Effect of polyamide on selectivity of its supported Raney Ni catalyst

Article abstract of DOI:10.1007/s11426-015-5541-4

A newly-developed polyamide supported Raney Ni catalyst, which is suitable for use in fix-bed reactions with high selectivity, was studied in this paper. Selective hydrogenation of acetone to isopropanol was chosen as a probe reaction. It has been found that clean preparation of isopropanol could be achieved, that is to say, the two main byproducts (isopropyl ether and methyl- iso-butyl carbinol) could be eliminated with the newly-developed polyamide supported Raney Ni catalyst. The elimination of these side reactions was attributed to the adsorption effect of polyamide support and a model was proposed. The proposed model was further proved by hydroamination reaction of acetone. According to this model, catalyst support can play an important role in chemical reactions. Different products could be produced when different catalyst support is used, the main reaction and side reactions can even be reversed sometimes when the chemicals, active component of catalyst and reaction condition are the same. This model could help to improve catalytic selectivity of many Raney metal catalysts used routinely in chemical and oil refining industry, and is also useful for hydrogenation reactions in pharmaceutical and food industry.

Full text of DOI:10.1007/s11426-015-5541-4

SCIENCE CHINA
Chemistry
• ARTICLES •
doi: 10.1007/s11426-015-5541-4
doi: 10.1007/s11426-015-5541-4
Effect of polyamide on selectivity of its supported
Raney Ni catalyst
Haibin Jiang, Shuliang Lu, Xiaohong Zhang, Baoliang Tian, Hui Peng,
Wei Dai* & Jinliang Qiao*
SINOPEC Beijing Research Institute of Chemical Industry, Beijing 100013, China
Received September 6, 2015; accepted October 8, 2015
A newly-developed polyamide supported Raney Ni catalyst, which is suitable for use in fix-bed reactions with high selectivity,
was studied in this paper. Selective hydrogenation of acetone to isopropanol was chosen as a probe reaction. It has been found
that clean preparation of isopropanol could be achieved, that is to say, the two main byproducts (isopropyl ether and me-
thyl-iso-butyl carbinol) could be eliminated with the newly-developed polyamide supported Raney Ni catalyst. The elimination
of these side reactions was attributed to the adsorption effect of polyamide support and a model was proposed. The proposed
model was further proved by hydroamination reaction of acetone. According to this model, catalyst support can play an im-
portant role in chemical reactions. Different products could be produced when different catalyst support is used, the main reac-
tion and side reactions can even be reversed sometimes when the chemicals, active component of catalyst and reaction condi-
tion are the same. This model could help to improve catalytic selectivity of many Raney metal catalysts used routinely in
chemical and oil refining industry, and is also useful for hydrogenation reactions in pharmaceutical and food industry.
polyamide, Raney Ni, acetone
Citation:
Jiang HB, Lu SL, Zhang XH, Tian BL, Peng H, Dai W, Qiao JL. Effect of polyamide on selectivity of its supported Raney Ni catalyst. Sci China
Chem, doi: 10.1007/s11426-015-5541-4
fix-bed reactors. Therefore, currently it is mainly employed
1 Introduction
in slurry phase reactors for small batch production. In this
case, catalytic selectivity is hard to control [6]; moreover,
Raney Ni is demanded to be separated from the reaction
medium. Another shortcoming of Raney Ni is that it inevi-
tably contains a certain fraction of Al2O3 [1], and the acidity
of Al2O3 often leads to some side reactions.
