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.
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