Catalizadores de nitrato de litio y nitrato de cesio para la combustión de material particulado. Tratamiento con vapor de agua.

MARIA LUCIA RUIZ ,; MARTA ISABEL PONZI; ILEANA DANIELA LICK; ESTHER NATALIA PONZI

Buzios, Brasil.

Congreso; 15 º Congresso Brasileiro de Catálise. 5º Congresso de Catálise do Mercosul.; 2009

Introduction The diesel soot is an environmental pollutant that affects the air quality. Soot emissions can be reduced by placing an oxidation catalyst within the exhaust stream. In this order, the research of efficient and low cost catalysts is a technologic challenge [1]. The beneficial influence of a good contact between the soot, oxygen and catalyst on the soot oxidation rate has been pointed out by several authors [2]. Molten salt catalysts with compounds that melt at temperatures near to the ones of the soot oxidation have phases with wetting capacity and are good catalysts for the soot combustion [2-5]. It is stated that when improving the interaction soot-catalyst, the oxygen transfer process of the reducible species to the soot is improved to give COx. Among these catalysts, it is possible to find those ones that contain alkaline nitrates. It is also reported that the nitrate ion participates in soot combustion [6-8] by means of a reaction between the nitrate ion and the soot, to give a nitrite ion that is oxidized by the oxygen of the gaseous phase, thus completing the catalytic cycle [6-8]. The deactivation of catalysts is an important issue in the design and formulation of a commercial catalytic system. A catalyst used for the combustion of soot in diesel emissions may lose its activity for high temperatures and wet air [9-10]. Studies previously performed show that cesium nitrate and lithium nitrate supported on simple oxides (ZrO2 y SiO2) present a good catalytic activity [7-8]. The aim of this work is analyze the hydrothermal stability of CsNO3 and LiNO3 supported catalysts. Materials and Methods Catalysts have been prepared by incipient wetness method with an aqueous solution of LiNO3 or CsNO3. The precursors and catalysts are characterized by TGA, DSC, XRD and FTIR. Activity measurements for fresh and hydrothermal treatment catalysts were performed in a thermogravimetric reactor feed with an air/He mixture. Commercially available carbon black (Printex-U) was used as a model soot. Hydrotermal treatment experiments were carried out on samples of fresh catalyst loaded in a quartz reactor fed with a gaseous current containing helium saturated with water vapor (7% vol). This treatments were performed at 600 ºC for 5 h. Results and Discussion The thermal stability of alkaline nitrates can be correlated with the cation atomic radius. The supported CsNO3 is thermically more stable than the Li NO3 then the superficial concentration of CsNO3 is higher than the superficial concentration of LiNO3. For this reason, the activity of fresh CsNO3 catalysts is higher. However, the CsNO3 concentration can decrease during the hydrotehermal treatment. The lithium nitrate catalysts present a good hydrothermal stability with respect the cesium nitrate catalysis. In these catalysts the lithium can be integrated into the zirconia lattice. According to the results we could associate the catalyst activity with the presence of nitrate ions. We suppose that nitrate ions are more available to soot combustion, but also are the less resistant to hydrotermal treatment. Mean while, coordinated nitrate ions are remained into the catalyst and they yield intrite ions by redox proccess. References 1.        R. Jiménez; X. García; C. Ellier; P. Ruiz; A. Gordon. Appl. Catal. A. 314 (2006) 81-88. 2.        N. Russo; S.Furfori; D. Fino; G. Saracco; V. Specchia. Appl. Catal.B. 83 (2008) 85-95. 3.        R. Jiménez; X. García; C. Ellier; P. Ruiz; A. Gordon. Appl. Catal. A. 297(2006) 125-134. 4.        D. Hleis; M. Labaki; H. Laversin; D. Courcot; A. Aboukaïs. Colloides and Surfaces A: Physicochem. Eng. Aspects. 330 (2008) 193-200. 5.        D. Uner; M.K. Demirkol; B. Dernaika. Appl. Catal. B. 61 (2005) 334-335. 6.        A. Carrascull; I. D. Lick; E. N. Ponzi; M. I. Ponzi. Catal. Comun.4 (2003)124-128. 7.        M. Ruiz; M. Ponzi; E. Ponzi. XX Simposio Ibero-Americano de Catálise. 2006. 8.        M. Ruiz; M. Ponzi; E. Rodriguez-Castellón; A. Jiménez-López; D. Lick; E. Ponzi. XXI Simposio Ibero-Americano de Catálise. 2008. 9.        C. Grzona; I. Lick; M. Ponzi; E. Ponzi. XXI Simposio Ibero-Americano de Catálise. 2008. 10.     B. van Setten; C. Spitters, J. Bremmer; A. Mulders; M. Makkee; J. Moulijn. Appl. Catal.B.42 (2003) 337-347.