Introduction

1. 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 1 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 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 post-treatment 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 Effect of impregnation solvent and manganese content (continued) Manganeseparticlesinside the SBA-15 channel Water impregnation + calcination* Study of the effect of the manganese content 20%Mn-W-C200 40%Mn-W-C200 Manganeseprecursor: Mn(NO3)2, 4H2O Manganeseparticlesoutside the SBA-15 channels Fig 3: TEM images of the samples 40%Mn-W-C200 (left) and 40%Mn-2S-C200 (center and right) 20%Mn-2S-C200 20%Mn-2S-C400 20%Mn-2S-C600 40%Mn-2S-C200 Initial SBA-15 (Dchannel = 8 nm) (Preparation, seeRoggenbucket. al.[5] Studies of the effect of the calcination temperature and the manganese content * 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. « 2 solvents » impregnation [6] +calcination* Effect of impregnation solvent and manganese content 40%Mn-W-C200 40%Mn-2S-C200 ° ° 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 40%Mn-2S-C200 ° ° Table 1: Physico-chemicalproperties Effect of calcination temperature Fig 1: X-ray powderdiffractograms • The crystallographic framework remains -MnO2 Pyrolusite (PDF # 01-081-2261) regardless the impregnation solvent and the manganese content (Fig. 1) • 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) • “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) ° « 2 solventsmethod » 20%Mn ° 600°C ° ° 400°C 200°C ° ° Fig. 7: HCHO conversion vs. temperature Fig. 6: H2 – TPR profiles Fig 2: Nitrogen physisorption isotherms • Calcination temperature increase  H2 consumptiondecrease 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) • 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) [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 USTL - Bâtiment C3 - 59655 Villeneuve d’Ascq Cedex - France -  +33 (0)3 20 43 49 49 Email : remy.averlant@gmail.com - http://uccs.univ-lille1.fr