Ni-modified Mo ₂C catalysts for methane dry reforming

Dry reforming of methane with CO ₂ (DRM) was studied over Ni-Mo ₂C catalysts with Ni/Mo molar ratios of 1/3, 1/2, and 1/1 (denoted as Ni-Mo ₂C (1/3), Ni-Mo ₂C (1/2), and Ni-Mo ₂C (1/1), respectively) aiming to investigate the catalytic roles of Ni and the carbide. The results of XRD and XPS characterizations indicated that the carbonization process was promoted by the presence of Ni. The CH ₄-TPR and CO ₂-TPO over the fresh samples proved that CH ₄ dissociation was greatly enhanced by Ni. The Ni-Mo ₂C (1/2) catalyst showed the best catalytic activity and stability for CH ₄/CO ₂ (1/1) dry reforming. Above 80% of CH ₄ and CO ₂ conversions were maintained at 800 °C during a test run of 20 h at W/F = 0.3 g s cm ^-3. Characterizations of the spent samples revealed that the deactivation of Ni-Mo ₂C (1/1) was due to coke formation whereas that of Ni-Mo ₂C (1/3) was due to bulk oxidation of Mo ₂C into MoO ₂. Only at a Ni/Mo molar ratio of 1/2, a catalytic oxidation-reduction cycle could be established. It was suggested that Ni-Mo ₂C was a typical bi-functional catalyst. In CH ₄/CO ₂ dry reforming, the dissociation of CH ₄ was catalyzed by Ni, while the activation of CO ₂ took place on Mo ₂C. By regulating the molar ratio of Ni and Mo ₂C, a catalytic redox cycle could be established.