The valorization of glycerol, a large-volume byproduct of biodiesel production, remains a key challenge for the biorefinery sector. Among the available strategies, its acetalization with acetone offers a sustainable route to produce solketal, a valuable fuel additive. The feasibility of this valorization route is, however, largely dependent on the continuous research towards highly performant, stable catalysts with carefully designed acidic sites. In this work, hybrid porous zirconium phosphonate-phosphate materials were synthesized and evaluated as recyclable heterogeneous catalysts. The acidity was systematically investigated using Hammett indicators, supported by solid-state 31P NMR, XPS, and ammonia TPD analyses. Their structural and thermal stability was also assessed. The incorporation of phosphate groups was found to be essential to provide sufficient Brønsted acidity and enhance the long-term stability of the catalysts, as evidenced by their successful recyclability during multiple catalytic runs. In addition, yields of 85%, with a selectivity of 98% can be reported in optimal conditions, and the catalyst was even found to offer very promising conversions at room temperature.
