Activité et caractérisation des matériaux lamellaires comme catalyseurs pour la conversion de la biomasse

In order to evaluate the potential of lamellar materials based on niobium ortantalum oxides as catalysts, the solids HTaMoO6, HTaWO6 , HNbMoO6 and HNbWO6 werestudied. The intercalation ability and acidity of these materials was characterised using organicbases like n-alkylamines and pyridine. Their catalytic activity was evaluated 2,5-hexanediolcyclodehydration in the liquid phase and the intercalation of alcohols and diols were thus alsostudied. Raman spectroscopy was used in these various stages, notably for the operandocharacterisation in the liquid phase. HNbMoO6 and HTaMoO6 are the most active catalysts,while tungstates show a weaker activity and zirconium phosphates or Nb2O5 were nearlyinactive. This was explained by the different accessibilities of the diols to the interlamellar sites.The analysis of the reaction by Raman spectroscopy also necessitates an adapted treatment ofthe spectra in order to follow the adsorbed species and the modifications to the solid. Adsorbedspecies show a modification of the diol geometry. For the most active solids, reaction is relatedto the diol interactions with molybdenum conversely to tungstates, which confirms theincreasing difficulty of the diol to intercalate between the inorganic sheets.Afin d’évaluer le potentiel des matériaux lamellaires à base d’oxydes de niobiumet de tantale comme catalyseurs, les solides HTaMoO6, HTaWO6, HNbMoO6 et HNbWO6 ontété étudiés. La capacité d’intercalation et l’acidité de ces matériaux a été caractérisée en utilisantdes bases organiques telles que les n-alkylamines et la pyridine. Leur activité catalytique a étéévaluée pour la cyclodéshydratation du 2,5-hexanediol en phase liquide et l’intercalation desalcools et diols a donc aussi été étudiée. La spectroscopie Raman a été utilisée dans cesdifférentes étapes, et en particulier pour le suivi operando en phase liquide. HNbMoO6 etHTaMoO6 sont les catalyseurs les plus actifs, alors que les tungstates montrent une activité plusfaible, et les phosphates de zirconium ou Nb2O5 sont presque inactifs. Ceci a été expliqué parla différence d’accessibilité des diols aux sites interlamellaires. Le suivi de la réaction parspectroscopie Raman impose également un traitement adapté des spectres afin d’analyser lesespèces adsorbées et les modifications au solide. Les espèces adsorbées montrent unemodification de la géométrie du diol. Pour les solides les plus actifs, la réaction est liée à desinteractions du diol avec le molybdène à l’inverse des tungstates, ce qui confirme la plus grandedifficulté du diol à s'intercaler entre les feuillets

Activity and characterization of layered materials as catalysts for biomass conversion

Afin d’évaluer le potentiel des matériaux lamellaires à base d’oxydes de niobiumet de tantale comme catalyseurs, les solides HTaMoO6, HTaWO6, HNbMoO6 et HNbWO6 ontété étudiés. La capacité d’intercalation et l’acidité de ces matériaux a été caractérisée en utilisantdes bases organiques telles que les n-alkylamines et la pyridine. Leur activité catalytique a étéévaluée pour la cyclodéshydratation du 2,5-hexanediol en phase liquide et l’intercalation desalcools et diols a donc aussi été étudiée. La spectroscopie Raman a été utilisée dans cesdifférentes étapes, et en particulier pour le suivi operando en phase liquide. HNbMoO6 etHTaMoO6 sont les catalyseurs les plus actifs, alors que les tungstates montrent une activité plusfaible, et les phosphates de zirconium ou Nb2O5 sont presque inactifs. Ceci a été expliqué parla différence d’accessibilité des diols aux sites interlamellaires. Le suivi de la réaction parspectroscopie Raman impose également un traitement adapté des spectres afin d’analyser lesespèces adsorbées et les modifications au solide. Les espèces adsorbées montrent unemodification de la géométrie du diol. Pour les solides les plus actifs, la réaction est liée à desinteractions du diol avec le molybdène à l’inverse des tungstates, ce qui confirme la plus grandedifficulté du diol à s'intercaler entre les feuillets.In order to evaluate the potential of lamellar materials based on niobium ortantalum oxides as catalysts, the solids HTaMoO6, HTaWO6 , HNbMoO6 and HNbWO6 werestudied. The intercalation ability and acidity of these materials was characterised using organicbases like n-alkylamines and pyridine. Their catalytic activity was evaluated 2,5-hexanediolcyclodehydration in the liquid phase and the intercalation of alcohols and diols were thus alsostudied. Raman spectroscopy was used in these various stages, notably for the operandocharacterisation in the liquid phase. HNbMoO6 and HTaMoO6 are the most active catalysts,while tungstates show a weaker activity and zirconium phosphates or Nb2O5 were nearlyinactive. This was explained by the different accessibilities of the diols to the interlamellar sites.The analysis of the reaction by Raman spectroscopy also necessitates an adapted treatment ofthe spectra in order to follow the adsorbed species and the modifications to the solid. Adsorbedspecies show a modification of the diol geometry. For the most active solids, reaction is relatedto the diol interactions with molybdenum conversely to tungstates, which confirms theincreasing difficulty of the diol to intercalate between the inorganic sheets

