Tandem catalysts for the selective hydrogenation of butadiene with hydrogen generated from the decomposition of formic acid

Article abstract of DOI:10.1039/d1cc01954f

We report for the first time the selective hydrogenation of 1,3-butadiene to butene using formic acid as the hydrogen source with 1 wt% Pd/carbon in a continuous flow reactor. The catalytic results show that the selectivity is even higher when formic acid is used compared to gas hydrogen.

Full text of DOI:10.1039/d1cc01954f

Showcasing research from D. H Carrales-Alvarado,
A. B. Dongil, A. Guerrero-Ruiz and I. Rodríguez-Ramos,
Laboratory at Instituto de Catálisis y Petroleoquímica
(CSIC), Spain.
As featured in:
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Pages 6455–6572
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Tandem catalysts for the selective hydrogenation
of butadiene with hydrogen generated from the
decomposition of formic acid
Chemical Communications
rsc.li/chemcomm
Pd/carbon nanofibers selectively catalyse the partial
hydrogenation of 1,3 butadiene with in situ generated
hydrogen from formic acid, surpassing the selectivity
obtained with molecular hydrogen. 1-butene is used for
the production of linear low-density polyethylene. The
results offer good prospects to further expand the
process to other hydrogenations.
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Tandem catalysts for the selective hydrogenation
of butadiene with hydrogen generated from the
decomposition of formic acid†
bc
Cite this: Chem. Commun., 2021,
57, 6479
Received 13th April 2021,
Accepted 7th May 2021
D. H. Carrales-Alvarado,a A. B. Dongil, *a A. Guerrero-Ruiz
*
and
ac
I. Rodrıguez-Ramos
´
DOI: 10.1039/d1cc01954f
rsc.li/chemcomm
We report for the first time the selective hydrogenation of 1, regard, some Pd optimised systems for liquid-phase FA decom-
3-butadiene to butene using formic acid as the hydrogen source position have been recently reported.4
with 1 wt% Pd/carbon in a continuous flow reactor. The catalytic
Recently we have developed a Pd-based catalyst supported
results show that the selectivity is even higher when formic acid is on carbon nanofibers, which is promising for conjugated
used compared to gas hydrogen.
double bond olefins and alkyne hydrogenations.5 For this
catalyst, we demonstrated that Pd4S nanoparticles are excep-
The chemical industry needs about 40 million tons of hydrogen tionally active, stable and selective for gas phase hydrogena-
per year for chemical transformations. Of them, refineries are tion, even under more challenging industrial conditions of
the second largest consumer with 25%. As is well-known, moderate pressure.
biomass upgrading is even more hydrogen demanding than
We selected this reaction as the starting point to study
upgrading fossil-based molecules, since biomass holds a larger tandem reactions with formic acid, since the partial hydroge-
amount of oxygen which needs to be reduced for valorisation. nation of alkadienes is one of the most important and challen-
However, nowadays around 96% of hydrogen is obtained from ging processes in the chemical industry.
fossil derived compounds.1 So, taking all this into account if we
To date the selective hydrogenation of C–C bonds in dienes
want to change to more sustainable chemical production, it is using FA directly as the hydrogen source has not been reported.
mandatory to find alternative hydrogen sources. In this context, And there are no studiesthat address the critical question of the
the use of biomass derived molecules emerges as an excellent role of the secondary by-products formed in the formic acid
and well-suited solution to be used in future biorefinery decomposition reaction, in particular H2O and CO.
schemes. Among those molecules, formic acid (FA) is highly
In this study we have simultaneously performed the decom-
interesting since it is produced in large amounts as a subpro- position of FA and the hydrogenation of 1,3-butadiene (HBD),
duct of cellulose hydrogenolysis, and its decomposition to H2 FA being the hydrogen supplier. The catalysts used are based
takes place under mild conditions.2,3
on Pd supported on carbon nanofibers and commercial high
One of the limitations of using FA is that the dehydrogena- surface area graphites. Two commercial carbon nanofibers,
tion reaction to produce CO and H2O also takes place at low Pyrograph (PR24-HHT and PR24-PS), were used as supports.
temperatures, ca. 150 1C.2 This reaction reduces the H2 avail- The difference between them is the final treatment tempera-
ability and the as-produced CO can poison the catalyst, so an ture. While PR24-HHT was subjected to temperatures over
optimal design of the catalytic system must be done. In this 3000 1C, PR24-PS was subjected to temperatures of 700 1C. This
indicates that the former holds a more graphitic surface with
less reactive sites, implying larger nanoparticles. The catalytic
a
´
´
Instituto de Catalisis y Petroleoquımica, CSIC, c/Marie Curie No. 2, Cantoblanco,
materials were prepared by incipient wetness impregnation,
with a 1 wt% Pd loading, and reduced as detailed in the ESI.† As
for these catalysts we can manage the selectivity to butenes, and
we aimed to verify the catalytic properties to hydrogenate
butadiene when the hydrogen reactant is produced in the same
catalytic bed by FA decomposition.
