Estudio mecanístico mediante espectroscopía infrarroja in situ de la oxidación selectiva de metanol sobre catalizadores de molibdeno y vanadio.
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Date
2025
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Universidad de Concepción
Abstract
Methanol oxidative dehydrogenation on titania supported metal oxide catalysts was studied to clarify different mechanistic proposals reported in the literature. Operando spectroscopic and isotopic transient experiments under controlled reaction conditions, combined with correlations between catalyst structure and product distribution, revealed how the nature of redox sites governs the methyl formate formation and integrates the reaction pathways into a coherent framework.
Sub-monolayer MoO3/TiO2 and V2O5/TiO2 catalysts, dominated by highly dispersed interfacial M–O–Ti linkages (M = Mo, V), stabilize formate-type intermediates which favor methyl formate production through the formate–mediated route. In contrast, catalysts featuring crystalline M–O–M domains promote the hemiacetal intermediate, where less stabilized intermediates lead directly to methyl formate and dimethoxymethane formation. These results indicate a common mechanistic framework for both Mo– and V–based systems, in which the dominant pathway is selectively expressed depending on the nature and distribution of redox sites rather than on the metal identity itself.
Isotopic labeling and transient experiments rule out extensive methoxy exchange and the Tishchenko pathway for methyl formate formation, under the studied conditions. Differences in intermediates stabilization, active sites distribution, and kinetic isotope effects account for the observed variations in reaction orders and selectivity.
Overall, the study demonstrates that the formation of oxygenates in methanol oxidative dehydrogenation critically depends on the type of redox site involved, establishing a structural – mechanistic framework that rationalizes the behavior of MoO3/TiO2 and V2O5/TiO2 catalysts and can be extended to other reducible oxide systems engaged in selective oxidation reactions.
Description
Tesis presentada para optar al grado de Magíster en Ciencias de la Ingeniería con mención en Ingeniería Química.
Keywords
Espectroscopía infrarroja, Catalizadores, Oxidación, Metanol