Síntese mecanoquímica solvent-free de La2NiO4 para aplicação na reforma a seco do metano: análise termodinâmica e contribuições na instrumentação de medidas de vazão gasosa.

Abstract

Dry reforming of methane enables the production of synthesis gas (syngas) with an H₂:CO ratio of approximately 1:1 from CH₄ and CO₂, both greenhouse gases, using nickel-based catalysts. In this work, a perovskite route was employed, with La₂NiO₄ reduced in situ to Ni/La₂O₃, aiming to propose a synthesis route that is more economical and sustainable than the conventional one through the milling of reactants without water. To comprehensively understand the system and the materials, thermodynamic calculations based on equilibrium constants and Gibbs free energy were performed and were found to be in agreement with experimental and literature data, allowing the inference of kinetic characteristics. During the study, the gas flow rate measurements were also automated in order to ensure reproducible tests, resulting in the development of an instrument that was incorporated into the laboratory and shows potential for patenting. The materials were synthesized via the citrate method (reference material) and by ball milling, varying the nickel precursors (oxide or nitrate) and the use of a milling aid (citric acid). To differentiate the materials, characterization techniques such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), temperature-programmed surface reaction (TPSR), nitrogen adsorption, and post-test temperature-programmed oxidation were employed, in addition to evaluating their performance in a continuous-flow reaction for 20 h. The influence of the nickel precursor and synthesis method on catalytic performance was evidenced through characteristics such as nanoparticle diameter and crystallite size. The reference materials and those obtained from nitrate precursors proved to be promising, as they were active and stable for 20 h. The best material obtained exhibited H2/CO ratio closer to 1, higher H₂ and CO yield, and up to 70% water savings during synthesis.