Intermetallic GaPd2 Thin Films for Selective Hydrogenation of Acetylene

Article abstract of DOI:10.1002/zaac.202000124

The preparation of single-phase and catalytically active GaPd₂ coatings was accomplished via DC magnetron sputtering using an intermetallic sputter target. Thin and uniform layers were deposited on borosilicate glass, Si(111) and planar as well as micro-structured stainless steel foils. The specimens were examined regarding their phase composition, film morphology and microstructure. Thin films of different layer thickness were catalytically characterized in the semi-hydrogenation of acetylene, which was conducted at 473 K and a feed gas composition of 0.5 vol.percent C₂H₂, 5 vol.percent H₂ as well as 50 vol.percent C₂H₄ in helium. Pre-reduction of the catalyst was found to be essential to enhance the catalytic selectivity. Sputtered GaPd₂ showed a high selectivity of 73 percent for the hydrogenation to ethylene at conversion levels above 80 percent. The surface-specific activity was strongly increased to 8.97 mol_acetylene·(A₀·h)^–1 compared to bulk- or nanoscale GaPd₂ (1.93 and 0.30 mol_acetylene·(A₀·h)^–1, respectively) caused by the high specific surface area of the thin films.

Full text of DOI:10.1002/zaac.202000124

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202000124
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Intermetallic GaPd2 Thin Films for Selective Hydrogenation of
Acetylene
René R. Zimmermann,[a] Martin Siebert,[b] Shyjumon Ibrahimkutty,[c] Roland Dittmeyer,[b] and
Marc Armbrüster*[a]
Dedicated to Professor Juri Grin on the Occasion of his 65th Birthday
Abstract. The preparation of single-phase and catalytically active gas composition of 0.5 vol.% C2H2, 5 vol.% H2 as well as 50 vol.%
GaPd2 coatings was accomplished via DC magnetron sputtering using
an intermetallic sputter target. Thin and uniform layers were deposited to enhance the catalytic selectivity. Sputtered GaPd2 showed a high
on borosilicate glass, Si(111) and planar as well as micro-structured selectivity of 73% for the hydrogenation to ethylene at conversion
C2H4 in helium. Pre-reduction of the catalyst was found to be essential
stainless steel foils. The specimens were examined regarding their levels above 80%. The surface-specific activity was strongly increased
phase composition, film morphology and microstructure. Thin films of to 8.97 molacetylene·(A0·h)–1 compared to bulk- or nanoscale GaPd2
different layer thickness were catalytically characterized in the semi- (1.93 and 0.30 molacetylene·(A0·h)–1, respectively) caused by the high
hydrogenation of acetylene, which was conducted at 473 K and a feed
specific surface area of the thin films.
sist of well-dispersed palladium alloys like Ag-Pd or Au-Pd
on a support material – e.g. α-Al2O3.[4] The disadvantage of
those catalysts is an occurring segregation effect under reaction
conditions, whereby the catalytically active sites, and thus the
selectivity, change with time. Additionally, the formation of
palladium hydrides is observed for the alloyed systems, which
is drastically decreasing the ethylene selectivity.[5]
Introduction
Heterogeneously catalyzed selective hydrogenations are im-
portant reactions, which are applied in several industrial pro-
cesses. One process with global relevance is the production of
high-purity ethylene, which is further used as feedstock for
polyethylene or ethylene oxide synthesis. Polyethylene is with
an annual production of 70 million tons in 2010 the most pro-
duced polymer and has an expected annual growth of 3%.[1]
The ethylene-enriched gas mixture originating from steam
cracking of the naphtha fraction contains 0.5 to 2 vol.% acetyl-
ene, which poisons the catalyst of the subsequent polymeriza-
tion reaction.[2] Therefore, the separation or conversion of
acetylene below 2 ppm is essential.[3] The latter is economi-
cally reasonable, as both, the quality and quantity of ethylene
is increased using this approach. State-of-the-art catalysts con-
In recent years, there was comprehensive research about in-
termetallic compounds and their application as catalysts.[6] In
contrast to alloys intermetallic compounds possess a well-or-
dered crystal structure causing different and unique material
properties. In the case of selective hydrogenation reactions, the
resulting strong active-site isolation with limited segregation
effects is beneficial for the selectivity. For the selective hyd-
rogenation of acetylene, intermetallic Ga-Pd compounds are
highly active and selective site-isolated catalysts, which show
no formation of Pd-hydrides.[7] Bulk intermetallic compounds
in this system are formed by melting the corresponding
amounts of gallium and palladium, followed by annealing and
grinding of the obtained materials. Among those compounds,
GaPd2 shows the most promising properties, combining a high
selectivity for the semi-hydrogenation of acetylene of about
75% at conversion levels above 90%.[6a] Due to the low spe-
cific surface area of the bulk material a synthesis route to pre-
pare GaPd2 nanoparticles was developed.[8] The obtained
nanoparticles have particle sizes of 2–10 nm and show a very
high specific surface area of ca. 40 m2·g–1, which results in
a 35,000-fold higher specific activity compared to bulk-GaPd
without forfeiting the good selectivity.
* Prof. Dr. M. Armbrüster
E-Mail: marc.armbruester@chemie.tu-chemnitz.de
[a] Materials for Innovative Energy Concepts
Institute of Chemistry
Faculty of Natural Sciences
Chemnitz University of Technology
09107 Chemnitz, Germany
[b] Institute for Micro Process Engineering (IMVT) and Institute of
Catalysis Research and Technology (IKFT)
Karlsruhe Institute of Technology
Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen, Germany
[c] Max Planck Institute for Solid State Research
Heisenbergstr. 1
70569 Stuttgart, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.202000124 or from the au-
thor.
Investigation of the catalytic performance of these highly
active catalysts in conventional chemical reactors is challeng-
ing due to the high exothermicity of the hydrogenation reac-
tion. A well-known issue in this context is the sintering of
© 2020 The Authors. Published by Wiley-VCH Verlag GmbH &
Co. KGaA. · This is an open access article under the terms of the
Creative Commons Attribution License, which permits use, distri-
bution and reproduction in any medium, provided the original work
is properly cited.
