ZnTa-TUD-1 as an easily prepared, highly efficient catalyst for the selective conversion of ethanol to 1,3-butadiene

Article abstract of DOI:10.1039/c8gc01211c

High performances in the conversion of ethanol to 1,3-butadiene were achieved with a Zn(ii) and Ta(v) catalyst supported on TUD-1, a mesoporous silica. The selectivity reached 73% after 3 h at 94% conversion. At an increased ethanol flow, the initial productivity increased to 2.45 g_1,3-BD g_cat^-1 h^-1, which remained stable for 60 h on stream, making it the most productive catalyst according to the literature. Preliminary characterization suggests that its morphological and acid properties contribute to these exceptional performances.

Full text of DOI:10.1039/c8gc01211c

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ZnTa-TUD-1 as easily prepared, highly efficient catalyst for the
selective conversion of ethanol to 1,3-butadiene
Received 00th January 20xx,
Accepted 00th January 20xx
G. Pomalaza,a G. Vofo, a M. Caprona and F. Dumeignila,*
DOI: 10.1039/x0xx00000x
www.rsc.org/
High performances in the conversion of ethanol to 1,3-butadiene
were achieved with a Zn(II) and Ta(V) catalyst supported on TUD-
1, a mesoporous silica. Selectivity reached 73% after 3 h at 94%
conversion. At increased ethanol flow, initial productivity rose to
2.45 g1,3-BD.gcat-1.h-1, which remained stable during 60 h on stream,
making it the most productive catalyst according to the literature.
Preliminary characterization suggests morphological and acid
properties contribute to these exceptional performances.
OH
C
A
B
2
2
OH
O
O
-
-
H2
-
H2O
+EtOH
D
E
OH
O
H2O
Figure
1 Main reaction pathway leading to 1,3-butadiene. Reaction steps are:
(A) ethanol dehydrogenation; (B) aldol condensation; (C) dehydration; (D) Meerwein–
Ponndorf–Verley-Oppenaur (MPVO) reaction; (E) dehydration.6
Introduction
1,3-butadiene (herein referred to as 1,3-BD) is considered the
most economically important unsaturated C4 compound; it is
indeed crucial to the manufacturing of several polymers, such
as synthetic rubber.1,2 1,3-BD is predominantly extracted from
the C4 fraction following ethylene manufacturing via the steam
cracking of naphtha.1,2 Because of scarcity issues and
environmental concerns, sustainable on-purpose production
methods for 1,3-BD are of topical interest. Bioethanol can be
obtained from renewable sources.3 For this reason, the
catalytic conversion of ethanol (EtOH) to 1,3-BD is attracting
much attention, despite being an old technology.4 Recent
research has focused on increasing 1,3-BD yield and
productivity through catalyst design, with the aim of turning
the ethanol-to-butadiene (ETB) reaction into an economically
viable process.5
known as aldolization (steps A and B in Figure 1) can occur on
basic sites.8,9 Metal nanoparticles are also suitable for step A.10
Furthermore, maximizing 1,3-BD formation necessitates a
catalyst with an adequate balance of such properties.11
Otherwise, alternative reaction pathways may be favoured,
leading to the formation of undesired by-products, such as
ethylene or butanol.12
Recent improvements in the design of catalysts for the ETB
reaction have yielded high-performing materials.4 The
combination of supported Lewis-acidic metal oxides [Zr(IV),
Hf(IV), Ta(V) or Nb(V)] with dehydrogenation promoters (Ag,
Cu) has afforded highly active catalysts.13–15 The use of
mesoporous catalyst carriers was also demonstrably increased
catalytic stability and 1,3-BD selectivity.14,16,17 Recently, Lee et
al. designed a highly selective and stable zirconia catalyst
supported on mesocellular siliceous foam.14 They attributed
the performances of their catalyst to two factors: (i) uniform
tridimensional mesoporous supports, enabling efficient mass
transfer and excellent resistance to coke, and (ii) highly
dispersed active metal oxides. The benefits of mesoporous
