by an oxide layer. The presence of RuO2 was also supported by the
O(1s) shoulder ca. 529 eV consistent with the RuO2.
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For the bimetallic catalysts, the two Ru oxidation states remain, although for the
3%Ruꢀ2%Pd/TiO2 catalyst and those with a higher Pd content, there was a 0.4 shift to higher
binding energy for the Ru(3d) signals and attributed to a particle size effect, however, the
Ru(0)/Ru(IV) ratio remained constant at ca. 1:1. No shift in Pd binding energy was seen with
changing the metal ratio, neither were shifts or reduced species observed in the Ti(2p) spectra
as reported previously by Luo et al for RuPd/TiO2 systems.36 Instead, the Pd was present at
335.5 eV (Pd(0)) and 337.1 eV (PdꢀCl) which was different to that of the monometallic
where both PdꢀCl and PdO were observed. It is worthy to note that the Pd(0) binding energy
was somewhat higher than that expected for metallic Pd particles and may be attributable to
(i) Pd2+ species formed by a charge transfer with Clꢀ1 which remains on the surface, or (ii)
particle size dependent screening effects of the Pd coreꢀhole which results in higher binding
energies for the smaller particles41ꢀ43 . Based on the microscopy (Figures 2 and 3) the latter is
considered to be the case here.
Conclusions
We have reported an efficient and novel catalyst composition for the conversion of
FFR into useful organic molecules (2ꢀMF, and 2FA) at room temperature and low hydrogen
pressure. Overall we conclude that the most effective catalyst for this reaction is the
1%Ru:4%Pd/TiO2. This catalyst represented the best compromise of conversion of FFR and
selectivity to the desired products 2ꢀMF and FA. TEM particle size distributions of the
catalysts indicated that for this reaction small metal particles are required; however, the
particle size is not the only consideration when trying to optimise these catalysts. XPS
suggested that the oxidation state of the ruthenium is also an important factor as when the
relative amount of ruthenium in the metallic sate was increased the activity was reduced. By
tuning the ratio of palladium to ruthenium we can form a catalyst where we can direct the
selectivity towards the products that are useful as fuel additives under mild, green reaction
conditions.
Acknowledgments
The authors would like to thank the EPSRC (EP/K014854/1) and the Research Campus at
Harwell for access to the transmission electron microscope. The raw data is provided in DOI:
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http://dx.doi.org/10.17035/d.2015.100119. Obaid F. Aldosari would like to thank Royal
embassy of Saudi Arabia for funding his PhD.
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Tables and figures
Table 1. Effect of solvents on FFR hydrogenation with 5%Pd/TiO2
Conversion (%)
Product selectivity (%)
THFA 2ꢀMTHF
Solvents
2ꢀMF FA
Others*
84.7
42.3
68
1,2ꢀdichloroethane
Toluene
100
98
2.5
42.8
0
0
9
3.7
0.6
4.8
0
4.1
0
10.3
26.9
4.8
Methanol
92.2
65.4
Octane
36.2
35.6
22
Reaction conditions: RT, 3 barg H2, 5%Pd/TiO2 catalyst (0.1g), FFR (1g), solvent (15ml),
120 min.
*Acetals, ketals and polymeric species
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Table 2. Effect of Pd metal loading on FFR hydrogenation
Catalysts
Conversion (%) Product selectivity (%)
2ꢀMF
7.0
20
FA
73
40
35
THFA
14
7.0
5
Others*
6.0
33
1% Pd/TiO2
2.5% Pd/TiO2
5% Pd/TiO2
20.7
53.2
65
38
22
Reaction conditions: RT, 3 barg H2, catalyst (0.1g), FFR (1g), octane (15ml), 120min.
*Acetals, ketals and polymers
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Table 3. Effect of addition of Ru into Pd/TiO2 catalyst
Catalysts
Conversion (%)
Product selectivity (%)
2ꢀMF
0
FA
THFA
Others*
6.8
TOF(10ꢀ2)
4.1
5%Ru/TiO2
4%Ruꢀ
8.2
5
100
83.8
0
0
9.2
2.5
1%Pd/TiO2
3%Ruꢀ
21.5
33.8
30
15.1
14
67.9
58
0
17.1
27.6
23.8
2.1
1.0
1.6
1.5
1.9
1.6
3.2
2%Pd/TiO2
2.5%Ruꢀ
0.4
0
2.5%Pd/TiO2
2%Ruꢀ
8.7
65.8
45.3
39.8
28.6
3%Pd/TiO2
1%Ruꢀ
39.3
39.2
65.4
51.5
50.8
36.2
1.1
1.8
4.8
4%Pd/TiO2
0.5%Ruꢀ
7.6
4.5%Pd/TiO2
5%Pd/TiO2
30.4
Reaction conditions: RT, 3 barg H2, catalyst (0.1g), FFR (1g), octane (15ml), 120min.
