Selective continuous flow phenylacetylene hydrogenation over Pd-biogenic calcium carbonate

Article abstract of DOI:10.1016/j.cattod.2020.03.057

CaCO₃ obtained from Sporosarcina pasteurii isolated from agricultural soils has been employed as catalytic support for Pd that was subsequently loaded on CaCO₃ by wet impregnation with a metal loading of 0.5 wt.% using Palladium acet

Full text of DOI:10.1016/j.cattod.2020.03.057

Journal Pre-proof
Selective continuous flow phenylacetylene hydrogenation over
Pd-biogenic calcium carbonate
´
Sandra Chaparro, Jose J. Martinez, Hugo A. Rojas, Antonio Pineda,
Rafael Luque
PII:
S0920-5861(20)30179-6
DOI:
https://doi.org/10.1016/j.cattod.2020.03.057
CATTOD 12770
Reference:
To appear in:
Catalysis Today
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Revised Date:
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4 December 2019
25 February 2020
27 March 2020
Please cite this article as: Chaparro S, Martinez JJ, Rojas HA, Pineda A, Luque R, Selective
continuous flow phenylacetylene hydrogenation over Pd-biogenic calcium carbonate,
Catalysis Today (2020), doi: https://doi.org/10.1016/j.cattod.2020.03.057
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Selective continuous flow phenylacetylene hydrogenation over
Pd-biogenic calcium carbonate
Sandra Chaparro 1, José J. Martinez1*, Hugo A. Rojas1, Antonio Pineda2, Rafael Luque2,3*
1Escuela de Ciencias Químicas. Universidad Pedagógica y Tecnológica de Colombia.
150003. Colombia.
2
Grupo FQM-383, Departamento de Química Orgánica, Universidad de Córdoba, 14014.
Córdoba, Spain.
3
Scientific Center for Molecular Design and Synthesis of Innovative Compounds for the
Medical Industry, People’s Friendship University of Russia (RUDN University), 6 Miklukho
Maklaya str., 117198, Moscow, Russia
*Correspondingauthor:
Rafael Luque: E-mail address: q62alsor@uco.es
José J. Martinez: E-mail address: jose.martinez@uptc.edu.co
Graphical Abstract
1

Highlights
 Biogenic CaCO3 was obtained from Sporosarcina pasteurii isolated from agricultural
soils.
 CaCO3 impregnated with Pd 0.5% was an effective catalyst in the continuous
phenylacetylene hydrogenation.
 Under optimized conditions, 30°C, flow rate 1mL/min and 10 bar pressure, a styrene
yield of 65% was reached.
 Pd0.5/CaCO3 was stable along twelve hours on stream with any decrease in the
catalytic performance.
Abstract
CaCO3 obtained from Sporosarcina pasteurii isolated from agricultural soils has been
employed as catalytic support for Pd that was subsequently loaded on CaCO3 by wet
impregnation with a metal loading of 0.5 wt.% using Palladium acetate as precursor. The

materials were characterized via nitrogen physisorption measurements, X-ray diffraction,
X-ray photoelectronic spectroscopy, TGA Analysis and TEM microscopy. Pd0.5/CaCO3 was
able to successfully hydrogenate phenylacetylene into styrene and ethylbenzene as
products. Thus, through the proper optimization of the reaction conditions (flow rate,
temperature, pressure) it was possible lead the reaction towards the selective production of
styrene, a monomer widely used in the polymer industry, from phenylacetylene as starting
material in yields up to 65 %.
Keywords: Biomaterials, continuous flow, hydrogenation reactions, Sporosarcina pasteurii,
Styrene.
1. Introduction
The hydrogenation of carbon-carbon multiple bonds has been widely used in industrial and
chemical processes for the production of high added-value chemicals. In this sense, the
selective hydrogenation of alkynes to alkenes minimising alkanes production has been
widely investigated due to its importance for both agrochemical and petrochemical industry
[1,2]. In particular, styrene (ST) is a relevant monomer for the production of polystyrene and
other synthetic rubbers such as Acrylonitrile Butadiene Styrene (ABS) resin, commonly
used in 3-D printers, and styrene-butadiene that owns good abrasion resistance [3,4].
Industrially, styrene can be obtained by ethylbenzene oxidative dehydrogenation as well as
by extractive processes in the gasoline pyrolysis (pygas, byproduct of naphtha cracking
process) [5]. In the recent years, research efforts has been focused on this area due to the
high styrene production from pygas, since a plant with an annual production capacity of 1
million tons of ethylene can produce about 24-42 kilo tons of ST per year [5]. However, raw
material contains small amounts of phenylacetylene (PA) that causes problems in process

