G Model
CATTOD-10260; No. of Pages9
ARTICLE IN PRESS
A.V. Chistyakov et al. / Catalysis Today xxx (2016) xxx–xxx
5
Table 2
regard to dehydrogenation with the formation of acetic aldehyde
and acetone (see Scheme 1, Substrate activation). Acetic aldehyde
and acetone exhibit markedly different activities: acetic aldehyde
rapidly converts into butanol-1 or interacts with isopropanol with
dency to accumulate in the reaction products.
Substrates conversion and cross-condensation products selectivity depending on
catalyst composition (275 ◦C, 5 h).
1
Catalyst
Au-Ni/Al2O3
Au-Ni/Al2O3
66.9
38.2
Au/Al2O3
33.8
46.7
Selectivityofalkylationproduct(%) 66.1
Ethanol conversion (%)
i-propanol conversion (%)
39.3
37.2
42.3
56.4
The primary product of the interaction of ethanol and iso-
propanol is pentanol-2, whose selectivity reaches 35%–37%. The
reaction products, there are no unsaturated alcohols or ketones (3,
6ɑ, 8b). Thus, the Au-Ni/Al2O3 catalyst shows the highest efficiency
during the dehydrogenation and hydrogenation of unsaturated
Product
N in Scheme 1
4
Selectivity (%)
pentanone-2
pentanol-2
heptanone-4
heptanone-2
heptanol-4
heptanol-2
nonanone-4
nonanol-4
14.2
35.7
3.1
1.1
7.0
0.8
0.4
0.5
15.1
37.2
3.4
1.9
7.2
0.9
0.5
0.7
10.4
19.1
1.1
0.1
2.8
0.1
0.1
0.1
5a
7a
6b
8a
7b
9b
10b
C
C bonds steps. Based on Scheme 1 and Table 2, pentanol-2
1
Data obtained after ten successive experiments (5 h each).
during interaction with acetic aldehyde primarily converts into
heptanone-4, followed by hydrogenation into heptanol-4. The
primary by-product of this step (4 → 8ɑ) is heptanone-2, which
undergoes hydrogenation into heptanol-2 (6b → 7b) or inter-
acts with acetic aldehyde molecule forming nonanone-4 and/or
nonanol-4. Alcohols containing more than nine carbon atoms in
its carbon skeleton were not observed among reaction products.
The cross-condensation process was performed under rather
sever conditions (275 ◦C, 150 atm, 5 h, batch mode). The supported
metals in the catalysts could interact with the alcohols and/or be
under these conditions. This process results in a decrease in the
concentration of active components and the deactivation of cat-
alyst. To verify this hypothesis, ten 5-h consecutive experiments
were performed. The results of the tenth experiment are shown
in Table 2. The conversion and cross-condensation products’ selec-
tivity are shown to be similar to those observed with the initial
catalyst after one 5-h experiment. Additionally, the concentration
of Au and Ni after 50 h corresponds to the initial concentration of
nickel and gold when considering the uncertainty of the instrumen-
tation used in this study. The most probable reason for the high
stability of the Au-Ni catalyst is the strong interaction between the
supported metals, which decreases their mobility.
conversion of ethanol. Conversely, the 0.06Ni system primarily
catalysed the dehydration of ethanol to provide diethyl ether and
ethylene, and dehydrogenation to provide acetic aldehyde. The
conversion and selectivity to linear alcohols in the presence of Ni
catalyst does not exceed 5.8 and 0.3%, respectively. An Au analogue
was then used to catalyse the conversion of ethanol primarily into
butanol-1 but produced a low conversion (30%) and low selectivity
(16.4%).
The results obtained in this study show the highest ratio of lin-
ear ␣-alcohols selectivity and ethanol conversion. The best known
analogues show that only 10%–15% of supercritical ethanol con-
verts at a 50%–60% selectivity of butanol-1 after 5 h in batch mode
with catalyst containing more than 20% Ni/Al2O3. The maximum
ethanol conversion (25%) was observed only after 72 h, which pro-
up to 40%, a decrease was observed down to a selectivity of 60%.