Z. Anorg. Allg. Chem. 2020, 646, 1–10
1
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
the catalytically active material due to hot-spot formation. In electronic beam evaporation to deposit Pd on a GaN surface.
contrast to conventional plug-flow reactors, micro-structured Subsequent annealing at 973 K for 30 s led to the formation
reactors are characterized by a very high surface-to-volume of a mixture of Ga2Pd5 and Ga5Pd intermetallic compounds.[18]
ratio, which provides excellent heat and mass transport proper- Grodzicki et al. sputtered a 1.5 nm thick Pd layer on a defined
ties to overcome the limitations owing to the fast and highly GaN surface. Annealing at 823 and 1073 K initiated the forma-
exothermic reaction.[9] To allow for process intensification, a tion of island-type conglomerates of GaPd2 and GaPd, respec-
controlled and homogeneous application of the catalytic mate- tively.[19] Furthermore, Mayr et al. thermally evaporated Ga
rial inside the micro-structured reactor is required, which is and Pd by turns on a Ta sheet and subsequently annealed at
mostly realized by preparing a micro-fixed bed or surface coat- 673 K. The obtained 400 nm thick layer showed a slightly Pd-
ing. The lower pressure drop as well as reduced sintering and enriched bulk-GaPd2 including the neighboring phase Ga5Pd13
segregation of catalyst coatings are advantageous compared to as minor impurity.[20] According to the deposition techniques
the use of micro-fixed beds.[10]
Convenient designs of laboratory micro-structured reactors mostly one neighboring phase.
shown, the resulting layers were mixtures of a main phase and
for catalytic investigations contain a single micro-structured
The objectives of the present work include the synthesis of
metal foil up to a stack of foils.[11] These open micro-structures an intermetallic sputter target, the deposition of thin intermet-
can be produced by etching or milling of a flat metal substrate, allic GaPd2 layers via DC magnetron sputtering and the evalu-
which generates multiple, parallel and well-defined micro- ation of their catalytic properties in the selective hydrogenation
channels. Several techniques like dip coating, sol-gel-methods of acetylene. Overall, the main challenge is to produce single-
or screen printing have been demonstrated as being practicable phase intermetallic coatings via sputtering, because only the
for coating of laboratory scale micro-channel reactors. How- intermetallic phase will provide the desired catalytic proper-
ever, these methods often showed certain limitations like poor ties.
uniformity and reproducibility if a multitude of channels is
covered. Additionally, undesired coating on top of the fins and
Results and Discussion
side bands of the micro-structures occurs. Recently, the use of
drop-on-demand inkjet-printing for depositing GaPd2 nanopar-
ticles into micro-structured channels was demonstrated.[12]
Common to all the mentioned techniques is the limitation to
produce very thin coatings with a thickness below 1 μm. DC
magnetron sputtering represents an alternative to overcome
this constraint. It obviates the need for the complex and time-
consuming synthesis of GaPd2 nanoparticles, which is an inte-
gral part of all the aforementioned coating procedures. Further,
it is possible to coat surfaces more efficiently and with lower
amounts of intermetallic material. Sputter deposition generates
very dense and compact coatings with a good reproducibility
and well-scalable thicknesses ranging from a few nanometers
to several micrometers. Further advantages of magnetron sput-
tering are the absence of organic solvents in the process and
thereby avoiding liquid waste, lower material costs compared
to other coating techniques and the possibility of applying
screens to perform the coating of multiple patterns (e.g. depo-
sition only into the channels but not onto the fins between each
channel). An example for thin film deposition of catalytically
active systems is the sputtering of Pd90Au10 and GaPd on top
of CuPd membranes, which was applied for the direct hydrox-
ylation of benzene to phenol.[13] Furthermore, the sputtered
alloy-based system Au-Pd was investigated by Guo and co-
workers for the oxidation of benzyl alcohol as well as benzyl-
amine.[14]
Sputter Target Engineering
The preparation of an intermetallic sputter target of GaPd2
was necessary, as there are no intermetallic sputter targets
commercially available. Commercial targets were not single-
phase or contained just stoichiometric mixtures of the constitu-
ent elements. Pre-requisite for the synthesis of intermetallic
sputter targets are high-purity base materials, which is here the
intermetallic compound GaPd2. The single-phase nature was
proven by powder X-ray diffraction (pXRD) (Figure S1, Sup-
porting Information).
The subsequent synthesis of the intermetallic sputter target
was carried out by spark plasma sintering (SPS) from pow-
dered bulk-GaPd2. All sinter experiments were conducted in
vacuum to avoid oxidation during the high-temperature treat-
ment. Test samples with a diameter of 10 and 25 mm were
successfully synthesized. After optimizing the sintering param-
eters, well-compacted samples with 97.6% of the crystallo-
graphic density were obtained. The mechanical stability of the
small sintered samples was sufficient for the metallographic
preparation of cross sections. Optical as well as scanning elec-
tron micrographs were taken to get further information on the
compacting behavior and homogeneity of the sintered samples
(Figure S2, Supporting Information). Another part of each
sample was crushed and analyzed concerning phase composi-
tion, where solely the reflections of GaPd2 could be detected
in the respective X-ray diffraction pattern. As thermal expan-
sion was expected to occur in the target during the sputter
experiments, the stability of the target had to be enhanced by
a supporting layer. Freshly polished 3 mm thick copper discs
were used to increase the stability and heat conductivity of the
Reports on successful sputtering of single-phase inter-
metallic compounds are rare. There have been publications on
complex intermetallic compounds like Al4(Cr,Fe)[15] or
β-Al(Cu,Fe),[16] and some results for sputtering of simple bi-
metallic compounds with an equimolar atomic ratio and just
two atoms in the unit cell like FeCo.[17] But up to now, there
are no reports in literature about the successful sputtering of sputter target, which is in total 6 mm thick. Sinter experiments
single-phase intermetallic GaPd2. For instance, Kim et al. used of small test samples showed the same compacting behavior as
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
2
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
without a supporting disc. This was concomitant with a partial sition of the catalytically active layers inside the micro-struc-
reaction of the intermetallic compound with the copper re- tured channels, a magnetron power of 100 W and an argon
sulting in diffusion layers of 80 μm with three ternary Cu-Ga- partial pressure of 1.0 Pa was chosen, which corresponds to a
Pd compounds (Figure S3, Supporting Information). Their deposition rate of 20(2) nm·min–1. The relatively high standard
composition was determined by energy dispersive X-ray spec- deviation of the deposition rates is due to the decreasing layer
troscopy (EDX), which revealed that the diffusion direction thickness with increasing distance from the target. For each
goes from copper into GaPd2. These 80 μm regions are toler- deposition experiment, two glass discs (to quicker determine
ated, as the total intermetallic layer thickness of 3 mm is much the standard deviation) were mounted on the rotatable substrate
higher. Thereby sputtering of the binary intermetallic com- holder in front of the sputter target at a distance of 60 mm. The
pound is guaranteed for the major part of the sputter target.
