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Hydrogen technology has been greatly increased in last decades as a promising solution to protect the environment. When carbon-based feedstocks are used, such as natural gas, biomass and biogas, the water gas shift reaction (WGSR) plays an important step in the production of high pure hydrogen for several purposes. By this reaction, the residual carbon monoxide in the gaseous stream (coming from steam reforming of carbon-based feedstocks) can be converted to carbon dioxide and then removed from the stream, avoiding the poisoning of industrial metallic catalysts as well as of electrocatalysts in fuel cells. Aiming to obtain no toxic catalysts that can replace the commercial chromium-doped hematite catalysts, lanthanum-doped hematite was studied in this work. Iron oxide-based samples with different amounts of lanthanum (La/Fe (molar) = 0.02; 0.08 and 0.2) were obtained by sol-gel method and calcined at 600. °C. The catalysts were characterized by X-ray diffraction, specific surface area measurements, temperature programmed reduction, Raman spectroscopy, Mössbauer spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. It was found that lanthanum affected the textural and reducing properties of hematite, depending on the amount. Moreover, lanthanum oxide increased the activity of hematite by decreasing the size of hematite crystals and then increasing the number of exposed active sites. In addition, lanthanum favored hematite reduction to produce magnetite (active phase). The activity increased with the amount of lanthanum in solids, the lanthanum-richest sample being the most active catalyst. Fil: Rangel, Maria do Carmo. Universidade Federal da Bahia; Brasil Fil: Querino, Peterson Santos. Universidade Federal da Bahia; Brasil Fil: Borges, Sarah Maria Santana. Universidade Federal da Bahia; Brasil Fil: Marchetti, Sergio Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas ; Argentina Fil: Assaf, José Mansur. Universidade Federal do São Carlos; Brasil Fil: Ruiz Vásquez, Doris Polett. Universidad de Concepción; Chile Fil: Rodella, Cristiane Barbieri. Centro Nacional de Pesquisa Em Energia E Materiais; Fil: Freitas Silva, Tatiana de. Universidade Federal do São Carlos; Brasil Fil: Marques da Silva, Alisson Henrique. Universidade Federal do São Carlos; Brasil Fil: Ramon, Adriana Paula. Universidade Federal do São Carlos; Brasil

Here, we have systematically investigated how the nature of the support influenced the oxygen mobility and activities in catalysts comprised of AgPt nanoshells deposited over inorganic oxides. We first synthesized AgPt nanoshells by galvanic replacement reaction between Ag nanospheres and PtCl6 2− (aq) combined with Pt reduction using hydroquinone as an auxiliary reducing agent. The nanoshells were then supported over TiO2, Al2O3 and CeO2. Through this methodology, we prepared materials with similar metallic nanoparticle AgPt compositions (~0.99 wt% Pt), sizes (43 ± 2 nm diameter), spherical shapes, surface morphologies, number of active sites $$ (\sim4.5\;\upmu{\text{mol}}\;{\text{g}}_{{{\text{cat}} .}}^{ - 1} ) $$ and uniform distribution over the supports, differing only in terms of the nature of the support. The oxide reduction temperature, its capability of re-oxidation and the presence of oxygen mobility were strongly dependent on the metal–support interaction between AgPt nanoshells and oxide supports. These properties have significantly influenced their catalytic performances toward the CO oxidation. At 230 °C, the CO oxidation TOF was 40.4 ± 0.4, 6.9 ± 1, 1.4 ± 0.8 min−1 for AgPt/CeO2, AgPt/TiO2, AgPt/Al2O3, respectively. These differences were attributed to the concentration of oxygen vacancies in each catalyst, which presented exactly the same trend as that of the catalytic activities. Our results may have important contributions to the design of highly active metal oxide-based catalysts toward gas-phase oxidation transformations.

