Effects of doping on the electrical properties and surface characteristics of NiO catalyst

Abstract

A series of nickel oxides doped with 10 at.% Li, 20 at.% Na and 10 at.% Fe was prepared by thermal dehydration of mixed hydroxides in air at temperatures in the range 300–1000 °C. The electrical properties, stoichiometric composition and surface characteristics of the pure and doped NiO samples were investigated. Alkali doping considerably increased the electrical conductivity and decreased the specific surface area of NiO. The modifications in the electrical and surface properties were more pronounced, however, in the case of lithium doping. In contrast, doping with Fe 2O 3 produced opposite effects on the electrical and surface properties of NiO. Lithium doping was accompanied by pore narrowing when the preparation temperature exceeded 500 °C. A less important pore narrowing was observed in the case of sodium doping at temperatures above 700 °C. At 300 °C the doping of NiO with foreign ions might proceed through coverage of a fraction of the NiO surface by some of these ions. Above 400 °C foreign ions could progressively substitute some of the lattice nickel ions according to the mechanism of Verwey and de Boer. Above 600 °C Fe 3+ ions could be incorporated in the NiO lattice according to another mechanism.