Spectroscopic and theoretical investigation of Brønsted acid sites in amorphous mixed Zr-Si oxide nanoparticles

Abstract

Mixed Zr-Si oxide nanoparticles were investigated to disclose the relation between the Brønsted acidity of these materials and the atomic composition of the particles. To this aim, we combined experimental structural characterizations via X-ray absorption and Solid State Nuclear Magnetic Resonance spectroscopies with Reactive Molecular Dynamics simulations and Quantum Chemistry calculations. Despite the materials’ complexity, we identified the surface hydrogens responsible for the Brønsted acidity by estimating the adsorption energy of pyridine on several topologically distinct hydroxyl groups. Among the investigated sites, the hydrogens connected to the oxygen atoms bridging surface Zr and Si atoms (i.e., Zr-O(H)-Si) exhibited the most marked Brønsted acidity. The agreement of all the employed techniques demonstrates how the proposed concerted characterization effectively elucidates these complex amorphous materials’ structure/properties relationships. These new insights allowed us to develop a material with exceptionally high Brønsted acid character that outperformed benchmark silica-alumina and sulfonated zirconia in the dehydrogenation reaction of 1-octanol to produce olefins.