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Volatile Organic Compound Adsorption on a Nonporous Silica Surface: How Do Different Probe Molecules Sense the Same Surface?

Herdes, C.; Ribeiro Carrott, M.M.L.; Russo, P.A.; Carrott, P.J.M.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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In this work, we compare experimental results to molecular simulation results of volatile organic compound (VOC) adsorption on nonporous silica.We adopted an effective model for the rough solid surface, obtained by a temperature annealing scheme, plus an experimental/simulation nitrogen adsorption tuning process over the silica energetic oxygen parameter. The measurement/prediction of selected VOCs, specifically, n-pentane and methylcyclohexane, is presented in terms of adsorption isotherms, with an emphasis on the angle distribution analysis of the three studied probe molecules with respect to the same modeled surface.

Valorisation of glycerol by condensation with acetone over silica-included heteropolyacids

Ferreira, P; Fonseca, I; Ramos, A; Vital, J; Castanheiro, J
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
POR
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The acetalisation of glycerolwasstudied using heteropolyacids, immobilized in silica, as catalysts, at 70 ◦C. The main product of glycerol acetalisation was solketal. The tungstophosphoric (PW), molybdophosphoric (PMo), tungstosilisic (SiW) and molybdosilisic (SiMo) acids were immobilized in silica by sol–gel method. It was observed that the catalytic activity decreases in the series: PW-S > SiW-S >PMo-S > SiMo-S. All catalysts exhibited good values of selectivity to solketal (about 98% near complete conversion). The effect of different parameters, such as catalyst loading, molar ratio of glycerol to acetone and temperature on the glycerol acetalisation, over PW-S catalyst, was studied. Catalytic stability of the PW-S, SiW-S, PMo-S and SiMo-S catalysts was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch, it was observed a stabilisation of the initial activity.

Alkoxylation of camphene over silica-occluded tungstophosphoric acid

Castanheiro, J; Caiado, M; Machado, A; Santos, R; Matos, I; Fonseca, I; Ramos, A; Valente, A; Vital, J
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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Silica-occluded tungstophosphoric acid (PW-Ssg) was used as an efficient, nvironmentally friendly heterogeneous catalyst for the liquid-phase alkoxylation of camphene into their more valuable alkyl isobornyl ether, which is used as perfume and cosmetic products, in the pharmaceutical industry, as well as in the food industry. The lkoxylation of camphene with C1–C4 alcohols (methanol, ethanol, 1- propanol, 2-propanol, 1-butanol and 2-butanol) to alkyl isobornyl ether was studied in the presence of PW-Ssg (4.2% w/w) at 60–80 ◦C. Different linear and branched alcohols are compared in relation to their activity for the alkoxylation of camphene. The catalytic activity decreased with the increase of number of carbon atoms in the chain alcohol, which can be explained due to the presence of sterical hindrance and diffusion limitations inside the porous system of the catalyst. High selectivity of PW-Ssg catalyst for the alkyl isobornyl ether was observed. The effect of various parameters, such as atalysts loading, initial concentration of camphene and temperature were studied to optimise the ethoxylation of camphene. The catalytic stability of PW-Ssg in the ethoxylation of camphene was studied by performing consecutive batch runs with the same catalyst sample at the same conditions. After the third run...

Análise das propriedades de grout endurecido - influência da adição de sílica de fumo a grouts de cal hidráulica

Jorne, Fernando; Henriques, Fernando M.A.; Baltazar, Luís G.
Fonte: PATORREB Publicador: PATORREB
Tipo: Artigo de Revista Científica
Publicado em /04/2012 POR
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4º Congreso de patología y rehabilitación de edificios. PATORREB 2012; As intervenções para a reabilitação e conservação de alvenarias antigas envolvem frequentemente acções de consolidação destinadas a melhorar o comportamento estrutural. Uma das técnicas de consolidação mais utilizadas consiste na injecção de grouts (caldas) no interior das alvenarias, permitindo a criação de ligações entre elementos da alvenaria e aumentar a sua homogeneidade através do preenchimento dos vazios existentes no núcleo da alvenaria. O processo de injecção apenas será bemsucedido se for assegurado um adequado escoamento do grout no meio poroso, daí a necessidade de uma concepção adequada. Uma vez que a preservação das alvenarias é indispensável, a concepção do grout deve também atender à melhoria das propriedades de grout endurecido. Assim, a aplicação de aditivos como os superplastificantes (maioritariamente orgânicos) e a sílica de fumo (material inorgânico) surge como uma consequência desta necessidade. O presente estudo incide na influência da adição de sílica de fumo nas propriedades de grout endurecido. Deste modo, será analisada a sua estrutura porosa através da realização de ensaios de capilaridade e de porosidade aberta...

