2
J. Yu et al. / Catalysis Communications 27 (2012) 1–4
(
S.V.) of 10,000 mL/(g·h) and pressure of 3 MPa. The feed gas con-
, 30% CO and 10% N . All post-reactor lines and valves
but high Fe loading (>0.1 wt.%) decreases the CO conversion and pro-
motes hydrogenation of CO to form CH and methanol. The increase
of ethanol selectivity with the increasing Fe content over the Rh–
Mn–Li–Fe/SiO catalysts may be caused by the increased acetalde-
tained 60% H
2
2
4
were heated to 150 °C to prevent product condensation. The products
were analyzed on-line (Agilent GC 6820) using a HP-PLOT/Q column
2
(
30 m, 0.32 mm ID) with an FID (flame ionization detector) and a
hyde hydrogenation, which was also proved by other reports [15,16].
TDX-01 column with a TCD (thermal conductivity detector). The CO
conversion was calculated based on the fraction of CO that formed
carbon-containing products and the selectivity of a certain product
was calculated based on carbon efficiency, as reported previously
3.2. Textural characterization
XRD patterns (not shown) of support and the corresponding cata-
[
10].
lysts show no crystalline phases, indicating that the SiO
amorphous and the metal particles are highly dispersed on the SiO
support due to the small content. The similar BET surface areas
2
is XRD-
2
2
.3. Catalyst characterization
2
(
~15 m /g) are obtained on all the samples.
The X-ray powder diffraction (XRD) spectra of samples were
3
3
.3. DRIFTS study
obtained on a Rigaku D/MAX-IIIA X-ray diffractometer with CuKα
λ=0.15418 nm). The BET surface area of the sample was obtained
by adsorption at −196 °C on Micromeritics ASAP 2020
apparatus.
(
.3.1. CO adsorption on the catalysts
The FT-IR spectra of the in situ reduced catalysts with different
N
2
a
amounts of Fe after CO adsorption at 30 °C for 80 min are compared in
Fig. 1. It can be seen that the IR spectrum is mainly composed of a
band at ~2067 cm
2
.4. DRIFTS
−
1
−1
and a doublet at ~2100 and ~2030 cm , which
can be attributed to linearly adsorbed CO [CO(l)] and dicarbonyl
CO adsorption was studied using a Nicolet 6700 FT-IR spectrome-
ter equipped with a DRIFT cell with CaF windows. The sample in the
cell was pretreated in 10% H /N at 400 °C for 2 h, and then the
temperature was dropped to 30 °C. After the cell was outgassed in
+
2
Rh (CO) [CO(gdc)], respectively [17–19]. It is widely accepted that
2
0
the CO(l) is formed on the Rh sites, and CO(gdc) species is on the
2
2
+
Rh sites which may be highly dispersed [20,21]. As the Fe loading in-
−
3
creases, the intensities of CO(l) and CO(gdc) decrease, and the degree
of decrease of CO(l) is larger than that of CO(gdc), which can be
reflected clearly by the peak area ratio of CO(l) versus CO(gdc)
vacuum to b10
troduced for 80 min (pco =8.0×10 Pa), the IR spectrum of CO
adsorbed on the catalyst was recorded. Then the 10% H /N was intro-
duced again, and the IR spectrum of CO adsorbed was recorded as a
Pa, the background was scanned. After CO was in-
3
2
2
(
CO(l)/CO(gdc)) shown in Table 2.
−
1
Based on the above results, it can be inferred that the addition of
function of time. The spectral resolution was 4 cm
of scans was 64.
and the number
Fe can decrease the Rh coverage and impede the CO adsorption,
which is in line with the results reported by Mo et al. [13] and Yin
et al. [7]. By comparing the degree of decrease of CO(gdc) with that
of CO(l), it is suggested that CO(gdc) is more stable on the Fe-
promoted catalyst. Similarly, Haider et al. [1] have also reported
that CO(gdc) is more thermally stable on the Fe-promoted catalyst.