control and increases production costs. Such difficulties root in the difficult separation of PA
from ST because of their similar chemical properties. Therefore, the most effective way to
separate them is to carry out a PA selective hydrogenation, process that converts
completely PA into styrene avoiding ethylbenzene production (Scheme 1) [6].
Scheme 1. Illustrative representation of the hydrogenation of phenylacetylene towards the
different products, styrene and ethylbenzene.
For this reductive approach palladium based heterogeneous catalysts are quite efficient due
to their high dissociation energy for molecular hydrogen [7,8]. With this respect, Lindlar
catalyst is the most used in this reaction and it is formed by palladium supported in calcium
carbonate doped with lead, which improves the selectivity by catalyst poisoning due to the
deactivation of some palladium active sites. However, the high toxicity related to lead limits
Lindlar catalyst use [9] boosting the research towards different alternatives. For this reason,
different supports and catalysts for selective phenylacetylene hydrogenation have been
reported. For instance, Akhmedov et al. [4] investigated the use of metal-free graphite-like
carbon nitrides in the selective PA hydrogenation to ST in gas phase, obtaining conversion
values up to 85.5% with a styrene selectivity of 76.4% at 250°C and 2 bar of H2 pressure.
However, the main limitation of such approach was the high temperature required, which
lead to increased production costs. Another interesting option for PA hydrogenation was the

use of titanium oxide as support loaded with Pd by photodeposition, obtaining a conversion
and selectivity of 85 and 100%, respectively [7]. In addition, the use of mesoporous
materials as support has been studied by Yang et al. [6], who studied PA hydrogenation
reaction with several mono- and bimetallic catalysts such as Ni and Ni-M (M = Zn, Ga, Cu,
or Fe) over SBA-15 aluminosilicates in a semi-batch reactor at 40°C and 1 bar H2 pressure.
Among them, the results showed that best performance was obtained through the use of
NiZn3/AlSBA-15 catalyst with a high selectivity towards the production of styrene (90.3%)
and a phenylacetylene conversion of 99.6%, after 16 hours of reaction. In addition, alumina
was investigated by Hu et al. [10] that carried out PA hydrogenation reaction using a Pd
loading of 0.5 wt.% on the catalyst in a batch reactor at 50°C and 1 bar of H2; showing a
conversion of 98% and 70% of selectivity towards the production of styrene. The effect of
Pd particle size was investigated by Markov et al. [11] in a Pd/Al2O3 catalysts (with Pd
loading of 1 wt.%), varying particle size from 1.5 to 22 nm, with 5 bar H2 pressure and room
temperature (25°C), leading to PA conversion values that ranged from 25 to 100% and
selectivity between 83 and 97%. Also, bifunctional Zn-Ti layered-double hydroxides
modified with PdAu alloy was used as catalyst in the PA hydrogenation reaction, achieving
high styrene selectivity (over 90%) and quantitative phenylacetylene conversion after 6
hours at 45 ºC using molecular hydrogen that was continuously circulated with a 10 mL/min
flow [12].
In the context of Green Chemistry, we developed a novel biogenic carbonate to be
used as support using a methodology eco-compatible that avoids thermal treatments
to obtain supports. The methodology is very simple and involves the microbial
induced carbonate precipitation (MICP) which commonly has been employed to

