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.