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Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

Evaluation of the Isomerization of α-Pinene Epoxide to

Campholenic Aldehyde Using a Catalyst Obtained from

Orange Peels (Citrus sinensis)

Marta Mediavilla-Quintero1,2 , Aída Luz Villa2*

1Facultad de Ingeniería, Universidad Central de Venezuela, UCV, P.O. Box 48.057,

Caracas 1041-A, Venezuela

2 Grupo de Investigación de Catálisis Ambiental, Departamento de Ingeniería

Química, Facultad de Ingeniería, Universidad de Antioquia UdeA, Calle 70 No.52-

21, Medellín, Colombia

*Corresponding author: aida.villa@udea.edu.co

https://doi.org/10.22209/rt.v46a03

Received: August 10, 2022 | Accepted: March 21, 2023 | Available: April 15, 2023

Abstract

Orange peels (Citrus sinensis) are an abundant lignocellulosic residue that can be used as a carbon source to

obtain solids with catalytic potential in the transformation of terpenes and their oxides into value-added products.

This research seeks to evaluate the isomerization of α-pinene epoxide to campholenic aldehyde using a catalyst

obtained from orange peels. The material OAC-Zn was obtained by activation of orange peel with ZnSO4.7H2O

followed by thermal treatment at 500 °C; an additional solid was obtained from orange peel by pyrolysis at 500 °C

(OC-500). XRD revealed the presence of ZnO and ZnS in OAC-Zn; TGA analysis indicated thermal stability in

OAC-Zn and OC-500 materials; SEM images showed porous surfaces of different morphology, and the presence of

microporosity in OC-500 and mesoporosity in the OAC-Zn that was confirmed by physical nitrogen adsorption. The

elements C, O, Zn and S were identified in OAC-Zn by EDX analysis. The results of TPD-NH3 showed that the

solids contained medium and weak acidity. Campholenic aldehyde was synthesized with a 96 % selectivity over the

material OAC-Zn.

Keywords: carbon; mesoporous; terpenes; waste; XRD.

Evaluación de la Isomerización de Epóxido de α-Pineno a

Aldehído Canfolénico Utilizando un Catalizador Obtenido de

Cáscaras de Naranja (Citrus sinensis)

Resumen

Las cáscaras de naranja (Citrus sinensis) son residuos lignocelulósicos abundantes que pueden ser utilizados

como fuente de carbono para obtener sólidos con potencial catalítico en la transformación de terpenos y sus óxidos

en productos de valor agregado. Esta investigación buscó evaluar la isomerización de óxido de α-pineno a aldehído

canfolénico, utilizando un catalizador obtenido de cáscaras de naranja. El material OAC-Zn se obtuvo por activación

de las cáscaras con ZnSO4.7H2O, seguido de tratamiento térmico a 500 °C; también se obtuvo un sólido de la

pirólisis de la cáscara a 500 °C (OC-500). Mediante DRX se identificó la presencia de ZnO y ZnS en OAC-Zn; los

análisis por TGA indicaron estabilidad térmica en OAC-Zn y OC-500; las imágenes SEM mostraron superficies

Evaluation of the Isomerization of α-Pinene Epoxide to Campholenic Aldehyde 2

Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

porosas de diferente morfología, así como la presencia de microporosidad en OC-500 y de mesoporosidad en OAC-

Zn, que fueron confirmadas mediante adsorción física de nitrógeno. En los análisis EDX se identificaron los

elementos C, O, Zn y S en OAC-Zn; los resultados de TPD-NH3 mostraron que los sólidos contenían acidez media y

débil. Se sintetizó aldehído canfolénico con selectividad de 96 % con el material OAC-Zn.

Palabras clave: carbón; DRX; mesoporos; residuo; terpenos.