Adsorção do complexo H[Ru(III)Cl2(H2EDTA)] sobre a superfície da sílica gel modificada com [3-(2-aminoetil) aminopropil]trimetoxissilano em soluções etanólicas

Lazarin,Angélica Machi; Sernaglia,Rosana Lázara
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1999 PT
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Silica gel was functionalized with [3-(2-aminoethyl)aminopropyl]trimethoxysilane group (SF-AEATS) and the characterization by chemical analysis (N) and infrared spectroscopy confirmed the functionalization. The capacity of the modified silica to adsorb the complex Ru(III)-EDTA from ethanolic solution was studied. The selectivity coefficients of the complex formed on the support obtained was (Gñ), 2,07 x 10(4) L/mol and the average number of ligand bonded by one metal ion on the support (ñ) was ~ 1.

Propriedades fotofísicas de Eu3+ e Tb3+ imobilizados em sílica gel funcionalizada com beta-Dicetonas

Nassar,Eduardo José; Serra,Osvaldo Antonio
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2000 PT
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Synthetic procedures, characterization and luminescent properties of Eu3+ and Tb3+ ions supported on silica gel functionalized with beta-diketones are presented. The functionalization with propyl benzoyltrifluoroacetone (BPG), dibenzoylmethane (DBM) and hexafluoroacetone (HPG), leads to new luminescent materials which photophysical properties depend on the group substituent in the beta-diketone. These systems were evaluated in terms of luminescence and lifetime of the Eu3+ and Tb3+ ions. Silica functionalization was confirmed by TGA and Elemental Analysis. The sample contents of ions were from 0,2 to 0,3 % (w/w).

Caracterização de cinza de casca de arroz para uso como matéria-prima na fabricação de refratários de sílica

Della,Viviana Possamai; Kühn,Ingeborg; Hotza,Dachamir
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2001 PT
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The characterization of rice husk ash, a deriving by-product of the burning of the rice husk during the rice processing is the object of this study. This by-product, for being rich in silica, can be an important raw material for the production of siliceous ceramics, such as thermal insulators and refractory. A combination of surface analysis, thermal analysis and microscopy analysis techniques was used for the characterization. The characterized by-product presented as main component the silica, under amorphous form, with a maximum content of alkalis around 1%, features that become it potentially interesting for the production of ceramic materials.

Quimissorção de cátions divalentes em sílica gel modificada com ácido tioglicólico: a influência do pH e força iônica

Sousa,Kaline S. de; Augusto Filha,Vera Lúcia S.; Pinto,Victor Hugo e A.; Fonseca,Maria G. da; Espínola,José G. P.; Arakaki,Luiza N. H.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2007 PT
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A novel type of heavy metal adsorbent was prepared by the covalent grafting of thioglycolic acid molecules on a silica gel surface previsiouly modified with 3-aminopropyltrimethoxysilane. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This material displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting from aqueous solutions cations such as Cu(II), Ni(II), Co(II), influenced by pH and ionic strength. This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. A modified Langmuir equation describes the experimental data.

