Steam and steam-oxygen reforming of methane on NiAl2O3-MxOy (M: La, Ce) based monoliths: effects of catalyst and reaction mixture composition

摘要

The effect of rare earth oxides as modifying additives within Ni-MxOy-Al2O3 (M: La, Ce) based catalysts, supported on cordierite monoliths, and the influence of the H2O/CH4 ratio as well as O-2 content in the gas reaction mixture on the catalyst activity and selectivity in the steam and steam-oxygen reforming of methane are studied including by means of infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and quasi-equilibrium thermal desorption of ammonia as a probe molecule. The introduction of CeO2 and La2O3 into the catalyst composition as well as oxygen to the reaction mixture of methane steam reforming is shown to enable reducing the water vapor content (up to H2O/CH4 ratios close to stoichiometric) required for stable catalyst operation while maintaining high CH4 conversions and hydrogen yields. The carbon dioxide amount as a by-product in the syngas produced considerably decreases in the presence of Ni-CeO2-Al2O3/cordierite catalysts, which may be explained by slowing the water-gas shift reaction. The introduction of ceria into the catalyst composition leads to a slight decrease in the total number of Lewis acid sites (LAS), whereas the addition of lanthanum oxide causes their increase, which we attribute to formation of two LAS types on the surface of Ni-Al2O3-La2O3/cordierite: lanthanum cations and aluminum ones.