Avaliação da Isomerização de α-Pineno Epóxido a Aldeído

Campolênico Usando um Catalisador Obtido de Cascas de

Laranja (Citrus sinensis)

Resumo

Cascas de Laranja (Citrus sinensis) são abundantes resíduos lignocelulósicos que podem ser utilizados como

fonte de carbono para obtenção de sólidos com potencial catalítico na transformação de terpenos e seus óxidos em

produtos de valor agregado. Esta pesquisa buscou avaliar a isomerização do óxido de α-pineno a aldeído canfolénico,

utilizando um catalisador obtido a partir de cascas de laranja. O material OAC-Zn foi obtido pela ativação das cascas

com ZnSO4.7H2O, seguida de tratamento térmico a 500 °C; um sólido também foi obtido a partir da pirólise da casca

a 500 °C (OC-500). Através do DRX foi identificada a presença de ZnO e ZnS no OAC-Zn; As análises de TGA

indicaram estabilidade térmica em OAC-Zn e OC-500; As imagens de SEM mostraram superfícies porosas de

morfologia diferente, bem como a presença de microporosidade em OC-500 e mesoporosidade em OAC-Zn, que

foram confirmadas por adsorção física de nitrogênio. Nas análises de EDX, os elementos C, O, Zn e S foram

identificados em OAC-Zn; os resultados do TPD-NH3 mostraram que os sólidos continham acidez média e fraca.

Aldeído canfolénico foi sintetizado com uma seletividade de 96 % com o material OAC-Zn.

Palabras clave: carvão; DRX; mesoporos; resíduo; terpenos.

Introduction

Orange peel is considered one of the largest volume lignocellulosic residues worldwide, whose chemical

constitution makes it a material with great potential for recovery (Tovar et al., 2019; Battista et al., 2020).

Agroindustrial residues have the advantages of being abundant in nature, and their use could be adjusted to the

principles of green chemistry (Castro et al., 2011). Activated carbon is a material with appreciable surface area, well-

developed porosity, and high degree of surface reactivity that can be produced from bituminous coal (Hsu et al.,

2000), petroleum coke (Kawano et al., 2008), lignite (Navarro et al., 2006) and lignocellulosic residues (Hassan et

al., 2019). Due to its low cost, low toxicity, and high abundance, activated carbon produced from lignocellulosic

waste is considered as a green alternative that plays an important role in solving the problem of waste disposal and

environmental protection (Battista et al., 2021).

Pandiarajan et al. (2018) reported the preparation of activated carbon from shell of orange by chemical

activation with KOH and subsequent pyrolysis in a nitrogen atmosphere at 700 °C for 2 h. The solid exhibited a

specific surface area (BET) of 592.5 m2/g, while the diameter and pore volume were 1.301 nm and 0.242 ml/g,

respectively. Bediako et al. (2020) reported the synthesis of activated carbon from orange peel and the effect of

activation by KOH, ZnCl2 and pyrolized at 800 °C; it was found that the ZnCl2-AC exhibited a higher degree of

micro-porosity and BET surface area than the KOH-AC with values of 1439.50 and 1370.76 m2/g, respectively. Pan

et al. (2021) reported the first study of prepared sulfonated carbon derived from orange peel in the esterification of

oleic acid with methanol and of citric acid with n-butanol; it was reported that the time has a great influence on the

BET surface area of materials. When the sulfonation time increases from 10 min to 4 h, the BET surface area

decreases from 6.16 to 1.84 m2/g and the pore diameter increases from 22.02 to 44.66 nm. When the sulfonation time

was 2 h, the maximum conversion of oleic acid (92.8 %) and citric acid (81.3 %) was obtained. Wang et al. (2016)

reported the synthesis of porous carbon nanosheets (PCNs) using Zn5(OH)8(NO3)2.2H2O as a source of zinc and

template and gallic acid as carbon precursor. The obtained nanosheets porous carbon with large surface area (1138

m2/g) and surface groups that make it an ideal candidate for energy storage applications. Xi et al. (2021) reported

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Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

three-dimensional porous carbon with abundant mesopores by activating lignin from the corn stalks bio-refinery

residue with ZnCO3, and the resulting carbon had excellent lithium storage performance. Rezaee et al. (2008) used

activated carbon prepared from almond shell impregnated with ZnSO4 in nitrate removal. Santosh et al. (2021)

reported the synthesis of an ecological nanoadsorbent activated with zinc chloride from food residues for the removal

of contaminants from biodiesel wash water; the samples were calcined at 350 °C for 3 h and then activated with zinc

chloride for 2 h at 500-600 °C. The synthesis of heterostructured ZnS-ZnO/graphene nano-photocatalysts has been

reported (Lonkar et al., 2018), from a solid-state mixture of graphite oxide (GO), Zn salt and elemental sulfur by ball

milling followed by heat treatment; obtaining hybrids formed by ZnS-ZnO nanoparticles uniformly distributed

within the thermally reduced GO (graphene) matrix.

