Partial Oxidation of methanol over SiO 2 -supported Fe, Ru, Pd and Pt catalysts

1. 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 • Dipartimento di Ingegneria Chimica and CIMA, Università di Genova. • Dip. di Ingegneria dei Materiali e Tecnologie Industriali, Università di Trento. • Consorzio INSTM, Firenze.

2. Introduction VIII B group Fe, Ru, Pd and Pt dispersed over SiO2 CH3OH + 1/2O2 HCHO + H2O 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.

3. Experimental Ru (20% wt.)/SiO2 Pd (10% wt.)/SiO2 Pt (10% wt.)/SiO2 Fe (20% and 10% wt.)/SiO2 metals dispersed in silica gel 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. The same technique has been adopted to prepare Fe2+, Pd and Pt containing materials.

4. 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) Experimental Characterization The prepared materials have been characterized by: XRD dispersion of Ru @ 353 K dispersion of Fe2+ @ 353 K dispersion of Pt @ 353 K

5. 80C TREOS Q3 Q4 T3 Q2 T2 80C TREOS+Ru 400C TREOS+Ru Experimental Characterization 29Si-NMR 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. 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 FT-IR reveals a significant decrease of the feature typical of Si-H groups.

6. Sample Surface Average Pore volume Metal particle size 3 - 1 area pore diameter (cm g ) (nm) 2 - 1 (m g ) (nm) ± ± ± Ru/SiO 4.0 440( 2) 3.2( 0.1) 0.2651( 2·10 - 4) 2 80°C ± ± ± Ru/SiO 150 405( 2) 4.1( 0.1) 0.2498( 2·10 - 4) 2 400°C ± ± ± Pt/SiO 15 457( 2) 5.6( 0.1) 0.5889( 2 ·10 - 4) 2 80°C Fe2/SiO - ± ± ± 213 ( 2) 5.6 ( 0.1) 0.3084 ( 2 ·10 - 4) 2 80°C Fe 2/SiO - ± ± ± 143 ( 2) 9.6 ( 0.1) 0.3502 ( 2 ·10 - 4) 2 350°C Fe1/SiO - ± ± ± 130 ( 2) 9.4 ( 0.1) 0.3368 ( 2 ·10 - 4) 2 80°C Fe1/SiO - ± ± ± 173 ( 2) 8.4 ( 0.1) 0.3972 ( 2 ·10 - 4) 2 350°C Experimental BET and XRD results

7. thermocouple feeding inlet furnace catalytic bed tubular reactor outlet to GC Experimental 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 = 1/0,5 F = 105 ml/min mcat. = 60 mg in 240 mg of quartz  = 0,034 s

8. CO (S) CO2 (S) H2O (Y) HCHO (S) 100 CH3OH (C) O2 (C) 80 60 Conv./Sel./Yield (%) 40 20 0 350 400 450 500 550 600 650 700 750 T [K] Results and Discussion Ru/SiO2 @ 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.

9. CO (S) CO2 (S) H2O (Y) HCHO (S) CH3OH (C) O2 (C) 100 80 60 Conv./Sel./Yield (%) 40 20 0 350 400 450 500 550 600 650 700 750 T [K] Results and Discussion Pd/SiO2 @ 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)

10. CO (S) CO2 (S) H2O (Y) HCHO (S) CH3OH (C) O2 (C) 100 80 60 Conv./Sel./Yield (%) 40 20 0 350 400 450 500 550 600 650 700 750 T [K] Results and Discussion Pt/SiO2 @ 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.

11. CO (S) CO2 (S) H2O (Y) HCHO (S) 100 CH3OH (C) 100 O2 (C) 80 80 60 Conv./Sel./Yield (%) 60 Conv./Sel./Yield (%) 40 40 20 20 0 350 400 450 500 550 600 650 700 750 0 T [K] 350 400 450 500 550 600 650 700 750 T [K] Results and Discussion Fe (3,7)/SiO2 Fe (6,7)/SiO2 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.

12. Conclusions • Higher 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.