Guillermo Calleja

Development of high efficiency adsorbents for CO2 capture based on a double-functionalization method of grafting and impregnation

A functionalization method based on the impregnation of previously grafted pore-expanded SBA-15 is presented. The combination of tethered and mobile amino groups has led to a synergic effect, yielding samples with CO2 uptakes up to 235 mg CO2 per g (5.34 mmol CO2 per g) at 45 °C and 0.15 bar CO2 and high adsorption efficiencies.

Development of crystallinity and photocatalytic properties in porous TiO2 by mild acid treatment

Crystallization of amorphous mesoporous TiO2 synthesized by a surfactant-templated sol–gel route has been investigated by different methods in order to generate materials with photocatalytic properties. Crystallization by hydrothermal treatment is not a convenient alternative, as it leads to a strong reduction of the textural properties due to excessive coalescence of the inorganic framework. A new crystallization route, based on the treatment of m-TiO2 xerogels with acid–ethanol mixtures under reflux, has been investigated. Sulfuric and phosphoric acids cause severe structural and porous damage, whereas nitric and hydrochloric acids lead to the development of TiO2 photocatalysts with convenient textural properties. These last two acids produce the selective crystallization into anatase, the most active phase of titania in photocatalysis, with small nanocrystals being present within the pore walls. The materials so obtained are characterized by exhibiting high surface areas (210–260 m2 g−1), with an important contribution of microporosity and good photocatalytic activity for trichloroethylene degradation in the aqueous phase. In particular, the best balance between the textural and photocatalytic properties was achieved when the crystallization was carried out by treatment with a 0.5 wt% HCl–ethanol mixture.

Preparation of bimodal micro-mesoporous TiO2 with tailored crystalline properties.

A new mild crystallization procedure has been applied after a synthesis route in the presence of a non-ionic surfactant, leading to the preparation of bimodal micro-mesoporous TiO2, with remarkable textural properties and pore walls formed by anatase nanocrystals, which exhibit photocatalytic activity.

The Role of the Hydroxyl Groups on the Silica Surface When Supporting Metallocene/MAO Catalysts

The behaviour of mesoporous silica as a support for anchored catalytic species depends on its physical and chemical surface properties, particularly those related with the hydroxyl groups. #An earlier version of this paper was presented at ECOREP II, 2nd European Conference on Reaction Engineering of Polyolefins, Lyon, France, July 1–4, 2002. In this report, the number and nature of hydroxyl groups of a commercial silica sample calcined at different temperatures have been determined by titration with triethylaluminium and IR, respectively. The preparation of supported metallocene catalyst has been studied by different ways. The calcination temperature affects deeply the ability of the support to anchor the different species involved in this catalytic system. The polymerization reactions carried out using silica and MAO/silica supports show how the chemistry of the silica surface plays a determinant role in the immobilization of this catalytic system.

An investigation of the textural properties of mesostructured silica-based adsorbents for predicting CO2 adsorption capacity

Among the technologies proposed to reduce greenhouse gas emissions, adsorption with porous solids has been widely studied in the past few years. Herein, up to 30 inorganic porous adsorbents have been studied, obtaining their CO2 uptake at 45 °C and ambient pressure, typical conditions of industrial post-combustion facilities after the desulphurization step. A clear relationship between CO2 adsorption capacity and the combination of surface area (SBET) and sorbent affinity towards gas molecules through C parameter was found. This study provides novel findings that allow the prediction of CO2 uptake in mesostructured silica physisorbents from their textural properties.

Effect of Ion-Exchange Modification on Hydrogen and Carbon Dioxide Adsorption Behaviour of RhoZMOF Material

Zeolite-like metal-organic frameworks (ZMOFs) can adsorb hydrogen and carbon dioxide because of their negatively charged structures, being able to be ion exchanged with metal cations to further increase the electrostatic field inside the framework cavities. Ion exchange of RhoZMOF with alkaline and alkaline-earth metal cations was performed up to stoichiometric levels with one single ion-exchange step. Screen effect caused by water-coordinated molecules around the exchanged cations hindered the hydrogen uptake, although slightly higher heats of hydrogen adsorption were observed for Na+, Li+, Mg2+ and Ca2+ exchanged samples. Conversely, the same exchange treatment produced a very interesting enhancement in CO2 adsorption of RhoZMOF at 303 K. Moreover, because there are no water molecules surrounding the metallic cations, RhoZMOF material was exchanged with an Li+–crown–ether complex in the nitrobenzene/acetonitrile mixture, free of water. Nitrogen and hydrogen adsorption isotherms at 77 K showed higher specific surface area and hydrogen adsorption capacity than the material with hydrated cations.

Transition metal inclusion in RhoZMOF materials

Porous RhoZMOF is a negatively charged zeolite-like MOF material susceptible to post-synthesis modification by an ion-exchange process replacing as-synthesized organic cations with transition metals. This material exhibiting open transition metal sites is a very attractive candidate for industrial applications related to clean energy technologies, like electrochemistry and gas storage. In the present work, partial or total Co2+, Ni2+ and Cu2+ inclusions have been successfully carried out in the RhoZMOF structure by ion-exchange treatment. Particularly, complete exchange of HDMA+ with Co2+ could be reached at room temperature after 12 h of contact time. For Cu2+ exchange, a rapid transformation of the RhoZMOF structure into a new Cu-rich, crystalline and practically non-porous phase was observed at room temperature; its appearance can be avoided and the desired structure can be preserved when ion-exchange treatment is carried out at −20 °C for 6 h, reaching a partial ion-exchange degree of 30%. Moreover, for Ni2+ ion-exchange treatment at 25 and 0 °C, a covering of an amorphous Ni-rich organometallic phase over the crystals was detected by SEM analysis; its appearance can be prevented by reducing the amount of HDMA+ in the media by developing the ion-exchange process in two steps: exchanging HDMA+ with Na+ and Na+ with Ni2+. The results provide a post-synthesis modification route for obtaining porous MOF materials containing open transition metal sites accessible for redox catalysis and selective gas adsorption.

Influence of the feeding control on the final properties of ethylene/propylene copolymers obtained in laboratory semi-batch reactor

AbstractThe slurry polymerization reactors on the industrial scale operate in continuous mode at low monomer conversion per pass to minimize mass and heat transfer limitations. Nevertheless, for the screening of catalytic systems, the laboratory tests are carried out using batch or semi-batch reactors. In this work, ethylene/propylene copolymers were synthesized in a semi-continuous reactor under similar conditions, where the only difference involves the modification of the feed ratio during the reaction. The key point of the control system is a micro-gas chromatograph (MGC), which analyzes the molar ratio ethylene (C2) to propylene (C3) in the gas phase during the reaction, and the composition in the liquid phase was calculated using the Soave-Redlich-Kwong equation of state. The effect of the ethylene/propylene copolymer microstructure has been studied using different techniques that allow us to conclude that the method of synthesis influences the comonomer distribution and the final copolymer properties.