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Claude Lamy - One of the best experts on this subject based on the ideXlab platform.
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Activity of platinum–tin catalysts prepared by the Pechini–Adams method for the electrooxidation of ethanol
Journal of Electroanalytical Chemistry, 2009Co-Authors: F.l.s. Purgato, J.-m. Léger, Claude Lamy, Paulo Olivi, A.r. De Andrade, G. Tremiliosi-filho, Ernesto Rafael Gonzalez, Kouakou Boniface KokohAbstract:Abstract Pt–Sn electrocatalysts of different compositions were prepared and dispersed on carbon Vulcan XC-72 using the Pechini–Adams method. The catalysts were characterized by energy dispersive X-ray analysis and X-ray diffraction. The electrochemical properties of these electrode materials were also examined by cyclic voltammetry and chronoamperometric experiments in acid medium. The results showed that the presence of Sn greatly enhances the activity of Pt towards the electrooxidation of ethanol. Moreover, it contributes to reduce the amount of noble metal in the anode of dIRect alcohol fuel cells, which remains one of the challenges to make the technology of dIRect alcohol fuel cells possible. Electrolysis of ethanol solutions at 0.55 V vs . RHE allowed to determine by liquid chromatography acetaldehyde and acetic acid as the main reaction products. CO 2 was also analyzed after trapping it in a NaOH solution indicating that the cleavage of the C–C bond in the ethanol molecule did occur during the adsorption process. In situ IR Reflectance Spectroscopy helped to investigate in more details the reaction mechanism through the identification of the reaction products as well as the presence of some intermediate adsorbed species, such as linearly bonded carbon monoxide.
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How bimetallic electrocatalysts does work for reactions involved in fuel cells?: Example of ethanol oxidation and comparison to methanol
Electrochimica Acta, 2005Co-Authors: Jean-michel Léger, Françoise Hahn, Christophe Coutanceau, Séverine Rousseau, Claude LamyAbstract:Carbon-supported Pt-based nanosized electrocatalysts can be synthesized for methanol and ethanol electrooxidation. The electrocatalytic activity of Pt can be greatly enhanced by using Pt-Ru/C for methanol oxidation or Pt-Sn/C for ethanol oxidation. In situ IR Reflectance Spectroscopy is a convenient tool to better understand the importance of the different adsorption steps involved in the mechanisms of electrooxidation. With Pt/C, it appears clearly that linearly adsorbed CO is the poisoning species formed during methanol and ethanol oxidation. In the case of methanol, even with Pt-Ru/C (the most active catalyst), adsorbed CO is also a reactive intermediate. The enhancement of activity observed in such a case is due to the possibility to activate water at lower potentials in the presence of Ru. With Pt-Sn/C, the mechanism of the electrooxidation of ethanol is strongly modified. If at low potentials, poisoning with adsorbed CO still exists (as with Pt/C), the oxidation of ethanol at potentials greater than 0.4 V versus RHE occurs through an adsorbed acetyl species which can lead to the formation of acetaldehyde and acetic acid as final products in addition to carbon dioxide.
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Radioactive Labeling Study and FTIR Measurements of Methanol Adsorption and Oxidation on Fuel Cell Catalysts
Fuel Cells, 2002Co-Authors: C. Coutanceau, Françoise Hahn, Claude Lamy, P. Waszczuk, Andrzej Wieckowski, J.-m. LégerAbstract:The adsorption and the electrooxidation of methanol-derived surface CO on fuel-cell grade platinum and platinum-ruthenium alloy nanoparticle catalysts were studied using a combination of electrochemical measurements and radioactive labeling (thin foil radioactive labeling technique) and in situ infrared Reflectance Spectroscopy. The kinetics of formation of surface and bulk products coming from methanol and surface/bulk exchange processes were found to be significantly different on Pt compared to Pt/Ru. The observed difference in the kinetics of CO adsorption underlines the electronic effect in the surface catalytic activity due to modification of the electronic structure of surface platinum atoms by ruthenium. Correlation between FTIR and radiolabeling measurements indicated that the adsorption of CO from methanol is a very slow process at low potential but that the coverage by CO poison is greater at higher potential. Then, the results obtained from both analytical techniques (in situ IR Reflectance Spectroscopy and radioactive labeling method) displayed very good agreement and allowed us to validate them for the investigation of the methanol oxidation mechanism.
