Assessing the environmental performance of NADH regeneration methods: A cleaner process using recyclable Pt/Fe3O4 and hydrogen

Cofactor (reduced) Nicotinamide Adenine Dinucleotide (NAD(P)H) is an energy carrier in enzymatic redox reactions that are employed for the synthesis of valuable chemicals and pharmaceuticals. The high cost of NAD(P)H makes it impractical to use in stoichiometric amounts in industrial processes. This has led to the development of a variety of methods for NAD(P)H regeneration. In this work, process cleanliness of the current NADH recycling systems was evaluated using E-factor (kgwaste/kgNADH) as a green chemistry metric. The E-factor obtained, depending on the process method, reaches values higher than 20000, where non-recyclable agents, including sacrificial hydride/electron donors, catalysts and electron mediators, alongside by-products (from cosubstrates), account for the overall waste. A promising alternative methodology for NADH regeneration using H2 and recyclable Pt/Fe3O4 is presented and characterisation performed by temperature-programmed reduction (TPR), nitrogen adsorption (surface area/porosity), powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) is used to elucidate observed performance. The Pt/Fe3O4 system at room temperature delivers a turnover frequency of 20 h-1 and the catalyst can be recycled for reuse, producing a significantly low level of waste (E-factor = ˜1).