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5 (2008) 699–705

Catalysis Today 133–13

Citral hydrogenation over Ir/TiO2 and Ir/TiO2/SiO2 catalysts

H. Rojas a,*, G. Borda a, P. Reyes b, J.J. Martınez a,c, J. Valencia c, J.L.G. Fierro d

a Grupo de Catalisis (GC-UPTC) Universidad Pedagogica y Tecnologica de Colombia,

Escuela de Quımica, Facultad de Ciencias, Av. Norte - Tunja, Colombiab Facultad de Ciencias Quımicas, Universidad de Concepcion, Chile, Concepcion, Casilla 160-C, Concepcion, Chile

c Centro de Catalisis Heterogenea, Departamento de Quımica, Facultad de Ciencias,

Universidad Nacional de Colombia, Bogota, Colombiad Instituto de catalisis y Petroleoquımica, CSIC, Cantoblanco, 28049 Madrid, Spain

Available online 19 February 2008

Abstract

Catalytic hydrogenation of citral over iridium supported on TiO2, SiO2 and mixed oxides TiO2/SiO2 has been studied. The effect of the

reduction temperatures (473 or 773 K) and the successive enrichment of TiO2 were analyzed. The solids were characterized by H2 chemisorption at

room temperature, N2 adsorption at 77 K, XRD, TEM, FTIR and XPS. The obtained results show that the high temperature reduction treatment

(HT) produces an important enhancement in both the catalytic activity and selectivity towards the desired product. The behavior is explained on the

basis of a surface enrichment in titania due to the migration of TiOx species on the Ir crystallites, which does not occur in those catalysts reduced at

low temperature (LT) or in the catalyst supported on an inert oxide such as SiO2.

# 2008 Elsevier B.V. All rights reserved.

Keywords: Citral; Hydrogenation; Catalyst

1. Introduction

Citral hydrogenation is a process of increasing interest

within the set of reactions of selective hydrogenation of a, b-

unsaturated aldehydes especially important in the field of fine

chemistry [1]. The control of the selectivity by means of the

hydrogenation of C O bond without altering C C bond is

required to obtain the unsaturated alcohol. Supported noble

metal catalysts on inert supports showed generally a low

selectivity towards the reduction of carbonyl group and

consequently some efforts are realized through the nature of

the active metal, support effects, the addition of promoters and

metal particle size, among others [2,3]. It has been reported that

Ir/TiO2 can be very active and selective towards the

hydrogenation of carbonyl bond during citral hydrogenation

[4]. The significant enhancement in the selectivity is explained

by the SMSI effect (strong metal support interaction); reduction

at high temperature leads to surface decoration of the iridium

* Corresponding author.

E-mail address: hurojas@udec.cl (H. Rojas).

0920-5861/$ – see front matter # 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.cattod.2007.12.109

metal crystallites by TiOx species, which allows to the

polarization of carbonyl group.

High surface area of titania is desirable for these applications,

however, a great disadvantage of titania as a support is its rather

low surface area. Inert oxides such as silica have been used as

carrier to deposit titania in order to increase the area of this

partially reducible oxide. The morphology as well as the surface

properties of the TiO2�x coated supports depend on the

preparation procedure, often grafting methods are used to obtain

this type of solids. Its preparation requires the binding of a highly

reactive titanium precursor, such as TiCl4 or alkoxide organic to

the silanol groups of the silica surface [5–8].

There are two types of Ti species in these supported oxides:

segregated TiOx, and isolated Ti species that interact with Si-

OH groups [6,7]. It has been observed that the Ti(i-OPr)4 may

reacts with a silica surface and after a calcinations leads to

highly dispersed TiO2 [10–12,15] with strong interactions

among the two oxides as a consequence of Ti–O–Si bonds [15].

Capel-Sanchez et al. [8], using UV–vis spectroscopy, DRIFTS

and XPS, have studied the chemical environment of titanium in

these supported oxides. The results have demonstrated changes

in the molecular structure of titanium species, most of these

H. Rojas et al. / Catalysis Today 133–135 (2008) 699–705700

materials showed varying proportions of tetrahedral and

octahedral titanium species.

