Partial Oxidation of methanol over SiO2-supported Fe, Ru, Pd and Pt catalysts
C. Resini1,3, G. Busca1,3, G. Carturan2,3, E. Finocchio1,3, G. Ramis1,3, A. Sicurelli2, M. Venturini1
1. Dipartimento di Ingegneria Chimica and CIMA, Università di Genova.2. Dip. di Ingegneria dei Materiali e Tecnologie Industriali, Università di Trento. 3. Consorzio INSTM, Firenze.
Introduction
Results obtained make them interesting not only in formaldehyde production, but they can also be employed as methanol sensor, useful in the field of DMFC (Direct Methanol Fuel Cells) in detecting methanol crossover, for instance.
VIII B groupFe, Ru, Pd and Pt
dispersed over SiO2
CH3OH + 1/2O2 HCHO + H2O
The technique adopted to prepare this kind of materials allow to produce matrixes with high surface area keeping unchanged the functionalities Si-H. The matrix works as reducing agent towards metal species present in the bulk.
metals dispersed in silica gel
Ru (20% wt.)/SiO2
Pd (10% wt.)/SiO2
Pt (10% wt.)/SiO2
Fe (20% and 10% wt.)/SiO2
The same technique has been adopted to prepare Fe2+, Pd and Pt containing materials.
Experimental
ExperimentalCharacterization
The prepared materials have been characterized by:
XRD
29Si-NMR
TG-MS
FT-IR spectroscopy
BET
Dispersion of Ru ≤ 4.0 nm
Dispersion of Pt ≤ 15 nm
Fe is present as Fe(II) (FeCl2∙nH2O)
a. dispersion of Ru @ 353 K
b. dispersion of Fe2+ @ 353 K
c. dispersion of Pt @ 353 K
XRD
ExperimentalCharacterization
NMR analysis put in evidence that the R
groups are hydrolyzed at low temperature
(13C-NMR), siloxanic structure starts to
appear, but Si-H groups are still
important, even though less than in the
gel precursor without metal.
29Si-NMR
Q3 Q4
Q2
T2
T3
400C TREOS+Ru
80C TREOS+Ru
80C TREOS
The different species present are:
HSi(OSi)2OH, HSi(OSi)3, (HO)2Si(OSi)2, HOSi(OSi)3, Si(OSi)4.
The Si-H groups disappear by increasing temperature.
FT-IR reveals a significant decrease of the feature typical of Si-H groups.
FT-IR
Experimental
Sample Surface area
(m2 g-1)
Average pore diameter
(nm)
Pore volume (cm3 g-1)
Metal particle size (nm)
Ru/SiO2 80°C
440(2) 3.2(0.1) 0.2651(2·10-4) 4.0
Ru/SiO2 400°C
405(2) 4.1(0.1) 0.2498(2·10-4) 150
Pt/SiO2 80°C
Fe2/SiO2 80°C
Fe2/SiO2 350°C
Fe1/SiO2 80°C
Fe1/SiO2 350°C
457(2)
213(2)
143(2)
130(2)
173(2)
5.6(0.1)
5.6(0.1)
9.6(0.1)
9.4(0.1)
8.4(0.1)
0.5889(2 ·10-4)
0.3084(2 ·10-4)
0.3502 (2 ·10-4)
0.3368 (2 ·10-4)
0.3972 (2 ·10-4)
15 - - - -
BET and XRD results
The catalytic activity tests were carried out in a fixed-bed tubular quartz flow reactor connected to a GC Agilent 4890 equipped with a Varian capillary column “Molsieve 5A/Porabond Q Tandem” and TCD and FID detectors in series as well as a Nickel Catalyst Tube.
Feeding conditions
CH3OH/O2 = 1/0,5F = 105 ml/minmcat. = 60 mg in 240 mg of quartz
= 0,034 s
feeding inlet
catalytic bed
outlet to GC
tubular reactor
furnace
thermocouple
Experimental
Ru/SiO2
Results and Discussion
CO2 (S)
CH3OH (C)
O2 (C)
CO (S)
H2O (Y)
HCHO (S)
@ 373 K the catalyst showed no activity in POM or in Total Oxidation.@ 423 K, Total Oxidation reaction is favored. (@ 423 K, T = 150 K)No production of HCHO has been detected.
350 400 450 500 550 600 650 700 750
0
20
40
60
80
100
Co
nv.
/Sel
./Y
ield
(%
)
T [K]
Results and DiscussionPd/SiO2
CO2 (S)
CH3OH (C)
O2 (C)
CO (S)
H2O (Y)
HCHO (S)
@ 380 K the catalyst shows a moderate activity in POM evidenced by the production of HCHO as only product at 380 K.By increasing T, total oxidation reaction is by far favored. (@ 473 K, T = 180 K)
350 400 450 500 550 600 650 700 750
0
20
40
60
80
100
Co
nv.
/Sel
./Y
ield
(%
)
T [K]
Pt/SiO2
Results and Discussion
CO2 (S)
CH3OH (C)
O2 (C)
CO (S)
H2O (Y)
HCHO (S)
@ 373 K the catalyst is active both in POM and in Total Oxidation (T = 190 K).By increasing T, Total Oxidation reaction is favored as indicated by the decrease of the selectivity to HCHO from 20% to zero.
350 400 450 500 550 600 650 700 750
0
20
40
60
80
100
Co
nv.
/Sel
./Y
ield
(%
)
T [K]
Results and Discussion
Fe (3,7)/SiO2 Fe (6,7)/SiO2
CO2 (S)
CH3OH (C)
O2 (C)
CO (S)
H2O (Y)
HCHO (S)
350 400 450 500 550 600 650 700 750
0
20
40
60
80
100
Co
nv.
/Sel
./Y
ield
(%
)
T [K]
350 400 450 500 550 600 650 700 750
0
20
40
60
80
100
Co
nv.
/Sel
./Y
ield
(%
)
T [K]
Both of the catalysts start to be active above 500 K.The sample with a lower load of Fe showed an higher selectivity to HCHO.Selectivity to HCHO decreases by increasing T.The sample with an higher content of Fe showed a more pronounced activity in Total Oxidation than in POM.
ConclusionsHigher activity of Ru, Pd and Pt based catalysts in comparison with the Fe based ones.
Ru, Pd and Pt based samples showed an activity already at 373 - 423 K. On the contrary, methanol on the Fe based catalyst, starts converting above 473 K.
Ru, Pd and Pt samples mainly promote the production of COx, resulting from
total oxidation of methanol and decomposition of methanol and formaldehyde.
HCHO production:with Ru based sample no HCHO has been detected.with Pd and Pt, selectivity to HCHO has been observed decreasing
from 20 % at 573 – 650 K to zero at 650 – 700 K.Fe based catalyst, on the contrary, shows an higher selectivity to
HCHO than to COx in the range 500 – 600 K.
Ru, Pd and Pt based catalysts work better as total oxidation catalysts, in particular the Ru one, even though a small production of formaldehyde has been observed with Pd and Pt.
Fe based samples, showed a more pronounced behavior as partial oxidation catalyst at low temperature, whereas at higher temperature the total oxidation seems to prevail on the partial oxidation.