adsorb metals [13-16]. MICP employs a bacterium that secretes metabolic products
-2
-2
(CO3 ) that react with ions (Ca2+). The formation of CO3 occurs via enzymatic
through urea hydrolysis. To remove all organic matter is employed alcoholic solvents
with NaClO. Thus, it is possible to produce large homogenous quantities of CaCO3
with a strict morphology control. However, the use of biogenic calcium carbonate
impregnated with metals as catalyst remains unexplored. In this sense, from a
practical point of view, biogenic CaCO3 application is attractive in industrial reactions
due to advantages such as simple separation, high chemical and thermal stability.
CaCO3 is used as support in the Lindlar catalyst with 1%w/w of Pd, however, lead
content is this catalyst makes it toxic, while biogenic calcium carbonate can be an
adequate support in PA reaction with high conversion and selectivity. Thus, in this
work we report the preparation Pd by wet impregnation supported on biogenic
CaCO3. The synthesized material was investigated in the continuous flow
hydrogenation of phenylacetylene to styrene. Interestingly, the proper tune of the
reaction conditions (flow rate, temperature and hydrogen pressure) helps to improve
the reaction control, leading to improved selectivity towards the desired reaction
product, styrene in this case.
2. Experimental
2.1 Materials
Palladium (II) acetate (99.8%), phenylacetylene (PA) (98%) and toluene were purchased
from Sigma Aldrich (Berlin, Deutschland). They are analytical grade and used without any
further purification.

2.2 Catalyst preparation
Biogenic calcium carbonate was produced by Sporosarcina pasteurii was isolated from
agricultural soils from Boyacá (Colombia) according to protocol previously established by
Al-Thawadi and co-workers [17]. The strain was molecularly identified by amplification of the
16 S ribosomal gene (Fig. A.1). Bacteria growth in nutrient broth with urea (1M) at 30°C,
200 rpm during 24 h. After fermentation, CaCl2 1M was added in media and it was mixing
during 5 hours to CaCO3 crystal formation. After an hour settling, calcium carbonate was
recovered by centrifugation (6000 rpm during 15 min) and washed three times with distilled
water. Subsequently, the sample was treated for 12 hours with sodium hypochlorite (30 mL)
to reduce organic fraction. Finally, CaCO3 was mixed with ethanol to remove hydrophobic
particles in the sample and the final biogenic calcium carbonate was obtained by drying at
80°C along 24 hours.
Supported Pd catalyst was prepared by the wet impregnation method using biogenic CaCO3
synthesized in the preceding step as the support and palladium (II) acetate (C4H6O4Pd) as
metal precursor. In a typical preparation, the required amount of palladium (II) acetate was
adjusted to yield catalysts containing 0.5 wt.% Pd loading, was dissolved in acetone after
complete dissolution. Subsequently, CaCO3 was added and impregnation carried on under
vigorous stirring at room temperature. Then, the solid obtained was reduced with sodium
borohydride solution for 2 h. Finally, solvent was removed using a rotary-evaporator and the
material was named as Pd0.5/CaCO3.
2.3 Catalyst characterization

The textural properties of biogenic calcium carbonate containing Pd as well as the
respective support were obtained by N2 adsorption-desorption measurements at 77K by
means of a Micromeritic ASAP 2000 instrument (Micromeritics Instrument Corporation,
Norcross, GA, USA). Before the analysis, the samples were outgassed at 623 K for 6 hours
with a vacuum of 10-3 mmHg. Brunauer-Emmett-Teller (BET) method was used to evaluate
the specific surface area of sample. Pore size distribution as well as pore volume were
obtained by Barret-Joyner-Halenda (BJH) model in the adsorption branch.
CaCO3 crystalline phases were determined using the X-ray diffraction (XRD) using a Bruker
D8 DISCOVER A25 instrument (40 kV, 40 mA; Bruker AXS, Karlsruhe, Germany)
employing the Cu_Kα radiation (λ = 1.5418 Å). The diffractograms were acquire using a
speed of 1°/min was used in a 2θ range between 10 to 80°. This equipment is provided with
the “Diffract.Suite EVA” software (Bruker AXS, Karlsruhe, Germany) that easily permits
particle size determination and crystal phase assignment.
Thermogravimetric analysis was performed using a Setaram thermobalance using a heating
rate of 10 °C/min under an atmosphere of air flowing at 30 cm3/min, from 20°C to 1000°C.
TEM micrographs of the solids herein synthesized were acquired using a JEOL JEM 1400
High Resolution Transmission Electron Microscope at the Central Service for Research
Support (SCAI) of the University of Córdoba. Prior to the images acquisition, the samples
were suspended in ethanol and deposited on a copper grid.
X-ray photoelectronic spectroscopy (XPS) measurements were carried out using an
ultrahigh vacuum multipurpose surface analysis instrument, SpecsTM system with a