On the other hand, the pretreatment temperature, the

reaction temperature, and the molecular size and reactivity of

the precursors and taking in account the different positions of

silanols on silica [9–11], each titanium center can be bonded to

one, two or even three silicon atoms through Si–O–Ti bonds,

leading to the formation of monopodal, bipodal, or tripodal

species, respectively [10]. High hydroxyl group concentration

and low temperatures (>373 K) are preferred in order to

prepare high surface coverage of molecularly dispersed TiO2/

SiO2, The porosity and morphology of the silica can also

influence an efficient grafting. Srinivasan et al. [5] have

reported a maximum dispersion of TiO2 at �3.0 Ti atom/nm2

on a non-porous SiO2 (Stober silica spheres) due to its highest

surface hydroxyls concentration and highest accessibility to the

reagent. Gao and Wachs [12] claimed that the dispersion could

be increased up to 4.0 Ti atom/nm2 by a careful control of the

preparation variables. Anchored titanium should form a

monolayer on silica only for TiO2 loading in the range 15–

20 wt.%, depending on the silica surface area [13]. At higher

loading crystalline phase of rutile or anatase can be observed.

Binary oxides have been used as catalysts and supports for a

wide variety of reactions [9,10,14–16]; in addition, SMSI effect

ascribed to TiO2 in this type of solids when it has been used as

catalytic support. Kumbhar [14] have studied Ni/SiO2-TiO2

catalysts showed strong suppression in hydrogen chemisorption

capacity similar to a Ni/TiO2 catalyst indicating strong metal

support interaction, this latter catalyst showed good activity for

the liquid phase hydrogenation of acetophenone. However,

information about the use of this mixed oxide as support of metal

catalysts for the selective hydrogenation in a, b-unsaturated

aldehydes has not been reported. Hoffmann et al. [15], have

studied the metal–support interaction by following the shift in the

band due to the carbon monoxide adsorbed on platinum dispersed

on silica modified with titania; this effect was only observed on

Pt/TiO2/SiO2 catalyst with the highest titanium content and a

well defined anatase crystalline phase, being previously

submitted to high temperature reduction treatment (HT 773 K).

In this work, the hydrogenation of citral over Ir/TiO2/SiO2

(Ir/G) catalysts was studied. The main objective was to study

the catalytic behavior of Ir/TiO2, Ir/SiO2 and Ir supported in

mixed oxides (Ir/G) reduced to 473 and 773 K, in order to

analyze the effect of the partially reducible support, the

successive enrichment of titania and the reduction temperatures

of the catalysts. The solids were characterized by the following

methods: H2 chemisorption at room temperature, N2 adsorption

at 77 K, XRD, TEM, and X photoelectron spectroscopy (XPS).

The liquid phase hydrogenation of citral was studied in a batch

reactor at 0.62 MPa of H2 and 363 K of reaction temperature.

2. Experimental

2.1. Synthesis of Ir/TiO2 and Ir/SiO2

Ir/TiO2 and Ir/SiO2 catalysts were prepared by impregnation

at 313 K of TiO2 (Degussa P-25, SBET = 70 m2 g�1) and silica

(Syloid-266-Grace Davidson, SBET = 290 m2 g�1) with an

aqueous solution of H2IrCl6 to give an Ir loading of 1 wt.%.

The impregnated solids were dried at 373 K for 6 h, calcined in

air at 673 K for 4 h and reduced at 473 K (LT) and 773 K (HT)

for 2 h in flowing hydrogen.

2.2. Synthesis of Ir/TiO2/SiO2 (Ir/G)

Titanium isopropoxide (Aldrich, reagent grade)

(1 mmol g�1 of silica) was dispersed in toluene (150 ml) and

added to an Aerosil silica (Syloid-266-Grace Davidson) which

was activated at 423 K under vacuum. The resultant mixture

was stirred for 16 h under inert atmosphere at the solvent reflux

temperature. Then, the modified silica was filtered, washed

with toluene, ethyl ether and deionized water. The resulting

solid (G1) was dried for 5 h under vacuum at 423 K. One

aliquot of this material (G1) was impregnated with an aqueous

solution of H2IrCl6 to give an Ir loading of 1 wt.%. The

impregnated solid was dried at 343 K for 6 h, calcined in air at

673 K for 4 h and reduced at 473 K (LT) and 773 K (HT) for

2 h, obtaining Ir/G1 LT and Ir/G1 HT, respectively. A second

aliquot of the solid G1, was enriched with Ti(i-OPr)4 to obtain

G2 support, following the same procedure of reflux, dried, and

calcination described for the synthesis of G1. A portion of the

obtained solid G2 was impregnated with H2IrCl6 to obtain Ir/

G2 catalysts following the same preparation procedure

described previously for Ir/G1 obtaining the Ir/G2 HT and

Ir/G2 LT. Similar procedure was used for samples with higher

Ti loading, referred as G3 and G4 as supports and Ir/G3 LT, Ir/

G3 HT, Ir/G4 LT and Ir/G4 HT as catalysts.

