X. Li et al. / Applied Catalysis A: General 528 (2016) 168–174
169
Scheme 1. Reaction network of the hydrogenation of 2-ethylanthraquinone.
support acidity leads to the increasing production of by-products
[17–19]. Several methods have been proposed to avoid the nega-
tive effect of its acidity, such as support modification with Na2SiO3,
NaH2PO4 and some alkali metals [20–22]. Moreover, silica is an
excellent alternate for alumina due to its very weak acidity, but
tive weak interaction with metal nanoparticles [21,23]. A sintering
resistant support with weak acidity is in demand.
was 10 MPa. Obtained AlPO-5 tablets were crushed and sieved
(40–60 mesh) to prepare pure AlPO-5 support.
2.1.3. Preparation of the catalysts
2 g prepared support was impregnated in 4 mL Pd(NH3)4(NO3)2
aqueous solution (1.25 g·L-1, calculated by Pd mass) for 2 h, fol-
lowed by drying and calcination at 400 ◦C for 2 h. Before reaction,
the catalyst was reduced by H2 at 120 ◦C for 2 h.
With regular pore structure and good thermal stability, some
zeolites are used as catalyst supports [24,25]. In contrast to the
aluminosilicate zeolites, AlPO-n have strictly alternated Al and P on
the tetrahedral nodes, which yield charge neutral framework. Since
the lattice is overall charge neutral, aluminum phosphate does
not possess the ion exchange ability or strong acidity [26]. In this
work, Pd/AlPO-5 catalyst was prepared by impregnation method
and tested in the liquid phase hydrogenation of eAQ. Given reac-
tant molecular size, the microporous structure of AlPO-5 is unable
to meet the mass transferring demand of the reactant and product
molecules [26]. Hence, Pd catalysts with SiO2-AlPO-5 composed
support were also prepared and tested.
2.2. Characterization of the catalysts
Nitrogen physisorption was carried out to characterize specific
surface areas and porosity of samples at liquid N2 temperature in a
Quantachrome NOVA 2200e instrument. The specific surface area
and pore size distribution were determined by using the BET and
the DFT method, respectively. Prior to analysis, the samples were
degassed under vacuum condition at 200 ◦C for at least 2 h.
The transmission electron microscopy (TEM) measurement was
carried out with a JEOL JEM-2000 EX equipment operated at an
accelerating voltage of 120 kV. Before analysis, the catalyst was
reduced in H2/Ar at 120 ◦C for 1 h. The Pd loading was determined
by an inductively coupled plasma-atomic emission spectroscopy
(ICP-AES). The dispersion of palladium was measured through CO
chemisorptions experiments on a Quantachrome CHEMBET Pulsar
adsorption instrument. Before analysis, the catalyst was reduced
in H2/Ar at 120 ◦C for 1 h. The adsorption measurements were per-
formed 45 ◦C in a He flow.
2. Experimental section
2.1. Preparation of the catalysts
2.1.1. Preparation of AlPO-5
The molar ratio of the starting gels were 1.2 TEA: 1 Al2O3: 1
P2O5: 50 H2O. The gels were prepared by adding pseudoboehmite
(Catapal C, Sasol) to a solution of phosphoric acid (Sinopharm
Chemical reagent Co.) and stirred for 3 h. Then, tetraethylamine
(TEA, Sinopharm Chemical reagent Co.) was added to the mixtures
and stirred for 24 h. The resulting gels were introduced into teflon-
lined, stainless steel autoclaves and heated at 200 ◦C for 36 h. After
hydrothermal treatment, the formed zeolite was separated from
the mother liquor, rinsed repeatedly with distilled water and dried.
The dried zeolite was finally calcined at 600 ◦C for 6 h. N2 isotherms
and XRD patterns of calcined zeolite are shown in Figs. S1 and S2.
UV–vis spectra were recorded on a Cary 5000 Varian spec-
trophotometer in diffuse reflectance cell. The effluent was analyzed
using a TOF-MS 500 mass spectrometer made by Dalian Institute
of Chemical Physics.
In situ DRIFT spectra were recorded in the OH stretching fre-
quency region using a Thermo Nicolet 6700 spectrometer equipped
with a temperature-controllable diffuse reflectance reaction cell.
The powder samples were placed in a crucible inside the cell before
they were heated at increasing temperatures under He flow, which
removed any adsorbed water. Pd/AlPO-5 samples that displayed
different Pd loadings were pretreated using He flow at elevated
temperatures for 1 h before the measurements were taken.
The H2 temperature programmed reduction (H2-TPR) exper-
iments were performed on a flow system at a Quantachrome
CHEMBET3000 adsorption instrument equipped with a TCD detec-
tor. Prior to reduction, catalyst samples were dried in an argon flow
at 150 ◦C for 1 h. Then the sample was reduced in a 10 vol.% H2/Ar
flow system at a rate of 10 ◦C min−1 from −70 to 250 ◦C.
2.1.2. Preparation of composite support
SiO2 (Haiyang Co. Qingdao) and AlPO-5 was milled and sieved
to by a 200 mesh sieve, then mixed proportionally with silica sol
(Ludox HS-30) and water. Then the mixture was dried at 100 ◦C,
crushed and sieved (40–60 mesh). The pure AlPO-5 support was
prepared by powder press method. The pressure of tablet press