Unveiling the catalytic potential of K2ZnF6 fluoroperovskite for glycerol oligomerization

Abstract

This study systematically evaluates fluorine-containing materials with varying compositions of K, Al, Co, Cu, Mg, and Zn as catalysts for glycerol oligomerization. Comprehensive analyses were conducted for all of the catalysts, considering their structural, compositional, morphological characteristics, and basicity, to understand them in greater depth. Among these analyses, gas chromatography was employed to examine the composition of the reaction products. The investigation extended to a recycling study under optimized conditions. Thermogravimetric analysis and X-ray photoelectron spectroscopy were used to characterize the spent catalysts. Catalytic activity was found to be influenced strongly by the fluorine content, demonstrating remarkable performance for the materials containing fluoroperovskites such as KMgF₃ in the catalyst KMgAFC, and K₂ZnF₆ in KZAFC. Remarkably, KZAFC with 20% fluorine exhibited superior glycerol conversion (68%) and selectivity for diglycerol (27%). Comparative analysis with ZnAl-layered double hydroxide highlighted the positive impact of fluorine on catalytic activity. Introducing a calcination step in the catalyst recovery process also demonstrated improved activity during recycling. Interestingly, KZAFC exhibited stability over four reaction cycles, presenting an economic advantage over homogeneous catalysts. The study also shed light on the potential fluorine loss at the surface and potassium leaching into reaction products, correlating these phenomena with the observed decline in activity. These comprehensive findings contribute significantly to advancing sustainable glycerol valorization through heterogeneous catalysis.