Phoibos 150-MCD energy detector at SCAI facilities. XPS CASA software was employed to
study the obtained spectra. The binding energies (BE) were referenced by setting the
adventitious carbon C1s to 285 eV, as has been reported for carbonate samples [18].
2.4 Catalytic tests
The catalytic activity of as-synthesized Pd0.5%/CaCO3 was investigated in continuous
phenylacetylene hydrogenation using a X-cube Thalesnano Inc. reactor fitted with pressure
regulator. The catalyst (around 0.08 g) was located in a 30 mm metal cartridge, sealed and
attached to the reactor. A 0.1 M solution of phenylacetylene in toluene was circulated at
different flow rates (0.2, 0.5 and 1.0 mL/min) and system pressures (5, 10, 15 and 20 bar)
through the catalyst bed (feed/catalyst contact time: 1 min) at 30°C were investigated.
Samples were periodically collected at 0, 15, 30 min and 1 hour after achieving steady state
conditions.
All the collected samples were analyzed by gas chromatography in an Agilent-6890 N
Series II instrument equipped with FID and a HP-5 column Agilent 19091 J-413 (30 m x
0.32 mm x 0.25µm; phenyl methyl xylosan 5%). Injector and detector temperatures were set
as 250°C. Oven temperature was held for 1 min at 80°C, and then increased to 150°C
(10°C/ min). Phenylacetylene (PA), styrene (ST), and ethylbenzene (EB) signals (as the
reactant, desirable product, and byproduct, respectively) were recorded. A typical
chromatogram is showed in Fig. A.2. Products identification was done in a GC-MS
instrument (Agilent Technologies 7820A GC System coupled with a 5977B MSD mass
spectrometer) equipped with a HP-5MS column. The concentrations of each compound
were determined using the equations of calibration curves showed in Table A.1.

Conversion (PA) and selectivity (ST) were calculated based on areas as a function of
concentration:
푡표푡푎푙 푚표푙푒푠 − 푓푖푛푎푙 푚표푙푒푠 표푓 푃퐴
(
)
퐶표푛푣푒푟푠푖표푛 푃퐴, % =
× 100
푡표푡푎푙 푚표푙푒푠
푡표푡푎푙 푚표푙푒푠 푆푇
푡표푡푎푙 푚표푙푒푠
(
)
푆푒푙푒푐푡푖푣푖푡푦 푆푇, % =
× 100
3. Results and discussion
Biogenic CaCO3 has an extraordinary importance for the adsorption of heavy metal ions
such as Cd2+ and Pb2+ [19]. However, the use such Biogenic CaCO3 in the catalysis field
has been rarely explored. Regarding to the material characterisation, the textural properties
of the Pd0.5/CaCO3 catalyst as well as its respective support were evaluated by nitrogen
adsorption/desorption measurements and are listed on Table 1. Firstly, it is important to
remark the relatively low surface area in the biogenic CaCO3, which is decreased after Pd
incorporation from 25 to 11 m2/g. In addition, pore volume and pore size were affected by
Pd impregnation caused by pore saturation by metal particles. Furthermore, it is important
to remark the high pore volume may lead to increased catalytic activity. In contrast, the
relatively low surface area, in principle, is disadvantageous and may lead to nanoparticles
with larger particle as compared with the use of other supports such as activated charcoal
and zeolites among others with higher specific surface. The isotherm plots of the material
Pd0.5/CaCO3 is shown on Fig. A.3, shows a typical hysteresis type H3 loop at relative
pressures between 0.46 and 0.9, similar to other reported for analogous materials [20].

