M. Ma et al.
Molecular Catalysis 467 (2019) 52–60
Fig. 1. The characterization of catalysts with
different Cu/Al molar ratios. XRD patterns of
2 2 3
Cu (OH) CO /AlOOH with different Cu/Al
molar ratios (A). XRD patterns of in situ re-
duced catalysts with different Cu/Al molar ra-
tios after the reaction (B). XPS spectra of
Cu
alysts with 3/1 ratio of Cu/Al (C). FT-IR
spectra of Cu (OH) CO /AlOOH with different
Cu/Al molar ratios (D).
2 2 3
(OH) CO /AlOOH and in situ reduced cat-
2
2
3
3
. Results and discussion
.1. Characterization of catalysts
Cu (OH) CO /AlOOH catalysts were designed with Cu/Al molar
ML into γ-GVL. Apart from this, the XPS analysis further proved this
view (Fig. 1C). For Cu 2p3/2 and Cu 2p1/2, in situ reduced samples have
3
2 2 3
lower binding energy than Cu (OH) CO /AlOOH, demonstrating that
2
+
+
Cu species were reduced to Cu or Cu species after the CTH reaction.
2+
2
2
3
Meanwhile, Cu satellite peak becomes weaker, apparently confirmed
that more Cu2+ species were reduced to Cu or Cu+ species. In addition,
the XPS peaks of Cu 2p3/2 were deconvoluted to explore Cu species in
ratios of 0, 1:3, 1:1, 3:1 and ∞ (100% copper). And ICP results de-
monstrate that the real Cu/Al molar ratios is consistent with the theo-
retical value (Table S2). In a series of Cu
with different Cu/Al molar ratios, the surface areas, pore volume and
pore size of the catalysts were determined by BET, and the results reveal
that the catalysts have a rich pore structure. Furthermore, surface area
of the catalysts decreases as the Cu/Al molar ratio increases. (Table S3
and Figure S1 A).
2+
2
(OH)
2
CO
3
/AlOOH catalysts
different valence states (Figure S2), and Cu
is obviously reduced to
Cu° or Cu+ after the reaction. The fact that Cu/AlOOH can be prepared
by in situ reduced method in the process of CTH reaction is proved.
The FT-IR analysis (Fig. 1D) clearly reveals the characteristic ab-
sorption peaks of Cu
[38,39], the peaks at 3416 and 3343 cm
OeH stretching modes. The two vibration peaks appearing at 1508 and
2
(OH)
2
CO
3
and AlOOH. For the Cu
2
(OH)
2 3
CO
−1
are assigned to the (Cu)
XRD patterns of Cu
ratios are presented in Fig. 1A. When the Cu/Al molar ratio is 0 and 1/
, XRD patterns only indicate the faint characteristic peak of AlOOH
2θ = 14.5°, 28.2°, 38.3°, 48.9° and 64.9°. PDF, 21–1307). With the
increase of Cu/Al ratio from 1/1 to ∞, the characteristic peaks of
Cu (OH) CO (2θ = 14.8°, 17.5°, 24.0°, 31.2°,35.6° and 54.8°. PDF,
1–1390) strengthens, while the peak of AlOOH becomes weak or
disappears due to its low crystallinity or low content, which is also the
reason that no Cu (OH) CO peak exists in the pattern of the catalyst
2 2 3
(OH) CO /AlOOH with different Cu/Al molar
-
1
2-
1401 cm arise from the asymmetric stretching vibration of CO
3
. The
-
1
3
(
peaks at 1055 and 880 cm can be attributed to the symmetric
stretching and out of plane bending vibrations of CO
The peaks at 588 and 531 cm are assigned to the Cu-O stretching
modes. For the AlOOH, [40–42] the two peaks at 3297 and 3091 cm
are assigned to the symmetrical and asymmetrical stretching vibrations
2-
3
, respectively.
-
1
-
1
2
2
3
4
-
1
of (Al)O-H groups respectively. The peak at 1381 cm is attributed to
the OH bending vibration. The absorption peaks at 1068 and 1162 cm
-
1
2
2
3
with 1/3 ratio of Cu/Al. In Fig. 1B, XRD patterns of in situ reduced
catalysts with different molar ratios after the reaction are recorded and
metallic Cu is acquired. Except the catalyst with 0 ratio of Cu/Al, all
catalysts show the characteristic peaks of metallic Cu (2θ = 43.2°, 50.4°
and 74.1°. PDF, 04-0836). At the same time, it can be observed that as
the Cu/Al proportion increases, the intensity of Cu peak increases. And
no obvious diffraction peaks of AlOOH was observed in the XRD pat-
terns except for the catalyst with 0 ratio of Cu/Al, attributed to its low
crystallinity or low content. Therefore, we can draw preliminary con-
clusions that Cu/AlOOH is generated by in situ reduction of
correspond to the symmetric and asymmetric bending vibrations of
AleOH, respectively. And the three characteristic peaks at 762, 641,
-
1
and 480 cm were ascribed to the vibration mode of Al-O. The above
results verify that the composition of catalyst is Cu
AlOOH.
2 2 3
(OH) CO and
From TG/DTA analysis (Figure S1B), the temperature range of NH
TPD and CO -TPD tests are determined to be between 100 °C and 310 °C
(Figure S1 C–F). Figure S1C presents the NH -TPD profiles with various
3
-
2
3
Cu/Al molar ratio samples, which indicates that all samples exhibit a
medium strong acidic site at around 300 °C, especially high Cu/Al
molar ratio catalysts (3/1 and ∞). After the in situ reduction, the
2 2 3
Cu (OH) CO /AlOOH after catalytic transfer hydrogenation (CTH) of
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