Suchergebnisse

The catalytic properties of modified Au/TiO 2 catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H 2 TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au + . The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity. ; We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI). ; This work was funded by CONACYT project 260409 and PAPIIT-UNAM project IT200114 (Mexico); CSIC project 201180E104 and MINECO project CTQ2013-41507-R (Spain); and Government Program "Science" of Tomsk Polytechnic University, grant No. 4.1187.2014/K (Russia).

Trabajo presentado en el 11th Intl Symposium on Scientific Bases for the Preparation of Heterogeneous Catalysts, celebrado en Louvain-la-Neuve (Bélgica) del 6 al 10 de julio de 2014. ; Silica is one of the most used supports in heterogeneous oxidation catalysts due to its chemical inertness for such reactions. Its low interaction with the supported active phases usually results in their low dispersion. As a way to overcome this problem, big research efforts have been done to obtain high specific surface area silicas, such as mesoporous MCM-41, SBA-15 or hexagonal mesoporous silica (HMS). This work is dedicated to preparation of new structure supports of HMS. These new structures were formed due to three simultaneously occurring phenomena: hierarchical organization, biomorphism and self-assembling. Reports in the literature [1-3] are dedicated to one of these three phenomena; however, we did not find any description of simultaneous observation of two or three of them in one system. The closest analogous materials with similar biomorphic structures were reported for mixture of SiO2 and BaCO3 [4]. In this case Ba carbonate played a role of a template; while in our work we do not apply any templating substance. Moreover, in [4] biomorphic structures with sizes ≥ 300 µm were formed; while in the present work size of biomorphic SiO2 structures is at least three orders of magnitude smaller (~ 80 nm). These unusual structures of (pure and modified) SiO2 were used as supports for preparation of gold catalysts of CO and 1-octanol oxidation. ; The authors acknowledge funding for this research by CONACYT Project No 79062 (Mexico), PAPIITUNAM Project IN100908 (Mexico), Russian Government Program «Science» of Tomsk Polytechnic University 3.2702.2011; Target Federal Program project 14.B37.21.0058 (Russia); CSIC project 201180E104 (Spain), MICINN project ENE2009-14522-C05 (Spain) and E. Flores, R.Velez, Sh. Sandoval, I.Gradilla, J. Mendoza, J. Diaz, J. Peralta, M. Sainz for technical assistance. ; Peer Reviewed

Worldwide demands of Vanilla planifolia lead to finding new options to produce large-scale and contaminant-free crops. Particularly, the Mexican Government has classified Vanilla planifolia at risk and it subject to protection programs since wild species are in danger of extinction and no more than 30 clones have been found. Nanotechnology could help to solve both demands and genetic variability, but toxicological concerns must be solved. In this work, we present the first study of the cytotoxic and genotoxic effects promoted by AgNPs in Vanilla planifolia plantlets after a very long exposure time of six weeks. Our results show that Vanilla planifolia plantlets growth with doses of 25 and 50 mg/L is favored with a small decrease in the mitotic index. A dose-dependency in the frequency of cells with chromosomal aberrations and micronuclei was found. However, genotoxic effects could be considered as minimum due to with the highest concentration employed (200 mg/L), the total percentage of chromatic aberrations is lower than 5% with only three micronuclei in 3000 cells, despite the long-time exposure to AgNP. Therefore, 25 and 50 mg/L (1.5 and 3 mg/L of metallic silver) were identified as safe concentrations for Vanilla planifolia growth on in vitro conditions. Exposure of plantlets to AgNPs increase the polymorphism registered by inter-simple sequence repeat method (ISSR), which could be useful to promote the genetic variability of this species.

The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO 2 , Ag/Mg/TiO 2 and Ag/Ce/TiO 2 catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size <1 nm. The differences in catalytic properties and sensitivity to pretreatments, observed for the studied Ag catalysts, could not be explained taking into account only the Ag particles whose size distribution is measured by HRTEM, but may be explained by the presence of the subnanometer Ag species, undetectable by HRTEM, and their interaction with supports. This result highlights their role as active species and the need to take them into account to understand integrally the catalysis by supported nanometals. ; We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI). ; This research was supported by Government Program "Science" of Tomsk Polytechnic University, Grant No. 4.1187.2014/K, CONACYT Project 260409 and PAPIIT-UNAM Project IT200114 (Mexico), CSIC project 201480E077 and MINECO Project CTQ2013-41507-R (Spain). We gratefully thank O. Martynyuk, G. Torres Otañez, Z. I. Bedolla Valdez, E. Flores, F. Ruiz Medina, A. Olivas Sarabia, I. Gradilla, J. Mendoza, E. M. Aparicio Ceja, J. Peralta, David A. Domínguez, M. Sainz, R. Valdez Castro, M. Martínez, B. Acosta Ruelas, F. Ramírez Hernández and M. López Cisneros for valuable technical assistance.