Application of Laser Induced Breakdown Spectroscopy as a Novel Approach for Monitoring of the Activity of Nano Palladium Catalyst as Compared to Two Well-known Methods

Article abstract of DOI:10.1002/zaac.201900337

Catalyst deactivation is an unavoidable process that occurs in catalytic chemical reactions. Laser Induced Breakdown Spectroscopy (LIBS) is used here as a novel approach to investigate the activity of palladium supported with carbon catalyst (Pd/C) over the hydrogenation of cinnamic acid with tetralin. Their outputs for four catalyst samples are reported for different time intervals of 0, 5, 10, 15 min during the reaction. The results of LIBS analysis are compared to Inductively Coupled Plasma Mass Spectrometry (ICP-MS), which shows a good agreement. Experimental data specify that line intensities of palladium (Pd) are decreased significantly with an increment of the reaction time. Moreover, the Field Emission Scanning Electron Microscope with energy dispersive spectroscopy (FESEM-EDS) of catalysts samples show aggregation of palladium particles for some places in the catalyst surface. The changes of Pd content and sintering of Pd particles in the catalyst during the reaction play substantial roles in catalyst deactivation.

Full text of DOI:10.1002/zaac.201900337

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201900337
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Application of Laser Induced Breakdown Spectroscopy as a Novel
Approach for Monitoring of the Activity of Nano Palladium
Catalyst as Compared to Two Well-known Methods
Sahar Belyani,[a] Mohammad Hossein Keshavarz,*[a] Seyyed Mohammad Reza Darbani,[b] and
Masoud Kavosh Tehrani[b]
Abstract. Catalyst deactivation is an unavoidable process that occurs shows a good agreement. Experimental data specify that line intensities
in catalytic chemical reactions. Laser Induced Breakdown Spec-
troscopy (LIBS) is used here as a novel approach to investigate the the reaction time. Moreover, the Field Emission Scanning Electron
activity of palladium supported with carbon catalyst (Pd/C) over the Microscope with energy dispersive spectroscopy (FESEM-EDS) of
of palladium (Pd) are decreased significantly with an increment of
hydrogenation of cinnamic acid with tetralin. Their outputs for four catalysts samples show aggregation of palladium particles for some
catalyst samples are reported for different time intervals of 0, 5, 10, places in the catalyst surface. The changes of Pd content and sintering
15 min during the reaction. The results of LIBS analysis are compared
of Pd particles in the catalyst during the reaction play substantial roles
to Inductively Coupled Plasma Mass Spectrometry (ICP-MS), which in catalyst deactivation.
namic acid in tetralin is one of CTH reactions in which tetralin
1 Introduction
acts as both solvent and hydrogen donor via palladium catalyst
(Figure 1). In this procedure, tetralin provides hydrogen and
converts to naphthalene by Pd/C catalyst in the mild condition
under reflux. Derived hydrogen atoms from tetralin can reduce
cinnamic acid to hydrocinnamic acid as a sequence using
Pd/C catalyst.[7,10] It is widely known that Pd catalysts can
help hydrogenating double bonds well without affecting other
functional groups. Since Pd catalysts are expensive, monitor-
ing of their deactivation should be considered.
Metal nanoparticles are suitable materials with powerful
properties for applicable reactions, which are used in material
design and the development of new products such as medicine,
catalysis, electronics, and optics.[1] Among metal nanopar-
ticles, nanocatalysts have a great deal of interest due to the
acceleration of chemical reactions with the use of a few
amounts of the catalyst.[2] Palladium-based catalysts are wildly
used for, catalytic hydro dechlorination, transfer hydrogenation
reactions, methanol oxidation and explosive production.[3] Cat-
alyst deactivation is one critical issue associated with the cata-
lytic processes because it shows the loss of catalyst activity
over time. While catalyst deactivation is inevitable for most
chemical processes, a better understanding of this issue is on
focus.[4] Monitoring and following the deactivation of the cata-
lyst with a practical method is important for improving the
reaction conditions and avoiding further costs.[4b,5]
Catalytic Transfer Hydrogenation (CTH) has an effective
rule as a suitable method for the reduction of organic sub-
strates.[6] In CTH reaction, hydrogen derived by an easily aro-
matized cyclic compound can transfer directly to an unsatu-
rated substance with the use of catalyst.[7] Hydrogen gas can
be supplied by solvent as hydrogen donor compound using an
appropriate catalyst for such reactions.[8] With a comparison
of the effectiveness of various catalysts, palladium catalysts
are the most operative for hydrocinnamic production from cin-
namic acid.[9] The reduction of cinnamic acid to hydrocin-
Figure 1. Catalytic transfer hydrogenation of cinnamic acid using
Pd/C catalyst.