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An in situ IR Reflectance spectroscopic study of the electro-oxidation of D-sorbitol on platinum
Electrochimica Acta, 1998Co-Authors: Luís Proença, M.i.s. Lopes, Inês T.e. Fonseca, Françoise Hahn, Claude LamyAbstract:Abstract An in situ infrared (IR) Reflectance spectroscopic study of the electrooxidation of d -sorbitol on polycrystalline platinum in perchloric acid medium was carried out by Fourier transform IR Spectroscopy (FTIRS), under the SNIFTIRS and SPAIRS variants. Additional information was obtained by electrochemically modulated IR Reflectance Spectroscopy (EMIRS). In situ IR spectra show that the electrooxidation of d -sorbitol on platinum proceeds via a dual-path mechanism involving both reactive and poisoning intermediates. Linearly and bridge-bonded CO, resulting from the dissociative adsorption of d -sorbitol, which were identified as the main poisoning species present at the surface, are fully oxidised to CO 2 at higher potentials. The superficial coverage in adsorbed CO was found to be function of the electrode potential. Moreover, the electrooxidation process can occur without breaking the initial molecule skeleton, indicating that molecular adsorption of d -sorbitol is also possible. d -glucono-(δ and γ)-lactones, D -glucose and CO 2 were identified as the main reaction products.
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A kinetic analysis of the electro-oxidation of ethanol at a platinum electrode in acid medium
Electrochimica Acta, 1994Co-Authors: H. Hitmi, Claude Lamy, El Mustapha Belgsir, Jean-michel Léger, R.o. LeznaAbstract:In order to establish the kinetic laws which govern the oxidation process of ethanol on smooth platinum electrodes in acid medium, electrolyses of ethanol were carried out under different experimental conditions. The influence of the initial ethanol concentration and of the potential plateau of electrolysis were investigated and allowed us to improve our understanding of the reaction mechanism. In addition, some IR Reflectance Spectroscopy experiments were performed to identify the adsorbed intermediates and the reaction products.
Françoise Hahn - One of the best experts on this subject based on the ideXlab platform.
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How bimetallic electrocatalysts does work for reactions involved in fuel cells?: Example of ethanol oxidation and comparison to methanol
Electrochimica Acta, 2005Co-Authors: Jean-michel Léger, Françoise Hahn, Christophe Coutanceau, Séverine Rousseau, Claude LamyAbstract:Carbon-supported Pt-based nanosized electrocatalysts can be synthesized for methanol and ethanol electrooxidation. The electrocatalytic activity of Pt can be greatly enhanced by using Pt-Ru/C for methanol oxidation or Pt-Sn/C for ethanol oxidation. In situ IR Reflectance Spectroscopy is a convenient tool to better understand the importance of the different adsorption steps involved in the mechanisms of electrooxidation. With Pt/C, it appears clearly that linearly adsorbed CO is the poisoning species formed during methanol and ethanol oxidation. In the case of methanol, even with Pt-Ru/C (the most active catalyst), adsorbed CO is also a reactive intermediate. The enhancement of activity observed in such a case is due to the possibility to activate water at lower potentials in the presence of Ru. With Pt-Sn/C, the mechanism of the electrooxidation of ethanol is strongly modified. If at low potentials, poisoning with adsorbed CO still exists (as with Pt/C), the oxidation of ethanol at potentials greater than 0.4 V versus RHE occurs through an adsorbed acetyl species which can lead to the formation of acetaldehyde and acetic acid as final products in addition to carbon dioxide.
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Radioactive Labeling Study and FTIR Measurements of Methanol Adsorption and Oxidation on Fuel Cell Catalysts
Fuel Cells, 2002Co-Authors: C. Coutanceau, Françoise Hahn, Claude Lamy, P. Waszczuk, Andrzej Wieckowski, J.-m. LégerAbstract:The adsorption and the electrooxidation of methanol-derived surface CO on fuel-cell grade platinum and platinum-ruthenium alloy nanoparticle catalysts were studied using a combination of electrochemical measurements and radioactive labeling (thin foil radioactive labeling technique) and in situ infrared Reflectance Spectroscopy. The kinetics of formation of surface and bulk products coming from methanol and surface/bulk exchange processes were found to be significantly different on Pt compared to Pt/Ru. The observed difference in the kinetics of CO adsorption underlines the electronic effect in the surface catalytic activity due to modification of the electronic structure of surface platinum atoms by ruthenium. Correlation between FTIR and radiolabeling measurements indicated that the adsorption of CO from methanol is a very slow process at low potential but that the coverage by CO poison is greater at higher potential. Then, the results obtained from both analytical techniques (in situ IR Reflectance Spectroscopy and radioactive labeling method) displayed very good agreement and allowed us to validate them for the investigation of the methanol oxidation mechanism.
