Monometallic and Bimetallic Ni–Cu Catalysts Supported on Gd-Doped CeO2 for Hydrogen-Rich Syngas Production via Methane Partial Oxidation

Partial oxidation of methane is a highly attractive route for hydrogen-rich syngas production, provided that high H2 yields and H2/CO ratios above 3 can be achieved. Herein, we demonstrate that precise compositional tuning of Ni–Cu bimetallic catalysts supported on Gd-doped CeO2 enables direct control over defect chemistry and reaction pathways in partial oxidation of methane. A systematic investigation of Ni/Cu ratios was conducted to elucidate composition–structure–activity relationships using X-ray diffraction, Raman spectroscopy, temperature-programmed reduction/oxidation/desorption, and thermogravimetric analysis. While monometallic 5%Ni/GDC and promoted 1%Re4%Ni/GDC exhibited high methane conversion, they failed to deliver optimal hydrogen selectivity. In contrast, introducing Cu within a narrow compositional window fundamentally altered the reaction mechanism. The 2.5%Ni2.5%Cu/GDC catalyst showed limited oxygen vacancy formation and pronounced carbon deposition, leading to inferior catalytic performance. Remarkably, the 3.5%Ni1.5%Cu/GDC catalyst maximized both oxygen vacancy density and surface basicity, thereby selectively activating CO2- and H2O-assisted oxidation routes and enforcing the exclusive dominance of indirect POM pathways. This defect-mediated pathway control effectively decoupled methane activation from hydrogen-consuming side reactions while simultaneously promoting hydrogen-forming, CO-consuming reactions, most notably the water–gas shift reaction. As a result, the optimized 3.5%Ni1.5%Cu/GDC catalyst achieved an H2 yield of 84% with an H2/CO ratio of 3.11 and maintained stable operation for 40 h on stream at 600 °C. These findings establish Ni–Cu compositional tuning as a powerful strategy for defect engineering and reaction pathway regulation, providing new design principles for efficient and durable partial oxidation of methane catalysts targeting hydrogen-rich syngas production.