Effect of Mn doping on the activity and stability of Cu-SiO2 catalysts for the hydrogenation of methyl acetate to ethanol

Article abstract of DOI:10.1039/c6ra24252a

A series of xMn-Cu-SiO₂ catalysts with different manganese contents were prepared by an ammonia-evaporation method for methyl acetate hydrogenation. The activity and stability of the catalysts were greatly improved when manganese content was 3%. Besides, physicochemical properties of these catalysts were investigated by N₂ physisorption, X-ray diffraction, H₂-temperature programmed reduction and X-ray photoelectron spectroscopy. The results illustrated that doping a suitable amount of manganese onto silica-supported copper catalysts produced a strong interaction between cupreous species and Mn, diminished the copper crystalline size, enlarged the copper surface area and enriched the surface Cu⁺ species, so as to improve the catalytic activity and stability of the 3Mn-Cu-SiO₂ catalyst.

Full text of DOI:10.1039/c6ra24252a

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Effect of Mn doping on the activity and stability of Cu-SiO2 catalysts
for the hydrogenation of methyl acetate to ethanol
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Chenliang Ye, Cuili Guo*, Chenwei Sun, Yu Zhang
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072,
China
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ABSTRACT
A series of xMnꢀCuꢀSiO2 catalysts with different manganese contents were
prepared by an ammoniaꢀevaporation method for methyl acetate hydrogenation. The
activity and stability of the catalysts were greatly improved when manganese content
was 3%. Besides, physicochemical properties of these catalysts were investigated by
N2 physisorption, Xꢀray diffraction, H2ꢀtemperature programmed reduction and Xꢀray
photoelectron spectroscopy. The results illustrated that doping a suitable amount of
manganese to silicaꢀsupported copper catalysts produced a strong interaction between
cupreous species and Mn, diminished the copper crystalline size，enlarged the copper
surface area and enriched the surface Cu+ species, so as to improve the catalytic
activity and stability of the 3MnꢀCuꢀSiO2 catalyst.
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Keywords: Methyl acetate; Hydrogenation; Manganese; CuꢀSiO2 catalyst
18 1. Introduction
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Ethanol, one of the most important basic materials, plays an important role in
fuel additive, chemical feedstock, medical treatment, and so on [1]. In particular, the
mixture of ethanol and petrol can prepare ethanolꢀpetrol fuels, the use of which will
slow down the depletion of oil resources and reduce the pollution of air [2].
Nowadays, ethanol is mainly synthesized from ethylene hydration and microbial
fermentation of biomass [3]. However, due to the shrinking oil resource and costly
biological process, the established methods have faced many challenges [1]. Thus, it
Corresponding author: Cuili Guo, School of Chemical Engineering & Technology, Tianjin
University, Tianjin, 300072; Tel: +86ꢀ22ꢀ2270ꢀ4495; Eꢀmail: gcl@tju.edu.cn

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is of critical significance to explore new methods to meet increasing demands of
ethanol. Nowadays, methyl acetate (MA) is mainly resulted from natural gas and coal
[4, 5]. Because of the recent surge in shale gas production and the large amount of
coal reserve in the world, hydrogenation of methyl acetate become a very economic
process to synthesis ethanol.
Hydrogenation of MA to synthesis ethanol can be described as following:
CH3COOCH3+H2→CH3CH2OH+CH3OH
(1)
Besides, transesterification, the main side reaction, often occurs during the
process[6].
CH3COOCH3+ CH3CH2OH→CH3COOCH2CH3+CH3OH
(2)
For ester hydrogenation, the traditional catalysts are chromium oxide supported
copperꢀbased catalysts [7, 8]. Although the chromiumꢀsupported copper catalysts
achieve quite good activity and stability, the use of chromium makes a severe
pollution to the environments. Hence, the research of chromiumꢀfree catalysts is of
great importance. To develop chromiumꢀfree catalysts, most of studies have been
focused on CuꢀSiO2 catalysts, because a high initial copper surface area on silica
supports was believed to obtain good catalytic performance for ester hydrogenation
[9]. The main researches on CuꢀSiO2 catalysts are preparation methods and promoter
additives. The research on preparation methods, such as ammonia evaporation,
deposition precipitation, impregnation and ion exchange method, indicated that
different preparation methods made a great influence on the metalꢀsupport interaction
[10ꢀ13]. The studies in promoter additives of CuꢀSiO2 catalysts showed that additives,
such as Zn, Mo, Ni, B and Mg, can dramatically change the catalytic performance of
CuꢀSiO2 catalysts [6, 9, 14ꢀ17]. However, there are still many challenges of
silicaꢀsupported copper catalysts need to be overcome, especially the inherent
insufficient lifespan.
In methanol synthesis and dimethyl ether synthesis from syngas, it has been
suggested that the interaction between copper and manganese could greatly change
the chemical states of cupreous species [18, 19]. In addition, in CO hydrogenation
reaction, it also has been reported that Manganese was an effective promoter for

