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1.
Br J Sports Med ; 56(2): 68-79, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33619127

RESUMO

The cessation of amateur and recreational sport has had significant implications globally, impacting economic, social and health facets of population well-being. As a result, there is pressure to resume sport at all levels. The ongoing prevalence of SARS-CoV-2 and subsequent 'second waves' require urgent best practice guidelines to be developed to return recreational (non-elite) sports as quickly as possible while prioritising the well-being of the participants and support staff.This guidance document describes the need for such advice and the process of collating available evidence. Expert opinion is integrated into this document to provide uniform and pragmatic recommendations, thereby optimising on-field and field-side safety for all involved persons, including coaches, first responders and participants.The nature of SARS-CoV-2 transmission means that the use of some procedures performed during emergency care and resuscitation could potentially be hazardous, necessitating the need for guidance on the use of personal protective equipment, the allocation of predetermined areas to manage potentially infective cases and the governance and audit of the process.


Assuntos
COVID-19 , Pandemias , Consenso , Primeiros Socorros , Humanos , SARS-CoV-2
2.
Environ Manage ; 70(1): 105-116, 2022 07.
Artigo em Inglês | MEDLINE | ID: mdl-35524001

RESUMO

Impacts on households from large carnivores are frequently reported in the conservation literature, but conflicts between households and large carnivore conservation are not. Employing a human-wildlife coexistence framework that distinguishes between human-wildlife impacts on one hand, and human-conservation conflicts on the other, this paper presents data from Annapurna Conservation Area and Sagarmatha (Everest) National Park, Nepal, each with different models of conservation governance. Using systematic sampling, quantitative information from 705 households was collected via questionnaires, while 70 semi-structured interviews were conducted with key informants for cross-methods triangulation. 7.7% of households reported conflicts with snow leopard conservation in the previous 12 months, primarily due to damage to livelihoods; these were significantly higher in the Annapurna region. 373 livestock were reported lost by households to snow leopards in the previous 12 months, representing 3.4% of total livestock owned and US$ 132,450 in financial value. Livestock losses were significantly lower in the Everest area. In linear regression models, total household livestock losses to all sources best explained conflicts with snow leopard conservation and household livestock losses to snow leopards but the models for the former dependent variable had very low explanatory power. Conservation in general, and large carnivore conservation in particular, should distinguish carefully between impacts caused by coexistence with these species and conflicts with conservation actors and over the methods and interventions used to conserve carnivores, especially where these negatively impact local livelihoods. In addition, livestock husbandry standards are highlighted again as an important factor in the success of carnivore conservation programmes.


Assuntos
Carnívoros , Panthera , Animais , Animais Selvagens , Conservação dos Recursos Naturais , Humanos , Gado , Nepal , Parques Recreativos
3.
Br J Sports Med ; 2020 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-33361278

RESUMO

The COVID-19 pandemic has necessitated many novel responses in healthcare including sport and exercise medicine. The cessation of elite sport almost globally has had significant economic implications and resulted in pressure to resume sport in very controlled conditions. This includes protecting pitch-side medical staff and players from infection. The ongoing prevalence of SARS-CoV-2 and the desire to resume professional sport required urgent best practice guidelines to be developed so that sport could be resumed as safely as possible. This set of best practice recommendations assembles early evidence for managing SARS-CoV-2 and integrates expert opinion to provide a uniform and pragmatic approach to enhance on-field and pitch-side safety for the clinician and player. The nature of SARS-CoV-2 transmission creates new hazards during resuscitation and emergency care and procedures. Recommendations for the use and type of personal protective equipment during on-field or pitch-side emergency medical care is provided based on the clinical scenario and projected risk of viral transmission.