spatial alignment of the substrates leads to small deviations of
Graphite foils were used to encase the test samples and final the final layer thickness depending on the local position. The
target during the sinter experiments, which afterwards strongly influence of this effect is minimized by reducing the amount
adhered to the sintered samples. Subsequent polishing re- of substrates per experiment and their arrangement directly
moved the graphite foil. The single-phase nature of the final side by side.
target was verified by pXRD in Bragg–Brentano geometry.
Subsequent optical examination of the micro-structured foils
The most intense reflections of GaPd2 were observed in the after deposition shows a uniform and smooth, metallic-sil-
sintered target and all reflections could be assigned to this in- verish coating over the entire sputtered area. Due to the ex-
termetallic compound.
pected high catalytic activity of the GaPd2 thin films, the
micro-structured foils were partially shielded with aluminum
foil leaving only a small slit in the middle of each foil in the
range of 1–1.5 mm situated for deposition of GaPd2. This pro-
cedure works well, but during assembly of the partly covered
micro-structured foils on the substrate holder, a slight shift of
the aluminum foil could not be excluded. This leads to a small
deviation of the desired coating-width in the range of 0.1 mm,
limiting the accuracy of the calculated catalytic activity.
DC Magnetron Sputtering
Thin, compact and uniform GaPd2 layers were successfully
deposited on borosilicate glass, Si(111) and stainless steel via
DC magnetron sputtering using the intermetallic target. Both
hydrogen and argon plasma were successfully ignited and
glowed very stable for the considered magnetron powers of
80–140 W and operating pressures pAr of 0.4–1.2 Pa. During
initial usage of the target, it was required to sputter for 1 h
without deposition using a shield in front of the substrate until
a stable magnetron voltage was reached. After that, only short
pre-sputter times of 3–15 min were necessary to equilibrate the
target for changed operation settings. Initially, the deposition
rate was determined by sputtering of samples on glass discs
applying different argon partial pressures and sputter times.
The layer thickness was calculated based on the weight gain
of the samples, which was converted into deposition rates. De-
position rates obtained from different sputter parameters are
given in Table 1.
Thin Film Characterization
Shiny, silverish thin films of GaPd2 were obtained on all
tested substrates, which were borosilicate glass discs, Si(111)
single crystals as well as planar and micro-structured stainless
steel foils. All films had metallic luster, appeared optically
homogeneous and had no faint shadows. Thin films were
firstly sputtered on amorphous borosilicate glass to determine
GaPd2 deposition rates r(GaPd2) and rЈ(GaPd2) because this is
the thinnest and lightest substrate, which is ideal for weighing
purposes. Thereafter, the phase composition was analyzed by
powder X-ray diffraction (pXRD) in the as-sputtered state
(Figure S4, Supporting Information). The diffraction pattern
was background corrected as the amorphous glass substrate
causes a broad and intense signal at low diffraction angles.
Nevertheless, all reflections can be assigned to the crystal
structure of GaPd2.[21] As glass is a brittle substrate, the fol-
lowing step was coating of more stable substrates. Si(111) sin-
gle-crystalline slabs are much more mechanically stable than
glass, they are easy to cut and possess a highly ordered surface.
Firstly, the deposited layer was investigated by pXRD and
grazing incidence X-ray diffraction (GIXRD) regarding its
Table 1. Deposition rates for different DC magnetron powers and ar-
gon partial pressures using an intermetallic GaPd2 target. During depo-
sition, the substrate was biased with 80 V.
PMagnetron /W pAr /Pa
r(GaPd2) /
nm·min–1
rЈ(GaPd2) /
nm·(min·kW)–1
100
100
100
140
80
0.4
0.8
1.0
0.8
0.8
18(1)
20(2)
20(2)
29(3)
16(4)
185(9)
195(16)
195(19)
204(24)
196(53)
The deposition rates r(GaPd2) show marginal dependency phase composition, where the obtained reflections were as-
on the argon partial pressure. Increasing the DC magnetron signed to intermetallic GaPd2 (Figure 1). The angle of incom-
power leads to an increased deposition rate. For a better com- ing X-rays (ω) was varied between 0.2 and 10° to analyze the
parison, the normalized deposition rate rЈ(GaPd2) per time surface and bulk composition, respectively. There are partially
(min) and power (kW) is introduced. Their values show that significant differences between the calculated and experimen-
the normalized deposition rate rЈ(GaPd2) can be approximated tally observed reflection intensities for different ω values,
to be constant at argon partial pressures in the range of 0.4– which could be caused by a (210) preferred orientation of the
1.0 Pa and DC magnetron powers of 80–140 W. For the depo- thin films. Some reflections are even entirely missing in the
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
3
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
powder diffraction pattern. Another reason for odd reflection
intensities could be the fixed position of the sample because
there was no possibility to rotate the samples during the mea-
surement. Thus, the sample might be not statistically orientated
and examined. Additionally, electron backscatter diffraction
(EBSD) was applied to reveal a preferred orientation of the
thin films. This failed most likely due to the low film thickness
and is still under investigation on thicker films.
Figure 2. Top view (electron micrograph) of a GaPd2 layer grown on
Si(111) at 100 W magnetron power and 80 V bias voltage.
Figure 1. GIXRD pattern of GaPd2 sputtered on Si(111) for different
incident angles (ω) and calculated powder pattern of GaPd2.[21] An
enlarged diffraction pattern for ω = 10° is shown in the inset. Calcu-
lated GaPd2 film thickness 1050 nm.