3
. Results and discussion
3
.1. CO hydrogenation
The effect of Fe promoter on the catalytic properties of Rh–Mn–Li/
catalyst in CO hydrogenation is shown in Table 1. As observed,
3
.3.2. The desorption behavior of adsorbed CO in H
Fig. 2 shows the IR spectra of adsorbed species on the in situ re-
duced catalysts by H /N flow flushed into the cell after CO adsorbed
2
flow
SiO
2
+
2
the CO conversion and yield of C oxygenates increase first with
2
2
the Fe loading, then reach a maximum at Fe amount of ca. 0.1 wt.%,
and decrease when the Fe addition exceeded 0.1 wt.%. Interestingly,
at 30 °C. For all the catalysts, the intensity of CO(l) decreases rapidly
at first. As the time increases, the intensity of CO(gdc) decreases,
along with the new bands at around 2055 cm
ing slowly. The 1800 cm
the selectivities of CH
4
and methanol do not change obviously as
−1
−1
and 1800 cm
rais-
the Fe loading was below 0.1 wt.%, but they increase suddenly when
the addition of Fe reached 0.5 wt.%. On the other hand, it is found
that the selectivity of ethanol decreases when 0.05 wt.% Fe was
−1
band can be assigned to bridge bonded CO
−1
[CO(b)] [17] and the 2055 cm
band can be attributed to rhodium
carbonyl hydride species [H–Rh–CO] (i.e., re-formation of metallic
Rh from isolated Rh ) [21–23]. In related work, the researches by
Solymosi [21] and Guglielminotti [6] also gave IR spectra similar to
our observation for the changes of CO adsorption in the presence of
H
added into Rh–Mn–Li/SiO
2
catalyst. However, with the further in-
+
crease of Fe content, the electivity of ethanol increases notably and
the selectivity of acetaldehyde decreases.
Thus, it can be seen that the addition of low content of Fe
2
, suggesting that the absorbed CO can be changed in the presence
+
(
≤0.1 wt.%) can improve the activity and yield of C
2
oxygenates;
of H at room temperature. By comparing the time required for the
2
complete transformation of CO(gdc) over different catalysts, it can
be inferred that the increased amount of Fe could promote the rate
of transformation.
Moreover, it can be seen from Fig. 2 and Table 2 that the peak area
ratio of the final H–Rh–CO and CO(b) species versus original CO(gdc)
Table 1
Effect of Fe loading on performance of CO hydrogenation over Rh–Mn–Li–Fe/SiO
catalysts.
2
+
Fe
CO
conv.
Selectivity of products (C%)
CO CH MeOH AcH EtOH
STY(C
2
(%)
Oxy) (g/
(kg·h))
2
on the catalysts decreases in the order: Rh–Mn–Li/SiO >Rh–Mn–Li–
+
Oxyb
+
HCc
2
4
C
2
C
2
a
(C%)
0
.05Fe/SiO >Rh–Mn–Li–0.1Fe/SiO . This result suggests that the
2
2
0
0
0
0
18.9
.05 24.4
1.1
1.2
1.4
5.3
12.1
12.4
11.7
2.3
0
0.61
25.4 27.1
42.7 18.9
32.8 22.9
5.6 35.1
54.3
63.2
58.2
40.7
30.2
23.2
28.1
11.1
309.1
451.8
491.0
201.5
CO(gdc) species can be changed in two different modes: (a) desorbed
associatively, (b) transformed into H–Rh–CO and CO(b), and the in-
crease of Fe amount could enhance the CO(gdc) desorption rather
than transformation. In addition, it can also be seen from Table 2
that the peak area ratios of H–Rh–CO versus CO(b) species on the var-
ious catalysts at the final time were almost the same, which indicated
that the percentage of H–Rh–CO transformed from the CO(gdc)
species over the different catalysts was almost consistent.
.1
.5
28.2
14.8
30.2 12.7
2
Reaction conditions: 300 °C, 3 MPa, S.V.=10,000 mL/(g·h), V(H )/V(CO)=2, data
taken after 15 h when steady state was reached. Experimental error: ± 5%.
a
b
c
+
+
STY(C
2 2
Oxy): Space time yield of C Oxy
+
C
C
2
Oxy denotes oxygenates containing two and more carbon atoms.
HC denotes hydrocarbons containing two and more carbon atoms.
+
2
Yu, Jun