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An in situ IR Reflectance spectroscopic study of the electro-oxidation of D-sorbitol on platinum
Electrochimica Acta, 1998Co-Authors: Luís Proença, M.i.s. Lopes, Inês T.e. Fonseca, Françoise Hahn, Claude LamyAbstract:Abstract An in situ infrared (IR) Reflectance spectroscopic study of the electrooxidation of d -sorbitol on polycrystalline platinum in perchloric acid medium was carried out by Fourier transform IR Spectroscopy (FTIRS), under the SNIFTIRS and SPAIRS variants. Additional information was obtained by electrochemically modulated IR Reflectance Spectroscopy (EMIRS). In situ IR spectra show that the electrooxidation of d -sorbitol on platinum proceeds via a dual-path mechanism involving both reactive and poisoning intermediates. Linearly and bridge-bonded CO, resulting from the dissociative adsorption of d -sorbitol, which were identified as the main poisoning species present at the surface, are fully oxidised to CO 2 at higher potentials. The superficial coverage in adsorbed CO was found to be function of the electrode potential. Moreover, the electrooxidation process can occur without breaking the initial molecule skeleton, indicating that molecular adsorption of d -sorbitol is also possible. d -glucono-(δ and γ)-lactones, D -glucose and CO 2 were identified as the main reaction products.
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Integrated electromodulated IR Reflectance Spectroscopy bands: Part 2: Methanol adsorbates at polycrystalline platinum and Pt(111) single-crystal electrodes in acid medium
Journal of Electroanalytical Chemistry, 1993Co-Authors: M.i.s. Lopes, Inês T.e. Fonseca, P. Olivi, Bernard Beden, Françoise Hahn, J.-m. Léger, Claude LamyAbstract:Using electromodulated IR Reflectance Spectroscopy (EMIRS), absorption spectra of adsorbed species resulting from the chemisorption of HCHO, HCOOH and methyl formate, HCOOCH3, on both polycrystalline and (111) platinum surfaces, were fIRst obtained in the range 1400–1900 cm−1, to cover completely the carbonyl stretching mode region. The same experimental conditions were used for all systems. EMIRS bands were integrated and analysed, using the procedure described in Part 1 (B. Beden, J. Electroanal. Chem., 345 (1993) 1). Characteristic frequencies were located precisely, allowing the spectral discrimination of several types of adsorbates. The same procedure was then used to follow the chemisorption of methanol on platinum in perchloric medium with time. As expected, formate species were found to dominate on the two types of platinum surface. However, during the initial stages of chemisorption, and particularly on the Pt(111) electrode, the formation of adsorbed methyl formate is likely. A mechanism is suggested, taking into consideration the possibility of surface reactions between adsorbates.
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Electrosorption of sorbitol at platinum electrodes: Effect of the superficial structure
Journal of Electroanalytical Chemistry, 1993Co-Authors: J.-m. Léger, Inês T.e. Fonseca, Bernard Beden, Françoise Hahn, Claude Lamy, M.f. Bento, M.i.s. LopesAbstract:Abstract The electrosorption of sorbitol was investigated at polycrystalline and single-crystal platinum electrodes in an acidic medium. The coverage degree and the number of electrons per site involved in the electro-oxidation of the adsorbed species coming from the sorbitol were estimated from voltammetric measurements carried out at high sweep rates and for adsorption times varying from 0.1 to 500 s. The adsorption process depends on the superficial structure. The electrode surface was never saturated by the organic species coming from sorbitol adsorption and the number of electrons per site was found to be around 3, though this decreased to about 2 after long adsorption times. One of the main adsorbed species present at the electrode surface for long adsorption times is linearly adsorbed CO, as confIRmed by in situ IR Reflectance Spectroscopy. The presence of other kinds of adsorbed species is also discussed.
