Conversion of Spent Transformer Oil Into H ₂ ‐Rich Syngas via Microwave‐Induced Steam Reforming Over Ni─Co Catalysts Supported on Fe‐Rich Diatomite

Spent transformer oil (STO) represents a complex industrial liquid waste that poses significant environmental challenges. In this work, STO was converted into hydrogen‐rich synthesis gas via catalytic microwave‐induced steam reforming over monometallic (10%Ni/diatomite, 10%Co/diatomite) and bimetallic (5%Ni5%Co/diatomite) catalysts. The diatomite contained an inherent Fe ₂ O ₃ content of about 9.25 wt.%, which likely contributed to the catalytic activity in addition to its role as a thermally stable and porous support. The operating conditions were optimized without catalyst, and increasing the microwave power from 600 to 840 W and the steam‐to‐carbon ratio up to 3.6 enhanced both the H ₂ yield and carbon conversion through the promotion of endothermic reforming reactions. Among the catalysts tested, the bimetallic 5%Ni5%Co/diatomite achieved the highest H ₂ yield of 98.80 mmol g ⁻¹ _STO and carbon conversion of 70.58%, with a H ₂ /CO ratio of 2.83. The initially oxidized metals were reduced in situ to a metallic Ni─Co alloy during the reaction. Collectively, these findings highlight the potential of Fe‐rich diatomite as a low‐cost, naturally abundant support for converting hazardous waste oil into hydrogen‐rich syngas via microwave‐induced steam reforming.