Erika de Oliveira Jardim

Ammonia removal using activated carbons: effect of the surface chemistry in dry and moist conditions.

The effect of surface chemistry (nature and amount of oxygen groups) in the removal of ammonia was studied using a modified resin-based activated carbon. NH(3) breakthrough column experiments show that the modification of the original activated carbon with nitric acid, that is, the incorporation of oxygen surface groups, highly improves the adsorption behavior at room temperature. Apparently, there is a linear relationship between the total adsorption capacity and the amount of the more acidic and less stable oxygen surface groups. Similar experiments using moist air clearly show that the effect of humidity highly depends on the surface chemistry of the carbon used. Moisture highly improves the adsorption behavior for samples with a low concentration of oxygen functionalities, probably due to the preferential adsorption of ammonia via dissolution into water. On the contrary, moisture exhibits a small effect on samples with a rich surface chemistry due to the preferential adsorption pathway via Brønsted and Lewis acid centers from the carbon surface. FTIR analyses of the exhausted oxidized samples confirm both the formation of NH(4)(+) species interacting with the Brønsted acid sites, together with the presence of NH(3) species coordinated, through the lone pair electron, to Lewis acid sites on the graphene layers.

Is there any microporosity in ordered mesoporous silicas

The porous structure of nanostructured silicas MCM-41 and SBA-15 has been characterized using N2 adsorption at 77 K, before and after n-nonane preadsorption, together with immersion calorimetry into liquids of different molecular dimensions. Selective blocking of the microporosity with n-nonane proves experimentally that MCM-41 is exclusively mesoporous while SBA-15 exhibits both micro- and mesopores. Additionally, N2 adsorption experiments on the preadsorbed samples show that the microporosity on SBA-15 is located in intrawall positions, the micropore volume accounting for only approximately 7-8 % of the total pore volume. Calorimetric measurements into n-hexane (0.43 nm), 2-methylpentane (0.49 nm), and 2,2-dimethylbutane (0.56 nm) estimate the size of these micropores to be < or = 0.56 nm.

Influence of the metal precursor on the catalytic behavior of Pt/Ceria catalysts in the preferential oxidation of CO in the presence of H2 (PROX)

The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts are prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst.

Immersion calorimetry as a tool to evaluate the catalytic performance of titanosilicate materials in the epoxidation of cyclohexene.

Different types of titanosilicates are synthesized, structurally characterized, and subsequently catalytically tested in the liquid-phase epoxidation of cyclohexene. The performance of three types of combined zeolitic/mesoporous materials is compared with that of widely studied Ti-grafted-MCM-41 molecular sieve and the TS-1 microporous titanosilicate. The catalytic test results are correlated with the structural characteristics of the different catalysts. Moreover, for the first time, immersion calorimetry with the same substrate molecule as in the catalytic test reaction is applied as an extra means to interpret the catalytic results. A good correlation between catalytic performance and immersion calorimetry results is found. This work points out that the combination of catalytic testing and immersion calorimetry can lead to important insights into the influence of the materials structural characteristics on catalysis. Moreover, the potential of using immersion calorimetry as a screening tool for catalysts in epoxidation reactions is shown.

CO2 Adsorption on Ionic Liquid-Modified Cu-BTC: Experimental and Simulation Study

We analyzed the adsorption of CO2 in a Cu-BTC metal-organic framework (MOF) impregnated with ionic liquids (ILs) experimentally and by molecular simulation using the Monte Carlo method. The ILs [bmim][PF6] and [bmim][Tf2N] were impregnated in concentrations of 1, 5 and 10 wt%. Monte Carlo computations showed maximum impregnation load of approximately 30 wt% and improved CO2 adsorption up to 2 bar for all the concentrations tested. Experimentally, the impregnated material was carefully characterized and CO2 isotherms were measured. High concentrations of IL solution (10 wt%) had a pronounced detrimental effect on the textural properties of Cu-BTC, whereas for low concentration (5 wt%), no improvement in CO2 adsorption was observed. Based on the experimental and simulated data, the suitability of Cu-BTC as a target MOF for IL impregnation was examined.

Effect of support and pre-treatment conditions on Pt-Sn catalysts: application to nitrate reduction in water.

The effect of the support (activated carbon or titanium dioxide) on the catalytic activity and selectivity to nitrogen of Pt-Sn catalysts in nitrate reduction was studied. The effects of the preparation conditions and the Pt:Sn atomic ratio were also evaluated. It was observed that the support plays an important role in nitrate reduction and that different preparation conditions lead to different catalytic activities and selectivities. Generally, the catalysts supported on activated carbon were less active but more selective to nitrogen than those supported on titanium dioxide. The monometallic Pt catalyst is active for nitrate reduction only when supported on titanium dioxide, which is explained by the involvement of the support in the reaction mechanism. The catalysts were characterized by different techniques, and significant changes on metal chemical states were observed for the different preparation conditions used. Only metallic Pt and oxidized Sn were observed at low calcination and reduction temperatures, but some metallic Sn was also present when high temperatures were used, being also possible the formation of Pt-Sn alloys.

Hidrólise parcial da superfície do polyethylene terephthalate (PET): transformando um rejeito em um material de troca catiônica para aplicação ambiental

In this work it is proposed a simple and versatile undergraduate chemical experiment in polymer and environmental technology based on the process of polyethylene terephthalate (PET) hydrolysis. Polyethylene terephthalate from post-consume bottles is submitted to a controlled partial hydrolysis which allows the students to follow the reaction by a simple procedure. The students can explore the reaction kinetics, the effect of catalysts and the exposed polyethylene terephthalate surface area on the hydrolysis reaction. The second and innovative part of this experiment is the technological and environmental application of the hydrolyzed polyethylene terephthalate as a material with cation exchange properties. The surface hydrolyzed polyethylene terephthalate can be used as adsorbent for cationic contaminants.