The crystallinity of the samples was evaluated by X-ray diffraction and the results are shown
on Fig. 1, where it can be observed that the support CaCO3 it is a mixture of two phases,
calcite and vaterite. The presence of Pd particles could not be detected due to either a good
particle distribution over the catalyst surface or to the low Pd loading on the material. The
crystal size corresponding to vaterite in the Pd0.5/CaCO3 catalyst was measured using
Scherrer equation at 2θ ~ 27º was 3.5 nm, which corresponds to the most important phase
in the investigated materials. In contrast, this value before of impregnation with palladium
was 3.1 nm, slightly smaller. Interestingly, it is observed that vaterite phase proportion
increased with respect to the most stable phase calcite, indicating that some spherical
crystals evolve [21] while phenylacetylene hydrogenation reaction is taking place.
Thermogravimetric analyses were performed to understand the change in the phases of
CaCO3 after of reaction. Fig. A.4. shown thermograms of Pd0.5/CaCO3 obtained before
and after of phenylacetylene hydrogenation. Although, typical loss weight of carbonates is
evidenced, a minor weight loss of water was observed after of reaction; because of
physisorbed water was removed from solid with continuous flow, which probably changes
the polymorphism of calcite to vaterite [22].
The morphology of biogenic calcium carbonate loaded with 0.5 % wt. palladium sample was
investigated by Transmission Electron Microscopy (Fig. 2). In TEM micrograph there are
three regions that could be observed; firstly, it was possible to differentiate the two CaCO3
phases present in the material. While calcite phase can be observed as elongated
hexagonal shape crystals, in the lower part of the image (region 1), other spherical/ovoid
shape crystals can be appreciated corresponding to vaterite phase in the upper part of the
image (region 2). Likewise, a particle of palladium adhered to crystal surface (3) can be
evidenced.

Additional structural analysis corresponding to the sample Pd0.5/CaCO3 was performed by
X-ray photoelectron spectroscopy (XPS). Fig. 3a shows the deconvoluted XPS spectra of
Pd0.5/CaCO3 in the 3d region, where two contributions of Pd 3d5/2 are assigned to Pd0 and
Pd2+[23]. The proportion of these two species is 60:40, respectively. Although, reduced
2-
particles Me0 are obtained with NaBH4, it seems be that CO3 species inhibits complete
reduction of palladium. Ca2p core levels at 347.2 and 350.7 eV (Fig. 3b) are assigned to
vaterite phase [18], which is in agreement with results of XRD. Commonly, carbonates are
associated in the region C1s at 289.7 eV (Fig. A.5a) [18,24]. The peaks at 286.4 and 285
eV are ascribed at C=O groups and adventitious carbon. In the XPS O1s core level appears
two peaks in low BE at 531 and 532.6 eV assigned to oxygen in lattices and oxygen in OH
groups probably as adsorbed water [25], respectively (see Fig. A.5b). The values
2-
corresponding to O1s region at low BE could be associated with some interaction Pd-CO3 .
The catalytic activity of the catalyst was investigated in the continuous flow hydrogenation of
phenylacetylene for the selective production of styrene (ST), which is an important
monomer that participates in the production of plastics and rubbers. Therefore, the main
aim of this study was focused on finding out the optimized conditions for conversion of
phenylacetylene (PA) achieving the maximum selectivity towards the production of styrene
using Pd0.5/CaCO3 catalyst. The use of continuous flow reactors entails several
advantages as compared to batch reactors such as improved contact between reagents
and catalyst, better reaction parameters optimization and improved matter and energy
transference that promote the catalytic processes. In addition, with comparative purposes a
commercial Pd/C with a metal loading was investigated with comparative purposes at the
preliminary stages of the studies performed at 30 ºC, 20 bar and a flow rate of 0.2 mL/min