2.3. Characterization

Nitrogen physisorption at 77 K and hydrogen chemisorption

at 298 K were carried out in a Micromeritic ASAP 2010

apparatus, TEM micrographs were obtained in JEOL Model

JEM �1200 EXII System and XRD in a Rigaku apparatus.

FTIR spectra of the samples were recorded on Nicolet 550

FTIR spectrometer at room temperature with 64 scans and a

resolution of 4 cm�1 on sample wafers consisting of 150 mg

dry KBr and about 1.5 mg sample. Photoelectron spectra (XPS)

were recorded using an Escalab 200 R spectrometer provided

with a hemispherical analyzer, and using non-monochromatic

Mg Ka X-ray radiation (hy = 1253.6 eV) source. The surface

Ti/Si and Ir/Ti/Si atomic ratios were estimated from integrated

intensities of Ir 4f7/2, Ti 2p3/2 and Si 2p3/2 lines after

background subtraction and corrected by the atomic sensitivity

factors [17]. The spectra were fitted to a combination of

Gaussian–Lorentzian lines of variable proportion. The binding

energy of the Si 2p peak at 103.4 eV was taken as an internal

standard.

2.4. Activity measurements

Catalytic reactions were conducted in a batch reactor at a

constant stirring rate (1000 rpm). For all reactions, hydrogen

partial pressure was of 0.62 MPa, catalyst weight of 200 mg,

H. Rojas et al. / Catalysis Today 133–135 (2008) 699–705 701

25 ml of a 0.10 M solution of citral in n-heptane (Aldrich) and

reaction temperature of 363 K. The absence of oxygen was

assured by flowing He through the solution, as well as when the

reactor was loaded with the catalyst and reactants at

atmospheric pressure during 30 min. Prior the experiment,

all catalysts were reduced in situ under hydrogen flow of

20 cm3 min�1 at atmospheric pressure and temperature of

363 K. In all reaction internal diffusion limitations were also

shown to be absent by applying the Weisz–Prater parameter,

which gave a value maximum of 0.19. Blank experiment

showed no catalytic activity due to the supports under these

conditions. Reaction products were analyzed in an GC-Varian

3400 furnished with an HP Wax column of 30 m and 0.53 mm

i.d. The GC analysis was performed using a flame ionization

detector, using He as carrier, and the column was kept at a

constant temperature, 393 K. Under these analytical conditions,

the retention time of the reported reactants and products were:

citral (E): 21.2 min; citral (Z): 23.7; nerol: 31.2 min; geraniol

36.5 min and citronellol: 33.5 min.

3. Results and discussion

3.1. Catalysts characterization

Table 1 summarizes the results of TiO2 content, specific

surface area and H/Ir ratios and the Ir particle size from

evaluated TEM of supported Ir catalysts. The porosity of SiO2

allows that Ir/SiO2 presents a specific BET surface area larger

than Ir/TiO2. Specific surface of the Ir/G catalysts decreases

with the increase in TiO2 content, which is explained as a

gradual coverage of the SiO2 by TiO2, similar results were

found by Castillo et al. [7]. The H/Ir ratio is relatively low for

the catalysts supported on SiO2 and TiO2 and it is considerably

superior for Ir/G, it is possible by the creation of other

anchorage sites for the metallic precursor, which explains the

obtained results. In the series of HT catalysts, the presence of

titania leads to a decrease in the H/Ir ratio. This behavior is

frequently reported when partially reduced species of the

support migrates on the metallic particle covering part of the

Table 1

TiO2 content (wt.%), specific surface area, H/Ir ratios and metal particle size

obtained by TEM of supported Ir catalysts

Catalyst TiO2 content

(wt%)

SBET

(m2 g�1)

H/Ir dTEM

(nm)

