Efficient PdNi and PdNi@Pd-catalyzed hydrogen generation via formic acid decomposition at room temperature

Article abstract of DOI:10.1039/c3cc46248j

Formic acid (FA) holds great potential as a convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage. Herein, the non-noble metal nickel (Ni) exhibits superior promoting effect in improving the catalytic activity of Pd toward high activity and selectivity for FA decomposition at room temperature.

Full text of DOI:10.1039/c3cc46248j

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Efficient PdNi and PdNi@Pd-catalyzed hydrogen
generation via formic acid decomposition at room
temperature†
Cite this: Chem. Commun., 2013,
4
9, 10028
Received 15th August 2013,
Accepted 4th September 2013
ab
ab
a
ac
a
Yu-ling Qin, Jun Wang, Fan-zhi Meng, Li-min Wang and Xin-bo Zhang*
DOI: 10.1039/c3cc46248j
www.rsc.org/chemcomm
7
Formic acid (FA) holds great potential as a convenient source of limit further improvement in the performance of the catalyst.
hydrogen for sustainable chemical synthesis and renewable energy Therefore, coupling the merits of both GNs and CB to enable the
storage. Herein, the non-noble metal nickel (Ni) exhibits superior facile and effective synthesis of a well dispersed metal NC catalyst in
promoting effect in improving the catalytic activity of Pd toward high aqueous solution and further discovering the intrinsically catalytic
activity and selectivity for FA decomposition at room temperature.
performances are highly desirable.
Herein, we advantageously combine Pd and Ni and use GNs–CB
Formic acid (FA), as a major product of biomass processing, as a support to form PdNi/GNs–CB NCs, which exhibit excellent
has attracted considerable attention as a potential hydrogen catalytic activity and hydrogen selectivity toward FA decomposition.
storage material due to its intrinsic advantages, including high Furthermore, PdNi@Pd/GNs–CB obtained via a substitution
4À
hydrogen content, nontoxicity and easy recharging as a liquid reaction between PdNi/GNs–CB and PdCl in aqueous solution
1
,2
(
the availability of the existing infrastructure for gasoline and oil).
To maximize the efficacy of FA as a hydrogen storage material, one
must follow the desired reaction pathway (HCOOH - CO + H
exhibits enhanced cycle stability.
Fig. 1A shows the plots of the volume of generated gas
2
,4
2
)
(CO
2 2
+ H ) versus the reaction time during dehydrogenation
3
and avoid the unwanted reaction (HCOOH - CO + H
2
O). So far, of aqueous FA solution catalyzed by different catalysts. Clearly,
most of the attention on nanocatalysts (NCs) toward FA decom- the amount of gas generated from the FA decomposition over the
position has been focused on noble metals, of which Au, Pt, and Ni/GNs–CB catalyst is very small. In sharp contrast, compared to the
5
especially Pd exhibit excellent catalytic activity. Unfortunately, Pd/GNs–CB catalyst, the PdNi alloy catalyst exhibits a much higher
monometallic Pd is still prone to deactivation due to the adsorption activity to complete the decomposition reaction of FA, indicating
of poisonous carbon monoxide (CO) intermediates. Alloying with that Ni plays a critical role in improving the catalytic activity of Pd.
another metal, which holds superior CO anti-poisoning ability Especially, when the atom ratio of Pd/Ni is 1/2, FA decomposes
1d,2e,f
over Pd, seems to be a promising technique.
highly desirable to further increase the CO tolerance and catalytic show that no detectable amount of CO can be found in the gas
performance of Pd NCs by integration of low-cost components. mixture generated from the decomposition of FA. The reaction
Thereafter, it is completely within only 35 min. Mass spectral profiles (Fig. S1, ESI†)
Aside from tuning the catalyst composition, adjusting and completeness is confirmed by the results of liquid chromatogram
optimizing the interaction between the active metal phase and spectra (LC, Sbefore Z 2Safter, Fig. S2, ESI†). In contrast, only B70%
the support materials are also key approaches to further improve of H can be released from FA over Pd/GNs–CB even after 120 min,
2
6
catalytic performance. Currently, graphene and carbon black
1b
are widely used as catalyst supports. However, the aggregation
of graphene nanosheets (GNs) in aqueous solution and the weak
interaction between carbon black (CB) and active metals still
a
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China.
E-mail: xbzhang@ciac.ac.cn; Fax: +86 431-85262235; Tel: +86 431-85262235
b
University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
c
Changzhou Institute of Energy Storage Materials & Devices, Changzhou 213000,
Jiangsu, China
†
Electronic supplementary information (ESI) available: Detailed synthesis con-
Fig. 1 (A) FA decomposition from 5 mL of aqueous FA (1 M HCOOH and 1 M
HCOONa) and PdNi NCs with different atomic ratios of Pd/Ni. (B) Stability test of
carbon supported PdNi catalyst from (A) (amount of catalyst: nPd = 0.067 mmol).
ditions, experimental procedures, TEM characterization, XRD characterization,
MS analyses of gas, LC characterization. See DOI: 10.1039/c3cc46248j
1
0028 Chem. Commun., 2013, 49, 10028--10030
This journal is c The Royal Society of Chemistry 2013