leading to almost the complete conversion of PA but with a low selectivity towards styrene
(Table A.2). Under analogous conditions, Pd0.5/CaCO3 catalyst achieved lower PA
conversion but higher ST selectivity (15 %). Thus, considering the higher selectivity that
could be achieved by Pd0.5/CaCO3 catalyst, despite of its lower Pd loading, the
optimization of the reaction conditions was carried out using this catalyst.
Firstly, three different reaction temperatures, a relevant parameter in any chemical reaction,
30, 50 and 100°C were evaluated using Pd0.5/CaCO3 catalyst. A conversion of 100% was
evidenced in the three tests performed at the different investigated temperatures. At 30 ºC,
it was shown on Table A.2 that PA was converted at this temperature independently
of the flow (from 0.2 to 1.0 mL/min) and system pressure (from 5 to 20 bar). For
instance, conversion was complete when flow is 0.2 mL/min and at 10 bar pressure as well
as at 0.5 mL/min flow rate regardless the pressure. However, ST selectivity was low
obtaining mainly the hydrogenated product, ethylbenzene. Though, when flow is 1.0 mL/min
and pressure is 10 bar, ST selectivity and yield showed the highest values. Considering the
reduction of energy costs, it was decided to carry out the experiments at a fixed
temperature of 30°C as well as phenylacetylene concentration (0.1 M in toluene) in the
feeding solution. Therefore, system pressure as well as flow rate would require optimization
in other to achieve the maximum styrene yield.
The effect of pressure on phenylacetylene reaction was studied in a range of 3 to 20 bar at
30 °C and the flow rate was fixed at 0.5 mL/min of 0.1 M PA solution in toluene using
Pd0.5/CaCO3 (Fig. 4). When pressure increases, styrene selectivity and yield decrease,
although conversion increases possibly because ethylbenzene production is promoted by
increasing hydrogen amount injected into reaction. Besides, it is possible that PdO can be

reduced fully to Pd0 modifying the selectivity obtained when the pressure is highest than 10
bar, this effect is more pronounced at high temperatures (Table A.2). Thus, at 15 bar,
conversion is 100%, but ST production is 36% and ethylbenzene is the main reaction
product with a yield of 64%. The most convenient system pressure investigated was 10 bar
when the maximum ST yield was achieved. Therefore, this pressure value (10 bar) was
selected to evaluate flow rate effect on the reaction.
Fig. 5 shows the flow rate effect on PA hydrogenation with Pd0.5/CaCO3 that is going to
strongly influence ST yield and selectivity, whose highest investigated value was 1.5
mL/min. According to the displayed results, the most adequate flow rate was 1.0 mL/min,
where also EB yield is the lowest (about 15%) among all the investigated conditions. This
fact suggests that rapid diffusion of the reagents through the catalyst that partially
hydrogenates phenylacetylene to styrene with high effectiveness. The best results were
obtained using a flow rate of a 0.1 M PA solution of 1.0 mL/min at 30 ºC and 10 bar
hydrogen pressure obtaining a yield of 65.8% and a selectivity of 83.3% towards styrene.
Yang et al. [6] studied commercially available catalysts, Pd/Al2O3 and Lindlar catalyst, which
have selectivity to styrene of 47.8% and 90.2%, with conversions of 99.5 and 99.3%,
respectively. Firstly, it is important to note that Lindlar catalyst has a reaction time 20 times
higher (2000 min) than Pd/Al2O3 (100 min). The differences in selectivity found in Pd/Al2O3
and Lindlar catalyst could be related with the proportion of metallic species present in these
solids. The formation of ethylbenzene is favored on Pd0 species which occurs on Pd/Al2O3,
while the partial hydrogenation favored is related with a minor proportion of hydrogenated
species as is the case in Lindlar catalyst. Although Pd0.5/CaCO3 has a selectivity of 83%
and a conversion of 78%, this occurs only in shorter reaction times, below one hour on

