Avaliação de catalisadores Níquel-Diatomita promovidos com Boro ou Cério na reação de Reforma a Seco do Metano

Abstract

Greenhouse gases, particularly methane and carbon dioxide, represent a significant environmental concern. Dry Reforming of Methane (DRM) is a technology that can mitigate these impacts by converting these gases into syngas (CO and H₂), which is useful for the production of methanol, ammonia, and in Fischer-Tropsch synthesis. The choice of catalytic support, active phase, and promoters is crucial for the efficiency and stability of the catalysts. Nickel catalysts are commonly used due to their low cost, despite their susceptibility to coke formation, necessitating improvements in their formulation. Diatomite, a natural form of silica, emerges as an efficient support due to its textural properties and thermal stability. Promoters such as cerium (Ce) and boron (B) have been tested to improve the stability and activity of the catalysts. Ce facilitates carbon removal and improves nickel dispersion, while B enhances resistance and reduces coke formation. The catalysts were synthesized using diatomite as the support, Ni as the active phase, and Ce and B promoters in different concentrations. The synthesized materials were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Nitrogen Physisorption, and Temperature-Programmed Reduction (TPR). The DRM performance was evaluated in terms of CH₄ and CO₂ conversion, H₂ and CO yield, and the H₂/CO ratio in stability and activity tests. Post-test catalysts were characterized using XRD and Thermogravimetric Analysis (TGA) to assess coke formation. XRD results demonstrate that the impregnation of materials resulted in the formation of the active Nickel phase. TPR analysis showed that catalysts containing Boron increased the reduction temperature of the catalyst, hindering the activation process, while those promoted by Cerium maintained behavior similar to the Ni-Diatomite catalyst. Regarding DRM performance, catalysts promoted with 2% of each promoter showed significant improvements in stability after 15 hours of testing. In terms of activity, Boron promotion decreased activity by increasing the activation energy of the Methane dehydrogenation reaction on the metallic Ni surface, whereas Cerium promotion enhanced activity. TGA results indicate that the promoted catalysts reduced coke formation, with Boron-promoted materials showing 17% and 24% less coke compared to Ni-Diatomite. The results demonstrate that the combination of diatomite, Ni, and Ce and B promoters can create promising materials for DRM catalysis.