The main phase for all incoming angles is GaPd2. Neverthe-
less, elemental palladium cannot be fully excluded in the most
surface sensitive powder diffraction pattern (ω = 0.2) due to
partially identical positions of the most intense reflections.
The top view of a GaPd2 thin film as-sputtered on Si(111)
exhibits a flat and homogeneous surface that contains some
randomly distributed holes (Figure 2). EDX analysis and ele-
mental mapping were conducted on a cross section of GaPd2/
Si(111) to prove the elemental composition as well as a homo-
geneous distribution of Ga and Pd in the thin film. According
to EDX spectra, the thin film has the formula GaPd2.2(2), which
confirms the expected composition. Elemental mapping was
done for gallium, palladium and silicon to verify a homogen-
eous distribution of Ga as well as Pd in the thin film and for
exclusion of significant reactions of the sputtered layer with
the Si(111) substrate. According to EDX analysis, no preferred
deposition of Ga or Pd was detected (Figure 3). Instead, there
is a sharp boundary of the intermetallic layer and the substrate,
which confirms that no substantial reactions occurred during
the sputter process. Thus, crystal structure, chemical composi-
tion and elemental distribution for thin films deposited on
Si(111) turned out as expected for intermetallic GaPd2. The
substrate was accordingly changed from the model system sili-
con to stainless steel, which is the aimed-for substrate for the
subsequent catalytic investigations.
Figure 3. EDX mapping of a cross section of GaPd2 on Si(111). The
box in the BSE image represents the area that was used for EDX
compositional analysis presented in the text.
Thin films were deposited on stainless steel and initially in-
vestigated by GIXRD regarding their phase composition. The
incident angle (ω) was similarly varied between 0.2 and 10°
to analyze the surface and bulk composition, respectively. The
GaPd2 reflections overlap especially at low incident angles
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
4
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
partially strongly but most of the obtained reflections could be intrinsic roughness of the etched microstructured channels.
assigned to intermetallic GaPd2 (Figure 4). Additional reflec- Attempts to evaluate the specific surface area of the films by
tions that are caused by the stainless steel substrate are more electron microscopy and X-ray diffraction failed due to the
prominent for higher ω values as these measurements are more thin nature of the films as well as the structuring of the foils.
bulk sensitive. As already observed for GaPd2 on Si(111), there Characterization of the films on the flat substrates revealed
are partially significant differences between the calculated and very smooth surfaces (within an estimated roughness of 5 to
experimentally observed reflection intensities.
max. 10 nm), suggesting the use of the geometric surface area
resulting in an upper limit for the surface specific activity.
EDX analysis revealed a composition of GaPd2.0(1) on planar
steel as well as inside of the micro-structured stainless steel
foils. This is in full agreement with the expected composition
of GaPd2 as well as the thin films on Si(111). Hence, intermet-
allic GaPd2 thin films were successfully grown on borosilicate
glass, Si(111) and stainless steel, which enables catalytic in-
vestigations on a well-defined intermetallic compound.
Figure 4. GIXRD pattern of GaPd2 sputtered on planar stainless steel
for different incident angles (ω) and calculated powder pattern of
GaPd2.[21] An enlarged diffraction pattern for ω = 10° is shown in
the inset. Asterisks denote reflections of the stainless steel substrate.
Calculated GaPd2 film thickness 2280 nm.
Figure 5. Top view (electron micrograph) of a GaPd2 layer grown on
planar stainless steel at 100 W magnetron power and 80 V bias volt-
age.
Here, these differences are less pronounced but the reason
for this might be a preferred orientation of the thin films, too.
Due to the higher resolution of GIXRD data in contrast to
GaPd2/Si(111), elemental palladium can be excluded in all
powder diffraction patterns. Furthermore, there are no indica-
tions for other Ga-Pd phases or oxides in the GIXRD patterns,
whereby the thin film on the stainless steel foil is single-phase
GaPd2. Phase composition was also analyzed in the as-sput-
tered and annealed state for 20, 40 and 60 nm thick films,
which were later catalytically investigated. All samples
showed in as-sputtered state just two reflections that are caused
by the stainless steel substrate. After annealing at 723 K for
4 h in flowing Ar/H2, three reflections appeared for the 40 and
60 nm samples (Figure S5, Supporting Information). Due to
the very thin layer and thereby expected low intensities, there
are still no reflections for the 20 nm thin film (not shown).
The detected reflection positions can be explained by the most
intense reflections of the GaPd2 crystal structure.
Figure 6. SEM micrograph of the cross section of a GaPd2 coating on
the bottom of a micro-structured channel of a stainless steel substrate.
Catalytic Testing
The sputtered layers were firstly catalytically investigated
in the selective hydrogenation of acetylene without any pre-
The microstructure of thin films deposited on stainless steel treatment. This was based on experience with bulk-GaPd2,
was investigated from top and on a cross section to verify ide- where reduction is not necessary to exhibit 75% selectivity at
ally the same properties like on Si(111). Figure 5 shows a top conversion levels of 90–95%.[8] The as-sputtered sample
view of GaPd2 on planar steel and reveals a flat and homoge- shows at high conversion of slightly below 90% only a poor
neously appearing surface. In contrast to layers on silicon, selectivity of 20% (Figure 7), which reminds of supported ele-
there were no holes visible on the surface. The micrograph mental or alloyed Pd catalysts.[8] As elemental palladium can-
of a cross section of GaPd2 inside of a micro-structured foil not be fully excluded, this could be one reason for such a low
(Figure 6) reveals a dense and homogeneous layer. The rough selectivity. According to previous investigations of bulk- and
surface of the GaPd2 layer in Figure 6 could be due to the printed GaPd2, a pre-reduction step at 723 K for 4 h with
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
5
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Table 2. Catalytic performance of GaPd2 catalyst materials compared to 5% Pd/Al2O3.[8,12]
Catalyst
Conversion /% Selectivity /% nPd /mmol
Activity /molacetylene·(molPd·h)–1 Activity / molacetylene·(AO·h)–1
Bulk-GaPd2 [8]
94.7
86.5
91.8
41.1
39.8
36.1
44.9
75
67
76
72
74
71
17
7.08ϫ10–2
5.17ϫ10–5
7.82ϫ10–4
4.31ϫ10–5
8.62ϫ10–5
1.29ϫ10–4
7.05ϫ10–5
5.44
1.93
0.30
0.13
8.97
8.69
7.88
0.21
Nano-GaPd2/Al2O3 [8]
printed GaPd2/Al2O3 [12]
Sputtered GaPd2 20 nm
Sputtered GaPd2 40 nm
Sputtered GaPd2 60 nm
5% Pd/Al2O3 [8]
7.12ϫ103
4.80ϫ102
3.93ϫ103
1.90ϫ103
1.15ϫ103
2.45ϫ103
5 vol.% H2 in Ar was conducted prior to the catalytic test.[12] of Pd) of the compared systems. The first reason for the big
This treatment could remove thin oxide layers from the mate- difference between sputtered foils and nanoparticulate GaPd2
rial as well as improve the atomic arrangement within the sput- is the surface area, which is actually accessible for the catalytic
tered films. The beneficial effect of this pre-treatment is re- conversion. In case of the sputtered foils, this equals exactly
vealed by a catalytic test resulting in a selectivity of 73% at the calculated surface area and neglects the influence surface
82% conversion, which is very close to that of bulk-GaPd2 roughness on the nanometer scale, thus, these values represent
(Figure 7).