In order to overcome the disadvantages of Raney cata-
lysts, a number of researchers have devoted their efforts to
shaping Raney catalysts for fix-bed reactions. Some acti-
vated merely the superficial layer of granular Raney alloys
[7–10]. In this case, the activation must be controlled in a
low degree in order to maintain mechanical strength of the
catalysts. Some added different substances into Raney alloy
powder to shape Raney alloys [11–14] or deposited metallic
vapor on certain shaped substances [15], then calcined and
Ni powders have been regarded as very good hydrogenation
catalysts for more than a century. The preparation of a well
dispersed metal Ni, which leads to high specific activities,
used to require the use of mineral supports [1]. Raney [2]
discovered another way to obtain high specific activities Ni
in 1925. Since then, Raney Ni has been extensively used in
chemical reactions [3–5]. Raney Ni offers the advantage
over supported Ni catalysts of having a high catalytic activ-
ity at a relatively low temperature. Nevertheless, Raney Ni
has some disadvantages as well, which limit its application.
For example, powdered Raney Ni cannot be applied in
*Corresponding authors (email: daiw.bjhy@sinopec.com; qiaojl.bjhy@sinopec.com)
© Science China Press and Springer-Verlag Berlin Heidelberg 2015
chem.scichina.com link.springer.com

2
Jiang et al. Sci China Chem January (2016) Vol.59 No.1
activated the shaped Raney alloys. These procedures were
complex and difficult to be industrialized. Some others ex-
truded the mixture of Raney alloy powder, polymer and
mineral oil together, then calcined and activated the extru-
dates [16–21]. Before calcination, only a small part of al-
loys can be activated because of the covering polymer; after
calcination, however, the mechanical strength of the catalyst
was sharply diminished.
In our previous communication [22], Raney metal cata-
lyst supported by polymer was developed for fix-bed reac-
tions with high selectivity. It has been found that the newly-
developed polymer supported Raney Ni catalyst could
achieve clean preparation of n-butanol because the main
side reaction could be reduced and even eliminated in prep-
aration of n-butanol from n-butyraldehyde. The major dis-
advantages of Raney Ni catalyst were satisfactorily over-
come. However, the reaction studied in our previous work
had only one main side reaction. In this work, polyamide
supported Raney Ni catalyst (Raney Ni/PA) was used in
selective hydrogenation of acetone to isopropanol, which
had two main side reactions, and the effect of polyamide
support on reducing or even eliminating side reactions was
studied. A model was proposed to explain the clean prepa-
ration of isopropanol and was proved by hydroamination
reaction of acetone.
after alkaline leaching of the Ni-Al/PA granules.
For comparison, Al2O3-supported Ni catalyst (Ni/Al2O3,
20 wt% Ni), Al2O3-supported Raney Ni catalyst (Raney
Ni/Al2O3, 20 wt% Ni) and unsupported granular Raney Ni
catalyst were also prepared. Ni/Al2O3 catalyst was prepared
according to the commercial impregnation method, using
Al2O3 support and Ni(NO3)2·6H2O solution, dried at
120 °C for 12 h, calcined at 360 °C for 4 h and reduced at
400 °C for 8 h. Raney Ni/Al2O3 catalyst was prepared ac-
cording to the previous literature [23]. Granular Raney Ni
catalyst was obtained by alkaline leaching of 10–20 mesh
Ni-Al alloy powders (50 wt% Ni).
The hydrogenation of acetone reaction was performed in
a 14 mm (internal diameter) tube microreactor made of
stainless steel under pressure of 1.3 MPa and at temperature
of 132 °C (preheated at 85 °C). The amount of catalyst used
was 40 mL. The flow of acetone was controlled by a micro-
syringe pump with a flow rate of 20 mL/h. H2 gas flow was
60 mL/min. The product was analyzed by gas chromatog-
raphy equipped with a flame ionization detector (FID, Ag-
ilent 7890, DB-WAX, China). The residual acetone content
and isopropanol, isopropyl ether, methyl-iso-butyl carbine
(MIBC) contents were determined with an external standard
to indicate the activity and selectivity of the catalysts.
Hydroamination of acetone to isopropylamine was per-
formed at atmosphere pressure and at the temperature of
153 °C. The amount of catalyst used was 50 mL. The flow
of acetone was controlled by a micro-syringe pump with a
flow rate of 25 mL/h. H2 and NH3 gas flow was both
75 mL/min. The product was analyzed by gas chromatog-
raphy equipped with a flame ionization detector.