4.
Angew Chem Int Ed Engl ; 57(51): 16672-16677, 2018 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-30328259

RESUMO

The majority of harmful atmospheric CO and NOx emissions are from vehicle exhausts. Although there has been success addressing NOx emissions at temperatures above 250 °C with selective catalytic reduction technology, emissions during vehicle cold start (when the temperature is below 150 °C), are a major challenge. Herein, we show we can completely eliminate both CO and NOx emissions simultaneously under realistic exhaust flow, using a highly loaded (2 wt %) atomically dispersed palladium in the extra-framework positions of the small-pore chabazite material as a CO and passive NOx adsorber. Until now, atomically dispersed highly loaded (>0.3 wt %) transition-metal/SSZ-13 materials have not been known. We devised a general, simple, and scalable route to prepare such materials for PtII and PdII . Through spectroscopy and materials testing we show that both CO and NOx can be simultaneously completely abated with 100 % efficiency by the formation of mixed carbonyl-nitrosyl palladium complex in chabazite micropore.

5.
Chemphyschem ; 17(5): 699-709, 2016 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-26756645

RESUMO

We have developed a general X-ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3-x NCs), as a model polymorphic nanoscale material system. Rod-shaped WO3-x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as-synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best-matching candidates (static analysis). Subtle stoichiometry deviations from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3-x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3-x NC lattice, rather than a variation in stoichiometry. The time behavior of such structural change is identified on the basis of multivariate analysis.

6.
Zoo Biol ; 34(5): 483-91, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26186494

RESUMO

Food procurement can play an important role in sustainable food supply chain management by zoos, linking organizational operations to the biodiversity conservation and sustainability mission of zoological collections. This study therefore examines the critical factors that shape sustainable food procurement in zoo and aquariums. Using a web-based survey data was collected from 41 members of the British and Irish Association of Zoos and Aquariums (BIAZA). This included information on the sustainable food procurement practices of these institutions for both their human and animal food supply chains, as well as profile information and data on the factors contributing to and inhibiting sustainable procurement practices. Zoological collections operated by charities, and those with a certified sustainability standard, were found to have significantly higher levels of sustainable food procurement. Zoos and aquariums whose human food operations were not contracted to an external party were also found to have significantly higher levels of sustainable food procurement in their human food supply chain. The most important drivers of sustainable food procurement were cost savings, adequate financial support and improved product quality. The highest ranking barriers were higher costs, other issues taking priority and a lack of alternative suppliers. The results suggest that a number of critical factors shape sustainable food procurement in zoological collections in the British Isles. Financial factors, such as cost savings, were important considerations. The significance of mission-related factors, such as charity status, indicated that core values held by zoos and aquariums can also influence their food procurement practices.


Assuntos
Conservação dos Recursos Naturais/métodos , Abastecimento de Alimentos/métodos , Animais , Animais de Zoológico , Aquicultura , Biodiversidade , Comércio , Abastecimento de Alimentos/ética , Humanos , Irlanda , Reino Unido
7.
J Am Chem Soc ; 136(4): 1333-51, 2014 Jan 29.
Artigo em Inglês | MEDLINE | ID: mdl-24437378

RESUMO

A combination of multinuclear ultra-wideline solid-state NMR, powder X-ray diffraction (pXRD), X-ray absorption fine structure experiments, and first principles calculations of platinum magnetic shielding tensors has been employed to reveal the previously unknown crystal structure of Magnus' pink salt (MPS), [Pt(NH3)4][PtCl4], study the isomeric Magnus' green salt (MGS), [Pt(NH3)4][PtCl4], and examine their synthetic precursors K2PtCl4 and Pt(NH3)4Cl2·H2O. A simple synthesis of MPS is detailed which produces relatively pure product in good yield. Broad (195)Pt, (14)N, and (35)Cl SSNMR powder patterns have been acquired using the WURST-CPMG and BRAIN-CP/WURST-CPMG pulse sequences. Experimentally measured and theoretically calculated platinum magnetic shielding tensors are shown to be very sensitive to the types and arrangements of coordinating ligands as well as intermolecular Pt-Pt metallophilic interactions. High-resolution (195)Pt NMR spectra of select regions of the broad (195)Pt powder patterns, in conjunction with an array of (14)N and (35)Cl spectra, reveal clear structural differences between all compounds. Rietveld refinements of synchrotron pXRD patterns, guided by first principles geometry optimization calculations, yield the space group, unit cell parameters, and atomic positions of MPS. The crystal structure has P-1 symmetry and resides in a pseudotetragonal unit cell with a distance of >5.5 Å between Pt sites in the square-planar Pt units. The long Pt-Pt distances and nonparallel orientation of Pt square planes prohibit metallophilic interactions within MPS. The combination of ultra-wideline NMR, pXRD, and computational methods offers much promise for future investigation and characterization of Pt-containing systems.