Ir/SiO2 LT 0 290 0.200 3.1

Ir/SiO2 HT 0 290 0.186 3.2

Ir/G1 LT 7.3 283 0.39 1.2

Ir/G1 HT 7.3 280 0.026 1.3

Ir/G2 LT 13.6 273 0.25 1.4

Ir/G2 HT 13.6 273 0.043 1.4

Ir/G3 LT 19.2 271 0.26 1.3

Ir/G3 HT 19.2 261 0.086 1.3

Ir/G4 LT 24.0 254 0.37 1.3

Ir/G4 HT 24.0 253 0.017 1.3

Ir/TiO2 LT 99 39 0.09 4.0

Ir/TiO2 HT 99 39 0.03 4.0

metal sites generating a surface decoration of the Ir crystals.

Similar results have been reported by Hoffmann [15] in Pt/

SiO2/TiO2 catalysts using FTIR, where the electronic metal–

support interaction was observed only for samples with the

higher titanium content, after being submitted to HT treatment.

The results obtained by TEM suggest that the drops observed in

the H/Ir ratio cannot be attributed to a decrease in the metal

dispersion, because there are no changes in the metal particle

size in both, LTR and HTR catalysts. Supported catalysts in

mixed oxide (Ir/G) showed a narrow distribution of size,

however, in those supported on SiO2 and TiO2 the distribution is

wider, especially in the TiO2 support, in which metal particles

around 10 nm were detected.

The XRD patterns of mixed Ir/TiO2/SiO2 catalysts are

shown in Fig. 1. It can be observed that the Ir/SiO2 catalyst

exhibits a broad XRD peak assigned to the amorphous silica,

and a signal near to 2u � 408 due to the presence of crystallites

of iridium. This signal also is displayed by the Ir/TiO2 catalysts;

the metal particle size is rather large in the catalysts supported

on the mixed oxides TiO2/SiO2, such as Ir/G1. XRD results

revealed that the TiO2 is highly dispersed on the support. As the

TiO2 content increases XRD patterns exhibit weak diffraction

peaks associated with anatase.

The FT-IR spectra of Ir/TiO2/SiO2 catalysts are provided in

Fig. 2a. The peaks at 3444 and 1633 cm�1 (Fig. 2a) are

attributed to the stretching vibration of the OH group. Bands

due to Ti–O–Ti bonds appear in the range of 400–600 cm�1,

whereas the peaks at 473, 793, 1100 cm�1 (Fig. 2b.) correspond

to the Si–O–Si bending modes, symmetric Si–O–Si stretching

vibration and asymmetric Si–O–Si stretching vibration,

respectively [18]. The shoulder at 960–940 cm�1 is widely

accepted as a characteristic band of the Ti–O–Si linkages

[19,20], however, this band is masked due to the presence of the

band ySi–OH in 980 cm�1. The Ti–O–Si band area increases

from Ir/G1 to Ir/G4; which is indicative of the formation of

segregated TiOx species dispersed over the silica surface

[15,19–21].

Binding energies of core-level electrons and metal surface

composition were obtained from XP spectra. Table 2,

Fig. 1. X-ray patterns of the supported Ir catalysts.

Fig. 2. FTIR spectra of Ir/G; (a) in the 4000–1000 cm�1 range, (b) in the 1100–

400 cm�1 range. Series catalysts: a. Ir/G1 HT; b. Ir/G2 HT; c. Ir/G3 HT; d. Ir/G4

HT.

Table 2

Binding energies (eV) of supported Iridium catalysts

Si 2p Ti 2p3/2 Ir 4f7/2

Ir/SiO2 103.4 – 60.2

Ir/G1 103.4 458.5 60.3

Ir/G2 103.4 458.5 60.3

Ir/G3 103.4 458.5 60.3

Ir/G4 103.4 458.5 60.4

Ir/TiO2 – 458.5 60.6

Table 3

Bulk and atomic surface ratios derived from XPS of Ir/TiO2/SiO2 catalysts

(Ti/Si) (Ir/(Ti + Si))