Activité et caractérisation des matériaux lamellaires comme catalyseurs pour la conversion de la biomasse

In order to evaluate the potential of lamellar materials based on niobium ortantalum oxides as catalysts, the solids HTaMoO6, HTaWO6 , HNbMoO6 and HNbWO6 werestudied. The intercalation ability and acidity of these materials was characterised using organicbases like n-alkylamines and pyridine. Their catalytic activity was evaluated 2,5-hexanediolcyclodehydration in the liquid phase and the intercalation of alcohols and diols were thus alsostudied. Raman spectroscopy was used in these various stages, notably for the operandocharacterisation in the liquid phase. HNbMoO6 and HTaMoO6 are the most active catalysts,while tungstates show a weaker activity and zirconium phosphates or Nb2O5 were nearlyinactive. This was explained by the different accessibilities of the diols to the interlamellar sites.The analysis of the reaction by Raman spectroscopy also necessitates an adapted treatment ofthe spectra in order to follow the adsorbed species and the modifications to the solid. Adsorbedspecies show a modification of the diol geometry. For the most active solids, reaction is relatedto the diol interactions with molybdenum conversely to tungstates, which confirms theincreasing difficulty of the diol to intercalate between the inorganic sheets.Afin d’évaluer le potentiel des matériaux lamellaires à base d’oxydes de niobiumet de tantale comme catalyseurs, les solides HTaMoO6, HTaWO6, HNbMoO6 et HNbWO6 ontété étudiés. La capacité d’intercalation et l’acidité de ces matériaux a été caractérisée en utilisantdes bases organiques telles que les n-alkylamines et la pyridine. Leur activité catalytique a étéévaluée pour la cyclodéshydratation du 2,5-hexanediol en phase liquide et l’intercalation desalcools et diols a donc aussi été étudiée. La spectroscopie Raman a été utilisée dans cesdifférentes étapes, et en particulier pour le suivi operando en phase liquide. HNbMoO6 etHTaMoO6 sont les catalyseurs les plus actifs, alors que les tungstates montrent une activité plusfaible, et les phosphates de zirconium ou Nb2O5 sont presque inactifs. Ceci a été expliqué parla différence d’accessibilité des diols aux sites interlamellaires. Le suivi de la réaction parspectroscopie Raman impose également un traitement adapté des spectres afin d’analyser lesespèces adsorbées et les modifications au solide. Les espèces adsorbées montrent unemodification de la géométrie du diol. Pour les solides les plus actifs, la réaction est liée à desinteractions du diol avec le molybdène à l’inverse des tungstates, ce qui confirme la plus grandedifficulté du diol à s'intercaler entre les feuillets

Discriminating molybdate and tungstate layered materials by operando Raman spectroscopy at the solid-liquid interface

International audienceIn order to perform the characterization of liquid phase reactions catalysed by solid materials, several methodologies were developed using Raman spectroscopy. By following both the liquid and the solid-liquid interface, several layered materials could be discriminated. Indeed, molybdates or tungstates layered mixed oxides (with Nb or Ta oxides) show acidic properties that can catalyse several reactions including the conversion of polyalcohols. Therefore, these catalysts were extensively characterized not only initially to highlight their acidity and their capacity to favour molecular intercalation within their interlayers, but also to evaluate and monitor the catalysts under operando conditions. Layered molybdates, and HNbMoO6 in particular, proved to outperform the equivalent tungstates in hexanediol cyclodehydration, while tantalates were very similar to niobates. Our results show that while the moderate acidity of the molybdates is sufficient to perform this reaction, the overall catalytic activity is rather directly influenced by the accessibility of the reactant to the active sites in the interlayer

A comparison of layered materials used as catalysts for diols conversion

International audienc

A comparison of layered materials used as catalysts for diols conversion

International audienc

A comparison of layered materials used as catalysts for diols conversion

International audienc

A comparison of layered materials used as catalysts for diols conversion

International audienc

Acute respiratory failure secondary to a cervical goitre in a pregnant woman: a case report

Abstract Background Pregnancy constitutes a significant factor in thyroid hypertrophy and can rarely progress to respiratory distress. We describe case of pregnant woman with acute respiratory distress following a tracheal compression due to goiter, quickly resulting in respiratory arrest, requiring emergency orotracheal intubation and thyroidectomy. Case presentation A pregnant woman with a growing goiter was referred to the hospital with a respiratory difficulty. During the examination, we found a large homogeneous goiter. The patient showed signs of respiratory exhaustion with bradypnea and pulmonary auscultation revealing decreased ventilation of the two pulmonary fields. The evolution quick led to respiratory arrest. The patient was rapidly intubated, which saved her. A thoracic computed tomography was performed and revealed a large goiter, compressing the trachea in its thoracic area and oppressing the vascular structures. Obstetrical ultrasound was normal. Thyroidectomy was decided after the patient’s preparation. After 24 h, the patient was successfully extubated without incident and the postoperative period was uneventful. Conclusion Airway obstruction during pregnancy secondary to goiter is rare but can be fatal. Early diagnosis might have avoided the evolution towards the respiratory failure. Prevention requires early surgery preferably before pregnancy or in our case a surgery in the second trimester