Dry Reforming of Methane to Produce Syngas over Ni-Based Bimodal Pore Catalysts
CommitteeTo, Suminto D. Filip
Priddy, Lauren B.
Mlsna, Todd E.
Dry reforming of methane is an important reaction to generate syngas from two greenhouse gases. The syngas can be used in Fishcher-Tropsch synthesis to produce value-added chemicals. Chapter I reviews the catalytic conversion of methane and carbon dioxide to syngas, including DRM reaction chemistry, catalysts used in this process, catalyst deactivation, and the kinetics of DRM reaction. Chapter II discusses the development of bimodal pore NiCeMgAl catalysts for DRM reaction. Bimodal pore NiCeMgAl catalysts were synthesized via the refluxed co-precipitation method and systematically investigated the influence of active metal loading, calcination temperature, reduction temperature and gas hourly space velocity (GHSV) on the catalytic performance of DRM reaction. The Ni15CeMgAl sample with 15 wt% NiO loading was found to be active enough at 750 °C with a high CH4 conversion of 96.5%. The proper reduction temperature for the NiCeMgAl catalyst is either 550–650 °C or 850 °C. Higher calcination temperature favors the formation of NiAl2O4 and MgAl2O4 spinel structures. Compared with non-bimodal pore NiCeMgAl catalyst, bimodal pore NiCeMgAl catalyst has a longer stability in the feed gas without dilution. In chapter III, the kinetic behavior of bimodal pore NiCeMgAl catalyst for DRM reaction was investigated after the elimination of external and internal diffusion effects in a fixed-bed reactor as a function of temperature and partial pressures of reactants and products. A Langmuir-Hinshelwood model was developed assuming that the carbon deposition is ignorable but the RWGS reaction is non-ignorable and the removal of adsorbed carbon intermediate is the rate-determining step. A nonlinear least-square method was applied to solve the kinetic parameters. The derived kinetic expression fits the experimental data very well with a R2 above 0.97, and predicts the products flow rate satisfactorily. Chapter IV documents the results of in situ XRD study on the NiMgAl catalyst for DRM reaction. The phase evolution of a NiMgAl oxide catalyst at the reduction stage was qualitatively analysed and quantitatively determined by employing the continuous changes in XRD intensity and TPR information. The stable crystallite size of both active metal and spinel support is responsible for the long stability of NiMgAl catalyst without carbon deposition during the DRM reaction.