Carboxylic acid-modified metal oxide catalyst for selectivity-tunable aerobic ammoxidation

Abstract

Controlling the reaction selectivity of a heterobifunctional molecule is a fundamental challenge in many catalytic processes. Recent efforts to design chemoselective catalysts have focused on modifying the surface of metal nanoparticle materials having tunable properties. However, precise control over the surface properties of base-metal oxide catalysts remains a challenge. Here, we show that green modification of the surface with carboxylates can be used to tune the ammoxidation selectivity toward the desired products during the reaction of hydroxyaldehyde on manganese oxide catalysts. These modifications improve the selectivity for hydroxynitrile from 0 to 92% under identical reaction conditions. The product distribution of dinitrile and hydroxynitrile can be continuously tuned by adjusting the amount of carboxylate modifier. This property was attributed to the selective decrease in the hydroxyl adsorption affinity of the manganese oxides by the adsorbed carboxylate groups. The selectivity enhancement is not affected by the tail structure of the carboxylic acid.

Switching acidity on manganese oxide catalyst with acetylacetones for selectivity-tunable amines oxidation

“…As shown in Table 1, using well-crystallized MnO 2 catalysts, a near quantitative conversions were observed, and the yields of nitrile ( 3a ) varied from 24.6% to 58.9%, with 24.1–61.9% yield of imine ( 2a ) formed (Table 1, entries 1–4). In comparison, amorphous MnO x has much increased specific surface area and mass-specific activity (Supplementary Table 1) 23 , affording a complete conversion of amine and 86.5% yield of nitrile ( 3a ) (Table 1, entry 5). The time course of the synthesis of 3a over amorphous MnO x displays a steep volcano curves for 2a , indicating that the imine of 2a is the reaction intermediate and could be hardly obtained in high selectivity via tuning of the reaction time (Supplementary Fig.…”

“…MnO x was prepared according to the literature procedure 23 . A 100 mL aqueous solution containing 40 mmol KMnO 4 was added into another 250 mL solution of EtOH-H 2 O (5:1) containing 40 mmol MnAc 2 .…”

“…Owing to the fascinating flexibility of organic modifiers, organic modification has evolved into very powerful and effective technique for the selectivity control of supported metal catalysts 2,4,8,17–21 . Much less is known about the study on tuning the selectivity of metal oxide catalyst via organic modification 22,23 , although metal oxides are used in various fields of bifunctional catalysis as a result of their acid–base and redox properties with high thermal stability and durability 24–28 .…”

Aerobic and Additive‐free Oxidative Dehydrogenation of N‐heterocycles over Commercial MnCO3‐derived Manganese Oxides

“…Inspired by manganese-oxide catalysts with high activity towards oxidation reactions [19][20][21][22] , and encouraged by our recent investigations on preparing heterogeneous manganese catalysts for alcohol oxidation reactions [23,24] . Herein, we use commercial MnCO 3 as the precursor to prepare manganese oxides by simply pyrolyzing it at 400°C under an air atmosphere.…”

Ultrahigh‐Content Nitrogen‐doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural

“…Previously, our laboratory has been engaged in research of construction of functional catalytic materials and production of chemicals from biomass‐based feedstocks via catalytic methods . We found that both basic sites (pyridinic N‐doped carbon species in CoO x ‐N/C) and basic supports (MgO and Mg(OH) 2 ) could contribute to high catalytic performances in oxidation or oxidative esterification.…”