High-Performance Metal Oxide-Modified V/TiO₂ Catalysts for Selective Oxidation of 2-Methylnaphthalene to 2-Naphthaldehyde: An Experimental and Theoretical Study

Abstract

2-Naphthaldehyde is industrially produced from 2-naphthalene nitrile and 2-naphthoyl chloride in acid. Greener gas-solid catalytic oxidation of 2-methylnaphthalene to 2-naphthaldehyde has rarely been investigated. In this study, the preparation of 2-naphthaldehyde over V/TiO2 catalysts doped with 13 metal promoters was explored and the V-Cu(1)/TiO2 catalyst showed excellent performance with 63.37% 2-methylnaphthalene conversion and 70.09% 2-naphthaldehyde selectivity at 400 °C, gas hourly space velocity (GHSV) of 10 000 h–1, and feed flow rate of 3.87 × 10–4 mol·h–1, giving the highest turnover frequency (TOF) value of 17.05 × 10–6 s–1. We have consequently studied the effect of Cu doping on the physicochemical properties of the V/TiO2 catalyst and found that structural changes are not the main reason to improve the catalytic performance. Increased vacancies and oxygen mobility accelerate the formation of nucleophilic oxygen from electrophilic oxygen, which are the key factors to improve 2-NA selectivity. The synergy between V, Cu, and O through the V–O–Cu bridging bond also improves the weak acid ratio, redox ability, and the reactivity of active sites (bridging and terminal oxygen). X-ray photoelectron spectroscopy (XPS), in situ diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy, and density-functional theory (DFT) calculations have proved that this reaction obeys the Mars–van Krevelen mechanism and involves a reduction process of V5+ and Cu2+ during oxidation.