Understanding the Oxidative Properties of Nickel Oxyhydroxide in Alcohol Oxidation Reactions

Abstract

The NiOOH electrode is commonly used in electrochemical alcohol oxidations. Yet understanding the reaction mechanism is far from trivial. In many cases, the difficulty lies in the decoupling of the overlapping influence of chemical and electrochemical factors that not only govern the reaction pathway but also the crystal structure of the in situ formed oxyhydroxide. Here, we use a different approach to understand this system: we start with synthesizing pure forms of the two oxyhydroxides, β-NiOOH and γ-NiOOH. Then, using the oxidative dehydrogenation of three typical alcohols as the model reactions, we examine the reactivity and selectivity of each oxyhydroxide. While solvent has a clear effect on the reaction rate of β-NiOOH, the observed selectivity was found to be unaffected and remained over 95% for the dehydrogenation of both primary and secondary alcohols to aldehydes and ketones, respectively. Yet, high concentration of OH– in aqueous solvent promoted the preferential conversion of benzyl alcohol to benzoic acid. Thus, the formation of carboxylic compounds in the electrochemical oxidation without alkaline electrolyte is more likely to follow the direct electrochemical oxidation pathway. Overoxidation of NiOOH from the β- to γ-phase will affect the selectivity but not the reactivity with a sustained >95% conversion. The mechanistic examinations comprising kinetic isotope effects, Hammett analysis, and spin trapping studies reveal that benzyl alcohol is oxidatively dehydrogenated to benzaldehyde via two consecutive hydrogen atom transfer steps. This work offers the unique oxidative and catalytic properties of NiOOH in alcohol oxidation reactions, shedding light on the mechanistic understanding of the electrochemical alcohol conversion using NiOOH-based electrodes.

Suppressing carbon corrosion via mechanically mixing transition metal phosphide clusters: a comparative in situ study in alkaline media

“…, oxyhydroxides and radicals). 45 Compared with that on pure carbon, this oxidation rate seems slightly higher.…”

Heterometallic Electrocatalysts Derived from High-Nuclearity Metal Clusters for Efficient Overall Water Splitting

“…To evaluate the intrinsic catalytic abilities of the byproduct, Ni­(OH) 2 and NiOOH species were successfully prepared according to the literature for comparative analysis (Figure S26a,b). , The OER performances were investigated under the same conditions as Ni 2 P/MoS 2 -CoMo 2 S 4 @C; the catalytic activity of Ni­(OH) 2 and NiOOH was found to be significantly lower than that of Ni 2 P/MoS 2 -CoMo 2 S 4 @C (Figure S26c). Comprehensive analysis via XPS, in situ Raman spectroscopy, and HRTEM indicated that the MoS 2 and CoMo 2 S 4 phases in Ni 2 P/MoS 2 -CoMo 2 S 4 @C showed almost no reconstruction during the OER, due to the strong interfacial interactions and the existence of the carbon protective layer.…”

Direct Synthesis of Gem-β,β′-Bis(alkyl) Alcohols Using Nickel Catalysis via Sequential DCR Approach

“…Furthermore, the high KIE value ( P H / P D = 6) of this benzylic C–H bond cleavage indicates a rate-limiting step and supports the possibility of HAT. This hydrogen atom transfer from the benzylic position of alcohol with a metal catalyst was well supported in the literature. , Importantly, in-situ formed ketyl radical (ketyl-BHT adduct) was detected using HRMS. In the next step, ketone 1′ is formed, and intermediate C is generated from B .…”