Issue 25, 2023

Why a simple vanadate is inefficient as a catalyst in the oxidation of alkanes with H2O2 – the long-standing puzzle is solved

Abstract

In contrast to V(V) complexes with various organic ligands, a simple vanadate without any additive is inactive in neutral medium toward the oxidation of alkanes with H2O2. In this work, we discovered that the insufficient activation of H2O2 upon coordination to the simple vanadate – the commonly accepted reason for the low catalytic activity of the vanadate – cannot explain this phenomenon. Two main findings are reported here on the basis of DFT calculations. First, the generally accepted Fenton-like mechanism of the generation of the active oxidizing species (HO˙) in a vanadate/H2O2(aq)/MeCN system was revisited. A new mechanism based on the tremendous activation of the OOH ligand in the intermediate [V(OO)2(OOH)(H2O)] toward the homolytic O–O bond cleavage is not only feasible but significantly more favourable than the Fenton-like pathway. The surprisingly low activation barrier calculated for the HO˙ generation (15.4 kcal mol−1) demonstrates the efficiency of this process. The presence of easily oxidizable non-innocent OO ligands in this intermediate explains such an activation. Second, it was found that the generated HO˙ radicals may be easily captured by the V atom soon after their formation followed by the elimination of the molecular oxygen. This side reaction of the H2O2 dismutation efficiently consumes the produced HO˙ radicals decreasing their concentration in the reaction mixture and preventing the following oxidation of alkanes.

Graphical abstract: Why a simple vanadate is inefficient as a catalyst in the oxidation of alkanes with H2O2 – the long-standing puzzle is solved

Supplementary files

Article information

Article type
Paper
Submitted
29 Mar 2023
Accepted
18 May 2023
First published
22 May 2023
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2023,52, 8601-8612

Why a simple vanadate is inefficient as a catalyst in the oxidation of alkanes with H2O2 – the long-standing puzzle is solved

M. L. Kuznetsov and A. J. L. Pombeiro, Dalton Trans., 2023, 52, 8601 DOI: 10.1039/D3DT00967J

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