Zinc alendronate as an ossified catalyst for glycerol valorization to glycerol carbonate using urea as a CO2 surrogate

Abstract

The conversion of biomass waste into valuable chemicals is a sustainable approach for a green and circular economy. Herein, the highly efficient solvent-free catalytic carbonylation of glycerol to glycerol carbonate (GlyCO₃) using cost-effective and facile ossified zinc alendronate catalysts and urea as a CO₂ surrogate is reported. Zinc alendronate catalysts were synthesized in a single step using an ossification technique. The catalysts were characterized by various techniques, including XRD, FT-IR spectroscopy, N₂ physisorption, TGA, SEM-EDS, TEM, XANES, XPS, NH₃- and CO₂-TPD, and multinuclear CP MAS NMR spectroscopy. Among the catalysts tested, ALN1Zn2 exhibited enhanced performance, achieving 86.3% glycerol conversion and 96.1% GlyCO₃ selectivity with 82.9% yield under optimized conditions (10% catalyst loading, 150 °C, 7 h, 1 : 1 glycerol to urea ratio). All products and byproducts were identified using GC-MS/MS analysis. The catalyst exhibited good reusability over multiple cycles with only slight activity loss. The reaction progress was monitored by FT-IR spectroscopy. Mechanistic studies indicated that the reaction proceeded via a carbamate intermediate. The bifunctional acid-base properties of the catalyst enabled the simultaneous activation of urea and glycerol. This work demonstrates a facile approach to develop efficient heterogeneous catalysts for sustainable glycerol valorization.