Highly Dispersed Ru on Electride [Ca24Al28O64]4+(e–)4 as a Catalyst for Ammonia Synthesis

Abstract

A high surface area 12CaO·7Al2O3 electride (HT-C12A7:e–) was synthesized by the hydrothermal process and subsequent reduction with CaH2 as a reducing agent, and was then examined as a support for a Ru catalyst in ammonia synthesis. Electrons are successfully incorporated into the cages of C12A7 powder by reduction with CaH2 at 973 K. The concentration of encaged electrons increases with the dehydration temperature of the sample before the CaH2 treatment. The surface area of the resulting material (ca. 20 m2 g–1) is higher than that of the C12A7 electride prepared by conventional solid-phase reaction (SP-C12A7:e–, ca. 1 m2 g–1). The rate of ammonia synthesis over Ru/HT-C12A7:e– is twice that of Ru/SP-C12A7:e–, and there is no significant difference in the apparent activation energy between both catalysts under the optimal conditions. Transmission electron microscopy (TEM) and CO chemisorption measurements revealed that Ru nanoparticles are more highly dispersed on HT-C12A7:e– than that on SP-C12A7:e–, whic...