8.
Phys Chem Chem Phys ; 15(29): 12004-25, 2013 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-23660768

RESUMO

In this perspective article, we show how a series of in situ techniques {X-ray diffraction (XRD), pair-distribution-function analysis (PDF), X-ray absorption fine structure (XAFS), environmental transmission electron microscopy (ETEM), infrared spectroscopy (IR), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)} can be combined to perform detailed studies of the structural, electronic and chemical properties of metal oxide catalysts used for the production of hydrogen through the water-gas shift reaction (WGS, CO + H2O → H2 + CO2). Under reaction conditions most WGS catalysts undergo chemical transformations that drastically modify their composition with respect to that obtained during the synthesis process. Experiments of time-resolved in situ XRD, XAFS, and PDF indicate that the active phase of catalysts which combine Cu, Au or Pt with oxides such as ZnO, CeO2, TiO2, CeOx/TiO2 and Fe2O3 essentially involves nanoparticles of the reduced noble metals. The oxide support undergoes partial reduction and is not a simple spectator, facilitating the dissociation of water and in some cases modifying the chemical properties of the supported metal. Therefore, to optimize the performance of these catalysts one must take into consideration the properties of the metal and oxide phases. IR and AP-XPS have been used to study the reaction mechanism for the WGS on metal oxide catalysts. Data of IR spectroscopy indicate that formate species are not necessarily involved in the main reaction path for the water-gas shift on Cu-, Au- and Pt-based catalysts. Thus, a pure redox mechanism or associative mechanisms that involve either carbonate-like (CO3, HCO3) or carboxyl (HOCO) species should be considered. In the last two decades, there have been tremendous advances in our ability to study catalytic materials under reaction conditions and we are moving towards the major goal of fully understanding how the active sites for the production of hydrogen through the WGS actually work.

9.
Cureus ; 15(6): e41096, 2023 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-37519489

RESUMO

This is a case report of an 83-year-old female who presented to the emergency department within eight hours of symptom onset. A CT angiogram revealed a distal basilar artery occlusion, as well as a perfusion deficit in the right superior cerebellar artery. Her symptoms fluctuated, and she was started on a heparin drip, but later in the evening her symptoms worsened. A mechanical thrombectomy was performed by interventional radiology. The following morning, most of the patient's deficits had resolved, and, when seen in the clinic several weeks later, she continued to be asymptomatic. This case report highlights the importance of timely diagnosis and intervention in the management of distal basilar artery occlusion.

10.
bioRxiv ; 2023 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-37649909

RESUMO

One limitation on the ability to monitor health in older adults using Magnetic Resonance (MR) imaging is the presence of implants, where the prevalence of implantable devices (orthopedic, cardiac, neuromodulation) increases in the population, as does the pervasiveness of conditions requiring MRI studies for diagnosis (musculoskeletal diseases, infections, or cancer). The present study describes a novel multiphysics implant modeling testbed using the following approaches with two examples: - an in-silico human model based on the widely available Visible Human Project (VHP) cryo-section dataset; - a finite element method (FEM) modeling software workbench from Ansys (Electronics Desktop/Mechanical) to model MR radio frequency (RF) coils and the temperature rise modeling in heterogeneous media. The in-silico VHP Female model (250 parts with an additional 40 components specifically characterizing embedded implants and resultant surrounding tissues) corresponds to a 60-year-old female with a body mass index (BMI) of 36. The testbed includes the FEM-compatible in-silico human model, an implant embedding procedure, a generic parameterizable MRI RF birdcage two-port coil model, a workflow for computing heat sources on the implant surface and in adjacent tissues, and a thermal FEM solver directly linked to the MR coil simulator to determine implant heating based on an MR imaging study protocol. The primary target is MR labeling of large orthopaedic implants. The testbed has very recently been approved by the US Food and Drug Administration (FDA) as a medical device development tool (MDDT) for 1.5 T orthopaedic implant examinations.