Madrid 28049, Spain. E-mail: a.dongil@csic.es; Fax: +34915854760
b
c
´
´
´
Dpto. Quımica Inorganica y Tecnica, Facultad de Ciencias UNED,
Senda del Rey 9, Madrid 28040, Spain. E-mail: aguerrero@iccia.uned.es
˜
´
UA UNED-ICP(CSIC), Grupo de Diseno y Aplicacion de Catalizadores
´
Heterogeneos, Madrid, Spain. E-mail: a.dongil@csic.es, aguerrero@iccia.uned.es;
Fax: +34915854760
† Electronic supplementary information (ESI) available: Details of materials and
methods, characterization of materials and reaction results. See DOI: 10.1039/
d1cc01954f
Measurements of the catalyst activity both for vapor phase
FA decomposition and for HBD were carried out in a fixed-bed
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Fig. 2 TEM images of (a) Pd/H100, (b) Pd/H300, (c) Pd/PS and (d) Pd/HHT.
Fig. 1 FA conversion and selectivity with respect to temperature over a Pd
Table 1 Surface area, CO uptake and TEM particle size
based catalyst.
SBET (m2 gÀ1
)
CO-uptake (mmol gÀ1
)
PdTEM (nm)
a
Catalyst
Pd/HHT
Pd/PS
Pd/H100
44
41
69
272
2.3
2.3
10.1
10.7
3.2
2.4
2.2
2.2
flow reactor and the details are given in the ESI.† The first step
of this study was done to assess the temperature that could
offer at least a H2/BD ratio of 2 and the highest selectivity to Pd/H300
CO2 for all the tested catalysts. Hence, Fig. 1 shows the curves
a
Surface area of the reduced catalyst.
of conversion of FA and selectivity to CO2 vs. reaction tempera-
tures. Experimental data indicated that Pd/H100 and Pd/H300
have similar behaviour, reaching 100% conversion at 190 1C.
According to the results obtained through the light-off
The conversion profile shifted to higher temperatures for Pd/ curves, the conversion and selectivity obtained at 200 1C should
HHT and Pd/PS, so 100% conversion was obtained at 250 1C. be adequate to obtain a H2/BD ratio over 2 in every catalyst, i.e.
On the other hand, the selectivity to CO2 was high for all the 2.4 for Pd/H100 and Pd/H300 and 2.1 for Pd/HHT and Pd/PS.
catalysts and in the range of 94–97% with minor differences These ratios would be suitable to perform the HBD tests
within the experimental error. These selectivity values resulted avoiding apparent selectivity due to limiting hydrogen reactant
in CO concentrations of 0.04–0.20 mL minÀ1. However, when conditions.
analysing the activity per surface mol (TOF) estimated using the
Hence, we evaluated the catalysts in FA decomposition at 200 1C
CO uptake from chemisorption analyses, the values, included for 600 minutes and the obtained H2 flow (mL minÀ1) is included
in Fig. 1, indicate that Pd loaded onto nanofibers is slightly in Fig. S3a and b (ESI†). Under these conditions, the H2 flow
more active than that on the commercial graphites.
obtained reached a quite stable value of 3.3 mL minÀ1 for Pd/H100
,
The reaction mechanism of FA decomposition has been 3.4 mL minÀ1 for Pd/H300, 2.4 mL minÀ1 for Pd/PS and 2.1 mL
described previously by a formate mediated path, which can adsorb minÀ1 for Pd/HHT. However, these values resulted in lower H2/BD
either mono or bidentate.6 Tentatively, the bidentate formate ratios than those expected by a previous experiment at this
species would be more favoured on the largest Pd particles temperature, which for Pd/HHT is indeed below 2, i.e. 1.5, as
observed on the nanofibers HHT, in Fig. 2 and Table 1, and this shown in Fig. 3c. This results from the slight deactivation of the
could explain the higher activity of these catalysts. The adsorption catalysts under steady state operation. This minor deactivation of
through both carbonyl and hydroxyl groups in a bidentate mode the catalysts could be explained by CO poisoning which is pro-
promotes the formation of HCOO which is the precursor of CO and duced through the formic acid dehydration reaction, and would
could also explain the lower selectivity of the nanofibers compared remain irreversibly adsorbed on the Pd surface.