J.-m. Léger - One of the best experts on this subject based on the ideXlab platform.
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Activity of platinum–tin catalysts prepared by the Pechini–Adams method for the electrooxidation of ethanol
Journal of Electroanalytical Chemistry, 2009Co-Authors: F.l.s. Purgato, J.-m. Léger, Claude Lamy, Paulo Olivi, A.r. De Andrade, G. Tremiliosi-filho, Ernesto Rafael Gonzalez, Kouakou Boniface KokohAbstract:Abstract Pt–Sn electrocatalysts of different compositions were prepared and dispersed on carbon Vulcan XC-72 using the Pechini–Adams method. The catalysts were characterized by energy dispersive X-ray analysis and X-ray diffraction. The electrochemical properties of these electrode materials were also examined by cyclic voltammetry and chronoamperometric experiments in acid medium. The results showed that the presence of Sn greatly enhances the activity of Pt towards the electrooxidation of ethanol. Moreover, it contributes to reduce the amount of noble metal in the anode of dIRect alcohol fuel cells, which remains one of the challenges to make the technology of dIRect alcohol fuel cells possible. Electrolysis of ethanol solutions at 0.55 V vs . RHE allowed to determine by liquid chromatography acetaldehyde and acetic acid as the main reaction products. CO 2 was also analyzed after trapping it in a NaOH solution indicating that the cleavage of the C–C bond in the ethanol molecule did occur during the adsorption process. In situ IR Reflectance Spectroscopy helped to investigate in more details the reaction mechanism through the identification of the reaction products as well as the presence of some intermediate adsorbed species, such as linearly bonded carbon monoxide.
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Activity of platinum–tin catalysts prepared by the Pechini–Adams method for the electrooxidation of ethanol
Journal of Electroanalytical Chemistry, 2009Co-Authors: F.l.s. Purgato, P. Olivi, J.-m. Léger, C. Lamy, A.r. De Andrade, G. Tremiliosi-filho, Ernesto Rafael Gonzalez, Kouakou Boniface KokohAbstract:Pt-Sn electrocatalysts of different compositions were prepared and dispersed on carbon Vulcan XC-72 using the Pechini-Adams method. The catalysts were characterized by energy dispersive X-ray analysis and X-ray diffraction. The electrochemical properties of these electrode materials were also examined by cyclic voltammetry and chronoamperometric experiments in acid medium. The results showed that the presence of Sn greatly enhances the activity of Pt towards the electrooxidation of ethanol. Moreover, it contributes to reduce the amount of noble metal in the anode of dIRect alcohol fuel cells, which remains one of the challenges to make the technology of dIRect alcohol fuel cells possible. Electrolysis of ethanol solutions at 0.55 V vs. RHE allowed to determine by liquid chromatography acetaldehyde and acetic acid as the main reaction products. CO(2) was also analyzed after trapping it in a NaOH solution indicating that the cleavage of the C-C bond in the ethanol molecule did occur during the adsorption process. In situ IR Reflectance Spectroscopy helped to investigate in more details the reaction mechanism through the identification of the reaction products as well as the presence of some intermediate adsorbed species, such as linearly bonded carbon monoxide. (C) 2009 Elsevier B.V. All rights reserved.CAPES/COFECUB[498/05]CAPES[0509078]FAPESP, Brazi
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Radioactive Labeling Study and FTIR Measurements of Methanol Adsorption and Oxidation on Fuel Cell Catalysts
Fuel Cells, 2002Co-Authors: C. Coutanceau, Françoise Hahn, Claude Lamy, P. Waszczuk, Andrzej Wieckowski, J.-m. LégerAbstract:The adsorption and the electrooxidation of methanol-derived surface CO on fuel-cell grade platinum and platinum-ruthenium alloy nanoparticle catalysts were studied using a combination of electrochemical measurements and radioactive labeling (thin foil radioactive labeling technique) and in situ infrared Reflectance Spectroscopy. The kinetics of formation of surface and bulk products coming from methanol and surface/bulk exchange processes were found to be significantly different on Pt compared to Pt/Ru. The observed difference in the kinetics of CO adsorption underlines the electronic effect in the surface catalytic activity due to modification of the electronic structure of surface platinum atoms by ruthenium. Correlation between FTIR and radiolabeling measurements indicated that the adsorption of CO from methanol is a very slow process at low potential but that the coverage by CO poison is greater at higher potential. Then, the results obtained from both analytical techniques (in situ IR Reflectance Spectroscopy and radioactive labeling method) displayed very good agreement and allowed us to validate them for the investigation of the methanol oxidation mechanism.