morphology to the catalytic performances were also observed
by others.16–18 Yet, this strategy is underutilized, with many
recent works preferring tried-and-tested microporous zeolite
supports, such as dealuminated zeolite beta.13,19 Perhaps the
time-consuming synthesis of mesoporous materials, such as
mesocellular siliceous foam and SBA-15, including the post-
Owing to its complex mechanism (Figure 1), the ETB
reaction requires multifunctional catalysts; most illustrated
steps occur on different catalytic sites, generally provided by
combining metals and/or metal oxides possessing the
appropriate chemical properties. For instance, acid sites are
suitable for the aldol coupling and dehydration reactions
(steps B, C and E in Figure 1).6,7 Ethanol dehydrogenation and
aldol coupling, also
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synthesis modifications needed to introduce an active phase, was maintained for 2 h. A clear gel was obtained and left to
hinders their use and study. age at room temperature for 24 h. The aged gel was dried at
In this work, we report the facile preparation and study of 100 °C for 24 h before being gently ground to a white powder
a Zn(II) and Ta(V) catalyst supported on mesoporous TUD-1, and subjected to a hydrothermal treatment in a Teflon-lined
achieving the aforementioned high performance-driving stainless-steel autoclave for 24 h at 180 °C. The resulting
factors highlighted by Lee et al.14 TUD-1 is a sponge-like brown powder was calcined at 600 °C in a tubular quartz
mesoporous silica with an irregular three-dimensional pore reactor for 10 h with a temperature ramp of 1 °C.min-1 and an
system.20 This material has found many applications as a air flow of 0.3 L.min-1. A fine white powder was ultimately
support for heterogeneous catalysts due to its numerous recovered.
practical advantages. Its structural properties are easily tuned
For comparison, additional catalysts with the same
following the preparation of a precursor gel by adjusting the amounts of Zn and Ta were prepared. In one case, zeolite BEA
duration of its hydrothermal treatment. This way, siliceous from Zeolyst international (CP814C) was dealuminated
foam with mesopores ranging from 2 to 20 nm and with following a procedure detailed in the literature.30 In another,
specific surface areas between 300 and 900 m2/g can be fumed silica (Alfa Aeser) was used. In both cases, the
obtained. Furthermore, metals or metal oxides are easily appropriate amounts of Zn and Ta were introduced via
dispersed within the silica framework through a simple incipient wetness impregnation (IWI) using the same precursor
modification of the one-pot synthesis. This way, bimetallic or salts as those used in the preparation of the TUD-1-based
bi-metal oxide systems are effortlessly synthesized to take catalyst. Drying and calcination according to the procedure
advantage of synergetic effects between two different active described above followed, resulting in white powders in both
phases.20 In addition, TUD-1 catalysts are usually highly active cases. The as-obtained benchmark catalysts were labelled
while showing a remarkable hydrothermal stability.20–25 The ZnTa/deBEA and ZnTa/SiO2, respectively.
key to TUD-1’s versatility and straightforward preparation is
Catalyst testing
the use of a chelating agent during the gelification process,
which doubles as a structure directing agent. By chelating Catalytic activity tests were carried out with a Multi-R®
precursor ions prior to gelification, it also ensures an excellent apparatus from Teamcat Solutions SAS.31 Multi-R® is a high-
degree of dispersion during the oxidizing calcination, which throughput equipment for heterogeneous catalysts screening.
frees the agent and condenses the silica, simultaneously This device consists of 3 main components: the feed, the
generating mesopores via steric hindrance.