to the graphites. As for the catalyst Pd/PS, despite the microscopy
Although this lower H2/BD ratio was also used for BD
showing a high proportion of small nanoparticles, it also displays hydrogenation for comparison, for the purpose of this research
larger particles (see Fig. 2c) that allow the identification of the we tested both Pd/PS and Pd/HHT at 250 1C for 600 minutes. At
Pd(111) phases by XRD, as shown in Fig S2a and b (ESI†). This this temperature, the H2/BD ratio was ca. 2.1 and 2.3 for Pd/
probably favours a similar catalytic behaviour on FA decomposition HHT and Pd/PS respectively, so these conditions can be used to
to that observed on Pd/HHT.
evaluate BD selective hydrogenation to butenes.
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the trend: Pd/HHT 4 Pd/PS 4 Pd/H300 4 Pd/H100. However,
the highest value was quite modest, ca. 25%, and the latter
catalyst barely displayed any selectivity to butenes. Moreover,
the selectivity profile in Fig. S4b (ESI†) showed that it decreases
during the first 60 minutes on stream by 39% and 28% for
Pd/PS and Pd/HHT respectively at 200 1C, and then the values
remain quite constant. This behaviour might be due to mod-
ifications on the active phase due to carbon covering. Coke
deposition on low coordinated sites seems to enhance the
diffusion rate of subsurface hydrogen, favouring the hydroge-
nation of alkenes.8,9
With regard to the effect of the temperature in the experi-
ments using line H2, interestingly the selectivity to butenes with
the catalyst Pd/HHT increases at 250 1C compared to 200 1C
(30 vs. 25%), this being much more produced for Pd/PS (75 vs.
8%). Also, the selectivity of Pd/PS at 250 1C increases during the
first 180 min from 52 to 75%.
On the one hand, the particle size of Pd can influence the
selectivity since it is possible that smaller particles, which are
more positively charged, favour the BD and further butene
adsorption through their electron rich double bonds, leading
to the complete hydrogenation to the alkane.10 Thus, the small
particle size of both Pd/H100 and Pd/H300 could lead to a
stronger adsorption of reactants on the surface of Pd/H100
and Pd/H300, responsible for their lower selectivity to butenes.
Moreover, Pd hydride species could be more active in the
hydrogenation to the alkane since more H atoms are available
to react. The Pd hydride formation can occur during the
reduction step of the catalysts or during the reaction even at
room temperature, and their presence was indeed verified by
the appearance of negative peaks during the H2-TPR analyses in
Fig. S5 (ESI†) indicative of H2 evolution from the hydride.11
While Pd hydride is noticeable for all the tested catalysts, and
no apparent H2 consumption is observed during the TPR
Fig. 3 FA conversion and the selectivity to CO2 during the reaction tests
at 200 1C (H100 and H300) or 250 1C (PS and HHT). (a) Decomposition of
formic acid and (b) hydrogenation of butadiene using H2 from FA.
(c) Comparative HBD selectivity to butenes and butane using H2 produced
from FA or the H2 line at 100% conversion of BD.
Then, once the best conditions were selected, we evaluated experiment, the temperature at which it appears is higher for
the hydrogenation of BD using FA and H2 from the line. We Pd/H300 than Pd/H100, which means that more stable hydride
observed that for every catalyst, under the studied conditions,
the conversion of FA in the presence and absence of BD was
similar within experimental error. These results are in contrast
to those reported in the hydrogenation of ethylene and propy-
lene where authors observed a higher conversion of olefins in
the presence of formic acid.7 This was explained by the faster
species are formed on Pd/H300. It could then be expected that
the Pd hydride of Pd/H100 can provide more readily available H
atoms for the hydrogenation of butenes, which can explain the
lower selectivity of Pd/H100 compared to Pd/H300. Unfortu-
nately, the small Pd size on Pd/H100 and Pd/H300 does not
allow the identification of any Pd-hydride diffraction in XRD in
consumption of hydrogen in the presence of the olefin, which Fig. S1 (ESI†) and whose position could be used to compare the
would decrease the concentration of hydrogen on the surface extent of hydrogen adsorption on the catalysts.
allowing more formic acid molecules to react.