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Effect of the electrode structure on the electrocatalytic oxidation of low-weight alcohols. Applications to the dIRect alcohol fuel cell
1994Co-Authors: H. Laborde, J.-m. Léger, A. Rezzouk, C. LamyAbstract:The use of an electron conducting polymer, such as polyaniline (PAni), as a catalyst support, is a very convenient way to obtain highly dispersed electrodes for the electrooxidation of low-weight alcohols (methanol and ethanol). Such electrodes, containing very low amounts of platinum, can be modified by adding a second metal in order to promote the electrocatalytic activity of pure platinum. With Pt-Ru or Pt-Sn/PAni modified electrodes, a relative large negative shift of the oxidation potential was observed, particularly with ethanol, for which the electrooxidation starts at potentials as low as 0.2 V/RHE. Moreover a significant decrease of the poisoning phenomena was also observed. The nature of the adsorbed species and reaction products was also investigated by on-line liquid chromatography and in situ IR Reflectance Spectroscopy.
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Integrated electromodulated IR Reflectance Spectroscopy bands: Part 2: Methanol adsorbates at polycrystalline platinum and Pt(111) single-crystal electrodes in acid medium
Journal of Electroanalytical Chemistry, 1993Co-Authors: M.i.s. Lopes, Inês T.e. Fonseca, P. Olivi, Bernard Beden, Françoise Hahn, J.-m. Léger, Claude LamyAbstract:Using electromodulated IR Reflectance Spectroscopy (EMIRS), absorption spectra of adsorbed species resulting from the chemisorption of HCHO, HCOOH and methyl formate, HCOOCH3, on both polycrystalline and (111) platinum surfaces, were fIRst obtained in the range 1400–1900 cm−1, to cover completely the carbonyl stretching mode region. The same experimental conditions were used for all systems. EMIRS bands were integrated and analysed, using the procedure described in Part 1 (B. Beden, J. Electroanal. Chem., 345 (1993) 1). Characteristic frequencies were located precisely, allowing the spectral discrimination of several types of adsorbates. The same procedure was then used to follow the chemisorption of methanol on platinum in perchloric medium with time. As expected, formate species were found to dominate on the two types of platinum surface. However, during the initial stages of chemisorption, and particularly on the Pt(111) electrode, the formation of adsorbed methyl formate is likely. A mechanism is suggested, taking into consideration the possibility of surface reactions between adsorbates.
M.i.s. Lopes - One of the best experts on this subject based on the ideXlab platform.
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An in situ IR Reflectance spectroscopic study of the electro-oxidation of D-sorbitol on platinum
Electrochimica Acta, 1998Co-Authors: Luís Proença, M.i.s. Lopes, Inês T.e. Fonseca, Françoise Hahn, Claude LamyAbstract:Abstract An in situ infrared (IR) Reflectance spectroscopic study of the electrooxidation of d -sorbitol on polycrystalline platinum in perchloric acid medium was carried out by Fourier transform IR Spectroscopy (FTIRS), under the SNIFTIRS and SPAIRS variants. Additional information was obtained by electrochemically modulated IR Reflectance Spectroscopy (EMIRS). In situ IR spectra show that the electrooxidation of d -sorbitol on platinum proceeds via a dual-path mechanism involving both reactive and poisoning intermediates. Linearly and bridge-bonded CO, resulting from the dissociative adsorption of d -sorbitol, which were identified as the main poisoning species present at the surface, are fully oxidised to CO 2 at higher potentials. The superficial coverage in adsorbed CO was found to be function of the electrode potential. Moreover, the electrooxidation process can occur without breaking the initial molecule skeleton, indicating that molecular adsorption of d -sorbitol is also possible. d -glucono-(δ and γ)-lactones, D -glucose and CO 2 were identified as the main reaction products.
