The Synergic Effect of h -MoO 3 , α-MoO 3 , and β-MoO 3 Phase Mixture as a Solid Catalyst to Obtain Methyl Oleate

• Published in: ACS applied materials & interfaces 2024-11, Vol.16 (44), p.60103-60121
• Main Authors: Medeiros Leão, Gabrielle Sophie, Silva Ribeiro, Marcos Daniel, Filho, Rubens Lucas de Freitas, Saraiva, Libertalamar Bilhalva, Peña-Garcia, Ramón R, Teixeira, Ana Paula de Carvalho, Lago, Rochel Montero, Freitas, Flávio Augusto, de Sá Barros, Silma, Junior, Sérgio Duvoisin, Ruiz, Yurimiler Leyet, Nobre, Francisco Xavier
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.4c08804

Extensive research in the last few decades has conclusively demonstrated the significant influence of experimental conditions, surfactants, and synthesis methods on semiconductors' properties in technological applications. Therefore, in this study, the synthesis of molybdenum oxide (MoO ) was reported by the addition of 2.5 (MoO _2.5), 5 (MoO _5), 7.5 (MoO _7.5), and 10 mL (MoO _10) of nitric acid, obtaining the respective concentrations of 0.6, 1.10, 1.6, and 0.6 mol L . In this study, all samples were synthesized by the hydrothermal method at 160 °C for 6 h. The materials obtained were structurally characterized by X-ray diffraction (XRD) and structural Rietveld refinement, Raman spectroscopy, and infrared spectroscopy (FTIR), confirming the presence of all crystallographic planes and bands associated with active modes for the pure hexagonal phase ( -MoO ) when the solution's concentration was 0.6 mol L of nitric acid. For concentrations of 1.10, 1.60, and 2.10 mol L , the presence of crystallographic planes and active modes associated with the formation of mixtures of molybdenum oxide polymorphs was confirmed, in this case, the orthorhombic, monoclinic, and hexagonal phases. X-ray photoelectron spectroscopy reveals the occurrence of the states Mo , Mo , and Mo , which confirm the predominance of the acid Lewis sites, corroborating the analysis by adsorption of pyridine followed by characterization by infrared spectroscopy. The images collected by scanning electron microscopy confirmed the information presented in the structural characterization, where microcrystals with hexagonal morphology were obtained for the MoO _2.5 sample. In contrast, the MoO _5, MoO _7.5, and MoO _10 samples exhibited hexagonal and rod-shaped microcrystals, where the latter morphology is characteristic of the orthorhombic phase. The catalytic tests carried out in the conversion of oleic acid into methyl oleate, using the synthesized samples as a heterogeneous catalyst, resulted in conversion percentages of 52.5, 58.6, 69.1, and 97.2% applying the samples MoO _2.5, MoO _5, MoO _7.5, and MoO _10, respectively. The optimization of the catalytic tests with the MoO _10 sample revealed that the conversion of oleic acid into methyl oleate is a thermodynamically favorable process, with a variation in the Gibbs free energy between -67.3 kJ mol and 83.4 kJ mol as also, the energy value of activation of 24.6 kJ mol , for the temperature range from 80 to 140 °C, that is, from 353.15 to 413.