upper limits of the surface-specific activity. In contrast, for the
nanoparticles large parts of the surface are inaccessible be-
cause of the contact to the support. Additionally, agglomerates
with enclosed GaPd2 nanoparticles are not doing catalysis,
either. According to these points, it was estimated that the cata-
lytically accessible surface is just half of the total nanoparticle
surface, which would at the same time double their surface-
specific activity. The major reason for the huge difference be-
tween nanoparticles and the sputtered layers can be addressed
to structural differences of the nanoparticle surface, which do
not possess the ideal intermetallic structure like bulk GaPd2 or
the sputtered layers.[22] This is accompanied by strong surface
coverage with gallium oxides, which is another explanation for
the higher surface-specific activity of the sputtered layers.[22]
Finally, the potential (210) preferred orientation of the sput-
tered films could have led to the increased activity as well.
This option is evident because it is well-known that the cata-
lytic activity and selectivity can vary drastically on different
surfaces of the same intermetallic compound.[23] Thus, this
surface might be more active than the statistically orientated
bulk material.
The different dimensions of 7 and 20 nm for nanoparticulate
and sputtered GaPd2, respectively will cause higher mass-spe-
cific activity of the nanoparticulate sample. Going to even thin-
ner films should invert this behavior, which emphasizes the
great potential of thin film coatings like GaPd2 for their appli-
cation as catalytically active material and might be used for
other catalytic reactions as well. Due to technical limitations
of the used sputter device thinner films could not be synthe-
sized with the same set of sputter parameters. These param-
eters should be kept as changes could affect the layer proper-
ties.
Figure 7. Catalytic properties of GaPd2 thin films at 200 °C in the as-
sputtered state and after reductive pre-treatment for 4 h at 450 °C.
The specific activity of the thin films was determined by
covering the same area of three different micro-structured foils
with 20, 40, and 60 nm layers of intermetallic GaPd2, respec-
tively. The obtained conversion after 20 h time on stream is in
a close range for the three different layer thicknesses (Table 2).
Deviations from this will be mainly caused by the limited but
still high precision of the partial shielding of micro-structured
channels with aluminum foil during thin film deposition.
Based on the different total amount of palladium (nPd) within
the 20, 40, and 60 nm thick layers, having a proportion of
1 : 2 : 3, the expected mass-specific activities of those layers
should have a ratio of 1 : 0.5 : 0.333. The actual ratio (based
on the values in Table 2) of 1 : 0.48 : 0.29 is in good agreement
to our expectation and confirms the high precision of this coat-
ing approach. The surface-specific activity should be indepen-
dent of the layer thickness if the sputtered area would be the
same for all foils. As for the mass-specific activities the sur-
Conclusions
Thin films of the intermetallic compound GaPd2 were suc-
face-specific activities are very similar whereby the expected cessfully deposited as single phase on several substrates by
behavior could be proven. DC magnetron sputtering. The crystal structure of GaPd2 was
Very surprisingly, the surface-specific activities of these confirmed on all substrates and in as-sputtered as well as pre-
three foils are about 30 times higher than for nanoparticulate reduced state. Varying reflection intensities could be caused by
GaPd2/Al2O3, which possesses the highest activity (per amount a preferred orientation during thin film deposition. Differences
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
6
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
50 cut-off machine (Struers) and subsequently investigated for the
of the phase composition were pronounced for very thin films
compacting grade and possible reactions of the copper plate with inter-
metallic GaPd2 using an Axioplan 2 optical microscope (Zeiss) in
bright field and with polarized light. The grade of compacting was
determined by weighing the sample in ethanol and in air in the follow-
ing way:
Յ 60 nm, as the powder diffraction pattern after annealing at
723 K for 4 h revealed reflections that could be assigned to
intermetallic GaPd2. The layers are very dense and homogen-
eous. Differences between the thin films are the higher number
of holes for GaPd2 on Si(111) and the microscopically detected
higher surface roughness for layers inside of the etched micro-
structured reaction channels. Elemental composition of the lay-
ers was determined by EDX measurements, which approved
the expected composition of GaPd2. Subsequent EDX map-
pings showed homogeneous distribution of Ga as well as Pd
in the thin film and endorsed the absence of reactions between
substrate and the intermetallic layer. Catalytic tests were con-
ducted on thin films that were grown in micro-structured reac-
tion channels. The limited selectivity of as-sputtered GaPd2
proved a pre-reduction step to be necessary prior to the cata-
lytic experiments. This resulted in 73% selectivity, which is
very close to that of bulk-GaPd2. Small deviations from the
calculated values for activity per amount of palladium and sur-
face area were related to preparation accuracy. The highest ac-
tivity per molPd·h of the presented thin films (obtained on sput-
tered GaPd2 20 nm) is around 700 times higher than bulk ma-
terial, while the activity per surface area is for all thin films
about 4 and 30 times higher than values for bulk- and nano-
GaPd2, respectively. Films Ͻ 20 nm should have the potential
to outperform even the most active Ga-Pd catalyst material
reported in literature.[8]
ρEtOH(T) mair
ρarch
=
(1)
(2)
mair – mEtOH
100% ρarch
Grade of compacting =
ρIMC
where ρarch, ρEtOH(T), and ρIMC are the archimedean density, the tem-
perature dependent density of ethanol, and the density of intermetallic
GaPd2. The sample mass in air and in ethanol are denoted as mair and
mEtOH
.