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Integrated electromodulated IR Reflectance Spectroscopy bands: Part 2: Methanol adsorbates at polycrystalline platinum and Pt(111) single-crystal electrodes in acid medium
Journal of Electroanalytical Chemistry, 1993Co-Authors: M.i.s. Lopes, Inês T.e. Fonseca, P. Olivi, Bernard Beden, Françoise Hahn, J.-m. Léger, Claude LamyAbstract:Using electromodulated IR Reflectance Spectroscopy (EMIRS), absorption spectra of adsorbed species resulting from the chemisorption of HCHO, HCOOH and methyl formate, HCOOCH3, on both polycrystalline and (111) platinum surfaces, were fIRst obtained in the range 1400–1900 cm−1, to cover completely the carbonyl stretching mode region. The same experimental conditions were used for all systems. EMIRS bands were integrated and analysed, using the procedure described in Part 1 (B. Beden, J. Electroanal. Chem., 345 (1993) 1). Characteristic frequencies were located precisely, allowing the spectral discrimination of several types of adsorbates. The same procedure was then used to follow the chemisorption of methanol on platinum in perchloric medium with time. As expected, formate species were found to dominate on the two types of platinum surface. However, during the initial stages of chemisorption, and particularly on the Pt(111) electrode, the formation of adsorbed methyl formate is likely. A mechanism is suggested, taking into consideration the possibility of surface reactions between adsorbates.
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Electrosorption of sorbitol at platinum electrodes: Effect of the superficial structure
Journal of Electroanalytical Chemistry, 1993Co-Authors: J.-m. Léger, Inês T.e. Fonseca, Bernard Beden, Françoise Hahn, Claude Lamy, M.f. Bento, M.i.s. LopesAbstract:Abstract The electrosorption of sorbitol was investigated at polycrystalline and single-crystal platinum electrodes in an acidic medium. The coverage degree and the number of electrons per site involved in the electro-oxidation of the adsorbed species coming from the sorbitol were estimated from voltammetric measurements carried out at high sweep rates and for adsorption times varying from 0.1 to 500 s. The adsorption process depends on the superficial structure. The electrode surface was never saturated by the organic species coming from sorbitol adsorption and the number of electrons per site was found to be around 3, though this decreased to about 2 after long adsorption times. One of the main adsorbed species present at the electrode surface for long adsorption times is linearly adsorbed CO, as confIRmed by in situ IR Reflectance Spectroscopy. The presence of other kinds of adsorbed species is also discussed.
Hui-zhen Zhang - One of the best experts on this subject based on the ideXlab platform.
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A Novel Silica Gel Adsorption/Near-Infrared Spectroscopic Method for the Determination of Hexanal as an Example of Volatile Compounds
Journal of Agricultural and Food Chemistry, 1997Co-Authors: Hui-zhen ZhangAbstract:The present research has demonstrated the feasibility of using silica gel adsorption/near-infrared (near-IR) Reflectance Spectroscopy to determine hexanal as an example of volatile compounds. Using a fIRst-derivative mathematical treatment for the near-IR spectra of hexanal adsorbed on silica gel provides better results than the raw near-IR spectra. The wavelengths from 1650 to 1790 nm show a linear relationship between fIRst-derivative near-IR Reflectance and hexanal contents on silica gel. The two best simple linear regression equations [YL = 7.89 × 10-6 + 1.711 × 10-4(XL); YH = 4.319 × 10-4 + 8.69 × 10-5(XH)] obtained from the regression equations of eight groups fit in lower hexanal contents ranging from 7.8 to 39 mg/10 g of Si and higher hexanal contents ranging from 39 to 546 mg/10 g of Si, respectively. The correlation coefficient between the near-IR-predicted value using the two equations and the added standard value of hexanal adsorbed on silica gel is 0.997. The relative errors were less than 9%...
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A Novel Silica Gel Adsorption/Near-Infrared Spectroscopic Method for the Determination of Hexanal as an Example of Volatile Compounds
Journal of Agricultural and Food Chemistry, 1997Co-Authors: Hui-zhen Zhang, Tung-ching LeeAbstract:The present research has demonstrated the feasibility of using silica gel adsorption/near-infrared (near-IR) Reflectance Spectroscopy to determine hexanal as an example of volatile compounds. Using...