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ethanol synthesis [20]. However, a detailed research related to the influence of Mn
doping on CuꢀSiO2 catalysts for MA hydrogenation has not been reported. In this
paper, a series of Mnꢀmodified CuꢀSiO2 catalysts with different manganese doping
amount were prepared by an ammoniaꢀevaporation method, and their catalytic
performances for hydrogenation of MA were evaluated in a fixedꢀbed reactor. Besides,
several characterizations were carried out to investigate the relationship between the
structure and catalytic performance of the catalysts. The main aim of this study is to
develop catalysts with enhanced catalytic activity and lifespan for MA hydrogenation.
2. Experimental
2.1. Catalyst preparation
A series of xMnꢀCuꢀSiO2 catalysts with copper content of 30% were synthetized by
an ammoniaꢀevaporation method, where x is the mass loading of Mn. With a typical
procedure, a certain amount of Mn(NO3)2·4H2O and Cu(NO3)2.3H2O were dissolved
in 100 mL deionized water under stirring. An appropriate amount of 25 % ammonia
aqueous solution was added and stirred for 0.5 h. The initial pH of the suspension was
11ꢀ12. Next, a certain amount of 25 % silica sol was added to the above suspension
and stirred for 3 h. All the operations mentioned above were conducted at room
temperature. Then, the suspension was heated at 363 K in a water bath to evaporate
the ammonias. When the pH value of the suspension decreased to 6ꢀ7, the evaporation
process was completed. Finally, the precipitate was dried at 393 K for 24 h and
calcined at 723 K for 4 h to get the catalyst precursor. For comparison, the MnꢀSiO2
catalyst with manganese loading of 3% was also prepared by the same method as
above.
2.2. Catalytic Activity Tests
The activity of the catalysts was tested in a fixedꢀbed tubular reactor with an
internal diameter of 10 mm. A certain amount of catalysts were activated by pure
hydrogen (250 mL/min) at 623 K for 4 h, with a heating rate of 5 K/min starting from
room temperature. After cooling to the reaction temperature, MA was injected to a
gasification chamber by a highꢀpressure pump and mixed with hydrogen. Then, the
mixture went into the reactor and started reaction. The products were condensed and

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analyzed by a gas chromatograph (North Branch of Ruili SPꢀ3200A) fitted with a
HJꢀWAX capillary column and a flame ionization detector (FID).
The conversion and selectivity of products were calculated based on the following
equations：
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(3)
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(4)
2.3. Catalyst characterization
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The textual properties of the catalysts were measured by the method of N2
physisorption using a Quantachrome Nova 2200e instrument. Before the analysis, the
catalysts were outgassed at 573 K for 3 h under vacuum. The specific surface areas
were figured out by the BrunauerꢀEmmettꢀTeller (BET) equation and the total pore
volume (Vp) was calculated d from the adsorbed N2 volume at a relative pressure of
approximately 0.99.
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H2 temperature programmed reduction (TPR) was conducted by a Quantachrome
Instrument AMIꢀ90. Before the reduction, 100 mg catalyst was under He flow (30
mL/min) at 373 K for 0.5 h to drive off physically adsorbed impurities. Then the
catalyst was reduced by 10 vol.% H2/Ar (30mL/min) from 373 K to 1073 K with a
heating rate of 10 K/min. The consumption of hydrogen was tested by a thermal
conductivity detector (TCD).
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The Xꢀray diffraction (XRD) was executed on a D/MAXꢀ2500 diffractometer using
Cu Kα as the radiation source. The scanned range was from 30° to 90° with a
scanning rate of 5°/min. The particle size of copper was estimated by Scherrer
equation.
The Cu surface area was tested by N2O chemisorption on a Quantachrome
Instrument AMIꢀ90，using a procedure described in the literatures [21, 22]. Firstly,
100 mg catalyst was reduced at 623 K for 4 h. Then, the N2O pulse was conducted at
363 K, Cu+N2O→Cu2O+N2, and the consumption of N2O was measured by a TCD
detector. The Cu surface area was calculated from the total amount of N2O
consumption with 1.46×1019 copper atoms/m2.