11.
Elife ; 122023 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-38096104

RESUMO

One limitation on the ability to monitor health in older adults using magnetic resonance (MR) imaging is the presence of implants, where the prevalence of implantable devices (orthopedic, cardiac, neuromodulation) increases in the population, as does the pervasiveness of conditions requiring MRI studies for diagnosis (musculoskeletal diseases, infections, or cancer). The present study describes a novel multiphysics implant modeling testbed using the following approaches with two examples: (1) an in silico human model based on the widely available Visible Human Project (VHP) cryo-section dataset; (2) a finite element method (FEM) modeling software workbench from Ansys (Electronics Desktop/Mechanical) to model MR radio frequency (RF) coils and the temperature rise modeling in heterogeneous media. The in silico VHP-Female model (250 parts with an additional 40 components specifically characterizing embedded implants and resultant surrounding tissues) corresponds to a 60-year-old female with a body mass index of 36. The testbed includes the FEM-compatible in silico human model, an implant embedding procedure, a generic parameterizable MRI RF birdcage two-port coil model, a workflow for computing heat sources on the implant surface and in adjacent tissues, and a thermal FEM solver directly linked to the MR coil simulator to determine implant heating based on an MR imaging study protocol. The primary target is MR labeling of large orthopedic implants. The testbed has very recently been approved by the US Food and Drug Administration (FDA) as a medical device development tool for 1.5 T orthopedic implant examinations.


Assuntos
Temperatura Alta , Próteses e Implantes , Feminino , Humanos , Idoso , Pessoa de Meia-Idade , Simulação por Computador , Temperatura , Imageamento por Ressonância Magnética/métodos
12.
Cureus ; 15(8): e44165, 2023 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-37753051

RESUMO

The incidence of stroke in young individuals has been showing an increasing trend. In such cases, atypical mechanisms of stroke should be considered. Here, we report a case of a 37-year-old healthy female who presented with complaints of right-sided ataxia and clumsiness that started after an amusement park ride where she was swung rapidly. Imaging revealed an infarct in the right cerebellar hemisphere. This case report highlights certain mechanisms that can cause a stroke in this situation, with special emphasis on recognition, timely medical management, public awareness of such risk factors, and the prevention of complications.

13.
Br J Sports Med ; 46(16): 1097-101, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23080314

RESUMO

The prehospital management of serious injury is a key skill required of pitch-side medical staff. Previously, specific training in sports prehospital-immediate care was lacking or not of a comparable standard to other aspects of emergency care. Many principles have been drawn from general prehospital care or in-hospital training courses. This article discusses sports prehospital-immediate care as a niche of general prehospital care, using spinal injury management as an illustration of the major differences. It highlights the need to develop the sport-specific prehospital evidence base, rather than relying exclusively on considerations relevant to prolonged immobilisation of multiply injured casualties from motor vehicle accidents, falls from height or burns.


Assuntos
Serviços Médicos de Emergência/normas , Medicina de Emergência/educação , Traumatismos da Coluna Vertebral/terapia , Medicina Esportiva/educação , Pessoal Técnico de Saúde/educação , Traumatismos em Atletas/terapia , Currículo , Medicina de Emergência/instrumentação , Medicina de Emergência/normas , Desenho de Equipamento , Prática Clínica Baseada em Evidências , Humanos , Movimentação e Reposicionamento de Pacientes/métodos , Movimentação e Reposicionamento de Pacientes/normas , Oxigênio/uso terapêutico , Planejamento de Assistência ao Paciente/organização & administração , Planejamento de Assistência ao Paciente/normas , Medicina Esportiva/instrumentação , Medicina Esportiva/normas , Macas/normas , Tempo para o Tratamento , Triagem/métodos , Vácuo
14.
PLoS One ; 14(10): e0223565, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31644548

