Stability of clay-based catalysts in contact with water vapour

The search for cleaner processes is one of the major challenges in modern chemical industries. In this context clay derived materials are environmentally friendly catalysts that can be easily tailored to optimize their catalytic activity for a precise reaction of interest. Furthermore, clay-based catalysts can be easily separated, recovered and reused and their versatility, low cost, high catalytic activity and/or selectivity render them very attractive materials. Considering that the stability towards water vapour is a crucial aspect for catalytic performance and reuse of the catalysts, we present a study of the pore structure stability, in the presence of water vapour, of clay catalysts prepared by acid activation with HCl solutions and ion-exchange with sodium, aluminium and iron, from a natural clay collected at Serra de Dentro (Porto Santo Island, Portugal) [1]. For elucidating the influence of water vapour on the pore structure stability, water vapour adsorption- -desorption isotherm, at 298 K, was determined on each sample by gravimetric method as well as n-pentane adsorption−desorption isotherms, at 298 K, which were determined before and after the corresponding water adsorption-desorption isotherms. Prior to the measurements, the samples were outgassed during 5 h at 473 K and the adsorptives were outgassed by repeated freeze–thaw cycles. The results to be reported in the communication allow us to state that, upon contact with water vapour, the less acid activated catalysts suffered some reduction in pore volume reflecting changes in the pore structure, while the more acid activated catalysts and those prepared by ion-exchange presented excellent stability upon one cycle of water vapour adsorption-desorption. The results are corroborated by nitrogen adsorption-desorption isotherms determined, at 77 K, before and after the water and n-pentane adsorption-desorption measurements.

Study of different atmospheric environments associated to storms development in the Madeira Island

The study aims to improve the understanding about different atmospheric environments leading to the development of storms associated with heavy precipitation in Madeira Island. For this purpose, four main goals have been considered: 1) To document the synoptic and mesoscale environments associated with heavy precipitation. 2) To characterize surface precipitation patterns that affected the island during some periods of significant accumulated precipitation using numerical modelling. 3) To study the relationship between surface precipitation patterns and mesoscale environments. 4) To highlight how the PhD findings obtained in the first three goals can be translated into an operational forecast context. Concerning the large scale environment, precipitation over the island was favoured by weather systems (e.g, mesoscale convective systems and low pressure systems), as well as by the meridional transport of high amount of moisture from a structure denominated as “Atmospheric River”. The tropical origin of this moisture is underscored, however, their impact on the precipitation in Madeira was not so high during the 10 winter seasons [2002 – 2012] studied. The main factor triggering heavy precipitation events over the island is related to the local orography. The steep terrain favours orographically-induced stationary precipitation over the highlands, although maximum of precipitation at coastal region may be produced by localized blocking effect. These orographic precipitating systems presented different structures, associated with shallow and deep convection. Essentially, the study shows that the combination of airflow dynamics, moist content, and orography is the major mechanism that produces precipitation over the island. These factors together with the event duration act to define the regions of excessive precipitation. Finally, the study highlights two useful points for the operational sector, regarding the meridional water vapour transport and local effects causing significant precipitation over the Island; RESUMO: O estudo procura melhorar o entendimento sobre os diferentes ambientes atmosféricos que favorecem o desenvolvimento de tempestades associadas com precipitação intensa na ilha da Madeira. Nesse sentido foram definidos quatro objetivos: 1) Documentar os ambientes sinópticos e de mesoescala associados com precipitação intensa; 2) Caracterizar padrões de precipitação na superfície, em eventos de elevada precipitação acumulada, utilizando modelação numérica; 3) Estudar as relações entre os padrões de precipitação e ambientes de mesoescala; 4) Mostrar como tais resultados podem ser utilizados num contexto operacional de previsão do tempo. Em relação a ambientes de larga escala, verificou-se que a ocorrência de eventos de precipitação intensa sobre a ilha foi favorecida por sistemas meteorológicos, assim como pelo transporte meridional de humidade por meio de estruturas atualmente denominadas Rios atmosféricos. Neste último caso é de destacar a origem tropical de humidade, no entanto, o seu impacto na precipitação sobre a Madeira durante os 10 invernos estudados [2002-2012] não foi tão elevada. O principal fator que favorece os eventos de precipitação intensa está relacionado com a orografia local. O terreno complexo da ilha favorece a ocorrência de precipitação estacionária induzida orograficamente sobre as terras mais altas, embora a precipitação nas zonas costeiras possa ser produzida por um efeito localizado de bloqueio. Estes sistemas orográficos precipitantes apresentaram diferentes estruturas, associados a convecção pouco profunda e profunda. O estudo mostra que a combinação entre as características do escoamento, a quantidade de humidade, e a orografia são os condimentos essenciais para o desenvolvimento da precipitação sobre a ilha, atuando de maneira a definir as regiões de precipitação excessiva. Por fim, o estudo destaca dois pontos que podem ser úteis na previsão do tempo operacional, ligados a larga escala e aos efeitos locais, os quais podem levar ao desenvolvimento de tempestades e precipitação intensa sobre a ilha.