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Xꢀray photoelectron spectroscopy (XPS) and Xꢀray induced Auger spectra (XAES)
were performed on a PHI5000 VersaProbe spectrometer with monochromatic Al Kα
(E=1486.6eV) as the excitation source. Adventitious carbon (C1s = 284.8 eV) was
used to calibrate the binding energies.
3. Results
3.1. Catalytic performance of the catalysts
The influence of manganese content on the catalytic activity of xMnꢀCuꢀSiO2
catalysts for MA hydrogenation is shown in Table 1 (Reaction time was 8 h). The
effect of external diffusion and internal diffusion was eliminated during the activity
test (See the supporting information). The ethanol yield of 3MnꢀSiO2 catalyst was 0,
which suggested that Mnꢀbased catalysts without Cu do not show any catalytic
activity for MA hydrogenation. For the Mn modified CuꢀSiO2 catalysts, both MA
conversion and ethanol selectivity were gradually enhanced with the increasing
amount of manganese loading and reached to a maximum when the manganese
loading reached 3%. The 3MnꢀCuꢀSiO2 catalyst achieved 96.2% MA conversion and
95.2% ethanol selectivity, which were considerably better than the results of the
CuꢀSiO2 catalyst. However, further increase the amount of manganese loading
resulted in a decrease in both MA conversion and ethanol selectivity. The
8MnꢀCuꢀSiO2 catalyst obtained a very low ethanol yield, only 27.8%. These results
suggested that adoption of a proper amount of manganese to CuꢀSiO2 catalysts was of
critical importance to improve the catalytic activity for MA hydrogenation.
From both academic and industrial viewpoints, the stability of the catalysts is of
great importance besides activity and selectivity. A comparison of catalytic activity as
a function of reaction time on stream for the CuꢀSiO2 catalyst and the 3MnꢀCuꢀSiO2
catalyst is showed in Fig.1. The 3MnꢀCuꢀSiO2 catalyst maintained its high catalytic
activity during the 100 h stability test. For the CuꢀSiO2 catalyst, the MA conversion
and ethanol selectivity decreased to about 69% and 79% respectively after 100 h
stability test. For ester hydrogenation, it has been widely acknowledged that the
deactivation of copperꢀbased catalysts mainly results from copper aggregation and the
valence transition of cupreous species [9, 23].These results indicated that adding a

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suitable amount of manganese to CuꢀSiO2 catalysts was an effective way to improve
the stability of silicaꢀsupported copper catalysts.
3.2. Characterization of the catalysts
3.2.1. Physicochemical properties of the catalysts
The textural properties of different manganese content catalysts were investigated.
As shown in Table 2, the CuꢀSiO2 catalyst had a relatively high BET surface area of
316 m2/g. With the increase of manganese loading, the surface areas of the catalysts
gradually decreased. When the manganese content reached 8%, the surface areas of
the 8MnꢀCuꢀSiO2 catalyst was very small, only 59 m2/g. In contrast, the average pore
size of the catalysts increased with the increase of manganese loading, and the
average pore size reached 14.6 nm when the manganese content was 8%. It was
noticeably that the average pore sizes of all the samples varied from 6.9ꢀ14.6 nm,
which were typically mesoporous materials. The pore volume of the catalysts was
also greatly affected by the content of manganese. When the manganese loading
reached 3%, the largest pore volume was achieved. However, further increase of
manganese loading, the pore volume of the catalysts declined sharply.
Copper surface area has been viewed as a crucial factor affecting catalytic
performance of copperꢀbased catalysts [24]. The copper surface area of the CuꢀSiO2
and the Mnꢀmodified CuꢀSiO2 catalysts was determined by the N2O chemisorption.
As shown in Table 2, adding a suitable amount of manganese significantly enlarged
the copper surface area. The highest copper surface area was acquired on the
3MnꢀCuꢀSiO2 catalyst, which afforded the highest ethanol yield. Nevertheless, further
increasing manganese content led to a decrease of copper surface area. These results
indicated that adoption of a proper amount of manganese to CuꢀSiO2 catalysts was an
effective way to enlarge the copper surface area.
3.2.2. Crystalline phase
To investigate the crystalline structure of the catalysts, the XRD of the calcined
catalysts and reduced catalysts was carried out. As illustrated in Fig. 2 (A), the
characteristic peaks positioned at 2θ of 35.5o and 38.7o correspond to (002) and (111)
lattice planes of copper oxide species respectively [15]. With adoption of a small

