T. Ding et al. / Catalysis Communications 74 (2016) 10–15
11
Table 1
2.2. Catalyst characterization
Activity of different promoters adding to copper-based catalyst.
The copper-based catalysts with different promoters were
characterized by different techniques as follows. The wide-angle XRD
were conducted on a Bruker D8 FOCUS X-ray diffractometer with
Cu-Kα radiation, operating at a voltage of 40 kV and a current of
100 mA. The angle ranged from 10 to 80° with a continuous scanning
speed of 0.02°/min. TG analysis was measured on Simultaneous Q600
DSC-TGA equipment with air atmosphere at 10 K/min heating rate.
Flourier transform infrared spectroscopy (FT-IR) was performed on
Nicolet5700 spectrometer with KBr beam splitter. Scanning electron
micrograph (SEM) was conducted on Nova Nano SEM 450 and the
sample was gold-plated before measurement. The specific surface
areas and pore size distributions were measured on a Micromeritics
ASAP2020 instrument following the BET method and BJH method
respectively. The real content of copper and boron was determined by
inductively coupled plasma-atomic emission spectroscopy method
(ICP-AES: Agilent 725ES). N2O chemisorption was carried out in
Autochem II 2920 apparatus. The specific surface area of Cu was
estimated from the total amount of N2O consumption with
1.46 × 1019 copper atoms per square meter. X-ray photoelectron
spectroscopy (XPS) was conducted on a ESCALAB 250Xi system (Ther-
mo Fisher) operated at a pass energy of 100 eV with an Al Kα X-ray
source radiation source.
Selectivity (%)
Catalyst
LHSV (h−1
)
Conversion (%)
1,3-PDO 3-HPE NPA
EP
Cu-B/SiO2
Cu-Ag/SiO2
Cu-Zn/SiO2
Cu-Al/SiO2
Cu-Ni/SiO2
0.72
1.80
0.72
1.8
0.72
1.8
0.72
1.80
0.72
1.8
97.22
96.71
96.03
93.46
80.37
35.98
92.16
74.29
96.62
93.29
93.39
85.72
94.38
92.17
19.48
29.76
12.83
6.47
6.88
21.81
4.77
15.26
16.69
8.75
16.01
13.54
63.03
4.15
18.86 5.12
22.12 21.03
32.13 6.30
18.84 13.12
10.25 6.92
9.14
2.53
2.17
6.10
15.41
12.67
14.49
0.00
19.66
5.37
15.30 5.08
18.10 14.52
16.64 6.48
6.56
37.90 7.91
20.01 14.44
0.00
0.00
14.43
18.07
28.96
10.50
11.96
34.51
6.35
Cu-Mo/SiO2 0.72
1.8
Cu/SiO2
9.62
0.72
1.8
21.43
Reaction conditions: P(H2) = 2.0 MPa, T = 473 K, H2/DEM = 440 (mol/mol).
molybdenum as prompters showed zero selectivity of 1,3-PDO and a
certain selectivity for 3-HPE and side-products. During other four pro-
moters, the selectivity of 1,3-PDO varied considerably in the following
order: B N Ag N Zn N Al. At a high LHSV of 1.8 h−1, most promoters
showed high conversion (N74%) but a significantly decrease for zinc.
The activity decline of Cu-Zn/SiO2 catalyst indicated that it was easier
to deactivate, ascribing to the activation, storage or spillover of hydro-
gen [13]. The selectivity of 1,3-PDO and 3-HPE could increase for most
promoters at higher LHSV.
Compared with Cu/SiO2 catalyst, the selectivity of 1,3-PDO increased
from 28.96% to 29.76% and the selectivity of 3-HPE decreased from
21.43% to 16.69% under Cu-B/SiO2, while other chosen promoters had
an adverse effect on the selectivity of 1,3-PDO. It is obvious that boron
showed the highest selectivity of 1,3-PDO in the chosen copper-based
catalysts. In order to find out the related information, several character-
ization techniques have been carried out below.
2.3. Activity test
The catalytic activity test was conducted on a fixed-bed reactor.
Before reaction, 5 mL 40–60 meshes copper-based catalysts with
different promoters were loaded into a stainless steel tubular reactor,
the void of which was filled with quartz sand. The reactor was heated
with three stage heater in order to control the reaction temperature.
And the catalyst was deoxidized with H2 at 573 K for 4 h. Then dropping
to the reaction temperature, DEM in ethanol was pumped by an
advection pump to the reactor and combined with H2 at a H2/DEM
molar ratio of 440. The system temperature was set at 473 K and the
system pressure was 2.0 MPa. And the liquid hourly space velocity
(LHSV) of DEM was set at 0.72 h−1 and 1.80 h−1. The products were
condensed and analyzed on a gas chromatograph fitted with HT-5
capillary column (30 m × 0.32 mm × 0.5 μm) and a flame ionization
detector.
3.2. XRD analysis
The XRD patterns of calcined catalysts with different promoters are
shown in Fig. 1A. All catalysts show a broad and diffuse peak at 22°, ded-
icating that SiO2 as the support is amorphous. No CuO diffraction peak is
observed in Cu-B/SiO2 and Cu/SiO2 catalysts, indicating well dispersion
of copper particles or very small particle size [21]. Two visible peaks at
35.5° and 38.7° belonging to CuO with the crystal planes of (111) and
(200) are observed in Cu-Al/SiO2 catalyst. Aluminum oxide could incor-
porate into the framework of SiO2 to form tetrahedral coordination
bonded Si atoms by oxygen bridges [22], so it might increase the steric
hindrance of copper oxide particles precipitated on the surface of
support. The characteristic peaks of copper oxide also appear in Cu-
Zn/SiO2 and Cu-Ni/SiO2. So we conclude that the addition of aluminum,
zinc and nickel played an adverse effect on copper dispersion in Cu/SiO2
catalysts.
3. Results and discussion
3.1. Catalytic activity
Vapor phase hydrogenation of DEM to 1,3-PDO comprises several
cascade reactions as shown in Scheme 1, including DEM hydrogenation
to 3-hydroxy ethyl propionate (3-HPE), 3-HPE hydrogenation to 1,3-
PDO and deep hydrogenation of 1,3-PDO to n-propanol (NPA). More-
over, the other side product ethyl propionate (EP) could be produced
as the hydrogenation of hydroxyl group in 3-HPE. So it is important to
choose a proper promoter inhibiting the side reactions to increase the
selectivity of 1,3-PDO.
The XRD patterns of typical samples after reduction are presented in
Fig. 1B. The reduced catalysts show diffraction peaks at 43.2° and 50.3°
ascribed to Cu phase and a diffraction peak at 36.5° attributed to Cu2O
phase. The intensity of Cu peak is stronger and the intensity of Cu2O
The catalytic performance of different promoters on DEM hydroge-
nation to 1,3-PDO is shown in Table 1. At a low LHSV of 0.72 h−1, differ-
ent promoters exhibited high catalytic activities (N80%). Nickel and
Scheme 1. Reaction scheme for the hydrogenation of DEM to 3-HPE, 1,3-PDO and n-propanol.