Enhancement of naphthalene hydrogenation over PtPd/SiO 2–Al 2O 3 catalyst modified by gold

Abstract

This contribution describes the effect of support (amorphous silica–alumina: ASA and multi-wall carbon nanotubes: MWNT) on the catalytic response of bimetallic PtPd catalysts in naphthalene hydrogenation (HYD). In addition, the effect of Au incorporation on the activity of PtPd/ASA catalyst was studied. The ternary AuPtPd/ASA catalyst was prepared by the simultaneous reduction of metal precursors by ethanol in the presence of poly( N-vinyl-2-pyrrolidone) (PVP), whereas binary PtPd/ASA and PtPd/MWNT catalysts were prepared by a conventional impregnation method. The catalysts were characterized using chemical analysis, nitrogen adsorption–desorption isotherms at 77 K, CO chemisorption, FTIR spectra of chemisorbed CO, transmission electron microscopy (TEM), DRIFT of adsorbed NH 3, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) measurements. Under the reaction conditions employed ( T = 448–463–483 K, P = 2.0 MPa, WHSV = 45.7 h −1), the ternary AuPtPd/ASA catalyst showed highest naphthalene conversion and lowest deactivation among the catalysts studied. The S-tolerance of this catalyst was confirmed during simultaneous naphthalene and toluene HYD in the presence of dibenzothiophene (DBT; 100 ppm of S). The enhanced activity and S-tolerance observed with the AuPtPd/ASA catalyst was related to its larger metal surface exposure, as determined by XPS, and the “ensemble” effect of the Au 70Pd 30 and Au 42Pd 58 alloy particles formed on ASA, as demonstrated by XRD. It is proposed that surface gold weakens the adsorption of aromatic compounds (toluene/naphthalene/DBT), facilitating product desorption. Contrary to acidic AuPtPd/ASA, the less acidic PtPd/MWNT catalyst did not show S-resistance in reaction of benzene HYD in the presence of 1-butanethiol. The contribution of the acid sites of support to catalyst S-resistance and their deactivation by coke are discussed.