Browsing by Author "Costa, Carla"
Now showing 1 - 10 of 27
Results Per Page
Sort Options
- Activity–acidity relationship in zeolite Y: Part 1. Transformation of light olefinsPublication . Costa, Carla; Lopes, Jose M.; Lemos, Francisco; Ribeiro, F. RamôaReactions of ethene, propene, 1-butene and iso-butene over two series of catalysts, HNaY (prepared from NaY zeolite) and HNaUSY (prepared from NH4USY zeolite), were studied. The catalytic activity for the transformation of these olefins follows the expected order according to the ease of formation of the respective carbocations: ethene
- Activity–acidity relationship in zeolite Y: Part 2. Determination of the acid strength distribution by temperature programmed desorption of ammoniaPublication . Costa, Carla; Lopes, Jose M.; Lemos, Francisco; Ribeiro, F. RamôaIn this paper we will have a detailed look at a numerical procedure that allows the estimation of the acid site strength distribution using a single temperature programmed desorption (TPD) experiment. The possibility of estimating these parameters is of paramount importance in the determination of quantitative relationships between activity and acidity. The application of the procedure to a set of simulated thermograms gives a clear view of the applicability of this method. The procedure was tested both in single and multi energy distributions, as well as quasi-continuum distributions. Then the method has been applied on TPD thermograms obtained from catalysts based on two different forms of zeolite Y. In part 3 of this series, the acid site distributions obtained here will be used in an activity–acidity relationship, using a Brönsted type equation, similar to the one used in homogeneous acid catalysis.
- Activity–acidity relationship in zeolite Y: Part 3. Application of Brönsted type equationsPublication . Costa, Carla; Lopes, Jose M.; Lemos, Francisco; Ribeiro, F. RamôaThe relation between activity and acidity in a variety of Y zeolite catalysts for the transformation of small olefins: ethene, propene, 1-butene and iso-butene, is presented. The acid site distribution of these samples was estimated by temperature-programmed desorption of ammonia, by using a numerical deconvolution technique. This information was then correlated with catalytic activity measurements using Brönsted type equations. Despite the complexity of calculations it is clear that this gas phase solid acid catalysed reactions follow simple rules, similar to the one observed in homogeneous processes.
- Activity–acidity relationship in zeolite ZSM-5. Application of Brönsted-type equationsPublication . Costa, Carla; Dzikh, I. P.; Lopes, Jose M.; Lemos, Francisco; Ribeiro, Fernando RamôaIn this paper the relation between activity and acidity in a variety of ZSM-5 zeolite catalysts, with different Si/Al ratios and different protonic content, is analysed and a quantitative correlation is obtained. The acid site strength distribution was estimated using temperature-programmed desorption (TPD) of ammonia by applying a digital deconvolution method to the curves. These data were then correlated with experimental catalytic activity data for the same catalysts towards n-heptane cracking reaction, by means of a Brönsted-type equation similar to the ones used for homogeneous acid catalysis and already used for other zeolites. It can be noticed that the same types of equation that are used for homogeneous acid catalysis also hold for heterogeneous acid catalysis and that the activation energy for ammonia desorption can be used as acid-strength scale for the purpose of correlation with catalytic activity.
- Alkali-activated binders produced from petrochemical fluid catalytic cracking catalyst wastePublication . Costa, Carla; Ferreira, Cátia; Ribeiro, Maria Filipa; Fernandes, AugusteThis paper describes research on the viability of producing alkali activated binders using the aluminosilicate catalyst waste-generated by the fluid catalytic cracking (wFCC) unit in the Portuguese oil refinery company-as precursor. For this purpose, alkali-activated wFCC catalyst based mortars and cement pastes were produced. Tests were carried out to evaluate the effect of initial solids composition (wFCC catalyst/Ca(OH) 2 ratio) on mortars workability or mechanical strength. The mineralogy and microstructure of the hardened alkali activated wFCC catalyst pastes were studied by means of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results obtained at macroscale showed that the content of Ca(OH) 2 incorporated in the binder has a significant effect on compressive strength of hardened mortars. At microscale, FTIR and XRD results confirmed the occurrence of alkali-activation of the wFCC catalyst which leads to the formation of distinctive amorphous and crystalline products. Moreover, the obtained results also suggest that initial solids composition influences the alkali-activation reaction kinetics and mechanism.
- An SEM investigation of the pozzolanic activity of a waste catalyst oil refineryPublication . Costa, Carla; Marques, Paulo; Carvalho, P. A.The most active phase of the fluid catalytic cracking (FCC) catalyst, used in oil refinery, is zeolite-Y which is an aluminosilicate with a high internal and external surface area responsible for its high reactivity. Waste FCC catalyst is potentially able to be reused in cement-based materials - as an additive - undergoing a pozzolanic reaction with calcium hydroxide (Ca(OH)2) formed during cement hydration [1-3]. This reaction produces additional strength-providing reaction products i.e., calcium silicate hydrate (C-S-H) and hydrous calcium aluminates (C-A-H) which exact chemical formula and structure are still unknown. Partial replacement of cement by waste FCC catalyst has two key advantages: (1) lowering of cement production with the associated pollution reduction as this industry represents one of the largest sources of man-made CO2 emissions, and (2) improving the mechanical properties and durability of cement-based materials. Despite these advantages, there is a lack of fundamental knowledge on pozzolanic reaction mechanisms as well as spatial distribution of porosity and solid phases interactions at the microstructural level and consequently their relationship with macroscopical engineering properties of catalyst/cement blends. Within this scope, backscattered electron (BSE) images acquired in a scanning electron microscope (SEM) equipped with Energy-Dispersive Spectroscopy (EDS) and by X-ray diffraction were used to investigate chemical composition of hydration products and to analyse spatial information of the microstructure of waste FCC catalyst blended cement mortars. For this purpose mortars with different levels of cement substitution by waste catalyst as well as with different hydration ages, were prepared. The waste FCC catalyst used is produced by the Portuguese refinery company Petrogal S.A.
