Synthesis and Characterization of Ta₂O₅−ZrO₂Systems: Structure, Surface Acidity, and Catalytic Properties.

The preparation of binary materials based on Ta 2 O 5 −ZrO 2 by a sol−gel method and with a wide range of compositions is reported (Ta 2 O 5 nominal content from 4 to 74% w/w). Materials were characterized by X-ray diffraction, and infrared and Raman spectroscopy. Their acidic characteristics were evaluated from the model reaction of 2-propanol dehydration and the adsorption of CO at 77 K and 2,6-dimethylpyridine at 373 K, both followed by infrared spectroscopy. Increasing tantalum content brings about a development of a surface TaO x phase followed by a progressive formation of aggregates of amorphous Ta 2 O 5 . Increased stabilization of tetragonal zirconia was also observed with increasing Ta loading. The surface area, number and strength of Brönsted acid sites, and the catalytic activity in the 2-propanol dehydration increase with the increase in tantalum content up to ca. 50% w/w Ta 2 O 5 . A surface area of 103 m 2 g - 1 was obtained for a solid with a Ta 2 O 5 content of 53% w/w after calcination at 873 K. The abundance of Brönsted acid sites, determined by lutidine adsorption, and their strength, determined by CO adsorption at 77 K, correlated with the catalytic activity in the 2-propanol dehydration.