reaction section and the analytical system. The gaseous feed is
Although both Zn(II) and Ta(V) have been used separately split and fed into 4 reactors using a splitter provided by the
in other ETB catalysts, they are seldom reported together. Zinc manufacturer. The machine is adjusted so that every reactor
oxide is cited as a promoter of ethanol dehydrogenation.26,27 receives an equal inlet flow in terms of gas composition and
Tantalum oxide was shown to reach remarkable selectivity flowrate. Catalysts are loaded in specific liners with sintered
when converting mixtures of ethanol with acetaldehyde.16,28,29 glass filters and inserted in the device, acting as fixed-bed
In the present work, when supported on TUD-1, stable 1,3-BD reactors. The temperature of each reactor is controlled
selectivity peaking at 73 % for an EtOH conversion of 96% was independently. Their output is analysed with an online GC
achieved (T: 400 °C, WHSVEtOH: 5.3 h-1, TOS: 3 h). Productivity is (Agilent 7890 A) equipped with a FID detector calibrated to
also exceptionally high and stable, despite the high ethanol detect and quantify the major products of the reaction, i.e.
flow employed, outperforming any other formulation disclosed 1,3-BD, acetaldehyde (AcH), ethylene (C2=), propylene, etc.).
so far in the direct conversion to 1,3-BD under comparable Choosing from the output of one reactor to another is done by
conditions.
an independently controlled valve.
Reaction temperature was set at 400 °C with a pressure of
1 atm. Catalysts were ground and sieved to 120 mesh-sized
granules; 30 mg of catalyst were loaded in the glass reactors
and held in place using SiC. Ethanol was introduced into the
splitter and then each reactor by passing helium through a
bubbler containing ≥ 99.8 % ethanol maintained at 25 °C. EtOH
vapour concentration was set at 4.5 vol.%. Helium flow and
catalyst mass were adjusted to provide a weighted hourly
space velocity (WHSVEtOH) of 2, 5.3 and 8 h-1.
Experimental
Catalysts preparation
A catalyst consisting of Zn(II) and Ta(V) supported on TUD-1
(labelled ZnTa-TUD-1) was synthesized with tetraethylene
glycol as a chelating agent in a one-pot procedure based on a
sol-gel methodology as found in the literature.24 The
appropriate amounts of Zn and Ta salts (zinc acetate
dehydrate and tantalum ethoxide) were first dissolved in
absolute ethanol with a Zn:Ta molar ratio of 1.5. Tetraethyl
orthosilicate (TEOS) was added drop-wise to the ethanol
solution while stirring. The chelating agent was subsequently
added in a similar fashion. After 1 h of stirring, an aqueous
solution of tetraethyl ammonium hydroxide (35 wt.%) was
added dropwise to the mixture under vigorous stirring, which
Catalyst regeneration was carried out in the same reactor,
under synthetic air with a flow of 10 mL.min-1 for a period of 6
hours at 400 °C.
Catalytic activity was characterized by the conversion of
ethanol (X, %), the selectivity towards each product (Si, %), the
molar yield of each product (Yi, %) and the productivity in 1,3-
BD (P1,3-BD, g1,3-BD.gcat-1.h-1). Each value was calculated according
to the following formulas:
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c0EtOH -cEtOH
X=
Si=
·100
·100
c0EtOH
Results & Discussion
ci
c0EtOH-cEtOH
Table 1 Catalytic performances of Zn(II) and Ta(V) on TUD-1, dealuminated
BEA and SiO2 in 1,3-BD production at 400 °C, WHSVEtOH of 5.3 h-1 after 3 h.
