Effect of pH on the detailed chemical nature and metal‐carbonate species in as synthesized zirconia alumina composites

• Published in: Journal of the American Ceramic Society Vol. 103; no. 11; pp. 6615 - 6629
• Main Authors: Pathan, Ruhi H., Modi, Chetan K., Basrur, Arun
• Format: Journal Article
• Language: English
• Published: Columbus Wiley Subscription Services, Inc 01-11-2020
• Subjects: alumina; Aluminum oxide; bridged bidentate carbonate; Chelation; composites; Crystallites; Deactivation; Deposition; differential thermal analysis; precipitates/precipitation; Sodium carbonate; zirconia; Zirconium; Zirconium dioxide
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.17368

Zirconia was deposition precipitated on γ‐alumina in pH range 7‐10 from zirconium oxy‐nitrate and soda ash. Zirconium formed its hydroxycarbonate as deduced from ICP‐EOS, CHN, and TGA‐MS. Higher pH favored formation of carbonate species of zirconium over its hydroxide. TGA‐MS indicated formation of three different types of carbonate species. FTIR results corroborated this. Monodentate metal carbonate was observed irrespective of pH of preparation. In addition, bridged bidentate species formed at pH ≤ 8 which changed to chelating bidentate at pH > 8. XRD indicated that all the samples formed tetragonal‐zirconia upon calcination irrespective of pH of preparation. Higher pH resulted in smaller crystallites of t‐ZrO2. Changes in chemical moiety with pH reflected on acidity and the deactivation rate for 2‐methyl‐3‐butyn‐2‐ol which decreased by two orders of magnitude in samples prepared at higher pH. Surface area and pore volume benefited from deposition precipitation. SEM‐EDAX showed reasonable distribution of zirconia over γ‐Al2O3.
pH of precipitation strongly influences chemical nature of as synthesized zirconia‐alumina composites. Increasing pH from 7 to 10 forms relatively, more zirconium carbonate than the hydroxide, and co‐ordination of carbonates to zirconia changes from bridged bidentate to chelating bidentate. Calcination results in tetragonal ZrO2. Remarkable change is observed in catalyst deactivation behavior.