2
M. Campanati et al. / Journal of Catalysis 232 (2005) 1–9
(
(
1,2-PDIOL), 1,2-butanediol (1,2-BDIOL), 2,3-butanediol
2,3-BDIOL), 1,2-hexanediol (1,2-HEXDIOL), Zr(IV) ace-
tylacetonate, and CH3COOH were purchased from Aldrich
Chemicals (purity ꢀ 98.0%) and used as received without
any further purification.
We prepared N-(2-hydroxyethyl)-2-ethylaniline (NEE) in
liquid phase by adding 60 ml of chloroethanol to 150 ml of
2
-ETAN, performing the reaction for 3 h at 403 K under a
N2 atmosphere with energetic stirring, and adding at the end
0 g of K2CO3 dissolved in 10 ml of H2O to neutralise the
Fig. 1. General reaction scheme of the vapour-phase synthesis of indole and
its derivatives.
1
HCl formed. Then we distilled the reaction mixture at 323 K
under vacuum (395 Pa), obtaining NEE with a purity of
(
ꢀ10.0) of aromatic amine has to be used to avoid the for-
9
8%. We prepared N-(2-ethylphenyl)-2-aminoacetaldehyde
mation of useless polyalkylated indoles. Thus a high amount
of aniline derivatives has to be recycled, with significant
economic and environmental drawbacks. In a previous pa-
per [17], some of us reported that the best results can be
obtained with a commercial copper chromite containing only
promoters, improving the physical properties and permitting
operation at low temperature and LHSV values [17]. Fur-
thermore, with a mixture of a commercial SiO2 and this
catalyst, it was possible to operate at higher LHSV values,
thus improving the yield in alkylindoles [17].
The excess of aromatic amine and carrier gas (required to
operate at low contact times) has been avoided with the use
of a new family of ZrO2/SiO2 catalysts able to operate with
almost stoichiometric feeds and water as the main carrier
gas [18–20]. These catalysts showed better performances
than those reported in the literature and very good regenera-
bility. Finally, innovative Si/Zr mesoporous catalysts, with
a MCM41-type structure, have also been investigated, al-
though they demonstrate poorer catalytic performances [21].
However, it must be noted that almost no data are avail-
able in the literature on either the possible reaction pathway
in the vapour-phase synthesis of indole and, mainly, alkylin-
doles or the reactivity in these conditions of different aro-
matic amines or diols. The aim of this study was to shed
light on these two key points to check the applicability of the
vapour-phase synthesis to a wider number of alkylindoles
and to design tailor-made catalysts.
(
NEPA) in liquid phase by adding 50 ml of chloroacetalde-
hyde dimethylacetal to 75 ml of 2-ETAN, performing the
reaction for 3 h at 403 K under a N2 atmosphere with en-
ergetic stirring, and adding at the end 10 ml of a K2CO3
solution (50 wt%) to neutralise the HCl formed. The reac-
tion mixture was extracted with toluene, and the product
was recovered by solvent distillation at 323 K under vac-
uum (395 Pa). The NEPA dimethylacetal obtained was then
treated with a H2SO4 solution (6 wt%) to obtain the corre-
sponding aldehyde (purity ꢀ 98%).
X-ray diffraction (XRD) analyses were carried out with
a Philips PW 1050/81 diffractometer (40 kV, 25 mA),
equipped with a PW 1710 unit, and Cu-Kα radiation (λ =
◦
◦
0.154118 nm). A 2θ range from 10 to 80 was investigated
◦
at a scanning rate of 0.10 /s. BET surface area and poros-
ity values were determined by physical adsorption of N2 at
77 K, with a Micromeritics Asap 2020. FT-IR spectra were
−1
collected in the range of 4000–400 cm with a Perkin–
Elmer 1750 spectrometer, with the use of samples diluted
in KBr (0.2:99.8 wt/wt). The catalyst surface acidity was de-
termined with a ThermoQuest TPD/R/O 1100 equipped with
TCD. The samples were pretreated under a 100 ml/min He
flow at 673 K for 60 min, then at 433 K 10 pulses of NH3
were added, and the samples were maintained at this temper-
ature for 60 min, to favour the elimination of the physically
adsorbed NH3. Finally, under the same He flow, the samples
were heated from 433 to 823 K (heating rate 10 K/min) and
maintained at the latter temperature for 60 min.
2
. Experimental
The catalytic tests (T = 583 K, GHSV (gas hourly
−1
space velocity) = 2900 h ; H2/H2O = 20:80 v/v; LHSV =
−1
Catalytic tests were carried out with 4.0 ml (ca. 2.5 g,
25–850 µm particle size) of ZrO2/SiO2 (5:95 w/w) sup-
1.6 h ; amine/diol = 1:1 mol/mol) were carried out in a
fixed-bed glass micro-reactor (i.d. 7 mm, length 400 mm)
placed in an electronically controlled oven and operating
at atmospheric pressure. The isothermal axial temperature
profile of the catalytic bed during the tests was determined
with a 0.5-mm J-type thermocouple, sliding in a glass cap-
illary tube. The organic feed and H2O were introduced by
two Infors Precidor model 5003 infusion pumps, and the
gas composition and flow were controlled with Brook mass
flow meters. After 1 h of time on-stream to reach station-
ary conditions, the products were condensed in two traps
cooled at 268 K and collected in methanol, with tride-
cane as an internal standard. The analyses were carried out
4
ported catalysts, prepared by incipient wetness impregna-
ꢀ
ꢀ
tion of a commercial SiO2 (Si-1803 T 1/8 ; Engelhard)
with a solution of Zr(IV) acetylacetonate in acetic acid and
following calcination at 723 K for 5 h. The catalyst had
previously been activated in situ, with a progressive in-
crease in the temperature up to 603 K and a 6 l/h flow
of a H2/N2 (1:9 v/v) gas mixture. Aniline (AN), 2-meth-
ylaniline (2-METAN), 3-methylaniline (3-METAN), 4-meth-
ylaniline (4-METAN), 2-ethylaniline (2-ETAN), 3-ethyl-
aniline (3-ETAN), 4-ethylaniline (4-ETAN), 2-propylaniline
(
2-PRAN), ethylene glycol (EG), 1,2-propylene glycol