Catalytic dry reforming of natural gas for the production of chemicals and hydrogen

摘要

Carbon dioxide reforming of methane to synthesis gas was studied over Ni-based catalysts. It is shown that, in contrast to other Ni-based catalysts which exhibit continuous deactivation with time-on-stream, the rate over the Ni/La_2O_3 catalyst increases during the initial 2-3 h of reaction and then tends to be essentially invariable, displaying very good stability. X-ray diffraction, hydrogen and CO uptake studies, as well as high-resolution TEM indicate that, under reaction conditions, the Ni particles are partially covered by La_2O_2CO_3 species which are formed by interaction of La_2O_3 with CO_2. Catalytic activity occurs at the Ni-La_2O_2CO_3 interface, while the oxycarbonate species participate directly by reacting with deposited carbon, thus restoring the activity of the Ni sites at the interface. XPS and FTIR studies provide evidence in support of this mechanistic scheme. It was also found that methane cracking on Ni sites and surface reaction between deposited carbon and oxycarbonate species are the rate determining steps in the reaction sequence. A kinetic model is developed based on this mechanistic scheme, which is found to predict satisfactorily the kinetic measurements.