The role of defect-modulated HKUST-1 MOF nodes in non-oxidative ethanol dehydrogenation: an observed phenomenon of catalyst transfiguration

Abstract

Bioethanol production from agricultural residues has emerged as an important process of biomass valorization. The production of acetaldehyde from bioethanol has also started gaining ground. Since Cu-based catalysts are well-known for their ability to catalyse ethanol dehydrogenation, we have used a defect-modulated Cu-based metal–organic framework (MOF), HKUST-1, for obtaining mechanistic insights into the process. Defect-modulation in the form of a missing linker creates an easily accessible dual-atom site which can simultaneously participate in catalysing the reaction. Although ethanol dehydrogenation to ethylene competes with acetaldehyde production over both the defective HKUST-1(H) and HKUST-1(OH) MOF nodes, acetaldehyde formation occurs selectively. However, HKUST-1(OH) could not be regenerated at the end of the acetaldehyde formation pathway; HKUST-1(OH) ultimately transformed to HKUST-1(H) at the end of the cycle. This led to the introduction of the term ‘catalyst transfiguration’ where the catalyst, although transfigured, retains its ability to catalyse the reaction. Since, the HKUST-1(H) MOF node has the ability to selectively transform ethanol to acetaldehyde, we can safely conclude that the use of HKUST-1(OH) will not cause acetaldehyde formation to come to a halt and the reaction can go on beyond the first catalytic cycle. Thus, both the defective MOF nodes can selectively transform ethanol to acetaldehyde.