Influência do tamanho da cadeia carbônica no processo de fotoreforma de álcoois para obtenção de H2 de baixo carbono

Abstract

Alcohol photoreforming constitutes a promising route for the simultaneous production of low-carbon hydrogen and higher value-added products. In this work, the influence of carbon chain length (C1–C5) on the photocatalytic activity of TiO2 P25 was investigated by evaluating individual alcohols (methanol, ethanol, propanol, butanol and isoamyl alcohol), as well as binary, ternary and quaternary mixtures, aiming to represent multicomponent systems closer to real matrices. Additionally, the performance of TiO2 samples obtained under supercritical conditions (TiO2 - SC) was studied and compared to TiO2 P25, using methanol as the reference system. The materials were subjected to different thermal treatments and characterized morphologically and spectroscopically. Photocatalytic tests were carried out under aerobic conditions, in which oxidation products were identified and quantified, as well as under anaerobic conditions in the presence of Pt as a co-catalyst for monitoring H₂ evolution. The results showed that, for TiO2 SC, rapid thermal treatments (30 min) at high temperatures (700 ºC) favor photocatalytic activity. For the photoreforming of different alcohols, it was observed that, for individual alcohols, H2 production decreases with increasing carbon chain length, following the trend: Methanol ~ Ethanol > Propanol > Butanol ~ Isoamyl alcohol. Regarding the products, predominant formation of the corresponding aldehydes (methanal, acetaldehyde, propionaldehyde and butyraldehyde) was observed, accompanied by carboxylic acids as minor products. In multicomponent mixtures, ethanol exhibited dominant behavior, maintaining acetaldehyde as the major product and influencing the overall selectivity of the system, while the complexity of the reaction medium intensified competition effects for active sites, impacting the overall efficiency of photooxidation and hydrogen production. Thus, the overall results demonstrate that carbon chain length and the simultaneous presence of multiple alcohols are determining factors for the kinetics, selectivity and H2 evolution in TiO2 - based photocatalytic systems, contributing to a more integrated understanding of multicomponent conditions applicable to the valorization of complex organic streams.