Phase composition of the synthesized sputter target was analyzed by
pXRD in Bragg–Brentano geometry on a STADI MP diffractometer
(STOE) with CuKα1 radiation (λ = 1.540598 Å) and a Ge(111) mono-
chromator.
DC Magnetron Sputtering: Different materials were used as substrate
for the coating, namely: silicon (CrysTec, (111), CZ, p-type, boron
doped, polished), circular borosilicate glass discs (VWR, Mat. No.:
631–0172) as well as planar and micro-structured stainless steel foils
(Ätztechnik Herz, 1.4404). If the micro-structured foils should only be
partially coated, aluminum foil (ROTH Rotilabo, Al Ͼ 99%) was used
to protect those parts where no deposition should occur.
The PVD/CVD device STARON 6060 (PT&B Silcor) was used for
DC magnetron sputtering. The sputter target was installed vertically
into the vacuum chamber. The target was mounted on a copper plate
at the chamber wall for improved heat conduction to the cooling sys-
tem on the back side (Twater = 291 K). The substrate was connected to
a rotatable substrate holder and aligned parallel to the target at a dis-
tance of 60 mm. Vacuum below 5ϫ10–4 Pa was achieved using a
rotary valve pump (TRIVAC D65B), a roots pump (RUVAC WSU 501
H) and a turbo molecular pump (TURBOVAC T1600). During the
evacuation, the chamber was heated to 573 K for 30 min to improve
the removal of adsorbed species. After reaching the final vacuum, a
glow discharge cleaning was performed to remove impurities from the
surfaces of target, substrate holder and substrate. For this, a hydrogen
plasma (Air Liquide, 99.999%) was ignited and the substrate holders
were biased with a voltage ramp from 80 to 160 V and passed the
plasma several times until the measured current field was constant.
After that, a pre-sputtering step was conducted to remove any residual
species from the target surface (e.g. oxide layers) and to equilibrate
the plasma until a constant deposition rate was reached. For this, pure
argon (Air Liquide, 99.9999%) was supplied to the vacuum chamber
at a flow rate of 200 mL·min–1 and Ar partial pressure as well as mag-
netron power were set as required for the subsequent sputter deposi-
tion. During the pre-sputtering, the substrate was covered by a shield
to avoid contamination. After reaching constant conditions, the shield
was removed and the substrate holder was biased with 80 V during
the whole sputter deposition to improve coating adhesion. An overview
of the used parameters for all steps is given in Table 3. To determine
deposition rates, films with masses of 1.371–2.562 mg were deposited
and weighed with an accuracy of 0.001 mg.
Experimental Section
Sputter Target Synthesis: GaPd2 was synthesized as described pre-
viously by melting the appropriate amounts of gallium (ChemPur,
99.9999%) and palladium (KOOS Edelmetalle, 99.95%) in a high-
frequency furnace (Hüttinger TIG 5/300) in an argon atmosphere and
subsequent annealing in evacuated quartz glass ampoules for 10 d at
1073 K in batches of 20 g.[24] The phase composition of each batch
was analyzed by powder X-ray diffraction (pXRD) on an image plate
Guinier camera G670 (Huber) with CuKα1 radiation (λ = 1.540598 Å)
and a Ge(111) monochromator.
The compacting of the intermetallic sputter target was carried out by
spark plasma sintering (SPS) from powdered bulk-GaPd2. Test samples
were synthesized on a 515 ET (Syntex-Fuji) and had a diameter of 10
as well as 25 mm. The final sputter targets, which were synthesized
on a HP D 250C (FCT Systeme) possessed a diameter of 100 mm. The
experiments were carried out under vacuum at a background pressure
of less than 10 Pa. All samples were sintered on a freshly polished
3 mm thick oxygen-free copper disc (Allmeson, Ն 99.95%) of the
same diameter enhancing the stability and heat transport of the target,
which had a total thickness of 6 mm in the end. All SPS experiments
were conducted in appropriate graphite dies using graphite punches to
apply uniaxial pressure and graphite foil on all sides to isolate the
sinter samples from the punches as well as the dies. For the final
sputter target, the loaded die was heated to 673 K with 29 K·min–1
whereafter a force of 48 kN (equal to a pressure of 30 MPa) was ap-
plied. While keeping this pressure, the temperature was raised to
1223 K with 29 K·min–1 and held for 60 min. The graphite foil was Post-Treatment: The sputtered specimens were annealed exactly like
removed after sintering by manual polishing with silicon carbide paper. the reduction step before each catalytic experiment. This was con-
Cross sections of the test specimens were produced by an Accutom- ducted in 40 mL·min–1 flowing Ar/H2 (5 vol.% H2 in argon
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
7
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Table 3. Overview of DC magnetron sputter algorithm and main parameters for obtaining intermetallic GaPd2 coatings.
Step
t /min
UBIAS / V
PMagnetron /W
Sputter gas
p / Pa
Plasma cleaning
Pre-sputtering
Sputtering
10
30
1–3
80–160
–
80
100
100
100
H2
Ar
Ar
0.8
0.8
0.8
a)
a) Sputter times used for coating of micro-structured foils. Sputter times to obtain thicker or thinner layers for characterization purposes were
adjusted accordingly.