stream, which are good results as compared to previous studies and can be attributed to
the ratio Pd2+/Pd0 present in the catalyst. Interestingly, if reaction conditions change,
pressure and flow rate, solid catalytic activity increase due to change in the proportion of
such species and, consequently, the selectivity and yield to styrene or ethylbenzene are
modified. Finally, it is also important to notice that the low reaction temperature herein used,
30°C, to perform the hydrogenation reaction helps to the process economy. Although,
Lindlar catalyst is the most used solid in phenylacetylene hydrogenation, longer
times of reaction (more than 33 hours) are required to obtain these high values under
batch conditions.
In summary, the catalytic activity of Pd0.5/CaCO3 was compared with literature
values, which are summarized in Table 2. Different catalysts have been used but
some of them need drastic preparation conditions i.e. high temperatures that
increase costs in a scalable process. Batch or semi batch reaction limits industrial
production of styrene. Conversion and selectivity of PA hydrogenation using
biogenic Pd0.5/CaCO3 were low compared with other catalysts, but with biogenic
materials this process is short (1 h) and the catalyst did not require high
temperatures and complex procedures for synthesis.
Finally, a long-term experiment was carried out to investigate a possible deactivation the
Pd0.5/CaCO3 catalyst. The results are depicted on Fig. 6 where it can be seen that
Pd0.5/CaCO3 has a stable performance under continuous flow conditions after 12 hours on
stream, since during the evaluation period conversion PA, selectivity and yield of styrene
remained unchanged, i.e the species of palladium responsible of the activity did not
undergo further modification. However, the continuous flow conditions may help to remove

physisorbed water and change slightly the polymorphism in CaCO3 used as catalytic
support.
4. Conclusions
Pd0.5/CaCO3 catalyst was prepared using biogenic carbonate obtained by microbiological
precipitation with Sporosarcina pasteurii to be used as support for Pd nanoparticles. The
adequate ratio Pd0/Pd2+ in this material allows to obtain good yields to styrene in
phenylacetylene hydrogenation under continuous flow conditions. Once optimized the
reaction conditions, the best results were obtained when a temperature of 30°C, flow rate 1
mL/min of a 0.1 M PA solution in toluene and 10 bar of pressure were used to obtain a yield
and selectivity towards styrene of 65% 83%, respectively. Remarkably, after 12 hours on
stream, catalytic activity of Pd0.5/CaCO3 remained unchanged keep constant PA
conversion and selectivity to styrene as indicative of catalyst stability under investigated
condition. Thus biogenic Pd0.5/CaCO3 has been proved to be a robust catalyst in
continuous flow phenylacetylene hydrogenation to produce selectively styrene.
Funding
SC would like to thank to Boyacá Government for a PhD Fellowship with Announcement
733 of 2015 "High-level human capital formation for the department of Boyacá 2015"
Author contributions
SC performed all experiments and wrote the first draft of the manuscript. AP-S supported
the experimental work and revised the manuscript draft. JM and HR review the paper. RL
provided the lab for all experiments, planned the experimental work, and finalized and
submitted the manuscript.

Declaration of interests
The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or
financial relationships that could be construed as a potential conflict of interest.
Acknowledgements
SC would like to thank to Boyacá Government for their financial support granted through the
Call 733 of 2015 "High-level human capital formation for the department of Boyacá 2015"
and Chemical Sciences doctoral program of the Universidad Pedagógica y Tecnológica de
Colombia. AP express his gratitude to the support provided by “Plan Propio de
Investigación” from Universidad de Córdoba (Spain) and “Programa Operativo” FEDER
funds from Junta de Andalucía. The manuscript has been prepared with support from
RUDN University Program 5-100.

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LIST OF FIGURES
Fig. 1. X-ray diffractograms corresponding to Pd0.5/CaCO3 used in the phenylacetylene
hydrogenation.
Fig. 2. TEM image corresponding to the material Pd0.5/CaCO3.
Fig. 3. High-resolution XPS spectra corresponding to the Pd0.5/CaCO3 sample in the
regions: a) Pd3d and b) Ca2p
Fig. 4. Effect of system pressure in phenylacetylene hydrogenation with Pd0.5/CaCO3.
Reaction conditions: 30 °C and flow rate of 0.5 mL/min of 0.1 M PA solution in toluene.
Fig. 5. Effect of flow in phenylacetylene hydrogenation with Pd0.5/CaCO3. Reaction
conditions: 30 °C and system pressure of 10 bar, 0.1 M PA solution in toluene.
Fig. 6. Catalytic activity of Pd0.5/CaCO3 in phenylacetylene hydrogenation along 12 hours
on stream. Reaction conditions: 30 °C, system pressure of 10 bar, flow rate of 1.0 mL/min
and 0.1 M PA solution in toluene.