Yi=X·Si
P1,3-BD=X·S1,3-BD·ꢀꢁꢂꢃꢄꢅꢆꢇ·0.587/100
S1,3-BD
,
SAcH
,
SC2=
,
Y1,3-BD
,
P1,3-
CB,
Sample
X, %
a
%
%
%
%
,
%
BD
Where cEtOH is the amount of carbon moles from EtOH
entering the reactor, ci is the amount of carbon moles detected
for a given product i, the 0.587 coefficient represents the
100 % mass yield of butadiene and WHSVEtOH represents the
ZnTa-TUD-1
ZnTa/deBEA
ZnTa/SiO2
94
95
94
73
59
48
18
25
34
10
8
69
56
45
2.13 102
1.74
1.40
95
95
4
mass flow of ethanol per mass of catalysts (expressed as a1,3-Butadiene productivity in g1,3-BD.gcat-1h-1.
gEtOH.gcat-1.h-1). The carbon balance (CB) for each test was
Table 2 Metal loading and molar ratio in the studied samples.
calculated by dividing the sum of carbon moles detected with
the molar amount of carbon introduced as EtOH in
percentage.
Sample
Si/Zn
16.5
18
Si/Ta
29.6
30.3
31
Zn/Ta
1.79
1.67
1.61
Formula
ZnTa-TUD-1
ZnTa/deBEA
ZnTa/SiO2
Zn6.1Ta3.4-TUD-1
ZnT5.6Ta3.3/deBEA
Zn5.2Ta3.2/SiO2
19.2
Characterization
Physisorption experiments were performed at −196 °C on a
Micromeritics Tristar II instrument. Before analysis, a known
We benchmarked the performances of ZnTa-TUD-1 in terms of
1,3-BD selectivity and 1,3-BD productivity against those of
common materials: abundant publications on the Lebedev
process employ dealuminated zeolite and silica-supported
catalysts prepared through impregnation. 1,3-BD selectivity
demonstrably reflected the suppression of undesired
byproducts, the presence of which being detrimental to the
viability of bio-based processes.32 Productivity is also hailed as
an important indicator of industrial relevancy, unproductive
catalysts obviously preventing a robust economic viability.33
Carbon balance was within 95 and 105% over the course of the
experiments and considered as satisfactory. The results are
reported in Table 1.
mass of solid (∼ 50–200 mg) was outgassed under vacuum at
150 °C for 6 h. Specific surface area (SBET) could then be
calculated using the B.E.T. equation on the linear part of the
B.E.T. plot (P/P0=0.1–0.25). Average pore volume (Vp) was
measured from the adsorption branch of the isotherm, at a
P/P0 value of 0.98. The mean pore diameter (Dp) was
calculated by applying the Barrett-Joyner-Halenda model on
the desorption branch of the isotherm.
Powder X-ray diffraction (XRD) high angles patterns were
recorded on a Bruker AXS D5005 diffractometer using a CuKα
radiation (λ = 1.54184 Å) as an X-ray source in the 2θ range
from 10 to 50° with a step of 0.05° (integration time of 8 s).
Elemental analysis was performed with the catalysts using
inductively coupled plasma-optic emission spectroscopy 720-
ES ICP-OES (Agilent) with axial viewing and simultaneous CCD
detection. The quantitative determination of metal content in
the catalysts was made based on the analysis of certificated
standard solution. The analytes were prepared by dissolving
10 mg of dried and ground catalyst samples in concentrated
acid (HF:HNO3=1:3, v:v). Each sample solution was stirred
overnight in an ultrasonic cleaner heated to 50 °C before
dilution in 20 mL of ultrapure water and analysis.
EtOH conversion was equally high on all the catalysts,
reaching 94-95%. 1,3-BD selectivity depended on the catalyst,
peaking at 73 % over ZnTa-TUD-1. This value is relatively high
considering the elevated ethanol flow (WHSVEtOH: 5.3), most
articles reporting experimental conditions below 2 h-1 4
.
Conversely, selectivity over ZnTa/deBEA and ZnTa/SiO2 was
respectively 10 and 20 percentage points smaller. This
disparity was mirrored in the higher selectivity towards AcH
observed with both. These remarkable results are ostensibly
attributed to the choice of catalyst carrier, possibly to its
intrinsic properties or its synthesis procedure. To adequately
investigate this assumption, the three samples were prepared
with equal amounts of Zn(II) and Ta(V). Elemental analysis of
Si, Ta and Zn in the prepared catalysts was conducted using
ICP-OES, indicating that all the three catalysts containing
similar amounts of oxide phase and Zn/Ta ratio (Table 2). This
excludes the possibility that the performance difference
observed stemmed from uneven amounts of active phases.
