(109b) Characterization of Carbonaceous Materials by Simulations of CO2 Adsorption

One of the most employed techniques for the characterization of porous solids is the physisorption of gases like N2, CO2, Ar and He. Among them, adsorption of N2 at 77 K is the most widely used. It has been shown that for some systems at low relative pressure the N2 isotherms might present deviations.[1] Thus, the use of other adsorptives, such as CO2, offers more accurate information than the standard N2 isotherms.

In this work we present results concerning the characterization by molecular simulations of two highly ordered microporous carbons (Zeolite Templated Carbons - ZTCs). The two atomistic carbon structures are the hexagonal (EMT)[2] and the cubic (FAU-Y)[3] faujasite zeolite carbon replicas. ZTCs are synthesized using the templating method[4] with zeolites as the inorganic microporous host.

These materials offer several desirable characteristics[5] for industrial applications as adsorbent materials, such as: high porosity, large specific surface areas, tunable shape and narrow pore size distributions, hydrophobic surface chemistry, stiffness and robustness of their skeleton. These characteristics allow ZTCs, among other things, to be able to withstand high temperatures and pressures.

An interesting feature of ZTCs compared to other adsorbent materials is their high hydrophobicity and stability under acidic environment, which make them ideal for removing contaminants from steam gas. In fact, one of the most promising applications of these materials is in the context of CO2 capture and separation, a topic of great interest in recent years as it is related to the mitigation of anthropogenic greenhouse gases (GHG) emissions.

The solid structure were previously generated by Roussel et al[6] using Grand Canonical Monte Carlo (GCMC) simulations. Starting with a C2 dimer, the chemical potential was raised exploring the accessible space of configurations of the system.

We report the adsorption isotherms of CO2 at 298K in two synthesized ZTCs (EMT-ZTC and FAU-ZTC). We bring insights into the ZTCs nanostructure, using CO2 as a probe of their microporosity. We show a criterion to identify on the adsorption isotherm a successfully synthesized EMT-ZTC hollow skeleton. Results on the adsorption in FAU-ZTC show the influence of the high curvature of this material.

This work was partially financed by the Spanish Government under projects CTQ2008-05370/PPQ, NANOSELECT and CENIT SOST-CO2 (CEN-2008-1027), these last two projects belonging to the Programa Ingenio 2010. Additional support from the Catalan Government was also provided (2009SGR-666). S.B. and J.S.A. acknowledge a grant from MATGAS 2000 AIE.

REFERENCES

(1) Lozano-Castelló, D.; Cazorla-Amorós, D.; Linares-Solano, A. Carbon 2004, 42, 1233. (2) Gaslain, F. O. M.; Parmentier, J.; Valtchev, V. P.; Patarin, J. Chem Commun (Cambridge, U K) 2006, 991. (3) Ryoo, R.; Joo, S. H.; Jun, S. J Phys Chem B 1999, 103, 7743. (4) Kyotani, T. Carbon 2000, 38, 269. (5) Roussel, T.; Pellenq, R. J. M.; Bienfait, M.; Vix-Guterl, C.; Gadiou, R.; Béguin, F.; Johnson, M. Langmuir 2006, 22, 4614. (6) Roussel, T.; Bichara, C.; Gubbins, K. E.; Pellenq, R. J. M. J Chem Phys 2009, 130, 174717.