On the other hand, the selectivity results obtained with Pd/
PS and Pd/HHT can be tentatively ascribed to the effect of
particle size and the presence of sulphur species on Pd/PS. At
200 1C using line H2, the selectivity to butenes is higher on the
catalyst Pd/HHT in agreement with their larger average Pd
particle size and related to electronic effects, as explained
above. For the Pd/PS catalyst, possibly two opposite indiscern-
The average selectivity to butenes along with the H2/BD
ratios is shown in Fig. 3c. The experiments with the H2 line
were performed using a H2/BD ratio of 3. The reliability of the
experiments was assessed by testing the catalyst Pd/H100 using
a 2.5 H2/BD ratio, indicating that the selectivity to butenes is
not affected within these ratios.
The results in Fig. 3c clearly demonstrate that not only it is ible effects should be considered: the presence of a large
possible to use formic acid as the hydrogen source, but also
that the selectivity to butenes is enhanced significantly com-
pared to the selectivity when using hydrogen from the line. The
selectivity to butenes using H2 from the line at 200 1C followed
proportion of small particles which tend to diminish the
selectivity, and the sulphur species which could promote
the selectivity to butenes. In our previous work we showed that
the sulphur species are less prone to adsorb hydrogen and/or
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butadiene. The role of this S–Pd species is explained by changes more influenced during formic acid decomposition to be more
in the availability of surface and subsurface hydrogen.5,12 selective to butenes. This is better explained if CO poisoning of
However, upon increasing the reaction temperature up to the most active sites of the catalysts occurs. Also, this explana-
250 1C, the selectivity trend changes and now Pd/PS are much tion agrees with the estimated amount of CO produced from FA
more selective than Pd/HHT to butenes. A control experiment dehydration which is higher for Pd/H100 and Pd/H300. In con-
with Pd/H300 using the H2 line at 250 1C indicated that for this trast, although Pd/PS and Pd/HHT also increase the selectivity
catalyst the selectivity did not vary compared to that obtained at when FA is used at 250 1C, the relative increase is lower, i.e.
200 1C. Since the particle size of the spent catalyst Pd/PS from 30–75% to 75–100%.
(Fig. S1a, ESI†) does not vary either at 200 1C or at 250 1C,
another phenomenon should explain this difference.
The most interesting finding of the present work is the
significantly higher selectivity to butenes obtained when using
The higher selectivity obtained at 250 1C for both Pd/PS and formic acid as the hydrogen source. These results are relevant
Pd/HHT could be related to the favoured fast recombination of since they show that it is possible to directly hydrogenate C–C
H atoms from the hydride at higher temperatures, which would double bonds using formic acid as the source of hydrogen in
result in the reduced availability of hydrogen to hydrogenate the same catalytic bed, feeding simultaneously both reactants.
the butenes. In contrast, the palladium hydride formed on Interestingly, selectivity to butenes is much higher than that
Pd/H300 is more stable, likely hampering the recombination of obtained with the same catalyst using hydrogen gas as a
H atoms, hence not affecting selectivity.
reactant. In short, this tandem reaction gives place to an active
Finally, we evaluated the target process and the selectivity to and very selective catalyst for the partial HBD into butenes. This
butenes using formic acid as the hydrogen source at 200 or is an example of reutilization of a natural by-product that can
250 1C was measured. The higher selectivity at 200 1C with Pd/ additionally serve as a selectivity promoter for the partial
PS and Pd/HHT is well-explained by the lower H2/BD ratio, and hydrogenation of butadiene into butenes.
only the selectivity at 250 1C will be considered in the discus-
This work was supported by the Spanish Agencia Estatal de
´
sion. The selectivity followed the trend Pd/PS (99%) 4 Pd/HHT Investigacion (AEI) and EU (FEDER) (projects CTQ2017-89443-
(73%) 4 Pd/H100 (44%) 4 Pd/H300 (5%). In Fig. S3 (ESI†) the C3-1-R and CTQ2017-89443-C3-3-R). DHCA acknowledges
progress of production of H2 and H2 not consumed in financial support from the Consejo Nacional de Ciencia y
´
´
the conversion of BD is shown. These profiles indicate that Tecnologıa, CONACyT, Mexico [grant numbers 2019-000029-
the difference in H2 produced and consumed agrees well 01EXTV-00057].
with the theoretical BD fed and consumed in the HBD reaction.
Besides the measured concentration of H2 in the outlet, the
significantly different selectivity reached with Pd/H100 and
Pd/H300 despite using a similar H2/BD ratio during the experi-
ments with FA confirms that other parameters are responsible
Conflicts of interest
There are no conflicts to declare.
for directing the selectivity to partial hydrogenation products.
There are several factors that could explain the higher selectiv-
ity obtained with formic acid. Firstly, CO is produced during
Notes and references
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