C:12%-V:88%
Pd0.5/CaCO3 after reaction
V
V
C
V
C:30%-V:70%
V
C
V
V
V
V
V
V
V
C
Pd0.5/CaCO3 before reaction
20
30
40
50
60
70
2
Fig. 1.

2
3
1
Fig. 2.

a.
b.
3d5/2
Ca2p3/2
Pd3d
Ca2p
3d3/2
Pd(0)
Pd(II)
Ca2p1/2
354 352 350 348 346 344
346 344 342 340 338 336 334 332
Binding energy (eV)
Binding energy (eV)
Fig. 3.
100
80
60
40
20
0
Conversion
Selectivity EB
Selectivity ST
0
3
6
9
12
15
18
21
Pressure (bar)

Fig. 4.
100
80
60
40
20
0
Conversion
Selectivity ST
Selectivity EB
0.0
0.2
1.0
1.4 1.6
0.8
0.4 0.6
1.2
Flow rate (mL/min)
Fig. 5.

100
80
60
40
20
0
Conversion
Yield ST
0
1
2
3
4
5
6
7
8
9 10 11 12
Time on stream (hours)
Fig. 6.

TABLES
Table 1. Textural properties of the investigated materials in this work measured by nitrogen
adsorption/desorption measurements.
Catalyst
Specific
Surface BET
(m2/g)
CBET
Pore volume
BJH
Pore size
BJH
(cm3/g)
0.11
(nm)
CaCO3
25
67
59
28.0
Pd0.5/CaCO3
11
0.04
26.6

Table 2. Comparison of catalytic performance between Pd0.5/CaCO3 and the literature
Catalyst
Conditions
Conv*.(%) YST* (%)
SST* (%)
SEB* (%)
Ref
Pd0.5/CaCO3
0.08 g of catalyst, 0.1
M PA in toluene, 10
bar of H2 pressure,
flow: 1 mL/min 30°C,
t= 1 h
78
65
83
17
This
work
mpg-C3N4
0.4 g of catalyst,
86
76.4
89
94
10.6
[4]
[8]
0.0135 mol/h of PA in
hexane, 0.027 mol/h of
H2, 250°C, t= 1 h
Pd @mpg-C3N4 0.010 g of catalyst,
5.85 mmol PA in
˃99
-
-
ethanol, atmospheric
H2 bubbling, 30°C, t=
1.5 h (batch reaction)
Pd/TiO2
0.05 g of catalyst, 0.4
M PA in ethanol, 0.5
MPa in H2 pressure,
25°C (Batch reaction)
t= 40 min
100
100
98
-
-
-
95
90
70
-
-
-
[7]
[6]
NiZn3/AlSBA-15 0.15 g of catalyst, 0.4
M PA in methanol, 0.1
MPa in H2 40°C
(Semibatch reaction),
t= 13 h
nano-Pd/α-
Al2O3
0.3 g of catalyst, 0.72
M PA in ethanol, 0.1
MPa in H2 50°C
[10]
(Semibatch reaction),
t= 30 min
1% Pd/ND@G
PdAu/ZnTi
0.005 g of catalyst,
0.18 M PA in ethanol,
1 bar of H2, 30°C, t= 1
h (batch reaction)
100
100
85
85
90
-
-
[26]
[12]
0.005 g of catalyst, 0.3
M PA in ethanol, 10
mL/min of H2, 45°C, t=
1.5 h (batch reaction)
-

Cu/PNDs
0.01 g of catalyst, 0.02
M PA in ethanol, 12
mL/min of H2 , flow:
0.6 mL/min 20°C, t= 1
h
68
79
-
-
90
88
-
[27]
[28]
Ni2Si
0.10 g of catalyst, 1 M
PA in ethanol, 1 MPa
of H2 , flow: 0.6
12
mL/min 80°C, t= 4 h
*Conv: conversion, YST: yield to styrene, SST:selectivity to styrene, SEB:selectivity to ethylbenzene