Diana Iruretagoyena

Layered double hydroxides supported on multi-walled carbon nanotubes: preparation and CO2 adsorption characteristics

Layered double hydroxides (LDHs) are promising materials for CO2 sorption, although improvements in performance are required for practical applications. In the current study, the CO2 sorption capacity and multi-cycle stability were both increased by introducing an open supporting framework of multi-walled carbon nanotubes (MWNTs). This nanostructured inert network provides a high surface area, maximizing the gas accessibility and minimizing coarsening effects. Specifically, LDH nanoparticles were precipitated directly onto MWNTs, initially oxidised to ensure a favourable electrostatic interaction and hence a good dispersion. The dependence of the structural and physical properties of the Mg–Al LDH grown on MWNT supports has been studied, using electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), and BET surface area, and correlated with the CO2 sorption capacity, established via TGA and temperature programmed desorption measurements. The use of a MWNT support was found to improve the absolute capacity and cycle stability of the hybrid adsorbent under dry conditions.

Adsorption of carbon dioxide on graphene oxide supported layered double oxides

Abstract Adsorption of CO2 on layered double oxides supported on graphene oxide has been studied under dry and wet conditions. In the first exposure to the adsorptive gas, the isotherms obtained for supported and unsupported materials are shown to fit to the Freundlich model indicating the existence of heterogeneous adsorption sites. After multiple temperature-swing cycles, the adsorption capacity decreased and the data is better described by the Langmuir model. The presence of graphene oxide is shown to reduce the loss of adsorption capacity, and helps to maintain the heterogeneity of the basic sites on the adsorbents. The use of wet gas mixtures was found to have a positive effect on the CO2 adsorption capacity of the graphene oxide hybrids. The presence of residual sodium on the materials resulted in a Freundlich isotherm with increased adsorption capacity.

Selective Sulfur Removal from Liquid Fuels Using Nanostructured Adsorbents

In recent years, there has been an increasing pressure to develop strategies to reduce the level of sulfur in transportation fuels due to stringent environmental regulations. Currently, hydrodesulfurization (HDS) is the most mature (pre-FCC) technology to remove sulfur from gasoline and diesel. However, conventional HDS can hardly produce ultra-low sulfur fuels while maintaining important fuel requirements (i.e., oxygen content, overall aromatic content, olefin content for gasoline, and cetane number for diesel). As a consequence, improvement of existing HDS processes and development of new desulfurization technologies is needed. In this regard, selective adsorption removal of sulfur (SARS) is a promising emerging approach for ultra-deep desulfurization of refinery streams by means of solid adsorbents. Contrary to HDS, SARS is usually carried out at low temperatures and pressures with minimal hydrogen consumption, preventing olefin hydrogenation and thus maintaining the properties of the fuels. This chapter presents a general overview of SARS. Emphasis is given to the use of nanostructured materials as sulfur adsorbents. Section 5.1 introduces the chapter presenting a general description of HDS, SARS and other emerging desulfurization technologies. Section 5.2 describes the two main groups of SARS (adsorption desulfurization and reactive adsorption desulfurization). Subsequently, the three main mechanisms for sulfur adsorption (π-complexation, direct sulfur–adsorption site interactions, and bulk incorporation in reactive adsorption desulfurization) are reviewed. Section 5.3 gives an overview of relevant literature concerning the use of promising groups of nanostructured adsorbents for SARS including zeolites, MOFs, mesoporous silicas, and carbon-nanostructured adsorbents. Finally, Sect. 5.4 gives some concluding remarks.