Reactions of CO and CO 2 on [formula omitted] above 373 K as studied by infrared spectroscopic and magnetic methods

Abstract

Reactions of CO and CO 2 on Ni SiO 2 catalysts have been studied in the 373–700 K range by ir, magnetic (saturation magnetization), and volumetric measurements. At room temperature, CO is adsorbed as a mixture of the linear form, NiCO ads, and the bridged form, Ni 2CO ads. Upon heating the system beyond 400 K, these forms are irreversibly transformed into new CO adspecies bonded to four Ni atoms, Ni 4CO ads, with a vco frequency at about 1830 cm −1. This multibonded species is in equilibrium with gaseous CO 2 according to the reaction 2 CO CO 2 + C; the remaining carbon atom is reversibly dissolved into the bulk in an interstitial position. This CO disproportionation is assumed to occur via the CO rupture of Ni 4CO ads with formation of a surface carbon atom bonded to three nickel atoms Ni 3C surf and an oxygen atom bonded to one nickel atom. CO 2 is dissociated on pure nickel into CO, adsorbed as Ni 4CO ads, and adsorbed oxygen atoms.