Catalytic Oxidative CO2 Reforming of Methane Over Bimetallic Pd-Ni Catalyst

Abstract

Oxidative CO2 reforming of methane (OCRM), which is combination of CO2 (dry) reforming of methane (DRM) and partial oxidation of methane (POM), has more advantages for syngas production than individual DRM and POM since it can reduce the total energy requirement and amount of carbon deposition on catalyst. This thesis reports the development of a stable and active bimetallic catalyst for OCRM reaction. A fundamental understanding causing high activity and stability of the Pd-Ni catalyst was explored in depth in this thesis. The catalytic activity of Pd-Ni catalyst in OCRM reaction is higher than either Ni or Pd catalyst, due to the formation of bimetallic particles. Pd-Ni/Y2O3 and Pd-Ni/Al2O3 catalysts show very high CH4 and CO2 conversions due to the formation of metal-support compound on these catalysts. However, Pd-Ni/Y2O3 catalyst has higher stability than the Pd-Ni/Al2O3 catalyst due to the presence of surface b-oxygen species and ability of Y2O3 to form oxycarbonate species. The surface b-oxygen species are found to promote cracking of C-H bond in CH4 while the oxycarbonate species can oxidize the deposited carbon, respectively, hence leading to the stability of the Pd-Ni/Y2O3 catalyst. Further investigation shows that the formation of Pd-Y2O3 compound on the Pd(C)-Ni/Y2O3 catalyst (Pd-Ni/Y2O3 catalyst prepared from PdCl2) is found to play important roles on catalyst activity and stability. Moreover, the synthesized Y2O3 particles with smaller crystal size have higher surface oxygen mobility, resulting in higher catalytic activity and lower carbon deposition rate on Pd-Ni/Y2O3 catalyst. Two kinetic models for OCRM reaction over Pd-Ni/Y2O3 catalyst have been developed using Langmuir-Hinshelwood (LH) approach based on proposed reaction mechanism and those of individual reactions probably occurred during OCRM reaction. A good agreement was obtained between experimental and model for one of the proposed kinetic models.