Bulk Surface Bulk Surface

Ir/G1 0.057 0.021 0.00322 0.0026

Ir/G2 0.119 0.050 0.00327 0.0023

Ir/G3 0.180 0.070 0.00332 0.0028

Ir/G4 0.240 0.104 0.00421 0.0045

H. Rojas et al. / Catalysis Today 133–135 (2008) 699–705702

summarizes the observed binding energies of Si 2p, Ti 2p3/2, Ir

4f7/2 for the studied catalysts. The B.E. values of Si 2p, Ti 2p3/2

were 103.4 and 458.5 eV, respectively, which are exactly the

expected values considering the presence of oxides of Si(IV)

and Ti(IV) [22,23]. With regard to Ir 4f7/2 core level, a value of

60.2 eV may be observed for Ir0 species, which appear only Ir/

SiO2 catalyst. After the addition of Ti a slight increase B.E.

occurs suggesting the presence of a small fraction of Ird+

species generated from the electronic transfer between the

partially reduced titanium oxide and iridium particles [24,25].

The BE of Ti 2p3/2 peak (458.5 eV) obtained for these catalysts

are assigned at isolated Ti4+ ions in octahedral coordination as

in the bulk TiO2 anatase phase [24,25].

Table 3 compiles both the surface and the bulk Ti/Si and Ir/

Ti + Si ratios. It can be seen that the atomic (Ti/Si)b ratio is

approximately two times higher than the corresponding surface

ratio. This may be indicative that even the surface area of these

oxides are rather large, a partial segregation of TiO2 crystals

takes place, possibly in aggregates forms (clusters), as it has

been described in the literature [6,7]. With regard to (Ir/

Si + Ti)s ratio, there are not significant differences due to the

metal particle size and the surface area are similar, with a higher

decrease in the area of the sample with higher Ti content.

Fig. 3 displays the XP spectra for the Ir-supported catalysts.

Ti 3s peak appear just between the two spin-orbit (Ir 4f7/2 and Ir

4f5/2) levels of iridium. It is interesting to observe a significant

increase in the contribution of Ti 3s peaks respect to the Ir

components in the catalysts studied, this fact is indicative of a

surface enrichment in Ti, that can produce surface migration of

TiOx moities on the Ir surface.

3.2. Citral hydrogenation

Figs. 4 and 5 show the evolution of the conversion level with

time on stream for both studied series (LT and HT). It can be

seen that the reaction rate is higher during the first hour of

reaction, being lower the conversion levels displayed by the LT

series compared with the HT counterpart. Among them, the Ir/

SiO2 LT catalyst showed the lowest activity. The other LT

catalysts also show low activities, however Ir/TiO2 LTand Ir/G1

catalysts posses activities slightly higher.

With regard to the HT series the lowest activity is shown by

the Ir/SiO2 HT catalyst. The Ir/TiO2 catalyst displayed a lower

activity compared with those Ir supported on mixed oxides in

which an increases in the TiO2 loading lead to an enhancement

in the conversion level. This fact is attributed to the SMSI

effect, in which the Ir metal crystals me be decorated by

partially reduced TiOx species, producing electron deficient

iridium species (Ird+). These species are specially active to

polarize the carbonyl group favoring the conversion and

selectivity reaction toward the unsaturated alcohol [4].

Taking into account that the selectivity may be affected by

the conversion level, the results of initial activity and TOF at

10% of conversion are showed in Table 4. The LT series

displays lower activity and TOF values, with the exception of

the Ir/TiO2 catalyst. The HT series possess different behavior,

the initial catalytic activity and TOF is higher, which is

indicative of the creation of new different active sites at the

metal–support interface. The activity increases progressively as

TiO2 content increases, due to decoration with TiOx species

Fig. 3. Ir 4f core-level spectra for Ir/TiO2/SiO2 catalysts. (a) Ir/G1 HT; (b) Ir/G2 HT; (c) Ir/G3 HT; (d) Ir/G4 HT.

Fig. 4. Citral hydrogenation at 363 K and 6.2 bar. Conversion level as function

of time for Ir catalysts: (~)Ir/SiO2 LT; (^)Ir/TiO2 LT; (&) Ir/G1 LT; (~) Ir/G2

LT; (^) Ir/G3 LT; (&) Ir/G4 LT.

Fig. 5. Citral hydrogenation at 363 K and 6.2 bar. Conversion level as function

of time for Ir catalysts: (~) Ir/SiO2 HT; (^) Ir/TiO2 HT; (&) Ir/G1 HT; (~) Ir/

G2 HT; (^) Ir/G3 HT; (&) Ir/G4 HT.