Isomerization of α-pinene epoxide is an important transformation for obtaining compounds of interest in

fragrances and compounds with biological activity (Vrbková et al., 2020). There are several reports related to the

isomerization of α-pinene oxide using heterogeneous catalytic systems (Stekrova et al., 2014; Sánchez et al., 2019;

Singh et al., 2022). The highest selectivity towards campholenic aldehyde (96 %) at total conversion (100 %) was

obtained over Ti-MCM-22 at 70 °C using toluene as solvent (Stekrova et al., 2018). There are very few reports in the

literature that show α-pinene oxide isomerization over carbon type catalysts. Singh et al. (2020) reported the use of

carbon spheres from sucrose functionalized with phosphonate groups, for the isomerization of α-pinene oxide; this

solid showed 100 % conversion with 22 % selectivity towards campholenic aldehyde (1 h, 160 °C) in the presence of

N,N-dimethylformamide. Advani et al. (2019) reported that a bio-derived sulfonated carbon catalyst showed

excellent performance for the isomerization of α-pinene.

The objective of this work was to evaluate the isomerization of α-pinene epoxide to campholenic aldehyde

using a catalyst obtained from orange peels (Citrus sinensis). ZnO-ZnS-C material was obtained by activation of

orange peel with ZnSO4.7H2O followed by thermal treatment at 500 °C; furthermore, another solid was synthesized

by thermal treatment of orange peel without using activating agent. The obtained materials were characterized

through thermogravimetric analysis (TGA), differential termogravimetric analysis (DTG), X-ray diffraction (XRD),

physical adsorption of nitrogen, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-

EDX), temperature-programmed desorption of ammonia (TPD-NH3). The materials were used for α-pinene oxide

isomerization

Materials and Methods

Preparation of the solid ZnO-ZnS-C

The ZnO-ZnS-C material was prepared by a modification of the procedure reported by Wang et al. (2019).

The orange (Citrus sinensis) peels were washed with water and dried with absorbent paper. Subsequently, they were

dried at 80 °C for 24 h and pulverized. After microwave pretreatment, the fine powder obtained was mixed with 20

ml of water and subjected to microwave heating (Mars 5, CEM) from room temperature to 50 °C, keeping the

temperature constant for 3 min. Once the orange peel residue was separated from the aqueous phase, it was treated

with a solution of ZnSO4.7H2O (1.4 M) in a weight ratio of activator/peel of 2:1, and the system was kept under

stirring at 600 rpm at room temperature for 24 h. For comparison, a carbon was prepared from orange peels only

with heat treatment at 500 °C for 1 h in a nitrogen atmosphere at 100 ml/min. The samples obtained were labeled as

OAC-Zn (orange peel activated with ZnSO4.7H2O), OC-500 (orange peel without activation).

Characterization

The proximal analysis of the materials was carried out using a thermogravimetric analyzer (SDT-Q600, TA

Instruments). The XRD patterns of the samples were recorded using an X-ray diffractometer (Philips, X'pert) with

Cu-Kα radiation (λ= 0.1542 nm), in a diffraction angle range of 2 θ from 10 to 80 ° in steps of 0.02 °/sec. Surface

and textural properties of activated carbon were determined from adsorption-desorption isotherms using nitrogen as

adsorbate (ASAP 2020 PLUS, Micromeritics). Scanning electron microscopy (JEOL JSM 6490 LV) was used to

investigate the morphology of activated carbon; the elemental composition was identified by EDX (INCA

PentaFETx3 Oxford Instruments). Samples were fixed on graphite ribbon, plated with gold, and analyzed in a high-

vacuum scanning electron microscope operating at 20 kV. TPD-NH3 analysis (AutoChem II 2920, Micromeritics)

was carried out up to 600 °C by pretreating the samples at 400 °C for 50 min with He (80 ml/min).

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Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

α-pinene oxide isomerization

The catalytic tests were performed according to the methodology reported by Sanchez et al. (2019) using

activated carbons from orange peel with a particle size of 90 µm. Catalysts were mixed with 1 ml of a solution of

0.25 mmol of α-pinene oxide in ethyl acetate. The reaction mixture was heated using a hot plate (Radley tech) at

temperatures of 60 °C for 3 h and at 750 rpm. At the end of the reaction, the mixture was centrifuged and a sample

was analyzed by Agilent 7890 gas chromatography with FID detector and DB-1 column (30 m × 320 μm × 0.5 μm).

