Chemoselective nitrilation of dimethyl adipate with ammonia over carbon encapsulated WOx catalysts under continuous flow conditions

Abstract

Adiponitrile (ADN) is a key intermediate for the industrial production of polyamides represented by nylon 66. In this study, the chemoselective nitrilation of dimethyl adipate (DMA) with ammonia (NH₃) under continuous flow conditions was studied on carbon encapsulated oxygen-deficient WO_x<3 catalysts (WO_x@C/C). A combination of dispersed anchor sites at a poly(ionic liquid) (PIL) template, the porosity of active carbon support, and the calcination procedure allows the formation of effective WO_x@C-600-0.25-A1, persisting high BET specific surface area and WO_2.83 active phase of appropriate size. It delivers ADN and methyl 5-cyanopentanoate (MCP) with an excellent selectivity of up to 95.8% at a weight hourly space velocity of DMA (WHSV_DMA) of ∼0.64 g_DMA g_cat⁻¹ h⁻¹ and an NH₃/DMA molar ratio of 13 : 1. A tandem reaction route from DMA to ADN via MCP was elucidated, wherein the second nitrilation of MCP to ADN proceeds very slowly. Besides, both C_DMA and TON_ADN/TON_MCP are significantly influenced by the physical dispersion and size of the active WO_2.83 phase in WO_x@C/C.