Processos oxidativos avançados (POAs) são tecnologias alternativas para remoção eficiente de poluentes orgânicos com elevada estabilidade química e/ou baixa biodegradabilidade. Entre os POAs, os sistemas oxidativos baseados na reação Fenton são os mais utilizados para remoção de corantes. Nesse artigo, resíduos siderúrgicos de laminação, têmpera e aciaria foram avaliados como catalisadores na reação Fenton em processo contínuo, para a remoção do corante azul de metileno em solução aquosa. Esses resíduos foram caracterizados por difratometria de raios X (DRX) e fluorescência de raios X (FRX). Os resultados de caracterização mostraram que os resíduos possuem alto teor de óxido de ferro (hematita) entre outros elementos. Os resíduos foram ativos na reação Fenton e os resultados de cor remanescente na solução mostraram: têmpera (80%) > aciaria (30%) > laminação (23%). Os resíduos de aciaria e laminação apresentaram os melhores resultados de cor remanescente (≤ 30%) e de redução da DQO (≥ 75%). Os resíduos de aciaria e laminação se mostraram promissores para uso como catalisador no processo contínuo de remoção do azul de metileno, usando a reação Fenton heterogênea.

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.

We report herein a systematic investigation on the effect of the size of silver (Ag) nanoparticles employed as starting materials over the morphological features and catalytic performances of AgPt nanoshells produced by a combination of galvanic replacement between Ag and PtCl6(2-) and PtCl6(2-) reduction by hydroquinone. More specifically, we focused on Ag nanoparticles of four different sizes as starting materials, and found that the outer diameter, shell thickness, and the number of Pt surface atoms of the produced nanoshells increased with the size of the starting Ag nanoparticles. The produced AgPt nanoshells were supported into SiO2, and the catalytic performances of the AgPt/SiO2 nanocatalysts toward the gas-phase oxidation of benzene, toluene, and o-xylene (BTX oxidation) followed the order: AgPt 163 nm/SiO2AgPt 133 nm/SiO2AgPt 105 nm/SiO2AgPt 95 nm/SiO2. Interestingly, bigger AgPt nanoshell sizes lead to better catalytic performances in contrast to the intuitive prediction that particles having larger outer diameters tend to present poorer catalytic activities due to their lower surface to volume ratios as compared to smaller particles. This is in agreement with the H2 chemisorption results, and can be assigned to the increase in the Pt surface area with size due to the presence of smaller NPs islands at the surface of the nanoshells having larger outer diameters. This result indicates that, in addition to the overall diameters, the optimization of the surface morphology may play an important role over the optimization of catalytic activities in metal-based nanocatalysts, which can be even more pronounced that the size effect. Our data demonstrate that the control over surface morphology play a very important role relative to the effect of size to the optimization of catalytic performances in catalysts based on noble-metal nanostructures.

Although green catalytic transformations are very attractive, they often remain limited by low conversion percentages and selectivity. Here, we demonstrate that high catalytic performances (TOF = 590,000 h −1 ) could be achieved towards the green oxidation of silanes and H 2 production under ultralow Au loadings (0.001–0.0002 mol% in terms of Au) employing H 2 O as the oxidant, 25 °C as the reaction temperature, and MnO 2 nanowires decorated with ultrasmall Au NPs (3 nm) as catalysts. In addition to these high activities towards a variety of substrates, the MnO 2 –Au NPs displayed good stability/recyclability, in which no morphological changes or loss of activity were observed even after 10 reaction cycles. The improved catalytic activities observed for the MnO 2 –Au NPs can be assigned to: (i) the metal–support interactions, in which the presence of Au NPs could facilitate oxidative processes and thus yield high performances towards the oxidation of hydrosilanes; (ii) the significant concentration of Au δ+ species and oxygen vacancies at the catalyst surface that represent highly catalytically active sites towards oxidation reactions, and (iii) the Au NPs ultrasmall sizes at the MnO 2 surface that enable the exposure of high energy Au surface/facets, high surface-to-volume ratios, and their uniform dispersion. The MnO 2 –Au NPs could be synthesized by a facile approach based on the utilization of MnO 2 nanowires as physical templates for Au deposition without any prior surface modification/functionalization steps. The utilization of supported ultrasmall Au NPs having controlled sizes and dispersion may inspire the design of novel catalysts capable of enabling high catalytic performances towards green transformations at ultralow metal loadings.