Albers et al.[11] studied the carbon deposition on Pt/Al2O3
and Pd/SiO2 catalysts through X-ray Photoelectron Spec-
troscopy (XPS) and Secondary-Ion Mass Spectrometry
(SIMS). Pernicone et al.[12] performed detailed research on
commercial 0.5% Pd/C catalyst by the use several methods
including Scanning Electron Microscopy/Energy Dispersive
X-ray Spectroscopy (SEM/EDS), CO chemisorption, and
X-ray diffraction (XRD).[12] Koskin et al.[13] reported the deac-
tivation of a palladium catalyst in the synthesis of CL-20 by
hydro debenzylation reaction over high-resolution Trans-
mission Electronic Microscopy (TEM).[13] Yuan and Keane
studied deactivation of Pd/C and Pd/Al2O3 during the liquid
* Dr. M. H. Keshavarz
E-Mail: mhkeshavarz@mut-es.ac.ir; keshavarz7@gmail.com
[a] Department of Chemistry
Malek-ashtar University of Technology
Shahin-shahr, P.O. Box 83145/115, Iran
[b] Optics and Laser Science and Technology Research Center
Malek-ashtar University of Technology
Shahin-shahr, P.O. Box 83145/115, Iran
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lized catalyst was palladium (10 wt%) supported with activated carbon,
phase hydro dechlorination of 2,4-dichlorophenol using Induc-
which was supplied by Shaanxi Rock New Material Co., Ltd. and the
reaction time was 15 min. Four samples of Pd/C catalysts in different
time of hydrogenation reaction were selected for purposes of monitor-
ing deactivation of catalyst among the reaction. Pd/C catalyst was iso-
lated and washed with diethyl ether, water, and 10% aqueous sodium
hydroxide after 5, 10, and 15 min of reaction. Then, the powdered
sample of the washed catalysts dried in the oven. Due to the further
analysis via LIBS technique, a binder of palmitic acid with the pow-
dered samples was pressed to the pellets in the same conditions, which
tively Coupled Plasma (ICP) and Brunauer, Emmett and Teller
(BET).[14]
Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
is an analytical technique, which can be used for elemental
determinations. It has been applied for the determination of
trace element determination because it provides suitable ad-
vantages such as lower Limits Of Detection (LOD), multi-ele-
ment and isotopic-ratio measurement capability, small sample
amounts, reduced spectral interferences, high sensitivity, stead- include weighing, homogenizing with palmitic acid and pressing.
ily decreasing investment costs, and in situ.[15] Since spark is
applied to expose the electrons of argon gas inside ICP and
forming argon ions, the oscillating fields trapped them. These
2.2. LIBS Setup
ions have a collision with other argon atoms, which create an
argon discharge or plasma. The ICP source converts the atoms SCAN100, Applied Photonic LTD, United Kingdom), which was
All experiments were performed using a LIBS apparatus (LIB-
equipped with Q-switched Nd:YAG laser (Quantel, USA) operating at
1064 nm with the pulse duration of 7Ϯ2 ns. Laser irradiance on the
sample was about 1.8 GW/cm2. Samples were placed on a controlled
X, Y, Z motorized translational stage that was controlled by internal
software. The emitted radiation through the laser-induced plasma was
transferred to the detector by an optical fiber bundle for spectroscopic
analysis. The optical fiber system was connected to a detector with
eight spectrometers (Avantes-20–01–13- A, Netherland), which can
achieve 0.03–0.15 nm resolution for spectral analysis. The spectra
were acquired at 1.27 μs delay and 1.1 ms gate width. In our experi-
of the elements in the sample to ions. Then, the mass spec-
trometer separates and detects these ions. Thus, ICP-MS tech-
nology has superior detection capabilities.[15,16]
Laser Induced Breakdown Spectroscopy (LIBS) is a rapid
screening tool to evaluate the chemical constituents of materi-
als.[17] It was also used to assess shelf life and performance of
hazardous energetic compounds.[18] It was recently demon-
strated that deactivation of Pd(OH)2/C as fresh catalyst in de-
benzylation reaction of hexabenzylhexaazaisowurtzitane
(HBIW) for producing hexanitrohexaazaisowurtzitane (HNIW) ment, ten single-shot spectra for each sample were recorded and the
resultant spectra were obtained by averaging over these measurements.