The products were confirmed by CG-MS.

Results and Discussion

Characterization

The TGA analysis of the OAC-Zn and OC-500 solids are presented in Figures 1a and 1b. The moisture

contents of OAC-Zn and OC-500 are 7.8 and 3.0 % w/w, respectively. The volatile matter and ash content increased

with the use of the activating agent with values of 16.6 % w/w for the solid without activating agent up to 26.3 %

w/w for the solid with activating agent. The fixed carbon content decreased from 70.0 to 26.5 % w/w for the solid

OC-500 and OAC-Zn, respectively; this shows that ZnSO4.7H2O significantly inhibited the release of volatiles,

which was consistent with studies reported by Andas et al. (2018). In N2 atmosphere, the initial weight loss occurs

between 31 and 120 °C that could be attributed to water loss and the second stage at 120-800 °C may be associated

with the decomposition reactions of the organic compounds that have remained after the pyrolysis of the orange peel

at 500 °C.

Figure 1. Thermogravimetric analysis (TGA) curves and differential termogravimetric analysis (DTG) curves of (a)

OAC-Zn (orange peel activated with ZnSO4.7H2O) and (b) OC-500 (orange peel without activating agent).

The differences found between Figures 1a and 1b seem to indicate that the presence of ZnSO4.7H2O has a

significant effect on the thermal behavior of orange peel. The curves showed the loss of water up to 140 °C, between

143-800 °C there was a stage of significant weight loss, showing that the material still contained thermolabile and

abundant substances. These results suggest that the addition of ZnSO4.7H2O significantly inhibited the release of

volatiles (Andas et al., 2018). From the DTG, four peaks are observed; the first peak (84-115 °C) is attributed to

moisture evaporation and the other three peaks (212-287, 369-385 and 565-587 °C) are related to mass loss, which

according to Ozdemir et al. (2014) would be associated with the decomposition of hemicellulose, cellulose, and

lignin.

The crystal structures of the ZnO-ZnS-C compounds were studied by XRD (Figure 2). Figures 2a and 2b

show the diffraction patterns corresponding to OAC-Zn and OC-500, respectively. For solid OAC-Zn, signals are

observed at approximately 2 θ= 32, 34, 37, 47, 57, 63, 67, 68, 69 ° (PDF 98-006-7848), which may be attributed to

ZnO in the carbon structure (Pelech et al., 2021). In addition, low intensity signals are observed in the diffraction

pattern at 2 θ= 28.5, 47.5, 56.3 ° that correspond to the diffraction peaks (220) and (311) of ZnS, respectively

(Ghaedi et al., 2012). This result indicates that during the thermal treatment the solid ZnSO4.7H2O impregnated in

orange peel is transformed into ZnO-ZnS. The presence of ZnO was reported in the synthesis of an ecological

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Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

nanoadsorbent activated with zinc chloride from food residues (Santosh et al., 2021). The diffraction pattern of the

solid OC-500 shows a broad peak corresponding to the diffraction of the C (002) plane at an angle of 2 θ from 10 to

30 °, which is attributed to sheets of randomly oriented non-graphitic carbon, while the weak diffraction peak from

35 to 50 ° is due to the C (100) of crystalline graphite (Wei et al., 2019). The absence of sharp peaks in the

diffraction pattern indicates the amorphous structure of activated carbons and suggests a limited degree of

graphitization (Li et al., 2016).

Figure 2. X-ray diffraction (XRD) patterns of: (a) OAC-Zn (orange peel activated with ZnSO4.7H2O) and (b) OC-

500 (orange peel without activating agent).

