Remarkable effect of alkalis on the chemoselective hydrogenation of functionalized nitroarenes over high-loading Pt/FeOx catalysts

Abstract

The chemoselective hydrogenation of substituted nitroarenes to form the corresponding functionalized anilines is an important type of reaction in fine chemistry, and the chemoselectivity is critically dependent on the rational design of the catalysts. This reaction has rarely been accomplished over high-loading Pt catalysts due to the formation of Pt crystals. Here, for the first time, we report that alkali metals (Li⁺, Na⁺, K⁺, etc.) can transform the non-selective high loading Pt/FeO_x catalyst to a highly chemoselective one. The best result was obtained over a 5% Na–2.16% Pt/FeO_x catalyst, which enhanced the chemoselectivity from 66.4% to 97.4% while the activity remained almost unchanged for the probe reaction of 3-nitrostyrene hydrogenation to 3-aminostyrene. Using aberration-corrected HAADF-STEM, in situ XAS, ⁵⁷ and Fe Mössbauer and DRIFT spectroscopy, the active site of a Pt–O–Na–O–Fe-like species was proposed, which ensures that the Pt centers are isolated and positively charged for the preferential adsorption of the –NO₂ group.