Adjustment of W–O–Zr Boundaries Boosts Efficient Nitrilation of Dimethyl Adipate with Ammonia on WO_x/ZrO₂ Catalysts

In this study, a tungstated zirconia (WO_x/ZrO₂) catalyst was developed for the continuous synthesis of adiponitrile (ADN) by gas-phase nitrilation of dimethyl adipate (DMA) with NH₃. The highest TOF_ADN could be reached on WO_x/ZrO₂ bearing ∼1D WO_x species (highly dispersed and discontinuous status) at the surface, which, however, delivered the poorest selectivity toward nitrilation (S_ADN+MCP). In comparison, both efficient and selective transformation of DMA to ADN was achieved by fabricating WO_x/ZrO₂ with continuously distributed oligomeric WO_x species (∼2D) at the surface, either by varying the dosage of the W-reagent in the preparation of WO_x(m)/ZrO₂ or by doping a proper amount of the Mn element into WO_x(5.0)/ZrO₂, bearing WO₃ NPs. Furthermore, the in situ diffuse reflectance infrared Fourier transform spectroscopy investigations of both independent and competitive adsorptions of ester functionality and NH₃ over W–O–Zr, W–O–W, and Zr–O–Zr boundaries at the surface clarified the synergistic effect of these species in the activation of DMA/NH₃ and thereby nitrilation.