Nitrogen adsorption-desorption isotherms at 77 K were used to investigate the porosity, total pore volume,

mean pore diameter, and surface area of OAC-Zn and OC-500. Figure 3a shows the nitrogen adsorption-desorption

isotherms at 77 K for OAC-Zn and OC-500. It is clear that the shape of the isotherms changes gradually with the

activating agent. The gradual increase in nitrogen adsorption and the larger adsorbed volume (higher horizontal

plateau) suggests that additional pores were created and small pores were widened. Furthermore, the increase in

nitrogen adsorption is maintained over the entire pressure range, so that the isotherms take a shape resembling a

combination of type I and IV with a hysteresis loop suggesting a mixed microporous and mesoporous structure. The

pore size distribution curves of OAC-Zn and OC-500 are shown in Figure 3b, confirming the mesoporosity in the

material than contains Zn (Poleo et al., 2016). It was observed that the activating agent influenced the porosity of the

resulting activated carbon not only creates more new pores, but also widens the pores, thus both contributions cause

the development of mesoporosity. It can be seen in Figure 3a that sample OC-500 shows the type I adsorption

isotherm, characteristic of microporous materials. The pore size distribution shown in Figure 3b confirms the

presence of micropores with size of approximately 1 nm, with the presence of some narrow mesopores (~2.5 nm).

Table 1 presents the porosity parameters of the carbon samples. It is evident that the BET surface area

(SBET) increases with the addition of ZnSO4.7H2O from 26 to 157 m2/g for OC-500 and OAC-Zn, respectively; a

similar comparison applies is in the case of the pore volume. It is important to point out that the pore size distribution

of the samples prepared in this study is very narrow and also the value of the mean pore diameter exceeds the

reported values for carbons obtained from biomass (Fernández et al., 2014; Ajay et al., 2021), which are between 2

and 5 nm.

Table 1. Physicochemical properties of OAC-Zn and OC-500.

Sample

SBET (m2/g)

Pore volume (cm3/g)

Pore diameter (nm)

OAC-Zn

157

0.180

OC-500

0.018

OAC-Zn: orange peel activated with ZnSO4.7H2O, OC-500: orange peel without activating agent,

SBET: BET surface area.

Differences in the morphology of the synthesized activated carbons were identified by SEM analysis, Figure

4. The OAC-Zn material (Figure 4a) presents a smoother morphology with a more uniform distribution of pores.

Sample without activating agent (Figure 4b) shows the rough and irregular surface constituted by intercalated thin

plates or sheets. This could be explained considering that the thermal treatment favored the expulsion of volatile

Evaluation of the Isomerization of α-Pinene Epoxide to Campholenic Aldehyde 6

Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

matter during the carbonization stage. The release of these elements from the carbonized surface could result in the

formation of a rigid carbon skeleton (Pathak et al., 2017). The analysis of the constituent elements was performed by

EDX. The spectrum of the OAC-Zn solid (Figure 4a) is mainly formed by Zn (73.7 % w/w), O and C; S and Ca are

in lower amount. For the material OC-500 (Figure 4b), C and O are in larger amount that Mg, K and Ca.

Furthermore, mapping of Zn and S in the OAC-Zn sample (Figure 4a) showed a uniform distribution of carbon-

supported ZnO-ZnS species. The results of the EDX analysis agree with the diffraction patterns, indicating the

formation of ZnO-ZnS and carbon.

Figure 3. (a) Nitrogen adsorption-desorption isotherms and (b) pore size distribution of: OAC-Zn (orange peel

activated with ZnSO4.7H2O) and OC-500 (orange peel without activating agent).

The acid properties in terms of density and strength of sites were studied by TPD-NH3. Figures 5a and 5b

show the ammonia thermograms for the obtained carbon materials. It was observed that the carbon obtained from

orange peel activated with ZnSO4.7H2O exhibits acidity in the temperature range between 100 and 450 °C, which

would correspond to physisorbed NH3 low and medium strength acid sites. The signal that appears with a maximum

at a temperature of 550 °C can be attributed to carbon decomposition in correspondence with the TGA results.

The solid OC-500 coming from only the thermal treatment shows three low intensity signals, the first with a

maximum at 180 °C that can be assigned to physisorbed ammonia or low strength acid sites; the second signal with

maxima at 410 °C can be assigned to medium strength acid sites and the third at 550 °C could correspond to carbon

decomposition products. From this result is possible to infer that both solids have acid sites with the necessary

strength to catalyze the isomerization of α-pinene oxide (Barakov et al., 2022).