A schematic diagram of the experimental setup used is shown in Fig-
ure 2. The LIBS test was done under Ar gas injection with 99.9%
purity. The flow rate of 15 L·min–1 was directed over the sample sur-
face in order to reduce the effect of atmospheric gas and improve
spectral peaks.[17d,19]
can be distinguished by elemental information of analyzing the
spectral content of plasma, which results from the interaction
of a high power laser pulse with a sample of spent catalyst Pd/
C using LIBS method.[19] LIBS may be introduced a superior
technique to others because it provides the benefits such as
nondestructive, no need to initial preparation, simple, inexpen-
sive, no spectral and matrix interference, and suitable for all
types of material (solid, liquid, and gas).[20] It is used here to
permit the simultaneous analysis of the intensity of elemental
and molecular emissions in the sample for confirmation of cat-
alyst deactivation.
The purpose of this study is to extend previous work[19] for
investigation of the use LIBS technique of the deactivation of
Pd/C catalyst among the catalytic transfer hydrogenation reac-
tion of cinnamic acid. Deactivation of Pd/C catalyst has been
examined among the hydrogenation transfer during time inter-
vals of 0, 5, 10, and 15 min of reaction. Subsequently, ICP-
MS carries out mapping the amount of Pd in catalyst samples.
The Field Emission Scanning Electron Microscope with en-
ergy dispersive spectroscopy (FESEM-EDS) is also used to
examine the catalyst surface. Measurement parameters for both
the LIBS and ICP-MS are systematically optimized. A com-
parison is done between the result of LIBS analysis, ICP-MS,
and FESEM-EDS.
Figure 2. Schematic diagram of the experimental LIBS setup.
2.3. ICP-MS and FESEM-EDS Analysis
Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a type of
mass spectrometry that is highly sensitive for analyzing elements at
trace levels. The capability of ICP-MS to simultaneously measure the
majority of elements and can be applied to solutions, solids, and
2 Experimental Section
2.1. Materials and Hydrogenation Transfer
Catalytic hydrogenation transfer of cinnamic acid to hydrocinnamic gases.[21] Determining the concentrations of Pd in catalyst samples was
acid was performed with an excess amount of tetralin as solvent and greatly improved by the ability of ICP-MS to analyze the amount of
hydrogen donor via Pd/C catalyst at temperature of 190 °C. The uti- Pd with high sensitivity. The palladium content in the catalyst was
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determined by an Agilent 7500ce inductively coupled plasma (ICP)
mass spectrometry. The catalyst samples were burned in an oxygen
atmosphere furnace at a temperature of 900°C. The remainder of the
catalyst samples was dissolved into aqua regia (a 1: 3 mixture of nitric
acid and hydrochloric acid) due to the measuring the palladium content
in catalysts. The palladium content in the leached solution was mea-
sured by ICP-MS. The examination of catalyst morphology was
studied by a MIRA3 TESCAN Field Emission Scanning Electron
Microscope (FESEM) with energy dispersive spectroscopy (EDS).
3 Results and Discussion
3.1 LIBS Signal
The LIBS spectrum of palladium in argon ambient gas is
shown in Figure 3. The spectroscopic data were extracted from
the National Institute of Standards and Technology (NIST) dat-
abase for identification of all of the used peaks and those re-
lated to palladium adapted with wavelengths.[22] Every impor-
tant peak of Pd and some of argon peaks are summarized in
Table 1. The LIBS analyses of four sample catalysts were ac-
quired at different times of 0, 5, 10, and 15 min from the
beginning of the hydrogenation reaction. The LIBS analysis of
fresh catalyst samples (0 min) with corresponding to argon
emission lines are shown in Figure 4. As seen, the lines of
palladium and argon are well specified in Figure 4. Moreover,
in air atmosphere, due to the recombination of carbon from
sample and nitrogen of the air, the molecular radiation CN
violet system is seen but this radiation does not exist in the
presence of argon ambient gases. These results have an agree-
ment with other outcomes.[19]
Figure 4. Emission lines of Pd I and Ar in the spectral range of 320–
370 and 790–815.
reaction to end. The same conditions such as temperature,
washing step, kind and amount of binder, sample amount, and
flow rate of ambient gas were formed for attributing the pro-
cedure to deactivation. Figure 5 compares four samples of cat-
alyst at different times of reaction. Due to the same condition
of every LIBS analysis, all peaks were normalized to one of
the argon peaks (763.57 nm) in order to reduce the effect of
test parameters especially intensity shift. As seen, the inten-
sities of spectral peaks are reduced with passing reaction time
in the samples of 5, 10, and 15 min, respectively. The fresh
catalyst sample (0 min) has the most intense that is seen in
Figure 5. The observed trend in the intensity of spectral lines
of Pd is due to the deactivation of catalyst among the catalytic
transfer hydrogenation reaction.