RESUMO

The snow leopard Panthera uncia is a vulnerable wild felid native to mountainous regions of 12 Asian countries. It faces numerous overlapping threats, including killings by herders retaliating against livestock losses, the illegal wildlife trade, loss of prey and habitat, infrastructure, energy and mining developments, and climate change. The species ranges over large territories that often lie outside of protected areas (PA), so coexistence with human populations across its range is key to its persistence. Human attitudes to snow leopards may be an important factor to consider in reducing overlapping threats to this species. However, this nexus has not been widely studied to date. Attitudes to snow leopard conservation, including actors and interventions, may also be a significant aspect of coexistence. These have also received limited empirical attention. This study therefore explored human attitudes to snow leopards and to snow leopard conservation, the motivations for these attitudes and the individual factors that best explained them. Using systematic sampling, a quantitative questionnaire was administered to 705 households at two sites in the Nepal Himalayas: Sagarmatha National Park, with a less decentralised governance model, and Annapurna Conservation Area, with a more decentralised model. Linear regression models were the main form of analysis. Based on these, attitudes to snow leopard conservation emerged as the strongest influence on local attitudes to snow leopards, and vice versa. This was true in both PAs, despite their differing management regimes. Other important explanatory factors included numbers of livestock owned, years of education, household livelihoods and age. Furthermore, a positive intrinsic motivation was the most common reason given by respondents to explain their attitudes to both snow leopards and snow leopard conservation. These findings demonstrate that, in addition to the usual suite of factors that influence attitudes to a species, the way in which its conservation is pursued and perceived also needs consideration. How the snow leopard is conserved may strongly influence its coexistence with local communities.


Assuntos
Atitude , Conservação dos Recursos Naturais , Ecossistema , Felidae , Animais , Análise Fatorial , Nepal , Parques Recreativos , Comportamento Predatório , Inquéritos e Questionários
15.
J Am Chem Soc ; 130(3): 1093-101, 2008 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-18161978

RESUMO

Bimetallic nanostructures with non-random metal atoms distribution are very important for various applications. To synthesize such structures via benign wet chemistry approach remains challenging. This paper reports a synthesis of a Au/Pd alloy nanostructure through the galvanic replacement reaction between Pd ultrathin nanowires (2.4 +/- 0.2 nm in width, over 30 nm in length) and AuCl3 in toluene. Both morphological and structural changes were monitored during the reaction up to 10 h. Continuous changes of chemical composition and crystalline structure from Pd nanowires to Pd68Au32 and Pd45Au55 alloys, and to Au nanoparticles were observed. More interestingly, by using combined techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), UV-vis absorption, and extended X-ray absorption fine structure (EXAFS) spectroscopy, we found the formation of Pd68Au32 non-random alloy with Au-rich core and Pd-rich shell, and random Pd45Au55 alloy with uniformly mixed Pd and Au atom inside the nanoparticles, respectively. Density functional theory (DFT) calculations indicated that alkylamine will strongly stabilize Pd to the surface, resulting in diffusion of Au atoms into the core region to form a non-random alloy. We believe such benign synthetic techniques can also enable the large scale preparation of various types of non-random alloys for several technically important catalysis applications.

16.
J Chem Phys ; 129(23): 234502, 2008 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-19102533

RESUMO

We present a robust data analysis method of time-resolved x-ray absorption spectroscopy experiments suitable for chemical speciation and structure determination of reaction intermediates. Chemical speciation is done by principal component analysis (PCA) of the time-resolved x-ray absorption near-edge structure data. Structural analysis of intermediate phases is done by theoretical modeling of their extended x-ray absorption fine-structure data isolated by PCA. The method is demonstrated using reduction and reoxidation of Cu-doped ceria catalysts where we detected reaction intermediates and measured fine details of the reaction kinetics. This approach can be directly adapted to many time-resolved x-ray spectroscopy experiments where new rapid throughput data collection and analysis methods are needed.


Assuntos
Síncrotrons , Absorção , Cério/química , Cobre/química , Modelos Químicos , Oxirredução , Análise de Componente Principal , Análise Espectral , Fatores de Tempo , Raios X
17.
Chem Commun (Camb) ; (9): 984-6, 2007 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-17311142

RESUMO

Exposure of NO(2)-saturated BaO/gamma-Al(2)O(3) NO(x) storage materials to H(2)O vapour results in the conversion of surface nitrates to Ba(NO(3))(2) crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NO(x) storage/reduction properties of these materials.

