ChemComm
COMMUNICATION
DOI: 10.1039/C5CC06669G
Journal Name
Entry 1). Given the highly effective activity of Cu based catalyst in Table 2. Mass balance of MeOH based on a typical reaction
MeOH reforming and carbonyl hydrogenation, MeOH was added to
Supplied MeOH
Initial
MeOH (g)
In-situ generated
Total
(g)
a
MeOH (g)
the system to eliminate the reliance of external H . Unexpectedly,
2
Cu-Cr, as a bi-functional catalyst, showed a significantly higher
catalytic activity compared to CuO (Table S2), which provided high
GVL yield with a much lower MeOH dosage. During the reaction,
MeOH was decomposed on the catalyst and the in-situ generated H2
was immediately consumed by the reduction of ML to methyl 4-
hydroxypentanoate (MHP), which was then cyclized to form GVL,
as scheme 1 implied.
1
.25
b
3.87
5.12
Total
(g)
Consumed and
remained MeOH
ꢀm
(g)
Evaporated MeOH
c
from product (g)
2
.10
2.56
4.66
a: calculated based on GVL yield. b: the mass change of reactant during
reaction was ascribed to decomposed MeOH. c: the product was vacuum
evaporated at room temperature and the mass loss was ascribed to the
Equivalent mass of MeOH and ML as substrates led to a complete unreacted MeOH.
ML conversion (CML), but the GVL selectivity (SGVL) was only 63.6%
(Table 1, Entry 2). Considerable amount of GVL-derived molecules To study the recycle performance of the catalyst, the catalyst was
such as pentanoates and hydrocarboxylation products were observed, reused without any regeneration treatment process such as
1
8
which was in accordance with our previous report.
SGVL was calcination and hydrogenation, and a slight descending of GVL yield
significantly increased as MeOH:ML mole ratio reduced (Table 1, was observed in the successive 2 cycles (Table 3). A CML of 79.4%
rd
Entries 3-7), suggesting that the decreasing MeOH input would and a SGVL of 83.6% were still achieved after 6 h in the 3 run,
inhibit the downstream conversion of GVL to by-products. implying that the in-situ reduced Cu-Cr acted quite stably as a bi-
Interestingly, a CML of 93.5% and SGVL up to 96.1% were still functional catalyst. About 6.3% carbon deposit of the catalyst was
achieved even through the initial dosage of MeOH was only 1.25 g detected after 3 cycles (Table 3). ICP-MS result showed that the
(29 mol% of ML, Table 1, Entry 7). Meanwhile, a mass loss of concentration of Cu in liquid product was 1.1 ꢁg/g (Table S4),
reactant (ꢀm) of 2.1 g was observed after reaction, which was probably owing to the infiltration of Cu nano-particles. Oppositely,
ascribed to the decomposition of MeOH during the reaction. Cr was not detected in the liquid product, implying that there was no
However, further reducing the amount of MeOH to 1.0 g (23 mol% obvious ion leaching occurred. However, the introduction of
of ML) required a prolonged reaction time for ML conversion (Table impurities, such as O and water, was adverse to the system (Table
2
1
g, only 24.5 % CML was achieved within 4 h (Table 1, Entry 10).
, Entries 8 and 9). When the dosage of MeOH was decreased to 0.5 S5). Besides, the reaction was severely inhibited by high N pressure
2
probably due to the suppressed H production.
2
Table 1. In-situ H supplied GVL production from ML
2
Table 3. Performance and properties of recycled Cu-Cr catalysts
a
b
c
Entry
Mass ratio of mole ratio of CM
(%)
SGVL
(%)
ꢀm
(g)
Cycle CML SGVL ꢀm BET surface Carbon
2
(g) area (m /g)
MeOH:ML (g/g)
H (4 MPa)/20
MeOH:ML
-
(%) (%)
deposit (%)
a
1
2
3
4
5
6
7
8
95.0 97.6
99.6 63.6
99.5 74.9
99.2 85.4
96.2 85.6
92.6 96.4
93.5 96.1
70.9 97.0
91.3 87.0
-
1
2
3
93.5 96.1 2.1 44.3 (27.6 )
84.1 80.1 1.9 38.1
79.4 83.6 1.6 35.8
5.3
6.1
2
10/10
5/15
2.5/17.5
2/17.5
1.5/17.5
1.25/17.5
1.0/17.5
1.0/17.5
0.5/17.5
4.06
1.35
0.58
0.46
0.35
0.29
0.23
0.23
0.12
2.1
3.0
3.0
2.8
2.4
2.1
1.4
2.0
0.7
b
6.3
o
Reaction conditions: 17.5 g ML, 1.25 g MeOH, 0.35 g catalyst, 250 C, N
2
(1
bar), 500 rpm, 4 h. The used catalysts were washed by ethanol and dried in a
vacuum oven at room temperature before reutilization. a: fresh catalyst. b: 6 h.
2
The fresh Cu-Cr catalyst with a surface area of 27.6 m /g was in-situ
d
reduced in the first cycle. After reaction, mesoporous structure with
a diameter less than 10 nm was observed (Figure S2 and S3), leading
9
1
0
24.5 77.3
o
2
to a higher surface area of 44.3 m /g. The surface area declined to
Reaction conditions: 2 wt% catalyst (relative to ML), 250 C, N (0.1 MPa),
5
00 rpm, 4 h. a: percentage conversion of ML. b: selectivity to GVL. c: mass 38.1 and 35.8 m /g in the two following cycles, in keeping with the
loss of the reactant after reaction. d: 6 h.
2
2
less distribution of pore structure ranges from 4 to 10 nm (Table 3
and Figure S3). SEM and TEM images revealed that there were Cu
Besides the extremely low hydrogen source demand (MeOH), we nano-particles dispersed on the surface of catalyst after in-situ
noticed that ꢀm was larger than the initial MeOH input (Table1, activation (Figures 1 and S4), which is probably responsible for the
Entries 4-9). It was verified that MeOH generated during the increase of surface area of the catalyst after reaction. After 3
hydrocyclization process of ML (Figure S1) was subsequently successive cycles, sintering of Cu into larger particles was observed,
2
0
decomposed into H and CO/CO in the presence of Cu-Cr catalyst. thus resulting in the loss of surface area and catalytic activity.
2
2
As a result, MeOH greater than the initial dosage were consumed.
The mass balance of MeOH was analyzed and the result showed that
the initial MeOH occupied about 60% of ꢀm, that is, the in-situ
generated MeOH contributed up to over 40% of MeOH consumption
(Table 2), suggesting that H-donor utilization is rather high. The
gaseous product was also analyzed and N , CO and CO were the
2
2
main components (Table S3), while H only accounted for 9.6% of
2
the gas, implying that the in-situ generated H2 was effectively
consumed. Based on Scheme 1, it could be calculated that about 0.12
mol H was consumed for GVL formation which was supplied by
2
the decomposition of ~0.07 mol MeOH. This result agrees well with
Yong’s report that 2 mol H would be theoretically generated from
the decomposition of 1 mol MeOH in oxygen and water free system.
2
19
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012