Supported Fe catalysts prepared through layered double hydroxides for primary amine synthesis by reductive amination of carbonyl compounds†

Abstract

Reductive amination of carbonyl compounds with ammonia using H₂ as a reductant is a highly powerful method for synthesizing primary amines. To enhance sustainability, however, there is a need to develop heterogeneous catalysts based on iron, which is abundant and inexpensive. Previously reported Fe-based heterogeneous catalysts require a high reaction temperature and high H₂ pressure, probably due to the agglomeration of Fe particles during the reduction of iron oxide precursors. We discovered that layered double hydroxides (LDHs) were suitable precursors for preparing supported Fe catalysts. Reduction of Mg- and Fe-based LDHs (MgFe-LDHs) after introducing citrate furnished MgO-supported Fe catalysts (Fe–C/MgO) with small Fe and MgO particles. Fe–C/MgO worked as a reusable and stable heterogeneous catalyst for reductive amination at a low temperature and low H₂ pressure; the benzylamine yield from benzaldehyde reached 99% even at 80 °C under 1.5 MPa H₂ pressure. Introducing citrate to the LDHs not only suppressed the crystal growth of Fe and MgO particles but also facilitated the reduction of iron oxides to metallic Fe. This work demonstrates a promising method for the preparation of supported Fe catalysts with small Fe particles.