Effects of surface functional groups of the N-containing carbon support on the catalytic properties of supported palladium

Abstract

Nitrogen-containing mesoporous carbons (SNMC) were shaped by the drop ball method. A SNMC and a commercial coconut shell carbon (CSC) were oxidized by nitric acid to obtain the OSNMC and OCSC supports. Then, the Pd/OSNMC, Pd/SNMC, Pd/OCSC and Pd/CSC catalysts (5%wt) were prepared to study the effects of carboxyl group on the hydrogenation of C=C double bond. The results showed that both the doped N and surface O-containing functional groups increased the dispersion and surface electron density of supported Pd, leading to the increased heats for the adsorption of hexene and H 2 and thus the increased intrinsic activity for the hydrogenation of hexene on Pd. The pre-adsorption of propionic acid (PA) significantly inhibited the adsorption of hexene and H 2 and decreased the conversion of hexene on Pd. However, the surface O-containing functional groups inhibited the adsorption of carboxyl groups and offset the inhibition effect of carboxyl groups on the hydrogenation of hexene on Pd, while the doped N atoms played the opposite role. Thus, it is expected that the surface O-containing functional groups are beneficial to the hydrogenation of unsaturated fatty acids on Pd/C catalysts. The doped N and surface O-containing functional groups in carbon supports were electron donators that increased the electron charges of supported Pd on which the adsorption of hexene was enhanced and led to the increase in intrinsic activity for the hydrogenation of hexene. The strong adsorption of propionic acid (PA) inhibited the adsorption of hexene and lowered the conversion of hexene on Pd/C, which was offset by the surface O-containing functional groups. • Doped N in C supports enhanced dispersion of Pd and donated electron charges to Pd. • Surface O groups also enhanced dispersion of Pd and donated electron charges to Pd. • Electron enriched Pd favored adsorption of hexene and thus its hydrogenation. • Carboxyl groups strongly inhibited adsorption of hexene and thus its hydrogenation. • Surface O groups offset inhibition effect of -COOH on adsorption of hexene on Pd.