Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions

We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H2PtCl6 as precursor. The reaction was conducted in excess of oxygen. β-SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5 nm for 0.5 wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO2 and Al2O3 commercial supports (Pt particles very small in size, average particle diameter of 1 nm for 0.5 wt% Pt in both cases). The case of a SiO2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt0, indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7 nm for 0.5 wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalystś surface.Junta de Andalucía PE2012-TEP862Ministerio de Economía y Competitividad CTQ2012-32519, CTQ2015-65918-RConsejo Superior de Investigaciones Científicas PIE-201460E01

Tetravalent doping of CeO2 : the impact of valence electron character on group IV dopant influence

Fluorite CeO2 doped with group IV elements is studied within the density functional theory (DFT) and DFT + U framework. Concentration-dependent formation energies are calculated for Ce(1-x)Z(x)O(2) (Z = C, Si, Ge, Sn, Pb, Ti, Zr, Hf) with 0 <= x <= 0.25 and a roughly decreasing trend with ionic radius is observed. The influence of the valence and near valence electronic configuration is discussed, indicating the importance of filled d and f shells near the Fermi level for all properties investigated. A clearly different behavior of group IVa and IVb dopants is observed: the former are more suitable for surface modifications and the latter are more suitable for bulk modifications. For the entire set of group IV dopants, there exists an inverse relation between the change, due to doping, of the bulk modulus, and the thermal expansion coefficients. Hirshfeld-I atomic charges show that charge-transfer effects due to doping are limited to the nearest-neighbor oxygen atoms

Стеклокристаллический материал для опакового слоя металлокерамических зубных протезов

Стеклокристаллический материал для опакового слоя металлокерамических зубных протезов, включающий SiO2, Al2O3, SnO2, K2O, ZrO2, Li2O, ZnO и при необходимости Na2O, B2O3, CaO, MgO, F и CeO

Rose Bengal sensitized bilayered photoanode of nano-crystalline TiO–CeO for dye-sensitized solar cell application

There are two traditional ways to read Kant’s claim that every event necessarily has a cause: the weaker every-event some-cause (WCP) and the stronger same-cause same-effect (SCP) causal principles. The debate on whether and where he subscribes to the SCP has focused on the Analogies in the Critique of Pure Reason (Guyer, Allison, and Watkins) and on the Metaphysical Foundations of Natural Science (Friedman). By analysing the arguments and conclusions of both the Analogies and the Postulates, as well as the two Latin principles non datur casus and non datur fatum that summarise their results, I will argue that the SCP is actually demonstrated in the Postulates section of the First Critique

Coupling of soot oxidation and ammonia-mediated selective catalytic reduction of nitrogen oxides

L'abstract è presente nell'allegato / the abstract is in the attachmen

The strange magnetism of oxides and carbons

Magnetism is not usually expected in simple sp oxides like MgO or in carbons like graphite. Yet basic intrinsic defects in these systems can be magnetic in ways that seem to be shared by more complex oxides. A second puzzle comes from reports of possible room temperature ferromagnetism in simple oxides, where experiments are not always in agreement. This paper discusses what determines whether point defects like cation vacancies in oxides have magnetic or non-magnetic ground states. It also discusses the possible connections between point defect ground states and oxide ferromagnetism. The connectivity issue raises questions about possible diffuse states in nanocrystalline oxides, several possibilities being outlined. These ideas raise the further possibility that the magnetism might be written in these oxides at the nanoscale, perhaps using atomic force microscopy

Investigation of a Pt containing washcoat on SiC foam for hydrogen combustion applications

A commercial Pt based washcoat, used for catalytic methane combustion, was studied supported on a commercial SiC foam as catalytic material (Pt/SiC) for catalytic hydrogen combustion (CHC). Structural and chemical characterization was performed using Electron Microscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The reaction was monitored following water concentration by Fourier Transform Infrared spectra (FTIR). The FTIR method was compared with H2 detection by Gas Cromatography (GC) and has shown to be adequate to study the kinetics of the CHC reaction in steady state under our experimental conditions (very lean 1% (v/v) H2/air mixtures). The catalyst is composed of 5–20 nm disperse Pt nanoparticles decorating a mixture of high surface area Al2O3 and small amounts of ceria supported on the SiC foam which also contains alumina as binder. The Pt/SiC catalytic material has demonstrated to be active enough to start up the reaction in a few seconds at room temperature. The material has been able to convert at least 18.5 Lhydrogen min−1 gPt−1 at room temperature in conditions of excess of catalyst. The Pt/SiC material was studied after use using XPS and no significant changes on Pt oxidation states were found. The material was characterized from a kinetic point of view. From the conversion-temperature plot a T50 (temperature for 50% conversion) of 34 °C was obtained. Activation energy measured in our conditions was 35 ± 1 kJ mol−1.Peer reviewe