(Ͼ 99.998%) in a quartz glass tube. The tube was evacuated before The reactants were mixed using Bronkhorst mass flow controllers. The
and after each annealing to avoid oxygen contamination during the initial gas mixture with a total flow of 40 mL·min–1 consisted of 0.5
heat treatment. The annealing temperature was set to 723 K, which vol.% C2H2 [Praxair, 99.6%, 5 vol.% in He (99.996%)], 5 vol.% H2
was held for 4 h applying heating as well as cooling rates of (Praxair, 99.999%), 50 vol.% C2H4 (Westfalen Gas, 99.95%) and He
5 K·min–1. After cooling to room temperature, the samples were stored (Praxair, 99.999%). A Varian CP 4900 micro gas chromatograph (GC)
in vacuum until they were further analyzed.
was used to analyze the product gas stream in a 5 min interval on three
columns in parallel. The GC consisted of three modules, each with an
individual column and a thermal conductivity detector (TCD). A 5 Å
mol sieves column was used to detect hydrogen and helium from the
feed gas as well as nitrogen and oxygen, which are possible impurities
resulting from leaks of the experimental set-up. Acetylene, ethylene
and ethane were separated on an alumina column. A CP Sil 5 CB
column was used to separate the higher hydrocarbons, which are n-
butane, 1-butene, trans- as well as cis-2-butene and 1,3-butadiene.
Higher C6 and C8 hydrocarbons were not detectable.
Characterization of Sputtered Layers: Phase composition of the
sputtered layers was firstly determined by pXRD on an image plate
Guinier camera G670 (Huber) and in Bragg–Brentano geometry,
respectively. The fixed angle ω of the incoming beam was varied be-
tween 2 and 14.4° depending on the thickness of the sputtered layer.
Additionally, exemplary samples were investigated by grazing inci-
dence X-ray diffraction (GIXRD) at the MPI beamline at the synchro-
tron “Angström Quelle Karlsruhe“ (ANKA) in a helium flushed
dome.[25] The GIXRD measurements were conducted using a mono-
chromatic photon energy of 10 keV, which corresponds to λ =
1.239842 Å.
For the analysis of the catalytic performance, the conversion of acetyl-
ene (C) and the specific activity of the intermetallic nanoparticles (A)
were calculated. Additionally, the selectivities to ethylene (S), as well
as to C4 hydrocarbons [S(C4Hx)] were determined. The conversion (C)
was calculated by the following equation, where φin and φout are the
volume fractions of acetylene in the feed (in) and in the product stream
(out), respectively.
Microstructural arrangements of the sputtered layers were investigated
on cross sections and top views by a JSM-7800F (JEOL) scanning
electron microscope (SEM), which is equipped with a QUANTAX 400
EDX system (Bruker). The deposition rates r(GaPd2) at various argon
partial pressures were calculated by the following equation:
φin – φout
C =
ϫ100%
(4)
4 m(GaPd2)
π ρ(GaPd2) d2 t
φin
r(GaPd2) =
(3)
The activity is applied to compare various catalysts or the same cata-
lyst with different masses or shapes and was calculated according to
the following equations:
where m(GaPd2) is the mass of deposited GaPd2 that was sputtered
on a circular area with the diameter d. The deposition time and the
crystallographic density of GaPd2 are indicated by t as well as
ρ(GaPd2). For this, the weight gain of borosilicate glass probes was
measured after the sputter process. Knowing the density of the layer
and the sputtered area allows for calculating the height of the sputtered
layer. The layer thickness was additionally confirmed by SEM images
of the cross-section of selected samples. These measurements were
conducted on a JSM-6300 (JEOL) and a JXA-8530F (JEOL) electron
probe microanalyzer (EPMA).
C n
˙
ac
A =
(5)
(6)
nPd
p v˙ac
n˙ac
=
RT
where nPd is the total amount of palladium within the nanoparticles
and n˙ac is the amount of acetylene in the feed per hour, respectively.
Catalytic Testing: The catalytic measurements were carried out in The volumetric flow rate v˙ac is converted into the hourly amount of
a dedicated micro-structured clamp reactor fabricated by IMVT and acetylene by using the ideal gas law with the pressure p (1.013 bar),
described in[12] which was adapted to a Microactivity Reference sys-
the temperature
T (298 K) and the universal gas constant R
tem from PID Eng&Tech. The present reactor, which is applicable up (8.3144 J·mol–1·K–1). As the catalytic tests were carried out in a very
to 523 K and a process pressure of 10 bar, consists of a stack of up to
20 micro-structured foils, where each foil contains 40 parallel reaction
strong excess of ethylene compared to acetylene, the small change of
this volume fraction cannot be measured accurately enough and thus,
channels. The intermetallic layers were sputtered directly into these cannot be used to calculate the ethylene selectivity. Additionally, the
semi-circular reaction channels having a diameter of 150 μm. For the calculation of this selectivity is based on the assumption that only
catalyst pre-treatment, a reduction at 723 K was conducted for 4 h in acetylene, which is hydrogenated to ethylene, can be further hydroge-
a quartz glass tube at 40 mL·min–1 flowing Ar/H2 (5 vol.% H2 in Ar
(Ͼ 99.998%)). The pre-treated foils were loaded in air or inside an Ar
filled glovebox into the reactor. Subsequent catalytic tests were con-
ducted for 20 h at 473 K.
nated to ethane. The selectivities were calculated by the following
Equation where φin and φout are the volume fractions of acetylene in
the feed (in) and in the product stream (out). Additionally, the volume
fractions of C2H6 and the sum of all C4 hydrocarbons are required
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
8
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
[7] a) K. Kovnir, M. Armbrüster, D. Teschner, T. V. Venkov, F. C.
as these compounds are the main by-products and strongly affect all
selectivities:
Jentoft, A. Knop-Gericke, Y. Grin, R. Schlögl, Sci. Technol. Adv.
Mater. 2007, 8, 420–427; b) J. Osswald, K. Kovnir, M. Armbrüs-
ter, R. Giedigkeit, R. Jentoft, U. Wild, Y. Grin, R. Schlögl, J.
Catal. 2008, 258, 219–227.
(7)
[8] M. Armbrüster, G. Wowsnick, M. Friedrich, M. Heggen, R. Car-
doso-Gil, J. Am. Chem. Soc. 2011, 133, 9112–9118.