Estudo de alguns esfeitos na precipitação de partículas esféricas de sílica via microemulsão inversa

Flor,Juliana; Davolos,Marian Rosaly; Jafelicci Júnior,Miguel
Fonte: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Publicador: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2002 PT
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Partículas esféricas de sílica foram obtidas via microemulsão inversa em sistema AOT / Heptano / H2O, utilizando-se soluções de silicato de sódio como precursor. Variações de condições experimentais durante a precipitação levam à mudanças no tamanho e na forma das partículas. O objetivo deste trabalho é otimizar a obtenção de partículas de sílica com homogeneidade de forma e tamanho, variando-se a ordem de adição dos reagentes, a concentração da solução de silicato de sódio, a razão água/surfactante (W), a ordem de mistura dos reagentes e a purificação do produto obtido. As micrografias evidenciaram que para se obter partículas esféricas, com faixa estreita de tamanho, utiliza-se duas microemulsões inversas a partir das soluções de ácido nítrico e de silicato de sódio, sendo que a mistura destas deve ser feita adicionando-se a microemulsão contendo o silicato de sódio sobre a microemulsão contendo o ácido nítrico. A relação silicato de sódio:água mais adequada de para os objetivos do trabalho é de 1:10. A purificação mais eficiente é aquela feita em duas etapas, com etanol e com água quentes. A partir dos resultados obtidos, pode-se verificar também que quanto maior o W maior será o tamanho médio de partícula.

Structure of cobalt (II) perchlorate adsorbed on silica gel surface chemically modified with benzimidazole molecule

Dias Filho,Newton L; Rodrigues,Edson; Gushikem,Yoshitaka
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1997 EN
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Covalently attached benzimidazole molecules on silica gel surface, ºSiL (where L = N-propylbenzimidazole), adsorbs Co(ClO4)2 from non-aqueous solvent by forming a surface complex according to the reaction: m ºSiL + Co(ClO4)2 ® (ºSiL)mCo(ClO4)2. The equilibrium constant and the adsorption capacity, determined by applying the Langmuir equation were b = 3.0 x 10³ L mol-1 and Ns= 0.098 x 10-3 mol g-1, respectively. The metal is bonded through the nitrogen atom and the perchlorate ion is not coordinated. The ESR study indicated that the complex has essentially an octahedral geometry with tetragonal distortion, with the electrons of the four nitrogen atoms interacting with the cobalt central metal ion in the equatorial plane. Only one complex species was detected on the surface.

Cobalt(II) phthalocyanine bonded to 3-n-propylimidazole immobilized on silica gel surface: preparation and electrochemical properties

Fujiwara,Sergio T.; Gushikem,Yoshitaka
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/1999 EN
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Co-Phthalocyanine complex was immobilized on 3-n-propylimidazole groups grafted on a porous SiO2 surface (specific surface area S BET = 500 m² g-1) and efficiently electrocatalyzed the oxalic acid oxidation on a carbon paste electrode surface made of this material. Intermolecular interactions of the complex species which can normally interfere in the redox process practically are not observed in the present case because of a low average surface density, delta = 4.7 x 10-13 mol cm-2 (delta = Nf/S BET, where Nf is the amount of adsorbed Co-phtalocyanine per gram of modified silica gel) of the complex species material prepared. The linear response of the electrode to oxalic acid concentration, between 6.5 x 10-4 and 3.2 x 10-3 mol L-1, associated with its high chemical stability makes the covalently immobilized Co-phtalocyanine complex material very attractive in preparing a new class of chemical sensors.

Separation of acid diterpenes of Copaifera cearensis huber ex ducke by flash chromatography using potassium hydroxide impregnated silica gel

Pinto,Angelo C.; Braga,Waldenir F.; Rezende,Claudia M.; Garrido,Francisco M. S.; Veiga Jr.,Valdir F.; Bergter,Lothar; Patitucci,Maria Lúcia; Antunes,Octávio A. C.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2000 EN
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Various acid diterpenes of Copaifera cearensis Huber ex Ducke were isolated from the crude extract by flash Silica Gel/Potassium Hydroxide Chromatography. The main components were identified by GC-MS analyses. Further fractionation by reversed phase (RP) semi-preparative HPLC allowed isolation and identification of minor components and provided additional spectral data of those compounds. It was possible to detect the presence of eleven acid diterpenes in addition to a sesquiterpene acid. In addition to potassium hydroxide deposition on the silica surface, the presence of Si-OK residues, resulting from a cation exchange process, was established.

