ANDREOLI, SILVIA

DEORSOLA, FABIO ALESSANDRO

PIRONE, RAFFAELE

Andreoli, Silvia

Deorsola, Fabio Alessandro

Pirone, Raffaele

PORTO Publications Open Repository TOrino

Synthesis of nanostractured MnOx for low-temperature NOx SCR

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

September 7-10, 2014Synthesis of nanostractured MnOx for low-temperature NOx SCRS. Andreoli1 , *F.A. Deorsola1, R. Pirone11Politecnico di Torino, DISAT (Dept. ofApplied Science and Technology), Corso Duca degli Abruzzi 24, Torino, Italy*Corresponding author’s email address: fabio.deorsola@polito.itHighlights			Manganese oxides-based catalysts were synthesized for low temperature NOx SCR.	Different structures and morphology were obtained 	All the samples showed two reduction peaks corresponding to the two different steps of MnOx reduction. 	Catalytic activity tests showed that the presence of Mn3O4 seems a relevant factor.SummarySelective catalytic reduction of NOx is fully investigated on MnOx-based catalyst but is still not clear the oxidation state optimal to have high selectivity and activity at low temperature. For these purpose the attention is inverting on the investigation of the properties of these catalysts. Manganese oxides have been prepared by SCS, hydrothermal and precipitation methods. The samples have been characterized by XRD, BET, H2-TPR, FESEM and have been testing its catalytic activity for NOx remova in a NH3/NOx gas mixture. Were obtained MnOx with different structure and morphology but all have two reduction step as from the literature.KeywordsSelective catalytic reduction, Redox behavior, Manganese oxides, Low temperature activityIntroductionNitrogen oxides (NO, N2O and NO2) are by-produced and emitted in high-temperature combustion of stationary and mobile sources and constitute well-known atmospheric pollutants that can contribute to the ozone depletion, acids rains, photochemical smog and greenhouse effects. Selective catalytic reduction of NOx is an established method for power plant where the DeNOx works at high temperature. Given the stringent regulations, is necessary to apply the same technology in the stationary and mobile application to lower operating temperatures and for this purpose various studies are inverting their attention on the preparation and testing of catalyst based on transition metals.Manganese oxides are versatile materials used in reduction and oxidation reaction for the present of  different structures and morphology.The first goal of the present work is to investigate the properties of manganese oxide (MnOx) based catalysts, because manganese arouses a great research interest in low temperature SCR, to find the exact nature of active sites that hasn’t been clarified, neither the optimal oxidation state of the metal for the reaction has been assessed.MethodologyMn2O3 and Mn3O4 catalyst were prepared by solution combustion synthesis (SCS) at different oven temperatures (350°-400°-600°C) with two different C2H5NO/Mn(NO3)2 ratio; 1:2 in samples S1 and 2:1 in samples S2. The residence time in the oven of the samples at three different temperatures is respectively 1.5 has 350 ° C, 1h at 400 ° C and 20 min at 600 ° C. [1,2]Another method used is Hydreothermal Synthesis [3] as reagents are used  KMnO4 (1.77g) and MnSO4 monohydrate (2.25g). The initial pH was lowered in the range between 1 and 2 through the use of HNO3.The solution is placed in the PARR reactor, for 24h at 160 ° C, in order to form the final oxide. The sample PARR 3, instead, was left at 160 ° C for a time greater, equal to 30h (in order to be completely the reaction to produce the manganese oxide). Was thus obtained a cryptomelane structure.In the precipitation method [4] the reactants had a molar ratio (KMnO4) / (C6H8O6) = 2/3. The two compounds were placed in two different beakers containing 60 ml of water for the acid and 90 ml for potassium permanganate. The two solutions thus obtained were agitated for 30 minutes and then mixed together. The precipitate was immediately filtered and washed with water and ethanol. Subsequently the sample is left to rest for some hours and then is placed in the oven at 100 ° C. These method was used to prepare three samples:  first sample is inserted in the oven at a temperature of 300 ° C for 2 hours, a third sample instead at 400 ° C for 1 hour while the last of these is calcined at 600 ° C for half an hour.All the samples were characterized using: XRD, BET, FESEM, H2-TPR and tested their catalytic activity  under lab-scale conditions in the SCR process.  Results and DiscussionXRD spectra show that samples S1 have as principal phase Mn2O3, samples S2 and ASCORBIC Mn3O4, PARR and PARR3 cryptomelane structure.The BET surface area of S2 decreases with the increasing temperature of combustion, opposite behavior for S1. The higher values are 65 m2/g for S1_600 and S2_400 79 m2/g.PARR shows 30 m2/g and PARR3 50 m2/g.Even the samples ASCORBIC decrease their area with increasing calcination temperature going from 136 to 76 to get to 3 m2/g at 600 ° C.Mn3O4 is in the amorphous phase while crystalline Mn2O3; forwards the crystallinity increases as the synthesis temperature.FESEM images (Fig.1) showed that samples S1 have a rod-shape instead Mn3O4 and cryptomelane has a spongy structure.a)b)Fig. 1 (a) S1_350 (b) s2_400H2-TPR. In the case of the sample S1 only S1_600 has production values ​​and water temperatures of reduction corresponding all'Mn2O3 theoretical, with a ratio of the peaks of about 1:2. From the analysis of the values ​​of adsorbed gas , the samples S2 results are a mixture between Mn2O3 and Mn3O4 Fig.2: TPR profiles of S1 and S2.In figure 3. The second peak shows the presence of potassium.Fig.3: TPR profiles of PARR and PARR3.ReferencesReference to journal:[1] Mescia, D., Caroca, J.C., Russo, N., Labhsetwar, N., Fino, D., Saracco, G., Specchia, V. (2008): Catal. Today,137, 300-305;[2] Russo, N., Fino, D., Saracco, G., Specchia, V. (2006): Catal. Today,117, 214–219.[3] Sun M., Lan B., Yu L., Ye F., Song W., He J., Diao G., Zheng Y., 2012, Managanese oxides with different crystalline structures: facile hydrothermal synthesis and catalytic activities, Materials Letters, 86, pp. 18-20.[4] Wang Y.-T., Lu A.-H., Zhang H.-L. , and Li,2011 W.-C.,.- “Synthesis of nanostructured Mesopours  Manganese Oxides with three-dimensional frameworks and their application in supercapacitors”, The journal of Physical Chemestry,ACS Publications.

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Synthesis of nanostractured MnOx for low-temperature NOx SCR

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