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1 2
Fig. 2 TEM images of (A) Pd Ni /GNs–CB and (B) Pd/GNs–CB catalysts.
which is about more than 3 times worse than that over the
PdNi/GNs–CB catalyst.
To confirm the elemental composition of the as-prepared
catalysts, investigation using inductively coupled plasma 0.5 M H SO4 solution at a scan rate of 50 mV s . (C) Survey XPS spectroscopy of
Fig. 3 CO stripping voltammograms on (A) Pd/GNs–CB and (B) PdNi/GNs–CB in
À1
2
atomic emission spectroscopy (ICP-AES) is carried out and the three kinds of catalysts. Inset: XPS spectrum for Ni 2P regions of PdNi/GNs–CB.
(
D) XPS spectrum for Pd 3d regions of Pd/GNs–CB and PdNi/GNs–CB.
results are tabulated in Table S1 (ESI†). The transmission
electron microscopy (TEM) images of PdNi and Pd loaded on
GNs–CB are shown in Fig. 2A and B, where well dispersed NCs
could be found clearly. Particle size distribution (Fig. S4, ESI†) from Fig. S3A (ESI†) that there is severe agglomeration of NCs
derived from TEM images indicates that the addition of Ni after the reaction, and the average size of the nanoparticles also
decreases the particle size. From X-ray diffraction (XRD) patterns, becomes bigger (Fig. S4, ESI†). During the catalytic process, Ni
+
it is seen that the Pd/GNs–CB exhibits the characteristics of a in the catalyst is easily eroded by H , which is consistent with
single face-centered-cubic crystallographic structure of Pd (Fig. S5, the ICP results (Table S1, ESI†). Then the interaction between
ESI,† PDF#46-1043). For Ni/GNs–CB, only the (111) peak could be NCs and carbon supports becomes weak due to the erosion
found. Interestingly, the diffraction peaks of PdNi NCs are much and results in a severe detachment and agglomeration of NCs
weaker than those of Pd NCs, indicating that Ni addition can (Fig. S5, ESI†). Thus, further investigations are needed to
effectively restrain the growth of NCs, which is in accordance with improve the durability of the present PdNi/GNs–CB catalyst.
the TEM results. It should be noted that the characteristic (111)
To resolve the problem, Pd is employed to replace the Ni
peak of Pd in the PdNi/GNs–CB catalyst is shifted to higher 2y atom in the outer layers of the PdNi NCs to improve the stability of
values with respect to the corresponding peaks in the Pd/GNs–CB, the structure as well as the stability of the catalysis. Interestingly,
indicating the formation of an alloy between Pd and Ni.
the as-synthesized PdNi@Pd/GNs–CB exhibits much enhanced
Considering that a smaller particle size of Pd results in even catalytic activity and stability toward FA decomposition. Fig. 4A
4b
lower activity (rapid poisoning has been reported), the increase shows that 5 mL of FA decomposes completely in 10 min over
À1
in catalytic performance might be attributed to its enhanced PdNi@Pd/GNs–CB (TOF = 577 h ) which is higher than that over
À1
anti-poisoning ability to CO. The CO stripping voltammetry is PdNi/GNs–CB (TOF = 529 h ). Inspired by the enhanced catalytic
then used as one useful probe to reflect the anti-poisoning ability activity obtained from PdNi@Pd/GNs–CB, the cycle stability
5c
of a noble metal surface toward CO. As is shown in Fig. 3A and experiment is shown in Fig. 4B. Surprisingly, only a little degrada-
B, it is interesting to note that both the onset potential (0.6 V for tion could be found during the experiments, performed 4 times,
PdNi, 0.68 V for Pd) and the peak area of CO oxidation for indicating that the PdNi@Pd/GNs–CB catalyst possesses good
the PdNi/GNs–CB are very low as compared with those for the stability, which is supported by the TEM (Fig. S3B, ESI†), XRD
Pd/GNs–CB catalyst, which indicates that the PdNi/GNs–CB (Fig. S5, ESI†), and ICP (Table S1, ESI†) results.
catalyst possesses a strong capability of anti-poisoning to CO,
In summary, a facile method is used to synthesize well-dispersed
which might be attributed to the change of the electronic state of PdNi NCs grown on a GNs–CB composite support to combine
Pd deriving from the electron-donating ability of Ni. In addition, the advantages of GNs and CB. Unexpectedly, PdNi NCs loaded on
as shown in Fig. 3C, Pd, Ni and C can be found. Compared to GNs–CB exhibit higher catalytic performance for FA decomposition
Pd/GNs–CB, the peak of Pd 3d5/2 shifts from 335.81 to 335.55 eV at room temperature in aqueous media than on Pd or Ni alone.
in PdNi/GNs–CB, indicating a slight electron transfer from Ni to Furthermore, Pd is employed to replace the surface Ni of PdNi NCs
Pd. This decreased binding energy of Pd 3d might change the toward a novel PdNi@Pd catalyst to further improve the catalytic
8
,9
chemisorption energy of the adsorbate and thus might result activity and stability. The use of GNs–CB as a new kind of carbon
in a weak CO interaction with the PdNi NCs. support to disperse, anchor, and further promote NCs with active
Stability tests of carbon supported Pd–Ni catalysts are shown components would undoubtedly assist long-term endeavours to
in Fig. 1B. It is found that the catalytic activities of all the further optimize and enhance the catalytic efficacy of catalysts in
catalysts undergo serious losses in the 2nd run. TEM images, the development of FA as a hydrogen-storage material.
ICP, and XRD are employed to understand the underlying
This work was financially supported by the 100 Talents
mechanism of the instability of the PdNi catalysts. It is seen Programme of the Chinese Academy of Sciences, the National
This journal is c The Royal Society of Chemistry 2013
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0030 Chem. Commun., 2013, 49, 10028--10030
This journal is c The Royal Society of Chemistry 2013