A Combined Mechanochemical and Calcination Route to Mixed Cobalt Oxides for the Selective Catalytic Reduction of Nitrophenols

Abstract

Para-, or 4-nitrophenol, and related nitroaromatics are broadly used compounds in industrial processes and as a result are among the most common anthropogenic pollutants in aqueous industrial effluent; this requires development of practical remediation strategies. Their catalytic reduction to the less toxic and synthetically desirable aminophenols is one strategy. However, to date, the majority of work focuses on catalysts based on precisely tailored, and often noble metal-based nanoparticles. The cost of such systems hampers practical, larger scale application. We report a facile route to bulk cobalt oxide-based materials, via a combined mechanochemical and calcination approach. Vibratory ball milling of CoCl2(H2O)6 with KOH, and subsequent calcination afforded three cobalt oxide-based materials with different combinations of CoO(OH), Co(OH)2, and Co3O4 with different crystallite domains/sizes and surface areas; Co@100, Co@350 and Co@600 (Co@###; # = calcination temp). All three prove active for the catalytic reduction of 4-nitrophenol and related aminonitrophenols. In the case of 4-nitrophenol, Co@350 proved to be the most active catalyst, therein its retention of activity over prolonged exposure to air, moisture, and reducing environments, and applicability in flow processes is demonstrated.

Ultralow Loading Ruthenium on Alumina Monoliths for Facile, Highly Recyclable Reduction of p-Nitrophenol

“…Historically, catalytic reduction of 4NP has been promoted primarily with catalytic noble metal nanoparticles [7][8][9][10][11][12], to a lesser extent with non-noble metal nanoparticles [13][14][15][16][17], and more recently nonmetal species [18][19][20][21]. A significant majority of these catalyst systems are submicron-or even a few-nanometer-sized colloidal particles.…”

Recent advances in mechanochemical synthesis of mesoporous metal oxides

“…Elsewhere, a combined mechanochemical and calcination route led to mixed cobalt oxides attractive for the selective catalytic reduction of nitrophenols. 32 Mechanochemistry has also been employed for a waste free preparation of perovskites, e.g., LaMnO 3 directly from the corresponding metal oxide powders (La 2 O 3 and Mn 2 O 3 ). 33 Interestingly, mechanochemical redox-based synthesis using KMnO 4 , CoCl 2 and NaOH without any templates afforded highly porous Co x Mn 1-x O y catalysts with a specific surface area of 479 m 2 /g, which was higher than the values of the corresponding materials obtained by using other methods including co-precipitation method, sol-gel method or solution redox process ( Fig.…”

Human hair catalyzed selective reduction of nitroarenes to amines

“…1,2 Traditional approaches such as Béchamp reduction method, generates large amount of waste and requires mineral acids, which is not appropriate for acid sensitive functional groups. 3 In recent years, an increasing attention has been paid to catalytic nitro reduction using transition metals such as Cu, 4,5 Co, 6,7 Pd, [8][9][10][11] Ni, 12,13 Au [14][15][16][17] and Zn 18,19 . Along this line, due to the superior catalytic activity in bimetallic variants relative to their monometallic analogs, variety of bimetallic catalysts have been developed for organic reactions including the reduction of nitroarenes.…”