2 Experimental
Raney Ni/PA catalyst was prepared as follows [22]: poly-
amide 6 granules (PA6, BL2340-H, Sinopec Baling Com-
pany, China) were separately buried into a full mold of
Ni-Al alloy (50:50) powder at 250 °C. In other words, Ni-Al
alloy powders were embedded into the surface of the PA
granules. Thereafter, the mold was cooled down to get spe-
cial granules (Ni-Al/PA), in which the Ni-Al alloy particles
were embedded into PA granule surface, as shown in Figure
1. After sieving out Ni-Al/PA granules from the excess
Ni-Al alloy powder, Raney Ni/PA catalyst was obtained
3 Results and discussion
3.1 Hydrogenation of acetone to isopropanol
Isopropanol, with a global growing rate of 1% to 3% per
year, is widely regarded as essential commodity for fine
chemical synthesis, heat pumps and hydrogen storage in
fuel cell [24] in industry and academia. The commercial
isopropanol is mainly from acetone hydrogenation in the
presence of a hydrogenation catalyst. Reaction (1) shows
the hydrogenation reaction of acetone to isopropanol; Reac-
tion (2) represents the side reaction which generates iso-
propyl ether; Reactions (3) and (4) represent the side reac-
tions which generate methyl-iso-butyl carbinol (MIBC)
[25–27].
(1)
(2)
Figure 1 Photograph of Ni-Al/PA granules. Inset shows the sectional
view of a cut sample (color online).

Jiang et al. Sci China Chem January (2016) Vol.59 No.1
3
sorption ability of a catalyst support to reactants and prod-
ucts can largely affect the catalytic reactivity [28,29]. The
PA support, with lone pair electrons at the N atom for every
repeating unit (Figure 2), possesses strong adsorption ability
to isopropanol since the N atoms in PA can form hydrogen
bonds with the –OH groups in isopropanol and the interval
between every two neighboring N atoms in PA molecule
chain is only 0.86 nm. Therefore, the following processes
might have occurred (Figure 3). Process 1: acetone was ad-
sorbed by Raney Ni of Raney Ni/PA catalyst; process 2:
acetone was catalyzed to isopropanol by Ni metal; process
3: once produced, isopropanol was selectively adsorbed by
N atoms in the PA, rather than the acidic Al atoms inside
the pores of Raney Ni. Unlike the acidic Al atoms in Al2O3,
the basic N atoms in the PA support cannot catalyze iso-
propanol to isopropyl ether. Clearly, therefore, it is the in-
terplay of the alkalinity and strong adsorption ability to iso-
propanol intrinsically associated with the N atoms in the PA
support that makes the elimination of isopropyl ether.
Byproduct MIBC is generated through the reaction pro-
cesses as shown in Figure 4 [25]. Process 1: acetone is re-
versibly converted to diacetone alcohol (DAA); process 2:
DAA is catalyzed to MIBK by acid; process 3: MIBK is
hydrogenated to MIBC by Ni metal. As for Raney Ni, the
remaining Al2O3 inside the pores would adsorb and catalyze
DAA to MIBK, which would be hydrogenated to MIBC.
