Porosity of clay catalysts for biomass conversion: a comparative study

A detailed description of the porosity, in particular of microporosity, was reported and allowed a clear comparison of the effects on the porosity of chemical treatments on clays from the Source Clays Repository (USA) and SD clay from Porto Santo (Portugal)

Selective methoxylation of α-pinene to α-terpinyl methyl ether over Al3+ ion-exchanged clays

In this study, we report the use of clay-based catalysts in the methoxylation of α-pinene, for the selective synthesis of α-terpinyl methyl ether, TME. The main reaction products and intermediates were identified by GC-MS. The reaction conditions (stirring rate and catalyst load) that afford a kinetic regime were established. SAz-1 (Cheto, Arizona, USA) source clay and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal, were modified by ion-exchange with Al3+ to produce catalysts with markedly different acidities and textural properties. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150°C, afforded the highest number of Brønsted acid sites - a significant proportion of which were located in the clay gallery - and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize α-pinene conversion and selectivity, was studied over AlSAz-1. When the reaction was performed for 1 h at 60°C, the conversion reached 65% with 65% selectivity towards the mono-ether, TME. Similar conversions and selectivities required up to 50 h over zeolites and other solid acid catalysts. The kinetic dependencies of this reaction on temperature and reagent concentration, over the selected clays were also investigated. It was established that, in the temperature and reagent concentration regime studied, the reaction was first order with respect to α-pinene. The apparent activation energies over the two catalysts, calculated from Arrhenius plots, were almost identical at 72 kJ mol-

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

Do migrant remittances promote human capital formation? Evidence from 89 developing countries

The few published empirical studies on the effect of migrant remittances on educational attainments are roughly based on cross-sectional microdata from household surveys. This paper applies the generalised method of moments (GMM) estimator on aggregate level data from 1970 to 2010 in five-year intervals to examine the impact of migrant remittances on human capital formation in 89 developing countries. The estimation results show that, on average, an increase in migrant remittance inflows by 1% is associated with a 2% rise in years of schooling at both the secondary and tertiary levels. This suggests that migrant remittances have the potential to relax liquidity constraints and generate spillover effects that facilitate more schooling opportunities in remittance-receiving countries

Income, Consumption and Remittances: Evidence from Immigrants to Australia

working pape

Effect of dealumination of iron(III)-exchanged Y zeolites on oxidation of reactive yellow 84 azo dye in the presence of hydrogen peroxide.

This paper evaluates the catalytic effectiveness of three iron exchanged ultra-stable Y zeolites (USY) for the degradation of a reactive azo dye, C.I. Reactive Yellow 84 (RY84) using hydrogen peroxide, as an oxidant, under very mild conditions (atmospheric pressure and t=50 °C). The catalysts were prepared by ion exchange, starting from a commercially available ultra-stable Y zeolite. All experiments were performed on a laboratory scale set-up. Important variables such as effect of hydrogen peroxide concentration, the amount of catalyst, contact time and temperature for the catalytic wet peroxide oxidation (CWHPO) of Reactive Yellow 84 over Fe-Y11.5 zeolite were examined. The toxic potential of the dye’s degradation was investigated with the bioluminescence test using the LUMIStox 300 instrument and the results were expressed as relative toxicity index. In addition, the oxidation end-products (organic and inorganic anions) were analyzed using high performance ion chromatography (HPICE). Best experimental conditions can be described as pH 5, t=50 °C, a catalyst concentration of 1 g/l and 20 mmol/l H2O2. The results show that it is possible to remove 96.90% of color, 70.70% of COD and 34.52% of TOC using Fe-Y11.5 catalyst after the 60 min of oxidation at above-mentioned conditions. After the same reaction time and under the same conditions, using Fe-Y5 catalyst, 99.93% of color removal, more than 74.14% of COD and 64.21% of TOC removal were obtained. The catalysts allow almost total elimination of the dye and a significant removal of COD and TOC without the significant leaching of Fe ions. Acetate, nitrate, formate, malonate, and oxalate were identified as main oxidation products. The most effective results were obtained using of the Fe-Y5 zeolite

