Relação entre estrutura e atividade catalítica do cobre na hidrogenação de CO2 para formação do metanol

Abstract

In the context of the commitments made under the Paris Agreement to reduce greenhouse gas emissions and limit the global temperature increase to 1.5 °C above pre-industrial levels by mid-century, there is a clear need to transition current energy systems and to develop effective technologies for carbon dioxide (CO2) utilization. Among the strategies under investigation, the hydrogenation of CO2 to methanol has attracted considerable attention, both as a means of mitigating atmospheric CO2 and as a route to convert it into value-added chemicals. Methanol is a key commodity in the chemical industry, with global production exceeding 90 million tons in 2025. It is widely used as a solvent and as a feedstock for the synthesis of numerous chemical products. A variety of catalysts have been explored for methanol synthesis via CO2 hydrogenation, with copper-based systems consistently showing the most promising performance, particularly in terms of cost-effectiveness and activity. However, the relationship between catalyst structure and activity remains a matter of ongoing debate. In this work, the effect of Cu particle size on methanol synthesis was investigated. Cu/Zr-SBA-15 catalysts were prepared by the impregnation method and characterized using X-ray diffraction, nitrogen physisorption, H₂ temperature-programmed reduction, N2O decomposition and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). These analyses confirmed the successful preparation of catalysts with a range of particle sizes, with estimated diameters between 4.1 and 35.3 nm. Catalytic testing showed that CO2 hydrogenation to methanol follows behavior consistent with a class π reaction, although only minor variations were observed across the samples. Mechanistic insights obtained from ME-PSD-DRIFTS (Modulation-Excitation Phase Sensitive Detection Diffuse Reflectance Fourier Transform Spectroscopy) suggest that either the hydrogenation of methoxy species or the desorption of methanol is the slow step in the reaction. Apparent activation energy measurements indicated values below 44 kJ/mol for all catalysts in methanol formation. Taken together, these results suggest that methanol desorption is the rate-limiting step, possibly due to its interaction with oxophilic sites associated with zirconium.