Nature of Acid Sites in Silica-Supported Zirconium Oxide: A Combined Experimental and Periodic DFT Study
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A combined experimental and DFT study was carried out to investigate the acidity of silica-supported zirconium oxide synthesized via the grafting method. XRD results show the crystal phase of ZrO2 is tetragonal. Sample acidity was characterized via ammonia adsorption microcalorimetry and DRIFTS pyridine desorption. Theoretical results predict that on a vacancy-free surface of t-ZrO2 at low coverage NH3 binds preferentially to Lewis acid sites with an adsorption energy up to 120 kJ/mol and that ammonia adsorption energies below 100 kJ/mol calculated at higher coverage can be well explained by lateral NH3-NH3 interactions. Higher differential heats of adsorption at low coverage (up to 190 kJ/mol) on both the (101) and (201) crystal planes of t-ZrO2 are in agreement with dissociative adsorption of ammonia near an oxygen vacancy site. The theoretical results are in good agreement with our findings in ammonia adsorption microcalorimetry and DRIFTS pyridine desorption on the ZrO2/SiO2 sample. © 2015 American Chemical Society.
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Adsorption; Ammonia; Calorimeters; Catalyst activity; Desorption; Oxides; Oxygen vacancies; Pyridine; Silica; Zirconia; Zirconium; Zirconium alloys; Adsorption energies; Ammonia adsorption; Crystal phase; Crystal planes; Differential heat; Dissociative adsorption; Grafting method; Lewis acid site; Gas adsorption
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