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amount of manganese to CuꢀSiO2 catalysts, the CuO diffraction peaks became wider
and weak. However, too much manganese doping made CuO diffraction peaks
become stronger and sharper. The 3MnꢀCuꢀSiO2 catalyst exhibited the weakest CuO
diffraction peaks, indicating that the copper species was better dispersed in the
3MnꢀCuꢀSiO2 catalyst than other catalysts. Noticeably, no diffraction peaks attributed
to manganic species were observed in all the catalysts, which might result from the
low content of manages or well dispersion of manganic species.
The XRD patterns of the reduced catalysts were presented in Fig. 2(B). The
characteristic peaks at 43.5o, 50.4o and 74.1o ascribed to the (111), (200) and (220)
lattice planes of Cu0 species were detected in all samples [15]. The peak intensities of
Cu0 species were firstly weakened and then strengthened with the increase of
manganese loading. The 3MnꢀCuꢀSiO2 catalyst had the weakest Cu0 diffraction peak
and the size of copper crystallite was the smallest, only 12.5 nm as shown in Table 2.
Besides, a weak diffraction peak at 2θ of 36.6° ascribed to Cu2O was observed for all
the samples, and the 3MnꢀCuꢀSiO2 catalyst also exhibited the weakest diffraction peak.
It has been suggested that the active phase dispersion can be reflected by the peak
intensity [9]. Thus, the 3MnꢀCuꢀSiO2 catalyst achieved the best dispersion of active
species among all the samples. These results suggested that adoption of a moderate
amount of manganese to CuꢀSiO2 catalysts was an effective way to control the
crystalline size of cupreous species and improve the copper dispersion (The TEM of
the reduced catalysts can been seen in the supporting information).
3.2.3. Reducibility of the catalysts
To evaluate the reduction behaviour of the catalysts, the calcined CuꢀSiO2 and the
Mnꢀmodified CuꢀSiO2 catalysts were examined by H2ꢀTPR. As displayed in Fig. 3,
the CuꢀSiO2 catalyst showed a unique reduction peak centered at 553 K, which might
result from the collective effective of the reduction of Cu2+ to Cu0 and Cu2+ to Cu+
[25ꢀ27]. Obviously, adoption of manganese greatly affected reduction peak of the
samples. The reduction peak of the samples gradually shifted to a higher temperature
with the adoption of more manganese component, which indicated the strong
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the reduction process [17, 19, 28, 29]. It has been suggested that the interaction
between copper and Mn make CuO reduction more difficult and result in a higher
reduction temperature of cupreous species [17]. This effect may account for smaller
copper particles and higher stability of Mnꢀmodified copperꢀbased catalysts. For
comparison, the reduction property of the 3MnꢀSiO2 catalyst was also carefully
investigated. As shown in Fig.3, the 3MnꢀSiO2 catalyst showed two reduction peaks
at 653 K and 798 K. It has been suggested that the two manganese reduction peaks
correspond to the reduction of Mn4+ to lower oxidation states [17, 30]. Since the
catalysts were reduced at 623 K for 3 h before activity test, the manganese valence of
the reduced catalysts might coexist of different values.
3.2.4. Surface chemical states
Since manganese may be reduced during the reduction process, Mn 2p XPS was
recorded to analyze the surface chemical state of reduced catalysts. It has been
reported that Mn 2P XSP may display narrow peaks at 642.3 eV or 641.8 eV or 640.8
eV, corresponding to MnO2, Mn2O3 and MnO [17, 31, 32]. As represented in Fig. 4,
broad and asymmetric Auger peaks were observed in all the samples, suggesting
significant overlap between different Mn species and Coꢀexistence of multiple Mn
valence state of all the reduced catalysts [17, 30]. These results are consistent with the
TPR analysis.
To investigate the surface chemical states of copper species, the Cu 2P XPS
patterns of reduced catalysts are shown in Fig. 5. Only two peaks around 952.6 eV
and 932.8 eV were observed in the XPS, which were ascribed to Cu 2p1/2 and Cu 2p3/2
peaks, respectively. The disappearance of the 2p satellite peak centered at 942ꢀ944 eV
indicated that all Cu2+ species had been reduced into Cu0 or Cu+ [12].
The binding energy is very close between Cu0 and Cu+. Thus, the Cu LMM XAES
spectra was carried out to further distinguish the surface Cu+ and Cu0 species of
reduced catalysts [33]. As Fig. 6 displays, the broad and asymmetric Auger peaks
were observed, which indicated that Cu0 and Cu+ might coexist on the surfaces of the
reduced catalysts. Besides, the coexistence of Cu0 and Cu+ species of the reduced
catalysts was also proved in the XRD patterns. The Cu LMM XAES spectra could be