Carrier morphology has been shown to influence catalytic
activity in the ETB reaction. Jones et al. observed an increase in
1,3-BD selectivity by up to 17 percentage points when the pore
size diameter of a silica support was increased from 6 nm to
Acid sites were quantified using NH3-temperature
programmed desorption (NH3-TPD). The measurements were
performed on calcined samples of known masses with a
Micrometrics Autochem 2920 apparatus coupled with
a
Pfeiffer mass spectrometer (MS). NH3 adsorption was
performed at room temperature during 30 min using a NH3
flow consisting of 5 % NH3 in 95 % He). Desorption was
performed until 900 °C (ramp of 10 °C.min-1) and held for
30 min in He (30 mL.min-1).
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15 nm.17 Likewise, Chae et al. also noted an initial benefit to TPD. Desorption profiles are illustrated in Figure S2 and the
increasing pore size diameter from 2.5 nm to 10.9 nm when results are summarized in Table 4. Figure S2 suggests the
existence of a single type of acid sites covering a broad range
of strengths in each catalyst, as evidenced by the single broad
Table 3 Morphological properties obtained by N2 physisorption.
peaks at 260 °C. The combination of Zn(II) with Ta(V) may
Pore vol.a,
cm3.g-1
2.20
Average pore
diameter, nm
13.6
a
Sample
SBET , m2.g-1
ZnTa-TUD-1
ZnTa/deBEA
ZnTa/SiO2
640
501
185
0.60
0.82
6.0
16.05
75
70
65
60
55
50
45
a Specific surface area b Pore volume, measured at P/P0 = 0.98.
Table 4 Amount of acid sites measured by NH3-TPD expressed by weight and surface
units
Nb of acid sites per weight
No of acid sites per surface
Sample
(mmol.g-1)
0.88
0.43
0.17
(mmol.m-2)
563
ZnTa-TUD-1
ZnTa/deBEA
ZnTa/SiO2
213
30
0
100
200
300
400
500
600
using SBA-15 as a catalyst carrier. However, these became
modest after 10 h on stream due to deactivation.16 As
stipulated by Lee et al., large and uniform pore sizes
contribute to a stable catalytic activity.14 Furthermore, Jones et
al. also have drawn a direct correlation between specific
surface area and 1,3-BD yield.34,35 These observations highlight
the importance physical properties have in the ETB reaction,
which were promptly investigated. Table 3 summarizes the
results obtained by N2 physisorption regarding the morphology
of the catalysts prepared. ZnTa-TUD-1 possessed the expected
morphological features: a large specific surface area (300-
900 m2.g-1), a large porous volume and mesopores (2-20 nm).20
Figure S1 indicates that the pore size distribution is uniform,
peaking at around 18 nm, with a full width at half maximum of
6.2 nm. Conversely, ZnTa/deBEA had a large specific surface,
but smaller pore volume and diameter, the distribution of
which was uneven. Figure S1 illustrates how it ranges from
nanopores inherent to zeolitic materials to mesopores formed
during the dealumination process. ZnTa/SiO2 had larger
average pore diameter compared to the TUD-1 sample, but
much smaller specific surface area and pore volume. Part of
the inferior performances can be attributed in part to a lack of
uniform mesopores in the case of zeolite-supported catalyst
and the smaller specific surface area of the silica-supported
catalyst. However, other factors should also be taken in
consideration.
Amount of surface acid sites/mmol.m-2
Figure 2 Correlation curve between 1,3-BD selectivity (T: 400 °C, WHSVEtOH: 5.3 h-1, P:
1 atm, TOS: 3 h) and total surface acidity.
