Understanding the role of surface Lewis acid sites of Sn modified Pd/Al2O3 catalyst in the chemoselective reductive N-acetylation of nitrobenzene

Abstract

N-Aryl acetamides synthesis from the corresponding nitro compounds via a reductive N-acetylation was achieved over Pd supported on Sn modified Al2O3 catalyst using H2, acetic anhydride as acetylating agent in aqueous media at ambient temperature. The pyridine-IR data demonstrated a majority of Lewis acid sites compared to Bronsted acid sites on the catalyst surface. Pyridine-IR and CO pulse chemisorption results emphasized a combination of surface palladium in conjunction with Lewis acid sites were responsible for the high activity of 2wt%Pd/5wt%Sn–Al2O3 over 2wt%Pd/Al2O3 catalyst with consistent activity and selectivity for four recycles. The bulk and surface properties of the catalysts were characterized by BET-SA, XRD, XPS, TPD of NH3, H2-TPR, CO pulse chemisorption, TEM and the promotional effect of surface Lewis acid sites are rationalized by in situ pyridine adsorbed DRIFT spectroscopy.