Transcript Effect of impregnation solvent and manganese content

Noble metal free catalysts for VOC removal:
formaldehyde oxidation at low temperature over MnOx-SBA-15
R. Averlant1,2, S. Royer3, J.-M. Giraudon1, J.-P. Bellat4, J.-F. Lamonier1
Unité de Catalyse et de Chimie du Solide, CNRS UMR 8181 – Université Lille Nord de France
2French Environment and Energy Management Agency, 20 avenue du Grésillé BP 90406 49004 Angers Cedex 01 France
3 Institut de Chimie des Milieux et Matériaux de Poitiers, CNRS UMR 7285, – Université de Poitiers
4 Laboratoire Interdisciplinaire Carnot de Bourgogne, CNRS UMR 6303 – Université de Bourgogne
1
Introduction
Exposure to formaldehyde has been the topic of recent considerations of many governments around the world. This pollutant can be found in industrial air (e.g. wood and furniture industry) and in indoor
air. Serious health problems such as nasopharyngeal cancer can be caused by a long-term exposure to an air containing a low concentration of formaldehyde (even less than 1 ppm). Several posttreatment technologies have been studied. Catalytic oxidation seems to be a promising solution. Formaldehyde can be converted selectivity in carbon dioxide and water with a relatively low energy
consumption. Even though supported noble metals are the most active (e.g. Pt/TiO2 [1,2]), the development of low-temperature active and cheap catalysts is still a challenge [3].
Here is presented the use of mesoporous silica SBA-15 supported manganese oxides in low-temperature formaldehyde oxidation. Indeed, manganese oxides are known to be the most effective
transition metal oxides for this application. SBA-15 is an ordered mesoporous material with a large surface area (>600m²/g) [4]. A large manganese amount could therefore be impregnated. This study is
focused on the influence of the impregnation solvent, the manganese content and the calcination temperature on the morphology of the manganese particles of the final material and also on the catalytic
activity in the formaldehyde oxidation.
[1] C. Zhang et. al., Catal. Today, 126, 2007, 345. [2] H. Huang et. al., J. Catal., 280, 2011, 60. [3] T. Chen et. al., Micropor. Mesopor. Mater., 122, 2009, 270. [4] D. Zhao et. al., Science, 279, 1998, 548.
Catalyst preparation
20%Mn-W-C200
40%Mn-W-C200
Study of the effect
manganese content
of
the
40%Mn-2S-C200
100
* Calcination: 3h, 1°C/min
[5] J. Roggenbuck et. al., Chem. Mater., 2006, 18, 4151.
[6] M. Imperor-Clerc et. al., J. Am. Chem. Soc., 2000, 122, 11925.
Effect of impregnation solvent and manganese content
Sample
20%Mn2S-C200
40%MnW-C200
20%MnW-C200
10
30
50
2/°
70
Initial
SBA-15
20%MnW-C200
40%MnW-C200
20%Mn2S-C200
40%Mn2S-C200
Volume adsorbed (cm3/g STP)
Initial SBA-15
1.21
Dcrystal (nm)
-
18.6
393.7
0.64
15.7
37.6
117.1
0.19
19.5
15.2
484.4
0.96
12.3
33.7
373.6
0.72
13.2
 Water impregnation :
 increase in crystal size with manganese
content
 large decrease in the surface area and the
pore volume (Table 1)
 spoiling of the mesoporous character of the
material (Fig. 2)
20%Mn-2S-C200
40%Mn-2S-C200
20%Mn-W-C200
40%Mn-W-C200
200
0
0
637.8
Vp
40%Mn-WC200
0
200
400
600
Temperature /°C
0.2
0.4
0.6
0.8
Relative pressure / P/P0
Fig 2: Nitrogen physisorption isotherms
1
 “2 solvents” impregnation :
 no significant increase in crystal size
 less large decrease in specific area and
pore volume in comparison with the water
impregnation (Table 1)
 remain of the mesoporous character even
with a 40% manganese content (Fig. 2)
Conclusion
 Good catalytic result with the sample 40% Mn-W-C200 (100% HCHO conversion into CO2 at
120°C)
 The impregnation method deeply influences manganese particle morphology (particles are as a
majority included in the mesoporous channel of SBA-15 with the « 2 solvents » method)
 These different morphologies lead to different reactivity in HCHO oxidation (Catalytic activity is
better when the impregnation is performed in water)
Conditions:
120 ppm
HCHO/20% O2/He
100 mL/min
200 mg catalyst
1°
C/min
80
60
Quantification
of products
every 5 C with
a micro-GC
equipped with
a TCD
40
20
20%Mn-WC200
20%Mn2S-C200
40%Mn2S-C200
20%MnW-C200
40%MnW-C200
Selective
conversion of
HCHO into
CO2 and H2O
0
800
30
80
130
Temperature / °
C
°
180
Fig. 5: HCHO conversion vs. temperature
Fig. 4: H2 –TPR profiles
• Manganese content increase  higher H2 consumption and catalytic activity
• Catalytic activity better when manganese is impregnated in water
Effect of calcination temperature
 The crystallographic framework remains MnO2 Pyrolusite (PDF # 01-081-2261) regardless
the impregnation solvent and the manganese
content (Fig. 1)
800
400
-
SBET (m²/g)
20%Mn-2SC200
Table 1: Physico-chemical properties
Fig 1: X-ray powder diffractograms
600
Theoretical
Mn content
(MnO2 wt %)
(cm3/g)
40%Mn-2SC200
100
« 2 solvents method »
20%Mn
H2 consumption / mmol/g
Intensity / a. u.
40%Mn2S-C200
40%Mn-2S-C200
Fig 3: TEM images of the samples 40%Mn-W-C200 (left) and 40%Mn-2S-C200 (center and right)
HCHO conversion / %
« 2 solvents »
(Preparation, see Roggenbuck impregnation [6]
+calcination*
et. al.[5]
Studies of the effect of the
calcination temperature and the
manganese content
Manganese
particles
outside the
SBA-15
channels
"2 solvents" method
20% Mn
HCHO conversion / %
Initial SBA-15
(Dchannel = 8 nm)
40%Mn-2S-C200
Manganese
particles
inside the
SBA-15
channel
Manganese precursor:
Mn(NO3)2, 4H2O
20%Mn-2S-C200
20%Mn-2S-C400
20%Mn-2S-C600
40%Mn-W-C200
H2 consumption / mmol/g
Water
impregnation
+ calcination*
Effect of impregnation solvent and manganese content (continued)
600°C
400°C
200°C
80
200°
C
60
400°
C
600°
C
40
Selective
conversion of
HCHO into
CO2 and H2O
20
0
0
200
400
600
Temperature / °
C
Fig. 6: H2 – TPR profiles
800
30
80
130
Temperature / °
C
180
Fig. 7: HCHO conversion vs. temperature
 Calcination temperature increase  H2 consumption decrease and higher contribution of the
high-temperature region of H2 consumption : decrease in manganese oxidation state [7]
 -MnO2 Pyrolusite  Mn2O3 Bixbyite (T = 600°C) with crystal size increase
 Increase in catalytic activity when calcination temperature decreases (Fig. 6)
[7] J. Quiroz Torres et. al., Catal. Today, 17, 2011, 277-280
This work was supported by the French Environment and Energy Management Agency (ADEME)
and the Région Nord – Pas de Calais. We also want to thank ADEME for the financial support of
the project CORTEA / ADEME n° 11 81 C0108 « CAT » (http://cortea-cat.univ-lille1.fr).
Unité de Catalyse et de Chimie du Solide - UMR CNRS 8181
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