Produção de hidrogênio a partir da reforma a seco metano utilizando perovskitas LaNiO3 como precursores catalíticos: da análise bibliométrica ao machine learning

Abstract

Dry reforming of methane (DRM) is a catalytic reaction that uses two greenhouse gases (CH4 and CO2) to produce syngas, a mixture of H2 and CO. A bibliometric analysis on perovskites synthesized by the hydrothermal method was carried out and revealed that LaNiO3 has been employed as a catalytic precursor in DRM. However, this bibliometric analysis also showed a scarcity of studies directly relating synthesis parameters to morphology and catalytic activity. Therefore, the objective of this study is to investigate the influence of variables such as pH (9–13), time (6–24 h), temperature (160–200 °C), pressure (autogenous–85 bar), and the use of soft templates (cetyltrimethylammonium bromide and citric acid) on the morphology of LaNiO3 synthesized via the hydrothermal method, and to evaluate the relationship between these parameters and performance in DRM. A preliminary study indicated that pH is a key variable in the synthesis of LaNiO3, influencing particle morphology and, consequently, catalytic performance. Based on the bibliometric analysis and the preliminary results, a full factorial design of experiments (DoE) combined with machine learning (ML) was applied to explore the interactions between synthesis and reaction variables, as well as catalyst properties and performance. The results showed that the DRM reaction temperature was the most significant factor affecting catalytic performance, with higher temperatures (800 °C) leading to greater H2 yields (74–80%). Moreover, higher reaction temperatures also resulted in lower carbon deposition; however, the deposited carbon was more ordered (ID/IG = 0.56–0.79) and more crystalline (48–68 nm), making its removal and catalyst regeneration more difficult. The synthesis pH also proved to be a fundamental variable, where a more alkaline pH (13) positively influenced H2 yield (up to 10% higher) and negatively impacted carbon deposition (>57 wt%). The highest H2 yields were obtained with fresh catalysts containing between 20% and 100% of the LaNiO3 phase, associated with crystallite sizes in the range of 25 to 35 nm. The highest carbon depositions were observed in fresh catalysts containing between 60–100% of the LaNiO3 phase, small crystallite sizes (<30 nm), high reduction degrees (>60%), and low reduction temperatures (<540 °C). Finally, the synergistic effect between pH and synthesis pressure was also evaluated, identifying that the sample synthesized at pH 9 under 85 bar exhibited the best performance, with high H2 yield (76–77%) and moderate carbon deposition (20.43 wt%).