Iridium Nanoparticles on NiO as Heterogeneous Catalysts for Acceptorless Dehydrogenation of Primary Alcohols with Tunable Product Selectivity

Abstract

In this work, we introduced a nanostructured iridium catalyst supported on NiO (IrNP@NiO) for acceptorless dehydrogenative oxidation of primary alcohols. The catalyst was synthesized by a simple wet chemical technique and was characterized by HR-TEM, SEM-EDX, powder diffraction XRD, XPS, and ICP-AES analyses. The HR-TEM analysis revealed the formation of ultrasmall Ir nanoparticles with an average size of 1−2 nm over the NiO surface. A range of primary alcohols could selectively be converted to the corresponding acids or carboxylates with the concomitant evolution of 2 equiv of H 2 when the reactions were performed in the presence of a base. Interestingly, when the same reactions were performed in a base-free condition, keeping all other reaction variables the same, aldehydes were isolated as the main products along with evolution of 1 equiv of H 2 . Notably, our catalyst could efficiently convert relatively challenging biomass-based alcohols, such as furfuryl alcohol, piperonyl alcohol, or 1-adamantane ethanol, to their corresponding products, which have tremendous biological as well as industrial significance. The nanostructured iridium catalyst could be easily separated from the reaction mixture and reused for at least five runs without any significant drop in activity. The dehydrogenation strategy for benzyl alcohol was scalable up to the gram.

Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids

“…Carboxylic acids were conventionally prepared by oxidizing alcohols in the presence of various types of oxidants. However, their applications are limited due to poor atom efficiency and the production of toxic inorganic wastes when compared with oxidant-free catalytic oxidation of alcohols to carboxylic acids with concomitant generation of molecular hydrogen …”