ZnTa/deBEA
ZnTa-TUD-1
ZnTa/SiO2
0
10
20
30
40
50
2θ/degree
Figure 3 XRD patterns of synthesized Zn(II) & Ta(V) catalysts
explain the absence of acid sites desorbing at higher
temperatures, i.e., of stronger acid sites; some authors have
reported a passivation of strong acidity upon the introduction
of zinc oxide.15,36 Despite containing equal amounts of Ta and
Zn, the total amount of acid sites per gram differed according
to the catalyst carrier used. ZnTa-TUD-1 possessed the double
of acid sites than ZnTa/deBEA and five times more than
ZnTa/SiO2.
Sushkevich and Ivanova have identified a direct correlation
between the amount of Zr(IV) Lewis acid sites and the 1,3-BD
rate of formation.13 In their study of the reaction mechanism,
they propose that Lewis acid sites such as those brought by
Ta(IV) catalyze every reaction step subsequent to the initial
ethanol dehydrogenation step (aldol condensation, MPVO
reaction and alcohol dehydration).6 Since aldol condensation
has been identified as the rate-limiting step, the observed
accumulation of AcH suggests that the disparity in selectivity is
related to the acidic Ta(V) phase. The amount and strength of
acidic sites on the three catalysts were characterized by NH3-
A correlation between the amount of acid sites and
selectivity towards 1,3-BD after 3 h on stream was observed
(Figure 2). Considering that silicate-supported Ta(IV) is
predominantly Lewis acidic when reacting with alcohols, these
results are in line with the current theory regarding the ETB
mechanism.29 The amount of Ta being identical on each
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catalyst, this suggests that the dispersion was more successful commonly plagues the performances of ETB catalysts. Figure 4
using the TUD-1 methodology—thereby creating more isolated compares the conversion and selectivity to the three major
acid sites. ZnTa/deBEA was prepared using a method that products over ZnTa-TUD-1, ZnTa/deBEA and ZnTa/SiO2 over
generates isolated Ta(V) sites. However, it was successfully 20 h of reaction. Each catalyst suffered from a similar loss of
reported for Ta wt.% of 1, 2 and 3.29,37 In this work, the Ta activity in converting EtOH (about 10 percentage points in
loading reaches 10 wt.%, which may have proved too much for 20 h). The 1,3-BD selectivity also dropped over time, with AcH
proper dispersion using IWI. TUD-1 synthesis appears to be selectivity increasing as a result, suggesting that coke deposits
better suited for dispersing high active phase loadings.
gradually poison the active acid sites. The rate of deactivation
in terms of 1,3-BD selectivity depended on the material. ZnTa-
TUD-1 fell 7 percentage points over 20 h, whereas ZnTa/deBEA
and ZnTa/SiO2 decreased by 13 and 12 percentage points,
respectively. Ostensibly, the stability of the TUD-1 catalyst is
attributable to its uniform, three-dimensional mesopores.14
Having demonstrated both superior activity and stability,
ZnTa-TUD-1 was further tested to evaluate its performances
under different conditions. First, the effect of WHSVEtOH was
evaluated. As illustrated by Figure S3, ethanol conversion, as
well as 1,3-BD and ethylene selectivity decrease as function of
WHSVEtOH, while AcH selectivity increases. These results are
consistent with the model developed by Jones, Pinto et al.
regarding the effect of reaction conditions on catalytic
activity.38 The accumulation of AcH with increased WHSVEtOH is
also consistent with the conclusions that aldol condensation is
the rate-limiting step on solid acids.6
ZnTa-TUD-1
ZnTa/deBEA
ZnTa/SiO2
100
80
60
40
20
0
X, %
S1,3-BD, %
SC2=, %
SAcH,%
0
5
10 15 20
0
5
10 15 20
0
5
10 15 20
Time-on-stream/h
Figure 4 Performances of ZnTa-TUD-1 , ZnTa/deBEA and ZnTa/SiO2 over a 20 h period
Deactivation of ZnTa-TUD-1 was again tested. At WHSVEtOH
of 8 h-1, 1,3-BD selectivity was initially 66%, losing 13
percentage points over the course of 60 hours (Figure 5).
