Thermochimica Acta 516 (2011) 74–78 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Thermokinetic analysis of the MgO surface carbonation process in the presence of water vapor Daniela A. Torres-Rodríguez, Heriberto Pfeiffer ∗ Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito exterior s/n, Cd. Universitaria, Del. Coyoacán, CP 04510 México DF, Mexico article info Article history: Received 24 September 2010 Received in revised form 30 December 2010 Accepted 12 January 2011 Available online 26 January 2011 Keywords: Absorption Adsorption CO2 capture Magnesium oxide Water vapor abstract Experiments were performed on magnesium oxide, using water vapor with N 2 or CO 2 as carrier gases, between room temperature and 70 ◦ C, in order to elucidate its thermal stability. Initial experiments were performed with water vapor in the presence of N 2 to elucidate the different physicochemical pro- cesses produced by water vapor exclusively, as N 2 is an inert gas. These results showed that water is only adsorbed on the MgO surface. On the other hand, when CO 2 was used as carrier gas the MgO reac- tivity changed, producing hydrated magnesium carbonate, due to the CO 2 absorption. On the basis of these results and the fact that under dry conditions CO 2 is not absorbed on MgO at T < 70 ◦ C, a pos- sible MgO–H 2 O–CO 2 reaction mechanism is proposed, where MgO microstructural parameters play a significant role during the CO 2 absorption. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Since the beginning of the industrial revolution, the use of fuels has become an essential part of the human life. Therefore, carbon dioxide (CO 2 ) concentrations have been increased dramatically, producing climate changes through the green house effect [1–3]. In that intelligence, several propositions have been published in the last years for the CO 2 absorption or adsorption, concentration and its possible elimination [1,4–6]. Among these propositions, mag- nesium oxide (MgO), as well as other alkaline earth metal oxides, has been used in different manners [7–9]. For instance, MgO has been studied as a possible CO 2 absorbent mainly because of its low energy requirement for regeneration (compared to other oxides), although it possesses a low absorption capacity due to kinetic fac- tors [6,9]. Furthermore, in the last years MgO has been proposed as a catalytic support of different processes. For example, the synthe- sis of combined steam and carbon dioxide reforming of methane (CSCRM) [10–17]. Additionally, mineral carbonation between CO 2 and different natural magnesium and calcium silicates (olivine, serpentine and wollastonite among others) is a reaction process with geolog- ical implications [1,18,19]. Therefore, the reaction path for the MgO–CO 2 –H 2 O system at low temperatures (from room temper- ature to 70 ◦ C) is of great interest in different fields. In this sense, ∗ Corresponding author. Tel.: +52 55 5622 4627; fax: +52 55 5616 1371. E-mail address: pfeiffer@iim.unam.mx (H. Pfeiffer). most of the studies performed up to now have been developed in aqueous systems where magnesium oxide, or magnesium ceram- ics, is dispersed [18,20]. For example, Xiong and Lord [19] reported the CO 2 capture on a MgO aqueous suspension, where Mg(OH) 2 is initially produced and then Mg(OH) 2 reacts with CO 2 produc- ing different hydrated magnesium carbonates. However, the MgO hydration and carbonation processes, where H 2 O is present as vapor, and not in solution, has not been studied. This kind of sys- tems would be of high interest, for example, on different catalytic systems or during the CO 2 absorption processes, where the water and CO 2 quantities may be controlled in order to improve the cor- responding processes. Therefore, the aim of this work was to study systematically the different physicochemical phenomena and mechanisms present during the steam hydration process of MgO in the presence and absence of CO 2 . 2. Experimental Magnesium oxide was obtained by the magnesium carbonate (MgCO 3 , Aldrich) thermal decomposition at 800 ◦ C for 8 h. The com- position, structure and microstructural properties of MgO were confirmed by X-ray diffraction (XRD) and N 2 adsorption (data not shown). For XRD a diffractometer Bruker AXS D8 Advance was used coupled to a copper anode X-ray tube. MgO was identi- fied conventionally by its corresponding Joint Committee Powder Diffraction Standard (JCPDS) file. Textural properties of MgO were determined by N 2 adsorption. The equipment used in this case was 0040-6031/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2011.01.021