Core-and-shell nature of Stöber silica particles

Leite,Carlos A. P.; Souza,Elizabeth F. de; Galembeck,Fernando
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2001 EN
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Two different samples of monodisperse Stöber silica particles were examined in the analytical transmission electron microscope, using different imaging modes: bright-field, dark-field, energy-loss and elemental distribution maps. The particles (effective diameters = 141 and 36 nm) are formed by domains of variable O/Si ratio, which is consistent with a variable degree of hydration, and they coexist with particles with a high O/Si ratio measuring a few nanometers only, which appear dispersed in the picture background. Bright-field and energy-loss images of the larger particles show a core-and-shell morphology, and the shells have a higher amount of high-O/Si domains as well as contaminating carbon compounds. On the other hand, the smaller particles (effective diameter = 36 nm) are also formed by distinct domains, but their morphology is neither spherical or core-and-shell. The mechanisms for particle formation presented in the literature are discussed, considering the present findings.

Preparation of a silica gel modified with 2-amino-1,3,4-thiadiazole for adsorption of metal ions and electroanalytical application

Dias Filho,Newton L.; Caetano,Laércio; Carmo,Devaney R. do; Rosa,André H.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 EN
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Silica gel with a specific area of 382 m² g-1 and an average pore diameter of 60 Å was chemically modified with 2-amino-1,3,4-thiadiazole, for the purpose of selective adsorption of heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). The following properties of this functionalized silica gel are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II). The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination.

Synthesis of silica xerogels with high surface area using acetic acid as catalyst

Arenas,Leliz T.; Simm,Carolina W.; Gushikem,Yoshitaka; Dias,Silvio L. P.; Moro,Celso C.; Costa,Tania M. H.; Benvenutti,Edilson V.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 EN
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The influence of acetic acid on the pore structure and surface area of silica prepared by the sol-gel method was investigated. Experimental conditions of synthesis, such as gelation temperature and solvents, were also studied. N2 adsorption isotherms of the samples were type 1, typical of microporous materials, explaining the high surface area values (BET) observed. The simultaneous addition of acetic and hydrochloric acids as catalysts and of acetone as solvent, together with the use of a gelation temperature of 20 ºC, made it possible to prepare amorphous silica materials with surface area values up to 850 m² g-1. The high surface area value of these samples could be explained by the microporosity and the nanometric size of the particles.

Peak separation by derivative spectroscopy applied to ftir analysis of hydrolized silica

Aragão,Bernardo J. G. de; Messaddeq,Younes
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 EN
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Reliable spectral analysis is only achieved if the spectrum is thoroughly investigated in regard to all hidden and overlapped peaks. This paper describes the steps undertaken to find and separate such peaks in the range of 3000 to 4000 cm-1 in the case of three different infrared absorption spectra of the glass surface of hydrolyzed silica optical fibers. Peak finding was done by the analysis of the second and fourth derivatives of the digital data, coupled with the available knowledge of infrared spectroscopy of silica-water interaction in the investigated range. Peak separation was accomplished by curve fitting with four different models. The model with the best fit was described by a sum of pure Gaussian peaks. Shoulder limit and detection limit maps were used to validate the revealed spectral features.

Preparation of catalysts based on iron(III) porphyrins heterogenized on silica obtained by the Sol-Gel process for hydroxylation and epoxidation reactions

Castro,Kelly A. D. F.; Halma,Matilte; Machado,Guilherme S.; Ricci,Gustavo P.; Ucoski,Geani M.; Ciuffi,Katia J.; Nakagaki,Shirley
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
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Solid catalysts have been prepared by chemical interaction of iron(III) porphyrins with the surface of the pores of a silica matrix obtained by the sol-gel method. The presence of the complexes in the silica matrix and the morphology of the obtained particles were studied by UV-Vis spectroscopy, powder X-ray diffractometry, infrared spectroscopy, transmission electron microscopy, electron paramagnetic resonance and thermogravimetric analysis. The catalytic activity of the immobilized iron(III) porphyrins in the oxidation of (Z)-cyclooctene, cyclohexene and cyclohexane was evaluated in dichloromethane/acetonitrile 1:1 solvent mixture (v/v) using iodosylbenzene as oxidant. Results were compared with those achieved with the homogeneous counterparts.

