Catalyst for lactose hydrolysis based on zeolite Y modified with Fe species by ultrasound treatment

Abstract

Research has focused on biomass as a sustainable energy source, driving biomass valorization to convert carbohydrates. The price of lactose has dropped below the production cost, urging exploration for diverse applications, such as conversion into value-added compounds. Zeolites, especially Y zeolite, enhance hexose conversion when modified with metals. Fe-modified zeolites show promise, with controlled Si/Al ratios impacting acidity and selectivity. The recent challenges remain in active site comprehension, catalyst tunability, and reaction optimization. Therefore, this study explores the selective hydrolysis of lactose, limiting undesired side-product formation catalyzed through a sono-assisted modified zeolite Y with Fe. The obtained series of Fe-modified zeolite Y were evaluated for the hydrolysis of lactose in a screening experiment. The samples with the higher potential were further used to optimize reaction conditions by a response surface methodology (RSM). This revealed that the samples prepared at high pH generated more impurities and that higher temperatures and lactose concentrations favored hydrolysis. Despite their apparent similarities, the selected Fe-modified zeolite Y samples (Fe5Y and FeYII) highlight distinct catalytic behaviors and active sites. Employing UV-Vis spectroscopy, FTIR spectroscopy, and magnetic thermal gravimetric analysis (MTGA), various Fe active sites were detected, including α-Fe(II), FeOx nanoparticles, and iron oxides. These active sites give insight into the mechanisms involved with temperature and time, which play critical roles—evidencing the potential of sono-assisted iron modification of zeolite Y to achieve selective lactose hydrolysis. These findings contribute to understanding metal-zeolite composites as bifunctional catalysts and their application in sustainable processes. Furthermore, this research highlights the complexity of catalytic reactions of modified zeolites and their potential for fine-tuning active sites for various applications, particularly lactose hydrolysis. Such advancements hold the promise of propelling the field of sustainable energy and catalysis towards a more efficient and environmentally friendly future.