[9] K. Schubert, J. Brandner, M. Fichtner, G. Linder, U. Schygulla,
A. Wenka, Microscale Thermophys. Eng. 2001, 5, 17–39.
[10] P. Pfeifer, Application of Catalysts to Metal Microreactor Sys-
tems, in Chemical Kinetics (Ed.: V. Patel), InTech: Rijeka, 2012;
pp 325–344.
(8)
Supporting Information (see footnote on the first page of this article):
Additional characterization of the sputter target and sputtered films.
[11] a) F. Vidal Vázquez, P. Simell, J. Pennanen, J. Lehtonen, Int. J.
Hydrogen Energy 2016, 41, 924–935; b) A. K. Mogalicherla, S.
Lee, P. Pfeifer, R. Dittmeyer, Microfluid. Nanofluid. 2013, 16,
655–666; c) W. Ehrfeld, V. Hessel, H. Löwe, Microsystems for
Gas Phase Reactions, in Microreactors, Wiley-VCH: Weinheim,
2004; pp 173–227.
Acknowledgements
Financial support from the Deutsche Forschungsgemeinschaft (DFG,
German Research Foundation) is acknowledged (grants AR 617/7 and
DI 696/11). RZ and MA thank Prof. J. Grin and Dr. H. Borrmann for
gratefully providing research facilities as well as substantial assistance
with the pXRD measurements at the Max Planck Institute for Chemical
Physics of Solids in Dresden, respectively. We thank Dr. U. Burkhardt
for the metallographic preparation as well as SEM investigations and
Dr. K. Meier-Kirchner for carrying out the SPS experiments.
[12] M. Siebert, R. R. Zimmermann, M. Armbrüster, R. Dittmeyer,
ChemCatChem. 2017, 9, 3733–3742.
[13] R. Dittmeyer, L. Bortolotto, Appl. Catal. A 2011, 391, 311–318.
[14] H. F. Guo, M. Kemell, A. Al-Hunaiti, S. Rautiainen, M. Leskela,
T. Repo, Catal. Commun. 2011, 12, 1260–1264.
ˇ
[15] P. Panjan, M. Cekada, J. Dolinsˇek, B. Vrticˇ, A. Zalar, D. Kek-
Merl, Vacuum 2008, 82, 286–289.
ˇ
[16] M. Cekada, J. Dolinsˇek, P. Panjan, Vacuum 2005, 80, 137–140.
[17] a) C. Mathieu, M. J. Hadley, V. R. Inturi, J. Appl. Phys. 2008,
103, 07E715; b) Y. Fu, X. Cheng, Z. Yang, Phys. Status Solidi A
2005, 202, 1150–1154; c) M. Abuin, L. Perez, A. Mascaraque,
M. Maicas, CrystEngComm 2014, 16, 9528–9533.
Keywords: Ethylene; Heterogeneous catalysis; Micro-struc-
tured reactor; GaPd2; PVD
[18] C. C. Kim, W. H. Kim, J. H. Je, D. W. Kim, H. K. Baik, S. M.
Lee, Electrochem. Solid-State Lett. 2000, 3, 335–337.
[19] M. Grodzicki, P. Mazur, J. Pers, J. Brona, S. Zuber, A. Ciszewski,
Appl. Phys. A 2015, 120, 1443–1451.
References
[20] L. Mayr, H. Lorenz, M. Armbrüster, S. A. Villaseca, Y. Luo, R.
Cardoso, U. Burkhardt, D. Zemlyanov, M. Haevecker, R. Blume,
A. Knop-Gericke, B. Klötzer, S. Penner, J. Catal. 2014, 309, 231–
240.
[1] T. E. Nowlin, Global Polyethylene Business Overview, in Busi-
ness and Technology of the Global Polyethylene Industry, John
Wiley & Sons, Inc.: Hoboken, 2014; pp 1–45.
[2] A. N. R. Bos, K. R. Westerterp, Chem. Eng. Process. 1993, 32,
[21] K. Kovnir, M. Schmidt, C. Waurisch, M. Armbrüster, Y. Prots, Y.
Grin, Z. Kristallogr., New Cryst. Struct. 2008, 223, 7–8.
[22] R. Leary, F. de la Peña, J. S. Barnard, Y. Luo, M. Armbrüster,
J. M. Thomas, P. A. Midgley, ChemCatChem. 2013, 5, 2599–
2609.
[23] M. Krajcˇí, J. Hafner, ChemCatChem. 2016, 8, 34–48.
[24] J. Osswald, R. Giedigkeit, R. Jentoft, M. Armbrüster, F. Girgsd-
ies, K. Kovnir, T. Ressler, Y. Grin, R. Schlögl, J. Catal. 2008,
258, 210–218.
1–7.
[3] D. Jeremic, Polyethylene, in Ullmann’s Encyclopedia of Industrial
Chemistry, Wiley-VCH: 2014; pp 1–42.
[4] A. Borodzin´ski, G. C. Bond, Catal. Rev.: Sci. Eng. 2006, 48, 91–
144.
[5] a) D. Teschner, J. Borsodi, A. Wootsch, Z. Revay, M. Hävecker,
A. Knop-Gericke, S. D. Jackson, R. Schlögl, Science 2008, 320,
86–89; b) M. M. Johnson, D. W. Walker, G. P. Nowack, Catalyst,
method for the treatment of a gaseous mixture and use of the
catalyst for selectively hydrogenating acetylene, 0064301 B1,
1985.
[25] A. Stierle, A. Steinhäuser, A. Rühm, F. U. Renner, R. Weigel, N.
Kasper, H. Dosch, Rev. Sci. Instrum. 2004, 75, 5302–5307.
[6] a) M. Armbrüster, R. Schlögl, Y. Grin, Sci. Technol. Adv. Mater.
2014, 15, 034803; b) S. Furukawa, T. Komatsu, ACS Catal. 2017,
7, 735–765.
Received: March 11, 2020
Published Online: ᭿
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
9
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
R. R. Zimmermann, M. Siebert, S. Ibrahimkutty, R. Dittmeyer,
M. Armbrüster* ............................................................... 1–10
Intermetallic GaPd2 Thin Films for Selective Hydrogenation
of Acetylene
Z. Anorg. Allg. Chem. 2020, 1–10
www.zaac.wiley-vch.de
10
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim