A. Li, et al.
Molecular Catalysis 486 (2020) 110833
aldehydes or ketones as one of feedstocks to generate quinolines is a
good strategy [20,21], which could not only distinctly overcome alde-
hydes/ketones’s relatively high cost but also retard the polymerization
at relative high reaction temperature. Hence, the further development
of gas-phase aza-heterocyclic-aromatization from acrolein acetals and
aniline to quinolines is of great interest and highly necessitated.
Zn species supported on zeolites have been extensively applied in
different types of reactions, containing alkane methanol-to-for-
maldehyde [22], waste water treatment [23], photocatalytic degrada-
tion [24,25], hydrogenation and dehydrogenation [26,27]. Especially,
Zn species possess excellent catalytic performance of aromatization,
due to its more superior ability of leaching hydrogen from subtracts
compared to other traditional transition metal counterparts [28–30].
Hβ-typed zeolites, presenting three-dimensional structure with 12-ring
channel systems, have been considerably explored as catalyst for the
vapor-phase synthesis of quinolones [14,31,32]. Compared to others
catalysts [16,17,33–35], such as mixed metal oxides, amorphous silica-
alumina, modified-montmorillonite and halide clusters, the Hβ zeolites
possesses numerous obvious merits, involving high surface area, ex-
cellent stability of thermal and hydrothermal, shape selectivity, low
coke formation, adjustable acidity and appropriate microporous size
matching with bulky quinolines molecule size [36–38]. It is reported
that Hβ zeolite-base catalysts were effective catalysts for synthesis of
quinolines from various raw materials involving acetaldehyde [14],
glycerol [31], lactic acid [32], and formaldehyde [39]. For example,
Roald Brosius employed the Hβ zeolite and F-modified Hβ as catalysts
to vapor-phase synthesis quinolines from aniline and acetaldehyde; and
more than 83 % sum totals of quinolines (including quinoline, 2-me-
thylquinoline and 4-methylquinoline) were obtained [14]. When the
Hβ zeolite combined with Zn species, the catalytic activity of the Zn/Hβ
system could be significantly improved; because the addition of Zn
species into zeolite could regulate concentration and strength of acidity
of catalyst effectively. Moreover, Zn species itself can play determining
active sites in aromatization, which is necessary process in the reaction
of acrolein acetals and aniline to quinolones [40]. To the best of our
knowledge, little literatures known so far for the gas-phase catalyzed
aza-heterocyclic-aromatization to quinolines over Zn-modified Hβ
zeolite catalysts was shown in detail.
4 h, and the thus-obtained catalyst was named as Hβ.
2.2.2. Zn/Hβ zeolite catalyst prepared via deposition precipitation
The Zn-modified β zeolite catalyst was prepared via deposition
precipitation. Firstly, a homogeneous aqueous solution was prepared by
the mixture of zinc nitrate, urea and deionized water; and then, the
prepared Hβ zeolite powder was added to form the suspension.
Subsequently, the suspension was vigorously stirred under room tem-
perature for 2 h and then heated to 90 °C for refluxing 4 h. After cooling
down, the suspension was treated by filtrating, washing, and drying
completely. Finally, the obtained solid powder was calcined at 550 °C
for 4 h, named as Zn/Hβ.
As comparison, other metal-supported Hβ zeolite catalysts were also
prepared according to the above method, using corresponding nitrates
as the precursors, which named as M/Hβ (M = Cr- Ni- Mn- Cu- and Fe).
The P- and F-supported Hβ zeolite catalysts were prepared via im-
pregnation method as follow: the homogeneous precursor solution of
(NH ) HPO or NH F was firstly prepared, and then the Hβ zeolite
4
2
4
4
powder was added and continuous stirred for 6 h under room tem-
perature. Follow by filtrating, washing, and drying completely, the
obtained solid powder was calcined at 550 °C for 4 h, and the thus-
prepared catalysts were denoted as P/Hβ and F/Hβ respectively.
2.3. Catalysts characterization
X-ray diffraction patterns (XRD) for catalysts were performed on
Bruker D8 diffractometer, Cu-Kα radiation (λ = 1.54187 Å). Fourier
transform infrared (FT-IR) spectroscopy were recorded on a Varian
−1
3100 spectrometer using the GTGS detector under resolution of 2 cm
and scanning number of 32. Scanning electron microscopy (SEM) was
performed on a JEOL JSM 6700 F at an accelerating voltage of −5.0 kV.
Transmission Electron Microscope (TEM) was carried out with a JEM-
2100 F equipment with an accelerating voltage of 200 kV. Before
measurement, the sample was ultrasonic treated in order to disperse the
sample powder in ethanol, and then dropped onto a carbon-coated
copper grid. High-Resolution Transmission Electron Microscopy
(HRTEM) was made with a JEM-2200FS microscope. The Hβ and Zn/
Hβ catalyst samples were firstly suspended in ethanol and then de-
In the present paper, the Zn-modified Hβ catalysts were prepared
via deposition precipitation and employed in the gas-phase aza-het-
erocyclic-aromatization of aniline and acrolein dimethyl acetal to qui-
nolines. Reaction conditions, activity, stability as well as regeneration
of catalysts were systematically investigated. The influence of Zn-sup-
ported on zeolites for the activity and selectivity is addressed.
Meanwhile, a feasible vapor-phase reaction pathway was suggested in
this paper.
2
posited on carbon-film-coated copper grids. N adsorption-desorption
isothermal were measured on a Quantachrome Autosorb-1 analyzer at
77 K; all the catalysts were initially degassed at 300 °C in a vacuum
-
8
condition of 10 Torr for 12 h before measurement. Temperature-pro-
grammed desorption of ammonia (NH -TPD) was conducted on an
Autochem II 2920 instrument. Typically, all the catalysts were firstly
pretreated in He flow (60 ml/min) for 0.5 h at 400 °C before NH ad-
sorption, and then 10 vol. % NH in He (50 ml/min) was adsorbed to
reach saturation over catalyst. Subsequently, the physically adsorbed
NH was purged in a flow of helium at 100 °C, and then ammonia was
3
3
3
2. Experimental
3
desorbed from 100 to 800 °C with the heating rate of 10 °C/min. X-ray
photoelectron spectroscopy (XPS) were carried out a PHI Quantum
2.1. Chemicals
2000 instrument with Al Ka radiation source. The suitable amount
The parent β zeolite was purchased from Nankai University Catalyst
catalyst was compressed into a wafer for analysis. The signal of carbon
C 1 s was present at 284.6 eV. Thermogravimetry (TG) were measured
on a Diamond instrument; the deactivated catalysts were heated from
room temperature to 800 °C in air (30 mL/min) with the heating rate of
Factory. Urea, zinc nitrate and other metal salts were purchased from
Xilong Chemical Company. Acrolein diethyl acetal, aniline and ethanol
were supplied by Sinopharm Chemical Reagent Company.
5
°C/min.
2
2
.2. Catalyst preparation
2
.4. Catalytic performance evaluation
.2.1. H-typed β zeolite catalyst prepared via ion-exchange
The ion-exchange method was used to prepare H-typed β zeolite.
The gas-phase reaction was conducted in a fixed-bed reactor. Firstly,
Firstly, the parent β zeolite powder was added into 1.0 M NH
lution to form suspension, and then refluxed at 90 °C for 4 h under
vigorous stirring. Following by filtrated, washed with distilled water
and dried sufficiently at 120 °C, the NH
obtained. The above processes were repetitively operated three times.
Finally, the dried NH -typed β zeolite powder was calcined at 550 °C for
4
NO
3
so-
the catalyst was filled in the middle of the stainless steel reaction tube.
The reactor was heating to reaction temperature with a flow of ni-
trogen. Later on, feedstocks were initially vapored and subsequently fed
into the reaction tube. The reaction was carried out under different
reaction conditions, and the product mixtures were collected via
cooling with ice-water trap. The product mixtures were identified by
4
-typed β zeolite powder was
4
2