We describe herein an investigation on how the number of Pt surface atoms and nature of exposed surface facets affect the catalytic performances of AgPt nanomaterials displaying controlled surface morphologies (smooth or rough surfaces), shapes (spherical or one-dimensional), and hollow interiors towards CO oxidation. More specifically, we focused on AgPt nanoshells (smooth surfaces), assembled nanoparticles (rough surfaces), nanotubes with smooth surfaces, and nanotubes with rough surfaces. We found that their catalytic performances followed the order: nanotubes with smooth surfaces > nanoshells, nanotubes with rough surfaces > assembled nanoparticles. The better catalytic activity observed for the nanoshells relative to the assembled nanoparticles can be associated with their higher number of Pt surface atoms. Even though the nanotubes with rough surfaces had a higher number of Pt surface atoms relative to the nanotubes with smooth surfaces, the latter displayed higher catalytic activities as a result of the preferential exposure of {100} facets, which are the most active towards CO oxidation relative to {111} and {110}. Interestingly, the nanotubes with smooth surfaces also displayed higher catalytic activities when compared to the nanoshells, showing that the preferential exposure of {100} side facets compensated the decrease in their number of Pt surface atoms relative to the nanoshells. Our data showed that the catalytic performances were strongly dependent on the surface morphologies, in which the preferential exposure of more active surface facets may play a significant role in the optimization of performances relative to the number of Pt surface atoms.

Core–shell Pt@Fe3O4@SiO2 nanostructures were successfully prepared in three step procedure. FePt nanoflowers were first prepared by an oleylamine-mediated chemical synthetic route, and then coated with thin silica (SiO2) layer (~5 nm) by a method based in microemulsion. Then, the core–shell Pt@Fe3O4@SiO2 nanostructures were prepared thorough the calcination step at 550 °C in air static of FePt nanoflowers (FePt@SiO2) samples. The silica layer played an important role to avoid nanoparticles agglomeration during the heat treatment. Iron oxide (Fe3O4) shell grown on Pt nanoparticle surface showed able to act as promoter for CO conversion in Preferential Reaction of Oxidation of CO (PROX-CO).

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

Neste trabalho avaliou-se o uso de residuos industriais da laminacao, tempera e aciaria, para descoloracao do corante azul de metileno em processo continuo. Esses residuos foram caracterizados por difratometria de raios X (DRX) e avaliados como catalisadores na descoloracao do azul de metileno. Os resultados de DRX mostraram a presenca de hematita nos residuos industriais. No processo continuo de descoloracao do corante azul de metileno, na presenca de peroxido de hidrogenio e acido, foi observada a descoloracao da solucao para os tres residuos. No entanto, a ordem de atividade dos residuos foi: tempera (20%) < aciaria (70%) < laminacao (80%). O residuo de laminacao tambem apresentou maior estabilidade catalitica nas condicoes da reacao e mostrou-se promissor para o tratamento de efluentes de industrias texteis. Abstract In this work the use of industrial waste from the lamination, quenching and steel mill step in the continuous process of decolorization of methylene blue dye was studied. The wastes were characterized by X-ray diffraction (XRD) and evaluated as catalysts in the decolorization of methylene blue. XRD results showed the presence of hematite in the industrial wastes. Decolorization was observed in the continuous process of decolorization of methylene blue dye, in the presence of hydrogen peroxide and acid, when applying the three industrial wastes. The order of activity was waste from quenching (20%) < steel mill (70%) < lamination (80%). The waste from lamination also showed higher catalytic stability under the reaction conditions, and showed potential for the treatment of effluents from textile industries.