Alkali-Free Hydrogenation of Adiponitrile to Hexanediamine by Regulated Co/C-TiO2: Role of Carbon Residue and Electron-Donating Promoter

In this work, a series of Co-based catalysts were synthesized and used for the selective hydrogenation of adiponitrile (ADN) under alkali-free conditions. The influences of the carbon residue and supports, the thermal treatment, and the doping amount of secondary elements were analyzed for a maximized hexanediamine (HMDA) yield. It is worthy to note that the Co loading in this work was relatively low at 8–11 wt %, if compared with the reported catalysts (20–60 wt %). The sustained high HMDA yield of 86% by Co₅Ni₂/C-TiO₂ in the absence of any alkali can be ascribed to a combining result of the well-established Co–Ni–O_x electron synergy and the structural promotion by carbon residue (<5 wt %). Bimetallic CoNi alloy particles were dispersed on the support, facilitating electron transfer from Ni to Co centers as well as H₂ adsorption/activation ability. The presence of doping elements resulted in the differentiated catalytic behaviors by Co centers. Different from the Ni-doped catalysts, P-containing species regulated the surface acidity by forming a large number of acid sites and P–O bonds. Byproduct by cycloaddition (ACH) was produced as a result of a lower HMDA yield (70%). This work provides an available strategy to regulate efficient Co catalysts for the alkali-free hydrogenation of ADN toward HMDA.