Structural Characterization of Phosphate Species Adsorbed on γ-Alumina by Combining DNP Surface Enhanced NMR Spectroscopy and DFT Calculations

Obtaining an atomic-scale description of the chemical interactions phosphates with oxide support, such as γ-Al2O3, is essential to get a rational understanding role phosphate additives for great number heterogeneous catalysts, well improve use this element. Combining cutting-edge Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS) techniques Density Functional Theory (DFT) calculations, we provide accurate molecular speciation on γ-Al2O3 surfaces various P surface coverages after drying at 120 °C. Thanks 31P double- and triple-quantum filtered experiments 27Al–31P dipolar- scalar-based correlation spectra, demonstrate presence polyphosphates Al–O–P connectivities exposed facets γ-Al2O3. DFT-based thermodynamics shows that (mono- or di-) are preferentially covalently bonded (1 1 0) facet high-dentation modes. These modes favored by entropy gain due water desorption. We used gauge-including projector-augmented wave (GIPAW) DFT method shifts calculations propose systematic identification types noncovalently alumina surface. The confirm existence observed experimentally. Since condensation into endergonic, likely result from their direct adsorption in impregnation solution. increasing concentration coverage could be related less hydrolysis reduced availability sites stabilize fragmented oligomers. This opens way better control over species known key preparation supported catalysts alumina.