Figure 3. The LIBS spectrum of Pd.
Table 1. LIBS emission lines of palladium and argon gas.
Figure 5. Comparison of Pd strong lines in four times of reaction.
Pd
Ar
324.26, 340.45, 344.13, 348.11, 363.46, and 369.03
794.81, 800.61, 801.47, 810.36, and 811.53
3.2. ICP Analysis
Since the final goal was to assess the deactivation of Pd/C
catalyst among the reaction, four LIBS spectra of Pd/C were
The result of Pd concentrations in each of the four analyzed
compared in 0, 5, 10, and 15 min from the beginning of the catalyst samples using ICP-MS are given in Table 2. The
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analysis has shown that Pd concentrations were decreased by
moving from sample 0 to 15 min, respectively. Comparison of
the extent of Pd concentrations accumulation in the analyzed
catalyst samples with ICP and LIBS analysis showed that both
methods displayed a decreasing trend in the amount of Pd ac-
cording to deactivation of Pd/C catalyst.
Table 2. ICP analysis of Pd concentration in four catalyst samples.
Sample
%Pd concentration
0 min
5 min
10 min
15 min
9.2
8.8
7
3.7
3.3. Change in Surface Morphology (FESEM-EDS
Analysis)
The FESEM-EDS was employed to gain more insights into
the deactivation of catalyst samples. It characterizes the cata-
lyst surface before and after the catalytic transfer hydrogen-
ation reaction. FESEM-EDS images for fresh and spent cata-
lysts are shown in Figure 6. As shown in Figure 6a, b, c, and
d for fresh catalyst (0 min) and spent catalysts after 5, 10, and
15 min, respectively, palladium particles are uniformly de-
posited on the surface of the activated carbon in the fresh cata-
lyst. The palladium particles aggregate and form large particles
by passing time. The size of the aggregations and the surface
morphology of these catalyst samples were changed evidently
before and after their use in reaction.
As shown in FESEM-EDS images (Figure 6), the mor-
phology of catalyst surface has been changed by using in reac-
tion. Due to the deactivation of catalyst in hydrogenation reac-
tion, palladium nanoparticles coalesce and make large units.
Furthermore, the acidic environment of reaction can leach the
palladium particles from the catalyst into the liquid phase.
Hence, it can be concluded that the sintering and leaching of
palladium particles has a significant effect on the catalyst deac-
tivation.
4 Conclusions
Figure 6. FESEM-EDS images of (a) fresh catalyst (0 min), (b) cata-
lyst after 5 min of reaction, (c) catalyst after 10 min of reaction and
(d) spent catalyst after the reaction is over (15 min).
Catalyst deactivation through the chemical reaction is an in-
evitable process. In order to monitor the change in palladium
content in the catalyst and deactivation of the catalyst, the cata-
lytic hydrogenation transfer of cinnamic acid reaction was per-
formed at different time intervals. Deactivation of the catalyst
with an increment of reaction time was investigated by LIBS
analysis. Due to the advantages of the LIBS method including
nondestructive, no need for initial preparation, consumption
small amount of sample, and fast detection, it can be used as
a capable method to study the deactivation of Pd/C catalyst.
The result of LIBS was compared to ICP-MS analysis. More-
over, FESEM-EDS images of catalyst samples were acquired
to study the morphology of the surface. These results can be
explained that three methods demonstrated the decrease in Pd
of reaction time. Although the leaching of palladium particles
is the main reason for catalyst deactivation, the growing up of
palladium particles and forming large units can also cause cata-
lyst deactivation.
Acknowledgements
We would like to thank the research committee of Malek-ashtar Uni-
versity of Technology (MUT) for supporting this work. This research
did not receive any specific grant from funding agencies in the public,
amount because of Pd leaching and sintering with an increment commercial, or not-for-profit sectors.
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Keywords: Keywords. Laser Induced Breakdown Spec-
troscopy; Inductively Coupled Plasma Mass Spectrometry;
Palladium catalyst; Activity; Catalytic hydrogenation
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Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
S. Belyani, M. H. Keshavarz*, S. M. R. Darbani,
M. K. Tehrani .................................................................... 1–6
Application of Laser Induced Breakdown Spectroscopy as a
Novel Approach for Monitoring of the Activity of Nano Palla-
dium Catalyst as Compared to Two Well-known Methods
Z. Anorg. Allg. Chem. 0000, 0–0
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