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deconvoluted into two obvious overlapping peaks at 570.8 eV and 567.8 eV, which
were ascribed to Cu+ and Cu0, respectively [33, 34]. The results of deconvolution
were shown in Table 2. The distributions of surface Cu+ and Cu0 were greatly affected
by the manganese loading. The mole ratio of Cu+/(Cu0+Cu+) firstly went up and then
declined with the increase of manganese content. The maximum value of
Cu+/(Cu0+Cu+) was 58.5% when the manganese loading reached 3%. Generally
speaking, for copperꢀbased catalysts, the distribution of copper valence is subjected to
many factors, such as preparation method, type of silica species, copper loading,
additives and so on .These results illustrated that adoption of manganese to CuꢀSiO2
catalysts was an effective way to control the distributions of surface Cu+ and Cu0.
4. Discussion
Although copperꢀbased catalysts have been widely studied for acetic ester
hydrogenation and various additives have been adopted to improve the catalytic
performance of silicaꢀsupported copper catalysts, the insufficient activity and lifespan
of silicaꢀsupported copper catalysts still remains a great challenge. Modifying with
manganese was one of an effective way to improve catalytic performance of
silicaꢀsupported copper catalysts, and the catalytic performance was strongly affected
by the content of manganese loading. Compared to CuꢀSiO2 catalysts, the ethanol
yield was increased from 77.3% to 91.6% when the loading of manganese reached 3%,
and the 3MnꢀCuꢀSiO2 catalyst exhibited quite better stability than the CuꢀSiO2
catalyst.
There was a strong correlation between the copper surface area and the ethanol
yield. Among all the catalysts, the 3MnꢀCuꢀSiO2 displayed the highest copper surface
area, which afforded the highest ethanol yield. As XRD analysis illustrates, the
3MnꢀCuꢀSiO2 catalyst achieved the smallest copper crystallite size. It has been
suggested that smaller copper crystallite size tends to achieve higher copper
dispersion and higher copper surface area, so as to improve the catalytic performance
for ester hydrogenation [9, 35]. However, excessive adoption of manganese to
CuꢀSiO2 catalysts led to an aggregation of copper and decrease the catalytic activity.
As listed in table 2, adding manganese to CuꢀSiO2 resulted in a decrease of surface are

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of the catalysts. When the amount of manganese loading reached 8%, the surface area
of the catalyst was very small, only 42.7 m2/g. Too small surface area might account
for the aggregation of cupreous species and enlarge the copper crystalline size.
Although high reduction temperature is conducted to activated catalysts, the
coexistence of Cu+ and Cu0 in silicaꢀsupported copper catalysts is generally accepted
[9, 14, 34, 36, 37]. As well as the copper crystalline size, valence distribution of
cupreous species is widely viewed as an important factor that affect catalytic
performance of copperꢀbased catalysts. In our Mn promoted copperꢀbased catalysts,
the ethanol yield and valence distribution of cupreous species were strongly changed
by the amount of manganese loading. As shown in Table 1 and Table 2, the
3MnꢀCuꢀSiO2 catalyst exhibited the highest ethanol yield and the largest mole ratio of
Cu+/(Cu0+ Cu+). For ester hydrogenation, the cooperation of Cu0 and Cu+ for catalytic
performance is widely accepted and it is of critical importance to obtain a balance
valance distribution of Cu0 and Cu+ [9, 12, 25, 34]. It has been reported that the Cu0
species dissociatively adsorbs H2, and the Cu+ species may stabilize the methoxy and
the acyl specie [26]. Besides, Cu+ sites may act as electrophilic or Lewis acid sites to
polarize the C=O bond via the electron lone pair on oxygen [11, 29], which are
beneficial for improving the activity of the ester groups. Thus, the improvement of
catalytic activity of the Mnꢀmodified copperꢀbased catalysts could be partly attributed
to the enrichment of surface Cu+ species.
Adoption of manganese to copperꢀbased catalysts strongly affected the chemical
state of cupreous species, including copper crystalline size, valance distribution and
reduction temperature. In Mn promoted copperꢀbased catalysts, it has been suggested
that Mn3+ species is of critical importance to the Mn promotion effect, since the
appropriate oxidation ability of Mn3+ could oxidize Cu0 to Cu+, allowing higher
surface Cu+ species and better copper dispersion [17]. Thus, Mn3+ may be the main
species of manganese of our optimal catalyst. It has been widely acknowledged that
the deactivation of copperꢀbased catalysts mainly results from copper aggregation and
the valence transition of cupreous species. As shown in TPR results, the reduction
peak of CuO shifted to a higher temperature with the increase of manganese content,

