Synthesis and Comparative Catalytic Study of Zirconia–MnCO3 or –Mn2O3 for the Oxidation of Benzylic Alcohols

• Published in: ChemistryOpen (Weinheim) Vol. 6; no. 1; pp. 112 - 120
• Main Authors: Assal, Mohamed E., Kuniyil, Mufsir, Khan, Mujeeb, Al‐Warthan, Abdulrahman, Siddiqui, Mohammed Rafiq H., Tremel, Wolfgang, Nawaz Tahir, Muhammad, Adil, Syed Farooq
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.02.2017; John Wiley and Sons Inc
• Subjects: Aldehydes; Aliphatic alcohols; Benzyl alcohol; benzyl alcohol oxidation; Catalysts; Chemical synthesis; Comparative studies; Composition; Electron microscopy; manganese carbonate; manganese oxide; Manganese oxides; mixed metal oxides; Oxidation; Oxidizing agents; Oxygen; Roasting; Thermal stability; X ray powder diffraction; zirconia; Zirconium dioxide
• ISSN: 2191-1363; 2191-1363
• DOI: 10.1002/open.201600116

We report on the synthesis of the zirconia–manganese carbonate ZrOx(x %)–MnCO3 catalyst (where x=1–7) that, upon calcination at 500 °C, is converted to zirconia–manganese oxide ZrOx(x %)–Mn2O3. We also present a comparative study of the catalytic performance of the both catalysts for the oxidation of benzylic alcohol to corresponding aldehydes by using molecular oxygen as the oxidizing agent. ZrOx(x %)–MnCO3 was prepared through co‐precipitation by varying the amounts of Zr(NO3)4 (w/w %) in Mn(NO3)2. The morphology, composition, and crystallinity of the as‐synthesized product and the catalysts prepared upon calcination were studied by using scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, and powder X‐ray diffraction. The surface areas of the catalysts [133.58 m2 g−1 for ZrOx(1 %)–MnCO3 and 17.48 m2 g−1 for ZrOx(1 %)–Mn2O3] were determined by using the Brunauer–Emmett–Teller method, and the thermal stability was assessed by using thermal gravimetric analysis. The catalyst with composition ZrOx(1 %)–MnCO3 pre‐calcined at 300 °C exhibited excellent specific activity (48.00 mmolg−1 h−1) with complete conversion within approximately 5 min and catalyst cyclability up to six times without any significant loss in activity. The specific activity, turnover number and turnover frequency achieved is the highest so far (to the best of our knowledge) compared to the previously reported catalysts used for the oxidation of benzyl alcohol. The catalyst showed selectivity for aromatic alcohols over aliphatic alcohols. A designed synthesis of catalysts with compositions ZrOx(x %)–MnCO3 (where x=1–7) or ZrOx(x %)–Mn2O3, followed by their comparative catalytic performance for the oxidation of benzylic alcohols to corresponding aldehydes using molecular oxygen, is presented. The catalyst with composition ZrOx(1 %)–MnCO3 pre‐calcined at 300 °C offers high surface area, cyclability, thermal stability, and an excellent specific catalytic activity with complete conversion of benzyl alcohol to benzaldehyde in about 5 min. The catalyst also shows selectivity for the oxidation of aromatic over aliphatic alcohols.