Stable Ni/Nb 2 O 5 catalyst for the hydrotreating of diphenyl ether produced Key challenge in the design of solid catalysts for the HDO of lignin streams identified Lewis acidity crucial to HDO also assists catalyst deactivation via coke formation Recommendations for the catalyst design for lignin hydrotreating put forward

Structural stability is a pivotal property required for Nb2O5 to be applied as a solid-acid catalyst in heterogeneous catalytic reactions. When combined with Ni, Nb2O5 produces cheap and active hydrogenation catalysts. Ni-Nb2O5 operates as a bifunctional catalyst and is being widely explored for various catalytic applications without, however, exploring its structural stability and its effects on catalytic activity and durability. Herein we studied two forms of niobia, one with nonuniform morphology and another comprising a nanorod morphology. Various selected Ni loadings were dispersed on the two supports via a deposition–precipitation method. Physical and chemical characterization revealed that morphological control in combination with a highly efficient Ni deposition method is key in producing a structurally stable Ni-Nb2O5 catalyst. High surface area and porosity as exhibited by the Nb2O5 nanorods, in the pseudohexagonal phase, combined with small, well-dispersed Ni particles, provide a structurally stable material up to 500 °C, with high acidity (Lewis and Brønsted acid sites). Moreover, the local and long-range order, characterized in situ (XANES and XRD), determined the temperature limits for the optimization of metallic Ni particles in relation to the Nb2O5 structure.

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