Neither hexanol-1 nor octanol-1 were found in the resulting prod-
uct mixture [10]. The highest productivity in a plug-flow mode was
reported by Takahasi et al. [11]. The selectivity of alcohols C4–C10
achieved 86.1% at an ethanol conversion of 14.7%. A comparable
ethanol conversion (57.4%) was achieved at alcohols C4–C10 selec-
tivity of as low as 63.6%, which is similar to that shown in this study
(63.5%).
results of this study show that isopropanol undergoes no self-
condensation. The primary products were acetone and propane
over 0.2Au-0.06Ni and 0.2Au catalysts (Table 1). The 0.06Ni sys-
tem catalysed the isopropanol dehydrogenation into acetone and
dehydration into propene, as shown in Table 1. Alumina based sys-
hols and ketones (C5, C7, C9) was found to occur in the presence
of bimetallic Au-Ni/Al2O3 and monometallic Au/Al2O3 catalysts
(Table 2). The monometallic Ni/Al2O3 catalyst showed no activ-
ity in this process. Probable pathways of cross-condensation of
ethanol with isopropanol are shown in Scheme 1. Feeding alco-
hol conversions that are approximately equal may indicate the
equable filling of the active surface with chemisorbed substrates
and its equable activity. The total selectivity of cross-condensation
products is shown to be 66%; the primary by-products are diethyl
ether (S = 4%), butanol-1 (S = 10%) and acetone (S = 10.6%). Thus
ethanol takes part in two parallel reactions: cross-condensation
with isopropanol; and self-aldonyzation, leading to butanol-1 for-
mation. In the reaction products, only traces of acetic aldehyde
were found, indicating the equable activity of the substrates with
3.1. Structural peculiarities of mono and bimetallic systems
The XRD patterns of Au, Ni and Au-Ni catalysts are shown in
Fig. 1. Six diffraction peaks at 2 equal to 32.4, 37.5, 39.5, 46.0, 61.1,
and 66.8◦ are shown on each diffraction pattern. These peaks are
assignable to the (220), (311), (222), (400), (511), and (440) planes
of ␥-Al2O3 (JCPDS card, No. 29-0063). The patterns of the Au and Au-
Ni catalysts possess peaks at 2 equal to 38.1, 44.4 and 64.6◦. These
peaks are attributable to gold crystallites (JCPDS card, No. 04-0784).
Unfortunately, no peaks of any Ni species were found with the Ni
and Au-Ni catalysts in this study. The absence of diffraction peaks
in the XRD patterns of nanocomposites is a rather typical situation
and could be explained by the high dispersion and/or relatively low
metal content of the catalysts.
A previous investigation of the Au, Ni and Au-Ni catalysts
showed that nickel in both Au-Ni/Al2O3 and Ni/Al2O3 catalysts exist
as Ni2+ cations; gold in the Au/Al2O3 catalyst exists as Au0; and Au0
nanoclusters co-exist with Aun+ (1 ≤ n ≤ 3) cations in the bimetal-
lic Au–Ni/Al2O3 catalyst [47]. Those results were found using XPS,
Dark spherical spots are visible in the TEM and HRTEM images
of the Au catalyst (Fig. 2(a), (b)). The EDS spectrum of these spots
(Fig. 2(c)). The presence of Cu and C elements can be attributed
to the TEM grid and should not be considered. The remaining com-
bination of elements indicates that the dark spots visible in the
TEM images can be attributable to gold particles deposited onto the
alumina surface (Fig. 3(b)). The size of the detected gold particles
Please cite this article in press as: A.V. Chistyakov, et al., Direct Au-Ni/Al2O3 catalysed cross-condensation of ethanol with isopropanol