Transcript Folie 1 - Catbioetametcon

TA INVESTIGATIONS OF AG-DOPED H3PW12O40 HETEROPOLYACIDS SUPPORTED ON MESOPOROUS MAT
A. Popaa, V. Sascaa, I. Holclajtner-Antunovicb, O. Verdesa and L. Avrama
aInstitute of Chemistry Timisoara of Romanian Academy, 24 Mihai Viteazul Ave, 300223-Timisoara, Romania
bUniversity of Belgrade, Faculty of Physical Chemistry, P.O.Box 47, 11158 Belgrade, Serbia
INTRODUCTION
Aim: Heteropolyacids (HPAs) with Keggin structure and their salts unsupported and supported on different materials have been applied to catalyse a large spectrum of chemical reactions, both in the
heterogeneous and homogeneous systems.
Heteropolyacid salts are prepared by partially exchanging protons of the parent HPAs with different cations. As HPAs salts are insoluble, the SBA-15 supported Ag-acid salt was prepared by two-step
sequential impregnation and in situ reaction on the support.
In order to be more effective for catalytic reactions, HPAs are usually impregnated or incorporated on different porous materials with high surface area. Direct incorporation of heteropolyacid H3PW12O40
and its Ag salt Ag2HPW12O40 (AgHPW) into mesoporous silica molecular sieve SBA - 15 and titania TiO2 during the synthesis was studied. The goal of this work was to characterise the thermal stability of
these heteropolyacid salts supported on mesoporous silica and titania matrix in reference to the bulk solid heteropolyacid Ag salts.
Synthesis: Ag2HPW12O40 (AgHPW) - SBA15 composites were synthesised as follows: first silver nitrate was impregnated by aqueous incipient wetness onto SBA-15 molecular sieve, dried and calcined
at 300°C and finally 12-tungstophosphoric acid was impregnated by a similar aqueous impregnation route. For (AgHPW) - TiO2 composites the same preparation procedure was used. The effect of
incorporation of heteropolyacids species on SBA-15 and titania matrix was studied. The AgHPW was deposited in the concentration of 30 wt. % loading. Mesoporous silica SBA-15 was synthesized
according to the procedure developed by D.Zhao et al. by the hydrolysis of tetraethyl orthosilicate using as surfactant a P123 block copolymer.
RESULTS AND DISCUSSION
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1
The I.R. absorption spectra were recorded with a Jasco 430 spectrometer
(spectral range 4000-400 cm-1 range, 256 scans, and resolution 2 cm-1)
using KBr pellets.
2
1
470
3
441
Energy, a.u.
Energy, a.u.
1
1
595
582
2
534
3
Transmittance, a.u.
2
3
0
4
100
200
300
(1) HPW/SBA15
(2) Ag2PW/SBA15
(1) HPW/TiO2
(3) SBA15
(3) TiO2
400
500
(2) Ag2PW/TiO2
600
o
Temperature, C
(1) HPW
(2) HPW/SBA15
(3) Ag2PW/SBA15
Fig. 4. DSC of AgHPW - SBA15 composites
700
0
100
200
300
400
500
600
700
o
Temperature, C
Fig. 5. DSC of AgHPW – TiO2 composites
(4) SBA15
1800
1600
1400
1200
1000
Wavenumber, cm
800
600
400
-1
3
Transmittance, a.u.
Fig. 1. FTIR spectra of AgHPW - SBA15 composites
TGA/DTA - Thermal analysis
was carried out using a TGA/DTA 851-LF 1100 Mettler apparatus. The samples with mass of
about 100 mg were placed in alumina crucible of 900 ml. The experiments were conducted in air
or nitrogen flow of 50 mL·min–1, in the temperature range of 25–700°C with a heating rate of
10°C·min–1.
Fig. 2. FTIR spectra of
AgHPW – TiO2 composites
(1) HPW
(2) HPW/TiO2
(3) AgPW/TiO2
(4) TiO2
1800
1600
1400
1200
1000
Wavenumber/cm
800
600
400
-1
DSC - Thermal analysis
DSC analysis was carried out with a Mettler Star system DSC 823 apparatus.
The samples with mass of 20 - 40 mg were placed in Pt crucible of 150 ml.
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1
596
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Energy, a.u.
167
2
3
4
5
(1) HPW
(2) AgPW
(3) Ag2PW
(4) Ag2.5PW
(5) Ag3PW
0
100
200
300
400
500
600
700
o
Temperature, C
Fig. 3. DSC analysis of AgxH3-xPW12O40 (AgHPW)
with x= 1.0, 2.0, 2.5 and 3
Fig. 6 a - c Thermogravimetry analyses of AgH2PW12O40 (a) Ag3PW12O40 (b) Ag2HPW - SBA15 composites
TG-DTG and DTA analysis
CONCLUSIONS
The AgHPAs anions preserved their Keggin structure on the surface of AgHPW - SBA15 and AgHPW - TiO2 composites and forms finely dispersed HPAs species.
 The molecular sieves-HPW composites exhibit differential pore size distribution in the mesoporosity range.
Immobilization on SBA-15 molecular sieve maintain the thermal stability of the Keggin structures in comparison with their bulk heteropolyacid Ag salt, as decomposition
of the structure to corresponding oxides take place between 590-600ºC for both bulk salt and SBA-15 supported salts.
The favourable effect of HPAs incorporation on silica molecular sieve is the increasing of pore volume and specific surface area, which in fact make the silica-HPA
composites proper for heterogeneous catalysis.