BIO-INSPIRED MOF-BASED CATALYSTS FOR METHANE VALORIZATION

SSCI-VIDE+ING+KBA:JEC; International audience; Summary: Catalytic Methane Partial Oxidation to Methanol reaction represents a big challenge for both industrial and academic research because i) it is a concrete, sustainable solution to GHGs emissions, whose Methane is a major actor, ii) it is difficult to achieve hitherto high selectivity of the desired oxygenated intermediates and low COx products, iii) methanol is a clean and high-added value fuel source, whose market is in continuous expansion[1]. Among the low T (< 300°C) and pressure (atmospheric) catalytic routes, a valuable approach is the use of single-component catalysts which mimic the Methane Monooxygenase (MMO) enzyme structures, consisting in binuclear centers of Fe or Cu, that so far have been recreated in zeolites to benefit of their greater external surface area[2]. Nevertheless, the major drawbacks in using any zeolite are related to the hydrophilicity of the support, which is detrimental for desorption of products, and the need of a looping system to increase methane conversion which includes solvent extraction, recycling of unreacted methane, and sites reactivation. To circumvent some of these issues, the anchorage of the active metal into a Metal-Organic Framework (MOF) by post-synthetic treatment has been recently reported[3], demonstrating the potential of such class of materials, although a rational design of performing MOF-based catalyst is still needed. In this work, the recreation of the enzyme type structures with atomically dispersed atoms, specific coordination, and controlled loading has been achieved i) by substitution of Zn nodes with Fe inside hydrophobic zeolite imidazolate frameworks (ZIF) (Figure 1), or ii) by Cu immobilization in UiO-66. These strategies lead to isolated sites onto a porous support which itself acts as a transient nanoreactor to achieve higher methanol selectivity. The physico-chemical properties of each material synthesized have been determined by SEM-EDX, XRD, N2 sorption isotherms, and XPS techniques. Their catalytic properties have been then evaluated in Methane Partial Oxidation reaction under mild conditions (130-170 °C, 0.5-4 bar) using a CH4/O2 mixture (2-3/1 v/v%) in a Plug Flow Reactor configuration, and compared with those of Fe/ and Cu/ ZSM-5 as reference catalysts.