This is the cause of 0.02% content of byproduct MIBC over
granular Raney Ni catalyst. Obviously, removing the effect
of acidic Al2O3 is also the key to eliminating the byproduct
MIBC. As already known, the PA support possesses strong
adsorption ability to –OH groups of DDA; therefore, just
like the elimination of isopropyl ether, the following pro-
(3)
(4)
The numerical results from the hydrogenation of acetone
at 132 °C with four different catalysts (Ni/Al2O3 catalyst,
Raney Ni/Al2O3 catalyst, Granular Raney Ni catalyst and
Raney Ni/PA catalyst) are listed in Table 1. It can be seen
from Table 1 that the conversions over Raney Ni/Al2O3,
Granular Raney Ni, and Raney Ni/PA catalysts are all be-
yond 99.7% whereas that over Ni/Al2O3 catalyst is only
98.97%. Meanwhile, the selectivity to isopropanol over
Raney Ni/Al2O3, granular Raney Ni and Raney Ni/PA cata-
lysts all reach higher than 99.9% and are even close to
100% over Raney Ni/PA catalyst, whereas that over Ni/Al2O3
catalyst is only 99.87%. It is clear that three Raney Ni-related
catalysts all have both higher activity and selectivity than
Ni/Al2O3 catalyst, indicating Raney Ni’s good catalytic per-
formance for the hydrogenation of acetone to isopropanol.
The results are very simple to understand because the acidity
of Al2O3 could catalyze the generation of byproducts in this
reaction and Al2O3 in Ni/Al2O3 catalyst apparently has much
more opportunities to catalyze the side reactions than the
Al2O3 remaining inside the pores of Raney Ni resulted from
the incomplete leaching of Al in Ni-Al alloy [1].
For three Raney Ni-related catalysts, the conversions are
close to each other, but the selectivities are different: Raney
Ni/Al2O3<Granular Raney Ni<Raney Ni/PA, and the selec-
tivity over Raney Ni/PA catalyst is even close to 100%.
Clearly, Al2O3 support diminished Raney Ni’s selectivity to
isopropanol because of the acid-catalyzed side reactions,
while PA support eliminated these side reactions to achieve
clean preparation of isopropanol. It is interesting to know
why both isopropyl ether and MIBC, the two main byprod-
ucts in this reaction, could be eliminated by using PA sup-
port.
Figure 2 Chain structure of PA.
Byproduct isopropyl ether is generated from the main-
product isopropanol catalyzed by acidic Al2O3 as Reaction
(2). Once adsorbed by the remaining Al2O3 inside the pores
of Raney Ni, isopropanol would be catalyzed to byproduct
isopropyl ether. Meanwhile, it is well known that the ad-
Table 1 Hydrogenation of acetone with different catalysts at 132 °C
Selectivity (%)
Conversion
Catalyst
isopropa-
nol
isopropyl
ether
(%)
MIBC
0.08
Ni/Al2O3
98.97
99.71
99.87
0.05
Raney
99.91
0.04
0.05
Ni/Al2O3
Granular
Raney Ni
99.76
99.75
99.94
0.04
0.02
Figure 3 Schematic representation of elimination of isopropyl ether over
Raney Ni/PA catalyst (color online).
Raney Ni/PA
100.00
undetectable undetectable

4
Jiang et al. Sci China Chem January (2016) Vol.59 No.1
cess might have occurred as shown in Figure 5. Once re-
versibly generated from acetone, DDA was selectively ad-
sorbed by N atoms in the PA, rather than the acidic Al at-
oms inside the Raney Ni pores. Unlike the acidic Al atoms
in Al2O3, the basic N atoms in the PA support cannot cata-
lyze DDA to MIBK. Therefore, byproduct MIBC cannot be
generated.
It is obvious that basic N atoms having strong interaction
with reactants in the PA support play a key role in clean
preparation of isopropanol. In order to confirm the above
conclusion, the hydroamination of acetone to isopropyla-
mine was studied as well.
Raney Ni catalyst, and Raney Ni/PA catalyst) are listed in
Table 2. It can be seen from the table that conversion, selec-
tivity, and byproducts contents over these four catalysts
have the monotonical relationship shown as follows. Con-
version: Ni/Al2O3>Raney Ni/Al2O3>Granular Raney Ni>
Raney Ni/PA; selectivity: Ni/Al2O3>Raney Ni/Al2O3>
Granular Raney Ni>Raney Ni/PA; byproduct DIPA content:
Ni/Al2O3>Raney Ni/Al2O3>Granular Raney Ni>Raney
Ni/PA; and byproduct isopropanol content: Ni/Al2O3<
Raney Ni/Al2O3<Granular Raney Ni<Raney Ni/PA. The
above experimental results could also be explained accord-
ing to the interaction of catalyst support with reactants as
indicated by the proposed model for acetone to isopropanol.
