Loading...
4 results
Search Results
Now showing 1 - 4 of 4
- Selective methoxylation of limonene over ion-exchanged and acid-activated claysPublication . 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.
- Catalytic conversion of limonene over acid activated Serra de Dentro (SD) bentonitePublication . Fernandes, C.; Catrinescu, C.; Castilho, P.; Russo, P. A.; Carrott, M. R.; Breen, C.A series of acid-activated clay catalysts were prepared from a purified bentonite, rich in structural iron, collected at Serra de Dentro on the island of Porto Santo. The purified bentonite exhibited a surface area of 130 m2 g 1 which increased to values as high as 500 m2 g 1 following activation with 4M HCl at 95 8C for 30 min (SD-4M-95-30). The ability of the activated samples to convert limonene to p-cymene was evaluated using a reaction time of 15 min at 80 8C. The sample prepared using 3M HCl at 95 8C for 30 min (SD-3M-95-30) offered the optimum combination of surface area (470 m2 g 1 ) and acidity (0.26 mmol g 1 ) and 95% of the limonene was converted to product. About 15% of the product mixture was p-cymene whilst non-volatile products and polymeric species made up 54% of the product mixture. The presence of iron in the octahedral sheet of the SD bentonite appears responsible for the dehydrogenation activity. TG–MS analysis of acid activated samples, saturated with cyclohexylamine, reflected the dehydrogenation capabilities of the catalysts in that SD-3M-95-30 produced the most benzene and aniline as decomposition/ transformation products.
- 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/selectivityPublication . Catrinescu, C.; Fernandes, César; Castilho, P.; Breen, C.A bentonite collected at Serra de Dentro (SD), Porto Santo Island, Portugal, and the source clay SAz-1 (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 8C, to yield isomerization products (terpinolene, a-terpinene, g-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-1 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 Bro¨nsted acidity) and Ni2+-SD (with predominant Lewis acid character) provided no support for enhanced p-cymene production over Lewis acid sites.
- Argilas modificadas como catalisadores ácidos sólidosPublication . Fernandes, César EsmeraldoImportant bentonitic deposits are present in Porto Santo Island, part of the Madeira Archipelago. Several locations were selected and samples were collected and characterised. The bentonite obtained at Serra de Dentro (SD) was selected for further laboratorial work. The fine fraction of SD bentonite was purified using several methods and the sodium homoionic form was prepared. This was the starting material used in the three generic types of modifications: metal exchange, acid activation and pillaring. These modifications produce materials with markedly different acidic (e.g. Brönsted and/or Lewis acidity), textural (e.g. increase of the surface area and active site accessibility) or structural (e.g. creation of permanent porous structures) properties. The wide range of materials obtained (including reference clays counterparts) was characterised in terms of chemical, structural, textural and catalytic properties. Limonene is an important raw material produced in Portugal, and its aromatisation reaction was chosen for the catalytic characterisation of the clay catalysts prepared.