Ethanol conversion also decreased by 15 percentage points,
whereas AcH selectivity grew steadily to around 35% before
stabilizing at around TOS of 40 h. At TOS of 3 h, 1,3-BD
productivity is 2.45 g1,3-BD.gcat-1.h-1. A preliminary regeneration
attempt was conducted at 400 °C under air in an attempt to
remove coke deposits responsible for deactivation. Figure S4
illustrates how ethanol conversion, acetaldehyde selectivity
and ethylene selectivity were returned to their initial values.
However, 1,3-BD selectivity was only partially recovered and
continued the trend of deactivation following 15 hours of
reaction under the same conditions. These results suggest that
carbonaceous species are partly responsible for the loss of
catalytic activity. With regards to 1,3-BD selectivity,
deactivation may either be caused by species requiring
different, possibly harsher calcination conditions or that the
nature of the active site is compromised during the
reaction/regeneration procedure. Work is ongoing to
understand this phenomenon and to design an optimized
regeneration step.
(T: 400 °C, WHSVEtOH: 5.3 h-1, P: 1 atm).
100
X, %
S1,3-BD, %
SC2=, %
80
SAcH,%
60
40
20
0
0
10
20
30
40
50
60
Time-on-stream/h
Figure 5 Stability of ZnTa-TUD-1 at WHSVEtOH 8 h-1 (T: 400 °C, WHSVEtOH: 8 h-1, P: 1 atm).
Powder XRD diffractograms of the synthesized samples
(Figure 3) did not show the presence of bulk crystalline ZnO or
Ta2O5, suggesting only an absence of large extra framework
metal oxides particles. In addition, the diffractograms of ZnTa-
TUD-1 and ZnTa/SiO2 both possessed the broad bands around
15-30°, common on amorphous siliceous materials. Bands
typical of the BEA structure on the diffractogram of
ZnTa/deBEA—similar to those observed with other Ta-
containing dealuminated BEA—confirms that the carrier
retained its zeolite framework throughout the dealumination
and impregnation processes.37
Compared to the performances reported in the literature,
ZnTa-TUD-1 fared well: the other two most productive ETB
catalysts (hierarchical MgO-SiO2 from Men et al. and
ZnY/deBEA from Li et al.) lost their selectivity toward 1,3-BD
faster than ZnTa-TUD-1.19,39 Starting with a 1,3-BD selectivity
of 77%, MgO-SiO2 (T: 450 °C, WHSVEtOH: 4.1 h-1) lost 13
percentage points in 20 h.39 ZnY/deBEA (T: 400 °C, WHSVEtOH
:
7.9 h-1) decreased by 20 percentage points in 10 h from an
initial selectivity of 63%.19 Figure S5 illustrates the productivity
of the three catalysts as the reaction progresses. Figure S6
compares 1,3-BD productivity observed on ZnTa-TUD-1 with
Additional tests with the three synthesized materials were
conducted to measure their stability, as deactivation
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the other top 10 most productive catalysts found in the
literature at the different WHSVEtOH each were tested.
Admittedly, the difference in reaction conditions makes a
direct comparison partiality inaccurate, as we have
demonstrated that WHSVEtOH affects catalytic performances.
Nevertheless, these figures indicate that ZnTa-TUD-1 is the
most selective and stable catalyst at high ethanol flow,
boasting a 1,3-BD productivity of 2.45 g1,3-BD.gcat.h-1 after 3
hours. To the best of our knowledge, this makes it the most
productive catalyst recorded so far.
Conflicts of interest
There are no conflicts to declare.
Notes and references
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