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which suggested the strong interaction between cupreous species and Mn. The long
lifespan of the 3MnꢀCuꢀSiO2 catalyst might resulted from the strong chemical
interaction between cupreous species and Mn, which could maintain its copper
valence distribution and small copper crystalline size during long time stability test.
5. Conclusion
Modifying with manganese was one of an effective way to improve catalytic
performance of silicaꢀsupported copper catalysts. Among all catalysts, the
3MnꢀCuꢀSiO2 catalyst exhibited the best catalytic performance. The characterization
analysis showed that adding an appropriate amount of manganese to CuꢀSiO2
catalysts produced a strong interaction between cupreous species and Mn, diminished
the copper crystalline size, enlarged the copper surface area and enriched the surface
Cu+ species, so as to improve catalytic activity and stability of the 3MnꢀCuꢀSiO2
catalyst.
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Figure captions
Fig. 1. Catalytic performance of the catalysts as a function of reaction time. Reaction
condition: T=523 K, P=3.0 MPa, H2/MA=15 (mol/mol), LHSV=2 hꢀ1.
Fig. 2. XRD patterns of the calcined (A) and reduced (B) catalysts with different Mn
contents.
Fig. 3. H2ꢀTPR patterns of the catalysts with different manganese contents.
Fig. 4. Mn 2P XPS spectra of the reduced catalysts
Fig. 5. Cu 2P XPS spectra of the reduced catalysts with different manganese contents.
Fig. 6. XAES spectra of the reduced catalysts with different manganese contents.

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Fig. 1. Catalytic performance of the catalysts as a function of reaction time.
Reaction condition: T=523 K, P=3.0 MPa, H2/MA=15 (mol/mol), LHSV=2 h-1.

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Fig. 2. XRD patterns of the calcined (A) and reduced (B) catalysts with different Mn.

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Fig. 3. H2-TPR patterns of the catalysts with different manganese contents.

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Fig. 4. Mn 2P XPS spectra of the reduced catalysts.

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Fig. 5. Cu 2P XPS spectra of the reduced catalysts with different manganese
contents.

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Fig. 6. XAES spectra of the reduced catalysts with different manganese contents.

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Table 1
Activity of the catalysts with different manganese content
Conversion of
MA (%)
87.6
Selectivity of
Ethanol (%)
88.2
Yield of
Ethanol (%)
77.3
Catalyst
Cu-SiO2
1Mn-Cu-SiO2
3Mn-Cu-SiO2
5Mn-Cu-SiO2
8Mn-Cu-SiO2
3Mn-SiO2
92.0
96.2
90.1
42.7
91.2
95.2
89.1
65.1
83.9
91.6
80.3
27.8
0
-
-
Reaction condition: T=523 K, P=3.0 MPa, H2/MA=15 (mol/mol), LHSV=2 h-1.

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Table 2
Physicochemical properties of xMn-Cu-SiO2 catalysts with different Mn contents
Catalyst
BET surface
area (m2/g)
316
Pore volume Average pore
dCu (nm)a
XCu+ (%)b
Cu surface areac
(m2/g)
20.3
(m3/g)
0.54
size (nm)
6.9
Cu-SiO2
19.2
14.1
12.5
15.7
22.6
27.9
44.8
58.5
34.5
24.8
0.54
0.63
0.39
0.22
7.5
9.7
1Mn-Cu-SiO2
3Mn-Cu-SiO2
5Mn-Cu-SiO2
8Mn-Cu-SiO2
288
26.0
260
30.9
11.8
14.6
133
25.1
59
15.4
a Obtained by the Scherrer equation from the XRD data.
b Mole ratio of Cu+/(Cu0+Cu+) determined by Cu LMM XAES spectra.
b Determined by N2O chemisorption.