Catalisadores Ni/SBA-15 com adição dos promotores aplicados a tri reforma do metano

Abstract

Tri-reforming of methane (TRM) is a combination of steam and dry reforming and partial oxidation of methane reactions in the same reactor. Since it occurs at high temperatures and has water vapor in the reactor feed, TRM needs catalysts with thermal and hydrothermal stability, high oxygen storage capacity, resistance to carbon formation, and a high surface area. Aiming all these properties, Ni/SBA-15 catalysts promoted with CeO2, ZrO2, MgO, (CeZr)O2 were synthesized by two different synthesis methods: i) promoters impregnated on SBA-15 support which was already synthesized and calcined; ii) promoters incorporated into the SBA-15 structure during synthesis. The precursors were characterized with thermogravimetric and thermodifferential analysis, X-ray diffraction (XRD), nitrogen physisorption, temperature programmed reduction with hydrogen (TPR), temperature programmed desorption with carbon dioxide, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The formation of the SBA-15 structure in all materials was confirmed by XRD analysis. Nevertheless, the incorporated catalysts presented a higher degree of ordering in the pores construction than in the impregnated ones. Through TPR and XPS analyses, it was verified the existence of a strong interaction between nickel and support, which is increased with the presence of promoters. The TRM catalytic tests were carried out at 750 °C for five hours, with reagents being fed into the reaction stoichiometry (3CH4:1CO2:1H2O:0.5O2). In this reaction condition, catalysts promoted with (CeZr)O2 and MgO showed the highest methane and carbon dioxide conversions. All catalysts were also subjected to TRM in water scarcity at 750 °C for five hours (3CH4:1CO2:0.1H2O:0.5O2). In this reaction atmosphere, there was an increase in carbon dioxide conversion and inhibition of methane conversion for all samples. Through thermogravimetric analysis, it was observed that the incorporated catalysts presented greater amounts of carbon depositions on their surface than in the impregnated ones. However, even generating more carbon in the incorporated ones, exhibited better stability during the five reaction hours.