NH3, easily adsorbed by Al2O3 acidic sites, is indispensa-
ble for the production of both main product isopropylamine
and byproduct DIPA (Reactions (5) and (6)). Therefore,
Al2O3/Ni catalyst, with the largest Al2O3 content, possesses
the highest activity and byproduct DIPA content among
these four catalysts. Since there is just a small amount of
Al2O3 remaining inside the pores of Raney Ni, Al2O3 con-
tents of these four catalysts have this relationship:
Ni/Al2O3>Raney Ni/Al2O3>Granular Raney Ni>Raney
Ni/PA, which is accordant with that of conversion and by-
product DIPA content.
3.2 Hydroamination of acetone to isopropylamine
Reaction (5) shows the hydroamination of acetone to iso-
propylamine [30]; Reactions (6) and (7) represent the side
reactions generate diisopropylamine (DIPA) and isopropa-
nol, respectively. The numerical results from hydroamina-
tion of acetone at 153 °C with four different catalysts
(Ni/Al2O3 catalyst, Raney Ni/Al2O3 catalyst, Granular
(5)
(6)
(7)
Figure 4 Schematic representation of generation process of byproduct
MIBC (color online).
Furthermore, we still need to know why Raney Ni/PA
catalyst is so special, with very low activity and selectivity,
but the byproduct DIPA content is undetectable. The reason
is simple, because the repulsive interaction between N atom
in PA support and NH3 is very strong. As shown in Figure
6, although the remaining Al2O3 inside the pores of Raney
Ni can adsorb reactant NH3, the repulsive interaction of PA
support surrounding Raney Ni prevents NH3 from being
adsorbed by Al2O3 inside the pores of Raney Ni. In this
case, hydroamination reaction is difficult to conduct, indi-
cating very low activity and selectivity. Besides, as the very
limited amount of adsorbed NH3 is exhausted by main Re-
action (5), side Reaction (6) is eliminated. Moreover, be-
cause the generation of byproduct isopropanol does not
need reactant NH3, the content of byproduct isopropanol
over Raney Ni/PA catalyst even greatly exceeds that of
main product isopropylamine.
Figure 5 Schematic representation of elimination of MIBC over Raney
Ni/PA catalyst (color online).
It is clear and interesting that catalyst support can play an

Jiang et al. Sci China Chem January (2016) Vol.59 No.1
5
Table 2 Hydroamination of acetone with different catalysts over 153 °C
1
2
3
4
5
6
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Selectivity (%)
Conversion
(%)
Catalyst
isopropylamine
DIPA
7.00
isopropanol
13.94
Ni/Al2O3
Raney
Ni/Al2O3
Granular
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99.38
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56.83
37.95
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4 Conclusions
A newly-developed polyamide supported Raney Ni catalyst,
which is suitable for use in fix-bed reactions with high se-
lectivity, can make the selective hydrogenation of acetone
to isopropanol very clean. The two main byproducts (iso-
propyl ether and methyl-iso-butyl carbinol) could be elimi-
nated completely, which could be attributed to the adsorp-
tion effect of polyamide support and a model has been pro-
posed. The proposed model was further proved by hy-
droamination reaction of acetone. Based on this study, we
believe that the catalytic selectivity of Raney catalysts and
other hydrogenation catalysts in chemical industry, oil re-
fining industry, pharmaceutical industry, and food industry,
could be greatly improved by selecting appropriate polymer
support according to the features of specific reactions.
Conflict of interest The authors declare that they have no conflict of
interest.