- DNA damage in circulating leukocytes measured with the comet assay may predict the risk of deathPublication . Bonassi, Stefano; Ceppi, Marcello; Møller, Peter; Azqueta, Amaya; Milić, Mirta; Monica, Neri; Brunborg, Gunnar; Godschalk, Roger; Koppen, Gudrun; Langie, Sabine A. S.; Teixeira, João Paulo; Bruzzone, Marco; Da Silva, Juliana; Benedetti, Danieli; Cavallo, Delia; Ursini, Cinzia Lucia; Giovannelli, Lisa; Moretti, Silvia; Riso, Patrizia; Del Bo’, Cristian; Russo, Patrizia; Dobrzyńska, Malgorzata; Goroshinskaya, Irina A.; Surikova, Ekaterina I.; Staruchova, Marta; Barančokova, Magdalena; Volkovova, Katarina; Kažimirova, Alena; Smolkova, Bozena; Laffon, Blanca; Valdiglesias, Vanessa; Pastor, Susana; Marcos, Ricard; Hernández, Alba; Gajski, Goran; Spremo-Potparević, Biljana; Živković, Lada; Boutet-Robinet, Elisa; Perdry, Hervé; Lebailly, Pierre; Perez, Carlos L.; Basaran, Nursen; Nemeth, Zsuzsanna; Safar, Anna; Dusinska, Maria; Collins, Andrew; Anderson, Diana; Andrade, Vanessa; Pereira, Cristiana Costa; Costa, Solange; Gutzkow, Kristine B.; Ladeira, Carina; Moretti, Massimo; Costa, Carla; Orlow, Irene; Rojas, Emilio; Pourrut, Bertrand; Kruszewski, Marcin; Knasmueller, Siegfried; Shaposhnikov, Sergey; Žegura, Bojana; Stopper, HelgaThe comet assay or single cell gel electrophoresis is the most common method used to measure strand breaks and a variety of other DNA lesions in human populations. To estimate the risk of overall mortality, mortality by cause, and cancer incidence associated with DNA damage, a cohort of 2,403 healthy individuals (25,978 person-years) screened in 16 laboratories using the comet assay between 1996 and 2016 was followed-up. Kaplan–Meier analysis indicated a worse overall survival in the medium and high tertile of DNA damage (p < 0.001). The effect of DNA damage on survival was modeled according to Cox proportional hazard regression model. The adjusted hazard ratio (HR) was 1.42 (1.06–1.90) for overall mortality and 1.94 (1.04–3.59) for diseases of the circulatory system in subjects with the highest tertile of DNA damage. The findings of this study provide epidemiological evidence encouraging the implementation of the comet assay in preventive strategies for non-communicable diseases.
- Durability of an UHPC containing spent equilibrium catalystPublication . Matos, Ana Mafalda; Nunes, Sandra; Costa, Carla; Aguiar, JoséUHPC is an advanced cementitious material able to meet the current construction industry challenges regarding structural safety and durability. However, new UHPC formulations with limited shrinkage are still being pursued to reduce residual tensile stresses in the UHPFRC layers, for rehabilitation/strengthening applications. This investigation estimates the durability of a non-proprietary UHPC incorporating a by-product originated by the oil refinery industry (ECat), as an internal curing agent. Direct and indirect transport properties measurements as well as the carbonation assessment and evaluation of dimensional resilience to potential deleterious reactions revealed that the new UHPC possesses an excellent durability performance, typical of these materials. These results combined with its self-compacting ability, low autogenous shrinkage and high compressive strength confirm the belief in the role of this new UHPC towards a high-tech construction.
- Efeito da incorporação de resíduo da indústria petrolífera nas propriedades mecânicas de argamassasPublication . Costa, Carla; Geada, RitaO presente artigo apresenta resultados preliminares de um projeto, em curso, no qual o objetivo final é investigar a viabilidade da utilização de um resíduo produzido na refinação do petróleo em materiais à base de cimento. Os valores do Índíce de Atividade - determinados com base nos valores da resistência à compressão de argamassas com substituição parcial de cimento pelo resíduo - mostraram que, ao fim de 7 dias de hidratação, o resíduo já apresenta atividade pozolânica em argamassas com incorporação de resíduo até 15%, e que esta atividade é também evidente nas argamassas com incorporação de 20% de resíduo ao fim de 28 dias de hidratação.
- Effect of waste oil-cracking catalyst incorporation on durability of mortarsPublication . Costa, Carla; Ribeiro, M. Sofia; Brito, NunoThis paper presents research on transport properties and alkali-silica reaction (ASR) susceptibility of mortars containing a pozzolanic waste generated in the fluid catalytic cracking (wFCC) unit by the Portuguese oil-refinery. For this purpose, two series of mortars were prepared by partially replacing cement with 5%, 10% and 15% of wFCC catalyst. The main difference between the two series of mortars is the sand reactivity used in their composition. The results revealed that wFCC catalyst blended cement mortars exhibit an increased resistance against capillary water absorption and chloride migration, as well as a considerable inhibition effect on deleterious ASR expansion. However, under the adopted experimental conditions the incorporation of wFCC catalyst in mortars decreases their carbonation resistance.
- «
- 1 (current)
- 2
- 3
- »