*Acetals, ketals and polymers
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Scheme 1. Reaction pathways for FFR hydrogenation. Key: a. Furfural (FFR), b. Furan (F),
c. Tetrahydrofuran (THF), d. Butanol (BuOH), e. Tetrahydrofurfural (THFF), f.
Tetrahydrofurfuryl alcohol (THFA), g. Furfuryl alcohol (FA), h. 2ꢀMethyltetrahydrofuran (2ꢀ
MTHF), i. 2ꢀMethylfuran (2ꢀMF), j. 2ꢀPentanol (2ꢀPeOH), k. 1ꢀPentanol (1ꢀPeOH).
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100
80
60
40
20
0
30
60
90
120
150
180
TOL(min)
Figure 1. Time online data for FFR hydrogenation with 5% Pd/TiO2 catalyst. Key: ꢀ
Conversion, ꢁ 2ꢀMF, ꢀ FA, ꢂ THFA, ꢀ Other minor products
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i
h
g
f
e
d
c
b
a
10
20
30
40
50
60
70
80
Diffraction angle (2θ)
Figure 2: XRD patterns of (a) TiO2 P25 (b) 5%Ru/TiO2 (c) 4%Ruꢀ1%Pd/TiO2, (d) 3%Ruꢀ
2%Pd/TiO2, (e) 2.5%Ruꢀ2.5%Pd/TiO2, (f) 2%Ruꢀ3%Pd/TiO2, (g) 1%Ruꢀ4%Pd/TiO2, (h)
0.5%Ruꢀ4.5%Pd/TiO2, (i) 5%Pd/TiO2.
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Figure 3: TEM images of a) 4%Ruꢀ1%Pd/TiO2; b) 3%Ruꢀ2%Pd/TiO2; c) 2.5%Ruꢀ
2.5%Pd/TiO2, d) 2%Ruꢀ3%Pd/TiO2; e) 1%Ru4%Pd/TiO2 and f) 0.5%Ruꢀ4.5%Pd/TiO2.
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Figure 4: TEM PSDs a) 4%Ruꢀ1%Pd/TiO2; b) 3%Ruꢀ2%Pd/TiO2; c) 2.5%Ruꢀ2.5%Pd/TiO2,
d) 2%Ruꢀ3%Pd/TiO2; e) 1%Ru4%Pd/TiO2 and f) 0.5%Ruꢀ4.5%Pd/TiO2.
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h
g
f
e
d
c
b
a
0
100
200
300
400
T (°C)
Figure 5: TPR profile of (a) 5%Ru/TiO2, (b) 4%Ruꢀ1%Pd/TiO2, (c) 3%Ruꢀ2%Pd/TiO2, (d)
2.5%Ruꢀ2.5%Pd/TiO2, (e) 2%Ruꢀ3%Pd/TiO2, (f) 1%Ruꢀ4%Pd/TiO2, (g) 0.5%Ruꢀ(h)
4.5%Pd/TiO2, 5%Pd/TiO2.
Figure 6: XPS profiles of Pd(3d) and Ru(3d) coreꢀlevel spectra of TiO2 supported Pd with
different Pd:Ru ratios. (a) 5%Ru/TiO2, (b) 4%Ruꢀ1%Pd/TiO2, (c) 3%Ruꢀ2%Pd/TiO2, (d)
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2.5%Ruꢀ2.5%Pd/TiO2, (e) 2%Ruꢀ3%Pd/TiO2, (f) 1%Ruꢀ4%Pd/TiO2, (g) 0.5%Ruꢀ
4.5%Pd/TiO2, (h) 5%Pd/TiO2, (i) 5% Pd/TiO2 .
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Graphical abstract
39x19mm (300 x 300 DPI)