Lacunae Infills for in Situ Treatment of Historic Glazed Tiles

Knowledge of current conservation materials and methods together with those adopted in the past is essential to aid research and improve or develop better conservation options. The infill and painting of tile lacunae are subjected to special requirements mainly when used in outdoor settings. A selection of the most commonly used materials was undertaken and performed based on inquiries to practitioners working in the field. The infill pastes comprised organic (epoxy, polyester), inorganic (slaked lime,hydraulic lime and zinc hydroxychloride) and mixed organic–inorganic (slaked lime mixed with a vinylic resin)binders. The selected aggregates were those most commonly used or those already present in the commercially formulated products. The infill pastes were characterised by SEM, MIP, open porosity, water absorption by capillarity, water vapour permeability, thermal and hydric expansibilities and adhesion to the ceramic body. Their performance was assessed after curing, artificial ageing (salt ageing and UV–Temp–RH cycles) and natural ageing. The results were interpreted in terms of their significance as indicators of effectiveness, compatibility and durability

Numerical Simulations of Fog Events in Southern Portugal

This work aims at improving the knowledge on fog formation and its evolution in the Alentejo region (Portugal). For this purpose, brief regional fog climatology, essentially based on information from the Beja Air Base meteorological station, was produced and several numerical high resolution simulations were performed using the Meso-NH. The ECOCLIMAP database used to generate the model physiography was improved to include the Alqueva reservoir (~250 km2), filled in 2003. The model results were compared with surface and satellite observations, showing good agreement in terms of fog occurrence and persistence. Various forcing mechanisms for formation, development, and dissipation of fog were identified, confirming the influence of two small mountains that block the moist air from the Atlantic Ocean, preventing the fog from reaching innermost regions. The introduction of the Alqueva large reservoir induces changes in the landscape and environment. The effects of the water vapour addition and of the changes in mass and energy surface fluxes on fog formation and evolution were studied. It was found that the reservoir may have a direct impact on fog formation over the lake and its vicinity. Depending on the large scale meteorological conditions, their influence can be both positive and negative, in terms of spatial coverage and temporal persistence.

Lake–atmosphere interactions at Alqueva reservoir: a case study in the summer of 2014

The study of lake–atmosphere interactions was the main purpose of a 2014 summer experiment at Alqueva reservoir in Portugal. Near-surface fluxes of momentum, heat and mass [water vapour (H2O) and carbon dioxide (CO2)] were obtained with the new Campbell Scientific’s IRGASON Integrated Open-Path CO2/H2O Gas Analyser and 3D Sonic Anemometer between 2 June and 2 October. On average, the reservoir was releasing energy in the form of sensible and latent heat flux during the study period. At the end of the 75 d, the total evaporation was estimated as 490.26 mm. A high correlation was found between the latent heat flux and the wind speed (R = 0.97). The temperature gradient between air and water was positive between 12 and 21 UTC, causing a negative sensible heat flux, and negative during the rest of the day, triggering a positive sensible heat flux. The reservoir acted as a sink of atmospheric CO2 with an average rate of −0.026 mg m−2 s−1. However, at a daily scale we found an unexpected uptake between 0 and 9 UTC and almost null flux between 13 and 19 UTC. Potential reasons for this result are further discussed. The net radiation was recorded for the same period and water column heat storage was estimated using water temperature profiles. The energy balance closure for the analysed period was 81%. In-water solar spectral downwelling irradiance profiles were measured with a new device allowing measurements independent of the solar zenith angle, which enabled the computation of the attenuation coefficient of light in the water column. The average attenuation coefficient for the photosynthetically active radiation spectral region varied from 0.849 ± 0.025 m−1 on 30 July to 1.459 ± 0.007 m−1 on 25 September.