The Energetics of Surfactant‐Templating of Zeolites

Mesoporosity can be conveniently introduced in zeolites by treating them in basic surfactant solutions. The apparent activation energy involved in the formation of mesopores in USY via surfactant-templating was obtained through the combination of in situ synchrotron XRD and ex situ gas adsorption. Additionally, techniques such as pH measurements and TG/DTA were employed to determine the OH evolution and the CTA uptake during the development of mesoporosity, providing information about the different steps involved. By combining both in situ and ex situ techniques, we have been able, for the first time, to determine the apparent activation energies of the different processes involved in the mesostructuring of USY zeolites, which are in the same order of magnitude (30 – 65 kJ mol) of those involved in the crystallization of zeolites. Hence, important mechanistic insights on the surfactanttemplating method were obtained. For more than 25 years now, cationic surfactants have been widely applied to prepare mesoporous amorphous materials. Since then, researchers have made great efforts to extend the use of these surfactant-templating techniques for the preparation of mesoporous zeolites. Among the different methods used to impart secondary porosity within zeolites, the post-synthetic treatment with cationic surfactants has proved to be an effective tool to introduce tunable intracrystalline mesoporosity while maintaining the key features of the zeolite including strong acidity and excellent hydrothermal stability. Recently, we reported the first time-resolved observation of the development of mesoporosity in zeolites through surfactanttemplating by in situ XRD. Indeed, the combination of experimental data with theoretical calculations provided new insights on the formation of intracrystalline mesoporosity featuring short-range order in zeolites. Moreover, the use of LiqTEM rendered the first in situ real time visualization of this process. In spite of the numerous reports dealing with surfactanttemplating of zeolites and the fact that these materials are already a commercial reality, the driving forces responsible for this process are still unknown. Their investigation is one of the objectives of this paper. A systematic study of the apparent activation energies of the different processes involved in surfactant-templating in zeolites was undertaken to increase our understanding of this approach. With this aim, in situ synchrotron XRD and SAXS studies of this process were performed using the experimental setup shown in Figure 1a. This apparatus was specifically designed and built to get detailed information about the kinetics of the surfactanttemplating process, as it allows for the in situ monitoring of the pH and temperature while performing the XRD and SAXS measurements. The reaction mixture, containing the basic surfactant solution ([NaOH] = 0.09 M; [CTAB] = 0.07 M) was placed in a sealed reactor while the temperature was carefully controlled (± 0.1 oC) in the 45 – 90 oC range. The USY zeolite (CBV 720, Si/Al = 15) was introduced in the addition vessel on top of the reactor. The programmed opening of the lid between the reactor and the vessel allowed for the addition of the zeolite at once and thus the collection of data from the beginning of the reaction. Both pH and temperature probes were fitted in the reactor in order to continuously monitor both parameters. A peristaltic pump was used to circulate the mixture through a capillary where both the XRD and SAXS measurements were realized (see Figure S1 for further details). The evolution of the pH was in situ monitored (Figure S2a) providing kinetic information on the OH consumption. These experiments were carried out after calibrating the pH glass electrode with titrated NaOH solutions at the different temperatures studied, see ESI and Figure S3 for details. The decrease of the OH concentration is due to both the cleaving of Si-O-Si bonds and the ion exchange between H and Na/CTA ions in the zeolite. To distinguish between both processes, experiments in which the zeolite was firstly converted into its Na-form were carried out (Figure S2b) thus avoiding the ion exchange by H ions during surfactant-templating. Similar results were obtained in both cases (Figure S2) and thus experiments obtained from the Na-form of the zeolite were employed in this case (Figure 1b). As deduced from the consumption of OH the cleavage of the Si-O-Si bonds is a very fast process, occurring within the first 5 min of the treatment (Figure 1b). As previously described, the opening of the Si-OSi bonds and the formation of SiO sites is required for the mesostructuring to occur. Indeed, the process does not take place if base is not added to the reaction media (Figure S4) and the initial [OH] determines the amount of mesoporosity that can be formed within the zeolite. In order to obtain the apparent activation energy of the cleavage of the Si-O-Si bonds, its rate constant, k, at different temperatures was determined from the slope of the linear part of the evolution of [OH] versus time. These values were used to depict the Arrhenius plot, from where the Arrhenius apparent activation energy was obtained, Ea = 35 kJ mol (Figure 2b, OH data). After that, the step related to the surfactant uptake by the zeolite was investigated by TG to determine the amount of CTA incorporated. [a] Dr. N. Linares, Dr. E. O. Jardim, Dr. A. Sachse, Dr. E. Serrano, and Prof. Dr. J. Garcia-Martinez Laboratorio de Nanotecnología Molecular, Departamento de Química Inorgánica Universidad de Alicante Ctra. San Vicente-Alicante s/n, E-03690 Alicante, Spain. E-mail: j.garcia@ua.es; www.nanomol.es [b] Prof. Dr. J. Garcia-Martinez Rive Technology, Inc. 1 Deer Park Drive, Monmouth Junction, New Jersey 08852, United States Supporting information for this article is given via a link at the end of the document. 10.1002/ange.201803759 A cc ep te d M an us cr ip t Angewandte Chemie This article is protected by copyright. All rights reserved.