α-pinene oxide isomerization

From isomerization of α-pinene oxide the observed products were: campholenic aldehyde (CA) carveol (C)

and cymene (Cy), Table 2. The results show that the highest conversion was obtained over the carbon from the

orange peel activated with ZnSO4.7H2O. This result is not surprising due to the presence of mesopores and a larger

surface area of this solid, which offers greater accessibility and facilitates the diffusion of the molecules through the

internal surface to the available active centers of the catalyst where the substrate transformation reactions would take

place; furthermore, the presence of Zn favors the presence of Lewis acid sites that are required for α-pinene

isomerization into campholenic aldehyde. For the OAC-Zn catalyst, an increase in the conversion is observed from

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loadings of 25 to 90 mg at 24 h with conversion increase from 41 to 79 %. While a decrease was observed in the

selectivity towards campholenic aldehyde from 96 to 56 % and an increase in the selectivity towards carveol from 0

to 41 %.

Figure 4. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis and

elemental mapping of: (a) OAC-Zn (orange peel activated with ZnSO4.7H2O) and (b) OC-500 (orange peel without

activating agent).

Evaluation of the Isomerization of α-Pinene Epoxide to Campholenic Aldehyde 8

Rev. Téc. Ing. Univ. Zulia, 2023, Vol. 46, e234603

Figure 5. Temperature-programmed desorption of ammonia (TPD-NH3) of OAC-Zn (orange peel activated with

ZnSO4.7H2O) and OC-500 (orange peel without activating agent).

Table 2. Conversion and selectivity over synthesized solids from orange peel.

Catalyst

(mg)

Time

(h)

Conversion (%)

Selectivity

(%)

OAC-Zn (50)

OAC-Zn (25)

OAC-Zn (50)

OAC-Zn (75)

OAC-Zn (90)

OC-500 (75)

Reaction conditions: 60 °C, 750 rpm, 0.25 mmol α-pinene oxide; CA: campholenic aldehyde; C: carveol; Cy:

cymene; OAC-Zn: orange peel activated with ZnSO4.7H2O; OC-500: orange peel without activating agent.

Apparently, an increase in the number of active sites favors the reactions that lead to the formation of

carveol. These results are different from those reported in the literature by Advani et al. (2020) and Singh et al.

(2020) for carbon catalysts where carveol selectivity predominates. For a constant OAC-Zn loading, the conversion

increased with an increase in reaction time and it reached 61 % at 24 h. However, the selectivity towards

campholenic aldehyde decreased from 97 to 77 % while the selectivity towards carveol increases. A longer contact

time between α-pinene oxide molecules and the active center of the catalyst favors the formation of other reaction

products from campholenic aldehyde or carveol. The effect of reaction time (1-5 h) was studied by Sighn et al.

(2022) for α-pinene oxide isomerization over zirconium phosphate catalysts, reporting an increase of conversion

from 43 to 100 % and selectivity to trans-carveol from 69 to 73 %; with a selectivity towards campholenic aldehyde

of around 20 %.

Figure 6 shows the proposed reaction pathway for the formation of campholenic aldehyde and carveol from

the isomerization reaction of α-pinene oxide over the tested catalyst. The initial formation of a very stable tertiary

carbocation is proposed through the coordination of the substrate with the Lewis sites of the solid (Zn); subsequently,

the carbocation rearranges generating campholenic aldehyde and carveol (Pitínová-Štekrová et al., 2018).

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Figure 6. Proposed reaction pathway of product formation in the isomerization of α-pinene oxide.

Conclusions

Campholenic aldehyde was synthesized over a carbonaceous material obtained from orange peels using

ZnSO4.7H2O as activating agent. The solid obtained without using activating agent that showed microporosity was

not active for campholenic aldehyde synthesis; while the OAC-Zn material that presented mesoporosity, acidity and

zinc species showed a good α-pinene epoxide conversion and high selectivity to campholenic aldehyde.

Acknowledgements

The authors acknowledge the financial support from Universidad de Antioquia (UdeA). M.M-Q.

acknowledges to the International Institute of Education (IIE-SRF) and the ―Fondo de apoyo a la

internacionalización de la investigación-CODI (UdeA)‖.

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Editor Asociado: Roger José Solano

Instituto de Superficies y Catálisis ―Prof. Eduardo Choren‖, Facultad de Ingeniería,

Universidad del Zulia, Maracaibo, Venezuela

Departamento de Ingeniería Química, Grupo Catalizadores y Adsorbentes,

Universidad de Antioquia - UdeA, Calle 70 No. 52-21. Medellín, Colombia

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