CLAYCATS4 - Clay catalysts for biomass conversion

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Selective methoxylation of limonene over ion-exchanged and acid-activated clays

Publication . Catrinescu, C.; Fernandes, C.; Castilho, P.; Breen, C.; Carrott, M.M.L. Ribeiro; Cansado, I.P.P.

In this study, we report the use of clay-based catalysts in the methoxylation of limonene, for the selective synthesis of -terpinyl methyl ether. Na-SAz-1, Ca-SWy-2 and Sap-Ca source clays and a montmorillonite (SD) from Porto Santo,Madeira Archipelago, Portugal weremodified by (i) ion-exchange with Al, Fe, Ni and Na and (ii) acid activation, to produce catalysts with markedly different acidic and textural properties. The lack of activity of Ni2+-SAz-1 (with Lewis acidity maximized), provided evidence that the process occurs preferentially on Brönsted acid sites. 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 located in the clay gallery and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize limonene conversion and selectivity, was studied over Al-SAz-1. When the reaction was performed for 20 h at 40◦ C, the conversion reached 71% with 91% selectivity to the mono-ether. Mild acid activation (1 M HCl, 30 min, reflux) of the raw SAz-1 clay leads to a material with a good catalytic behaviour (slightly inferior to Al-SAz-1), while any increase in the severity of the acid-treatment (6 M HCl, 30 min, reflux), caused a marked decrease in catalytic activity.

2013Journal article

Open access

Acid-modified clays as green catalysts for the hydrolysis of hemicellulosic oligosaccharides

Publication . Vilcocq, Léa; Spínola, Vítor; Moniz, Patrícia; Duarte, Luís C.; Carvalheiro, Florbela; Fernandes, César; Castilho, Paula

The hydrolysis of hemicellulosic oligosaccharides (OS) was investigated using acid-activated clays (prepared from natural Porto Santo montmorillonite clay) as catalysts. Acid activation was performed in HCl solution or with aluminium exchange. The clay catalysts were characterized by XRD, N2 adsorption isotherms, CEC, FTIR, titration of acid sites in water and adsorption of sugars and disaccharides. They were tested for the hydrolysis of a model compound, maltose, and of OS-rich liquor from rice straw fractionation. The HCl-activated clays were the most efficient catalysts for maltose hydrolysis. It was demonstrated that the hydrolysis of OS into monomer sugars over a clay catalyst is technically feasible and that this reaction leads to the selective removal of glucose, arabinose and acetic acid side groups from the OS structure, thus yielding simpler xylo-oligosaccharide chains. Furthermore, no significant conversion of monomer sugars into furans was observed.

2015Journal article

Open access

Porosity in ion-exchanged and acid activated clays evaluated using n-nonane pre-adsorption

Publication . Ribeiro Carrott, M.M.L.; Cansado, I.P.P.; Carrott, P.J.M.; Russo, P.A.; Castilho, P.; Fernandes, C.; Catrinescu, C.; Breen, C.

The applicability of the n-nonane pre-adsorption method for characterising the porosity in clays is presented. Na-SD, a Naþ-exchanged purified bentonite, and materials obtained by Al3þ-exchange and acid treatments of Na-SD and SAz-1 were used. Nitrogen adsorption isotherms, at 196 C, were determined before and after n-nonane pre-adsorption on each of the samples. In all materials, n-nonane remained adsorbed in ultramicropores after outgassing at 25 C. Outgassing at higher temperatures (50, 75 and 200 C) removed nonane and ultramicropores became available for nitrogen adsorption. All treatments on Na-SD led to increase in micropore volume. Larger ultramicropore and supermicropore volumes were obtained for Na-SD acid activated with HCl at 95 C than for treatments at 25 C with HCl or following Al3þ-exchange (Al-SD), and increased with increasing acid concentration to 3 M. Activation with 4 M HCl led to the largest pore volume with contribution from mesopores. However, the specific external surface area was the same as that obtained for Na-SD, Al-SD and for most of the other acid activated samples. Treatments at 95 C with 1 M and 6 M HCl promoted increase in specific external surface area. The micropore volumes and specific external surface area for SAz-1 treated with 1 M HCl at 95 C were larger than those of Al-SAz-1, but lower than those obtained for corresponding materials derived from Na-SD. The n-nonane pre-adsorption method enabled micropore volumes and specific external surface areas to be obtained for all samples.

2016Journal article

Open access