Nb2C Mxene as a bifunctional acid–base and oxidation/hydrogenation catalyst†

Abstract

Nb₂C MXene, obtained from Nb₂AlC by Al³⁺ etching and exfoliation, was characterized using XRD, HRTEM and AFM, with the data confirming the crystallinity of the sample and the 2D morphology of the sheets with an average layer thickness of 1.5 nm. Surface analysis using XPS revealed the presence of structural defects, and NH₃- and CO₂-TPD profiles confirmed the low density of acid and basic sites in the range of tens of μmol g_catalyst⁻¹ of weak and moderate strengths. The combination of acid and basic sites in close proximity on the solid surface was responsible for the remarkable catalytic activity of Nb₂C MXene in promoting aldolic condensation with high turnover frequencies of up to 855 h⁻¹, which was comparable to the values of benchmark catalysts, such as MgO or HZSM-5. Nb₂C MXene also catalyzed the aerobic oxidative aniline coupling to azo- and azoxy-benzene and hydrogenation of azoxybenzene to azobenzene.