Influence of exchange cations on the catalytic conversion of limonene over Serra de Dentro (SD) and SAz-1 clays - Correlations between acidity and catalytic activity/selectivity

A bentonite collected at Serra de Dentro (SD), Porto Santo Island, Portugal, and the source clay SAz-I (Cheto, Arizona) were ion-exchanged with different cations (Al3+, Ni2+, Cr3+ and Na+). Variable temperature diffuse reflectance infrared Fourier transform spectroscopy (VT-DRIFTS) of pyridine treated samples, thermal desorption of cyclohexylamine and real time mass spectrometry of the evolved gases were used to evaluate the acidic properties of the prepared catalysts. The catalytic activity of these ion-exchanged clays was tested in the acid-catalysed conversion of limonene at 150 degrees C, to yield isomerization products (terpinolene, alpha-terpinene, gamma-terpinene and isoterpinolene), disproportionation products (p-cymene and p-menthenes) and high molecular-weight compounds. The possibility of increasing the selectivity toward p-cymene, over a catalyst with substantial Lewis acid character, was particularly envisaged. Catalysts derived from SD were significantly more active than their SAz-I counterparts. This was mainly attributed to the greater inherent acidity, to the higher structural iron content (providing dehydrogenation activity) and to the higher nitrogen surface area of the starting SD clays. Within the Mn+-SD series, the order of activity decreased as Ni2+ > Al3+ > Cr3+ > Na+. A direct comparison between Al3+-SD (with maximized Bronsted acidity) and Ni2+-SD (with predominant Lewis acid character) provided no support for enhanced p-cymene production over Lewis acid sites. (C) 2005 Elsevier B.V. All rights reserved

Porto Santo clays as environmentally friendly catalysts for the conversion of renewable terpene feedstocks. Limonene to p-cymene, an example

A bentonite collected at Serra de Dentro, Porto Santo Island, Portugal was selected as the starting material for the preparation of ion-exchanged clay catalysts. The pristine clay was characterized in terms of chemical composition (XRF), structure (XRD an FTIR spectroscopy), textural properties (nitrogen adsorption), acidity (TG of cyclohexylamine saturated samples) and catalytic activity (limonene conversion). Results show that clays exchanged with acidic cations (Al3+, Ni2+) are very active in limonene conversion, but the selectivity for p-cymene is low ( 15 %). In contrast, over the Na+-exchanged form, the reaction is slower but the selectivity to p-cymene is significantly increased (around 35 %). The inherent dehydrogenation activity of the SD clay could be considered responsible for this process

Entierros prehispánicos en viviendas: Un ensayo de interpretación

El propósito de este artículo es el de ofrecer una interpretación sobre la costumbre de hacer enterramientos en viviendas durante tiempos prehispánicos. Como primera medida haremos un inventario de las descripciones más relevantes que sobre esta práctica consignan las crónicas, documentos de archivo y arqueólogos. Luego, nuestra interpretación estará basada en el manejo político que se le daba a la conservación de cuerpos y la simbología que existía en torno a las viviendas entre los indígenas

Acid activated Serra de Dentro bentonite: chemical, structural, textural and catalytic properties

A bentonite collected at Serra de Dentro, Porto Santo Island, Portugal was selected as the starting material for the preparation of acid activated clay catalysts. These materials were prepared using a range of different HCl concentrations, contact times and temperatures. The materials obtained were characterized in terms of chemical composition (XRF), structure (XRD and IR spectroscopy), textural properties (adsorption-desorption isotherms of N2 at 77K), acidity (TG of cyclohexylamine saturated samples) and catalytic activity (limonene conversion). Results show that increasing the harshness of the acid treatments produces more active catalysts, although this increased catalytic behaviour does not correlate directly with the calculated surface areas nor with the acidity values. A tentative explanation for this catalytic behaviour is given