18.
J Phys Chem B ; 110(1): 428-34, 2006 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-16471552

RESUMO

New information about the active sites for the water gas shift (WGS) reaction over Cu-CeO2 systems was obtained using in-situ, time-resolved X-ray diffraction (TR-XRD), X-ray absorption spectroscopy (TR-XAS, Cu K and Ce L3 edges), and infrared spectroscopy (DRIFTS). Cu-CeO2 nanoparticles prepared by a novel reversed microemulsion method (doped Ce1-xCuxO2 sample) and an impregnation method (impregnated CuOx/CeO2 sample) were studied. The results from all of the samples indicate that both metallic copper and oxygen vacancies in ceria were involved in the generation of active sites for the WGS reaction. Evidence was found for a synergistic Cu-Ovacancy interaction. This interaction enhances the chemical activity of Cu, and the presence of Cu facilitates the formation of O vacancies in ceria under reaction conditions. Water dissociation occurred on the Ovacancy sites or the Cu-Ovacancy interface. No significant amounts of formate were formed on the catalysts during the WGS reaction. The presence of strongly bound carbonates is an important factor for the deactivation of the catalysts at high temperatures. This work identifies for the first time the active sites for the WGS reaction on Cu-CeO2 catalysts and illustrates the importance of in situ structural studies for heterogeneous catalytic reactions.


Assuntos
Cério/química , Cobre/química , Oxigênio/química , Água/química , Catálise , Oxirredução , Sensibilidade e Especificidade , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Temperatura , Fatores de Tempo , Difração de Raios X
19.
J Phys Chem B ; 110(21): 10441-8, 2006 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-16722751

RESUMO

Desulfation processes were investigated over sulfated Pt-BaO/Al2O3 with different barium loading (8 and 20 wt %) by using H2 temperature programmed reaction (TPRX), transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS), sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and in situ time-resolved X-ray diffraction (TR-XRD) techniques. Both sulfated samples (8 and 20 wt %) form sulfate species (primarily BaSO4) as evidenced by S K-edge XANES and in situ TR-XRD. However, the desulfation behavior is strongly dependent on the barium loading. Sulfated Pt-BaO8/Al2O3, consisting predominantly of surface BaO/BaCO3 species, displays more facile desulfation by H2 at lower temperatures than sulfated Pt-BaO20/Al2O3, a material containing primarily bulk BaO/BaCO3 species. Therefore, after desulfation with H2 up to 1073 K, the amount of the remaining sulfur species on the former, mostly as BaS, is much less than that on the latter. This suggests that the initial morphology differences between the two samples play a crucial role in determining the extent of desulfation and the temperature at which it occurs. It is concluded that the removal of sulfur is significantly easier at lower barium loading. This finding can potentially be important in developing more sulfur resistant LNT catalyst systems.

20.
J Phys Chem B ; 109(15): 7339-44, 2005 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-16851840

RESUMO

The changes in the morphology of Ba-oxide-based NO(x)() storage/reduction catalysts were investigated using time-resolved X-ray diffraction, transmission electron microscopy, and energy dispersed spectroscopy. Large Ba(NO(3))(2) crystallites form on the alumina support when the catalyst is prepared by the incipient wetness method using an aqueous Ba(NO(3))(2) solution. Heating the sample to 873 K in a He flow results in the decomposition of the Ba(NO(3))(2) phase and the formation of both a monolayer BaO film strongly interacting with the alumina support and nanocrystalline BaO particles. Upon NO(2) exposure of these BaO phases at room temperature, small (nanosized) Ba(NO(3))(2) crystals and a monolayer of surface nitrate form. Heating this sample in NO(2) results in the coalescence of the nanocrystalline Ba(NO(3))(2) particles into large crystals. The average crystal size in the reformed Ba(NO(3))(2) layer is significantly smaller than that measured after the catalyst preparation. Evidence is also presented for the existence of a monolayer Ba(NO(3))(2) phase after thermal treatment in NO(2), in addition to these large crystals. These results clearly demonstrate the dynamic nature of the Ba-containing phases that are active in the NO(x)() storage/reduction process. The proposed morphology cycle may contribute to the understanding of the changes observed in the performances of these catalysts during actual operating conditions.

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