H. Rojas et al. / Catalysis Today 133–135 (2008) 699–705 703

Table 4

Citral hydrogenation at 363 K and at H2 pressure of 6.2 bar over Ir catalysts

Catalysts Initial activity

(mmols�1 g�1)

Conversion

(%) (at 3 h)

TOF

(s�1)

Ir/SiO2 LT 0.031 7 0.003

Ir/SiO2 HT 0.021 5 0.005

Ir/G1 LT 0.365 17 0.018

Ir/G1 HT 0.463 21 0.344

Ir/G2 LT 0.141 10 0.018

Ir/G2 HT 0.772 27 0.347

Ir/G3 LT 0.119 10 0.009

Ir/G3 HT 0.820 34 0.184

Ir/G4 LT 0.074 8 0.004

Ir/G4 HT 4.437 47 0.540

Ir/TiO2 LT 0.344 17 0.074

Ir/TiO2 HT 0.463 19 0.298

Initial activity, conversion level at 3 h of reaction and TOF at 10% of conver-

sion.

Fig. 6. Hydrogenation of citral at 363 K and at 6.2 bar over Ir/G1 LT catalysts.

(a) Selectivity of the reaction as a function of conversion; (&) geraniol; (~)

nerol; (^) citronellal; (&) citronellol.

Table 5

Hydrogenation of citral at 363 K and 6.2 bar on Ir catalysts

Catalysts Selectivity (%)

Citronellal Citronellol Nerol Geraniol

Ir/SiO2 LT 16 16 30 38

Ir/SiO2 HT 24 29 38 9

Ir/G1 LT 1 4 30 65

Ir/G1 HT 5 5 27 63

Ir/G2 LT 6 5 24 65

Ir/G2 HT 2 5 26 67

Ir/G3 LT 3 4 25 68

Ir/G3 HT 4 5 28 63

Ir/G4 LT 12 7 18 63

Ir/G4 HT 0 7 33 60

Ir/TiO2 LT 5 4 24 67

Ir/TiO2 HT 9 0 21 70

Selectivity at 10% conversion.

H. Rojas et al. / Catalysis Today 133–135 (2008) 699–705704

over the metal that allow a higher conversion towards the allylic

alcohol. The H/Ir ratio and the TOF values account the

mentioned SMSI effect.

Fig. 6 shows the selectivity towards different reaction

products for representative catalysts, as a function of the

conversion level. It can be seen, that whatever be the studied

catalyst, up to conversion close to 50%, the selectivity to any

product does not change with the reaction time. The main

products were geraniol and nerol which corresponding to the

hydrogenation products of the carbonyl function, and in minor

extension, citronellal and citronellol. This is explained

considering the Ir/TiO2 and Ir/TiO2/SiO2 catalysts posses

active sites in which the metallic component exhibit a partial

decoration, with the creation of Ird+ species, which are more

active in the polarization of the C O bond. Additionally, the

reactivity of both isomers of citral is very similar, which can be

noted by the production of geraniol and nerol according to the

starting proportion. An exception appears for the Ir/SiO2

catalyst which displays higher selectivity towards citronellal

and citronellol. This behavior may be attributed to the fact that

the metallic component, iridium is completely reduced, as Ir0,

and in this oxidation state it displays lower ability to polarize

the C O bond. A summary of the selectivity levels towards the

different products is showed in Table 5.

4. Conclusions

The results show that the TiO2 loading and the reduction

treatment plays an important role on the catalytic behavior of Ir/

TiO2/SiO2 catalysts. The reduction temperature produces

significant differences in the activity, thus, at low reduction

temperature, the solids exhibit low activity without significant

differences in each series. The addition of increasing amount of

Ti to the SiO2 support increases the surface coverage making

easier the interaction with the metallic component which is

deposited on the mixed oxides by impregnation. Consequently,

an enhancement in the catalytic activity occurs as Ti content

increases in the catalysts reduced at high temperature. The

SMSI effect seems to be the main support of the observed

behavior. The characterization results, mainly those obtained

by hydrogen chemisorption, XPS, XRD and FT-IR support the

given explanation which attributed to the presence of Ird+

species by the ability to polarize the carbonyl bond of the citral

molecule to produce mainly geraniol and nerol as hydrogena-

tion products.

Acknowledgement

The authors would like to thank UPTC-COLCIENCIAS for

financially supporting this research under contract No.

110951717865.

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