Nanostructured semiconductor materials for dye-sensitized solar cells

Since O'Regan and Grätzel's first report in 1991, dye-sensitized solar cells (DSSCs) appeared immediately as a promising low-cost photovoltaic technology. In fact, though being far less efficient than conventional silicon-based photovoltaics (being the maximum, lab scale prototype reported efficiency around 13%), the simple design of the device and the absence of the strict and expensive manufacturing processes needed for conventional photovoltaics make them attractive in small-power applications especially in low-light conditions, where they outperform their silicon counterparts. Nanomaterials are at the very heart of DSSC, as the success of its design is due to the use of nanostructures at both the anode and the cathode. In this review, we present the state of the art for both n-type and p-type semiconductors used in the photoelectrodes of DSSCs, showing the evolution of the materials during the 25 years of history of this kind of devices. In the case of p-type semiconductors, also some other energy conversion applications are touched upon. © 2017 Carmen Cavallo et al

Optical properties and photocatalytic activity of the CeO2/SnO2 thin-film heterostructure

Известно, что утилизация сточных вод без надлежащей очистки создает экологические проблемы. Перспективным является фотокаталитическое разложение органических загрязнителей в сточных водах. Этот метод привлек внимание ученых своей простотой и дешевизной. В качестве фотокатализаторов используются в основном порошкообразные полупроводниковые оксидные ма-териалы, обладающие хорошими адсорбционными свойствами по отношению к органическим веществам, фотохимической стабильностью и нетоксичностью. Такие свойства имеют оксиды олова(IV), титана(IV), цинка(II) и церия(IV). В по-следнее время показана возможность применения в качестве фотокатализаторов тонкопленочных материалов, которые упрощают технологию их удаления из очищенной воды. Кроме того, известно, что гетероструктуры усиливают фотока-талитическую активность материала, в том числе и за счет уменьшения ширины запрещенной зоны, что позволяет больше поглощать веществам в видимой обла-сти спектра. В данной работе проведено сравнение оптических свойств тонкопленочных материалов SnO2, CeO2 и CeO2/SnO2 на кварцевых подложках, полученных золь-гель методом из пленкообразующих растворов на основе нитрата церия(III) или/и хлорида олова(IV) с салициловой кислотой. Толщина, показатель преломления пленок изучены методом эллипсометрии, пропускающая способность исследо-вана спектрофотометрией. Фотокаталитические свойства тонкопленочных мате-риалов CeO2/SnO2 показаны в модельной реакции разложения органического кра-сителя метиленового синего под УФ-излучением (312 нм) при дневном свете и в темноте. Установлено, что пленки с гетероструктурой CeO2/SnO2 толщиной 124 нм, показателем преломления 1,33 и значением коэффициента пропускания более 70% в диапазоне длин волн 440–1 000 нм поглощают в видимой области спектра больше, чем тонкопленочные материалы SnO2 и CeO2. Фотокаталитиче-ская активность пленок CeO2/SnO2 под УФ-воздействием при дневном освеще-нии выше, чем их фотокаталитическая активность под УФ-воздействием в тем-ноте. При дневном освещении под УФ-облучением метиленового синего разла-гается за одно и то же время в 1,2 раза больше, чем под УФ-излучением в темноте

Partitioning and dissolution behavior of metal-based engineered nanoparticles in sediment and soil suspensions

Nowadays engineered nanoparticles are being used in a whole range of commercial applications and are therefore expected to inevitably find their way into the environment where their fate and behavior are still largely unknown. The objective of this study was to investigate the behavior and fate of a number of engineered nanoparticles (CeO2, SnO2, Ag) in sediment and soil suspensions. In particular, the association of nanoparticles with solid phases, the kinetics of these interactions, and the solubility of the nanoparticulate matter in sediment and soil suspensions were studied. Four different sediments and three different soils were sampled at various locations in Flanders (Belgium), dried, grinded and characterized. Sediment and soil suspensions were prepared with Milli-Q water (1/10 S/L), spiked with the different metallic nanoparticles or corresponding ions, and continuously shaken for 24 hours. At regular time intervals, samples of the suspensions were collected and centrifuged at 500 or 2000 rpm, or left for gravitational settling. The supernatant was analyzed for total metal contents after aqua regia digestion and for dissolved metal ions after centrifugal ultrafiltration. In a second experiment, the impact of centrifugation speed on the amount of suspended matter in the supernatant was also studied. Relations between soil or sediment properties, suspended matter and metals in the supernatant were investigated. First data already point towards a strong association of nanoparticles with suspended material. The remaining data are still being collected and will be presented at the conference