Coprecipitation of Nickel−Copper−Aluminum Takovite as Catalyst Precursors for Simultaneous Production of Carbon Nanofibers and Hydrogen

Abstract

A series of nickel-, copper-, and aluminum-containing catalysts at a (Ni+Cu)/Al mole ratio of 3 and Cu/Ni mole ratio in the range of 0.03−0.4 was prepared by coprecipitation from corresponding metal nitrate solutions at alkaline pH. The composition and structure of the precipitates were determined by chemical analysis, thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The XRD patterns confirmed that the precipitates are of hydrotalcite-like structures and, more specifically, they are takovite. The brucite-like layers consist of nickel, copper, and aluminum ions of composition [CuyNix-yAl1-x(OH)2](1-x)+, while the interlayers consist of CO32- and crystalline water. The observed variation of lattice parameters with copper content led us to conclude that the copper and aluminum ions were randomly substituted for the nickel ions in the brucite layer. The catalytic conversion tests at 670 °C showed a significantly enhanced catalytic reactivity of 2 mol % copper-doped catalysts as compared to a pristine nickel catalyst. A higher copper doping led to a less significant improvement in catalytic reactivity. A scanning electron micrograph (SEM) confirmed the production of carbon nanofibers.