Preparation and characterization of catalysts based on nickel niobate modified with Mg, Ca or Sr for hydrogen production

The Brazil is the world's largest producer of niobium, which among its many applications has been highlighted its use as a component of nickel catalysts used to obtain hydrogen from organic compounds such as methane and ethanol [1-3]. Based on these aspects, this work aimed to prepare and characterize catalysts based on nickel niobate (NiNb), modified with alkaline earth metals (Mg, Ca and Sr), to evaluate the effect of these dopants on the properties of the catalyst. The samples were prepared by coprecipitation method of the metallic precursors solutions, followed by dry and calcination at 800 °C. The obtained solids were characterized by X-ray diffraction (XRD), specific area measurement, scanning electron microscopy (SEM), temperature programmed reduction (TPR) and acidity measurement by ammonia temperature programmed desorption (TPD). Results showed that metals addition changed the structural properties of the solids, with the formation of nickel oxide and of niobates in all samples (Fig. 1), BET results showed low specific areas values (3-6 m2g-1) typical of niobium oxides. Magnesium effect was the most pronounced, since this one, apparently incorporated to the nickel niobate structure (Fig. 1), increased the metal/niobium oxide interaction, making it difficult to reduce nickel species, as showed in Fig. 2. On the other hand, its presence contributed to increasing the specific area (from 4 to 6 m2g-1) and the acidity (from 3 to 13 μmolg-1) of the nickel niobate.