Modified silica nanoparticles with an Aminonaphthoquinone

Silveira,Gleiciani Q; Ronconi,Célia M; Vargas,Maria D; San Gil,Rosane A. S; Magalhães,Alvicler
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2011 EN
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The synthesis and characterization of silica nanoparticles (NPs) covalently modified with an aminonaphthoquinone are reported. The aminopropylsilicagelnaphthoquinone (APSGNQ) was obtained by nucleophilic substitution of 2-methoxy-1,4-naphthoquinone with aminopropylsilicalgel (APSG) NPs. Solid state 13C and 29Si nuclear magnetic resonance spectra confirmed that the naphthoquinone is covalently bonded to APSG. Due to the solubility of APSGNQ in common organic solvents, solution ultraviolet-visible spectroscopy was used to determine the amount of naphthoquinone on the NPs surface (0.56 mmol of incorporated naphthoquinone per gram of APSGNQ) by comparison with the spectrum of 2-aminobutyl-1,4-naphthoquinone (ABNQ). Elemental analysis indicated that about 8% of the surface propylamine remained unreacted in APSGNQ. These multifunctional silica NPs have potential in medical applications.

Propriedades mecânicas e comportamento a emissões de voláteis de compósitos de polipropileno/fibras curtas de sílica

Pizzitola,Ivani C. dos P.; Machado,Mariana M.; Wiebeck,Hélio
Fonte: Associação Brasileira de Polímeros Publicador: Associação Brasileira de Polímeros
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 PT
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A proteção à saúde humana constitui um dos princípios estabelecidos pelas indústrias automotivas visando ao desenvolvimento e à produção sustentáveis de seus modelos. Desafios residem na redução nos níveis de emissões não só de combustíveis, mas também dos voláteis presentes no interior dos automóveis. A incorporação de fibras curtas de sílica natural amorfa em compósitos de polipropileno foi investigada como uma proposta de desenvolvimento de novos materiais, os quais permitam a redução de peso do veículo e consequente economia de combustível, além de atenderem aos níveis de emissões especificados para componentes internos. Com o objetivo de avaliar o efeito de reforço e a influência do conteúdo de compatibilizante na interface fibra-matriz, amostras com 0 e 20% em peso de fibra, bem como com variações do teor de PP-g-MAH (0, 1, 2 e 4% em peso), foram analisadas. Os resultados satisfatórios obtidos para as propriedades de tensão no escoamento, módulo de flexão, alongamento na ruptura, resistência ao impacto Charpy com entalhe e comportamento a emissões sugerem que a concentração ótima do compatibilizante é de 2%, acima da qual as alterações não foram significativas. Conclui-se que fibras curtas de sílica constituem uma alternativa potencial de reforço para materiais empregados em peças automotivas.

MULTI-POINT IMMOBILIZATION OF PENICILLIN G ACYLASE ON SILICA-GLYOXYL: INFLUENCE OF THE DEGREE OF ACTIVATION

PEREIRA,G.H.A.; GUISÁN,J.M.; GIORDANO,R.L.C.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/1997 EN
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Multi-point immobilization, by an intense enzyme-support attachment, may increase the operational stability of a biocatalyst. Penicillin G acylase has many applications, from the hydrolysis of penicillin G (production of 6-aminopenicillanic acid) to the synthesis of semi-synthetic antibiotics. The application of this technique in macroporous silica involves support activation with 3-glycidyloxypropyltrimetoxysilane, followed by acidic hydrolysis and oxidation with sodium periodate. The aldehyde-glyoxyl groups so formed react subsequently with the enzyme. The degree of activation affects the yield and stability of the enzyme immobilization. For 20 UI of enzyme, the results show an immobilization yield equal to 100%, whenever there are more than 140 m Eq of aldehyde groups/g of dry silica. The immobilized enzyme half-life is 23 minutes at 60ºC; under the same conditions, the soluble enzyme has no residual activity after a few minutes. The increase in the degree of activation does not lead to higher stability, which indicates the negative influence of sub-products, formed during the activation of the support