New multifunctional metal-organic framework catalysts for mild oxidation of methane to methanol

• Grant number: 21/09775-1
• Support type: Scholarships in Brazil - Post-Doctorate
• Effective date (Start): October 01, 2021
• Effective date (End): September 30, 2023
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Inorganic Chemistry
• Principal researcher: Dalmo Mandelli
• Grantee: Luana dos Santos Andrade
• Home Institution: Centro de Ciências Naturais e Humanas (CCNH). Universidade Federal do ABC (UFABC). Ministério da Educação (Brasil). Santo André , SP, Brazil
• Associated research grant: 18/01258-5 - Novel chemical catalytic and photocatalytic processes for the direct conversion of methane and CO2 to products, AP.TEM

Abstract

The oxidation of methane to methanol catalyzed by metal-organic frameworks (MOFs) and derived materials still remains unexplored but represents a highly promising area of research. MOFs are porous crystalline coordination compounds consisting of infinite lattices built up of the inorganic secondary building units (SBUs, metal ions or clusters) and organic linkers (e.g., polycarboxylates, polypyridines). The flexibility with which the constituents' geometry, size, and functionality can be varied has already resulted in over 20,000 different MOFs. Their surface areas can be as high as 10,000 m2 g-1, which significantly exceeds other porous materials and catalysts, such as zeolites and activated carbons. Additionally, the permanent porosity, chemical and thermal stability, and synthetic tunability displayed by MOFs makes them very appealing for catalytic applications. In particular, some MOFs show high thermal stability ranging from 250 to 500 °C. Literature has shown that ethane is selectively oxidized to ethanol on Fe-containing MOFs at gas-phase environment, indicating that these materials can potentially be selective to the production of methanol by methane oxidation, although MOFs capable of activating methane are still very scant. Hence, in this pos-doc project, we propose the synthesis and catalytic investigation of new multifunctional Cu and Fe-based MOFs toward the selective oxidation of methane to methanol. The main goal of determining a group of candidate materials, with physical and chemical features adequately characterized. Aspects such as the specific activity, selectivity, and oxidation mechanisms will be the object of study for each material, in order to improve the catalytic activity and define optimized conditions. A set of new Cu, Zr, Ce and Fe-based MOFs (exploring the nature of the metal center and different types of organic linkers) will be prepared by hydrothermal and self-assembly methods and fully characterized by standard methods, including by single crystal X-ray diffraction and topological analysis in addition to thermal stability, porosity and gas sorption studies. The most promising MOFs will be screened as heterogeneous catalysts for the oxidation of methane under mild conditions, aiming at gaining a systematic knowledge on the effects of chemical and physical properties of these materials and the corresponding kinetic and mechanistic features. The obtained MOF catalysts will be tested in flow and batch reactors and computational studies will be performed. Air, O2 and/or H2O2 will be explored as standard oxidants. A competitive oxidation of methane in the presence of ethane, propane, and/or butane will also be attempted, aiming at a conversion of raw natural gas fractions and establishing an influence of the presence of other light alkanes on the methane oxidation. Porosity and potential selective sorption characteristics of the selected MOFs will also be explored to find further possible applications of porous MOFs as selective adsorbents for purification of natural gas (e.g., from C2-C4 alkanes and CO2) or selective capture of its components. A special emphasis will be given to the development of smart or multifunctional MOF catalysts, wherein metal nodes with a recognized activity in oxidation catalysis (e.g., Cu, Fe - present in the active sites of methane monooxygenases) will be coupled with organic linkers (e.g., N-heteroaromatic carboxylates) that can act as co-catalysts in such oxidation reactions, thus leading to a potential synergic effect. (AU)