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result(s) for
"Ribeiro, F. Ramôa"
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Enhancing the thermal stability of lipases through mutagenesis and immobilization on zeolites
The hydrolysis reaction of
p
-nitrophenyl butyrate catalyzed by lipases was followed with in situ UV/vis diode array spectrophotometry. Five enzymes -
Candida antarctica
lipase B and
Fusarium solani pisi
cutinase wild-type and three single-mutation variants - were tested as catalysts in homogeneous conditions and immobilized on zeolite NaY, on a polyacrylate support and as cross-linked aggregates. Using deconvolution techniques and kinetic modeling, the thermal stability of the different biocatalysts was compared in operational conditions and the results were supported by steady-state enzyme fluorescence measurements. We concluded that both the mutagenesis and the immobilization on zeolite NaY had a positive effect on the thermal stability of
F. solani pisi
cutinase.
Journal Article
Comparing the effect of immobilization methods on the activity of lipase biocatalysts in ester hydrolysis
The activity of various lipases was compared, in both free and immobilized forms, using the kinetics of the hydrolysis reaction of
p
-nitrophenyl butyrate, which was followed with in situ UV/Vis diode array spectrophotometry. Several enzymes were used to catalyze the reaction, namely
Candida antarctica
lipase B and
Fusarium solani pisi
cutinase wildtype and three single-mutation variants. The enzymes were tested in three different forms: free, immobilized as cross-linked aggregates and supported on zeolite NaY. A simple kinetic model was used to allow a quantitative comparison of the behavior of the different catalysts. It was concluded that although immobilization reduces the activity of the enzyme, the zeolite offers a much higher specific activity when compared to the cross-linked aggregates, thus supplying a heterogeneous catalyst with promising catalytic properties.
Journal Article
Preparation of HNaY zeolite by ion exchange under microwave treatment. A preliminary study
Acidic samples of Y zeolite were prepared by ion exchange promoted using microwave irradiation. Interesting exchange levels were obtained with only a few minutes of irradiation. The catalytic properties of these samples were evaluated using the transformation of iso‐octane; the observed conversions lie in the same range as those for the samples prepared by the conventional ion‐exchange method of stirring the mixture of the sodium form with an ammonium salt solution for several hours; the deactivation with time‐on‐stream was significantly reduced for the catalysts prepared by the irradiation method in the cases of highest activity.
Journal Article
Acidity-activity relationship in zeolite Y. A preliminary study for n-heptane transformation
The transformation of n-heptane at 350°C has been studied on a variety of Y zeolite catalysts. The acidities of these samples were determined by temperature-programmed desorption of ammonia and, by using a numerical deconvolution technique, the acid strength distribution for the sites of each catalyst was obtained. Using these results we were able to correlate the catalytic activity with the acid strength distribution for all the catalysts using a Brønsted type equation, similar to the one that is used in homogeneous acid catalysis.
Journal Article
Conformational changes induced by immobilization of a recombinant cutinase on zeolites
A recombinant cutinase from Fusarium solani pisi was immobilized by adsorption/deposition onto several zeolites. These preparations were used to catalyse the alcoholysis of butyl acetate with hexanol in isooctane. Ground state diffuse reflectance measurements were performed for the preparations previously equilibrated with salt solutions at well-defined optimum water activity. The corresponding cutinase fluorescence emission spectra were used to detect different conformational enzyme states, induced by different zeolite properties. Significant conformational changes were observed, with important consequences on the enzymatic activities.
Journal Article
Deactivation of CuMFI catalysts under NO selective catalytic reduction by propene: influence of zeolite form, Si/Al ratio and copper content
Deactivation of CuMFI catalysts under NO selective catalytic reduction (SCR) by propene in both the absence and the presence of water was investigated as a function of zeolite form, Si/Al ratio and copper content. It was verified that the CuMFI deactivation extent is higher on H-form zeolite compared to Na-form and decreases when the copper exchange level increases, which can be achieved either by increasing the zeolite Si/Al ratio or the copper content. Furthermore, the results indicated that the catalyst deactivation is mainly due to a change in copper species rather than in MFI structure.
Journal Article