Vanadium passivated TiO₂ nanoplate for selective molybdenum recovery from spent HDS catalysts

초록

Selective recovery of molybdenum (Mo) from spent hydrodesulfurization (HDS) catalysts is hindered by chemically similar vanadium (V) oxoanions in strongly acidic leachates. We report an adsorption strategy that couples crystallographic facet engineering with dynamic surface passivation to achieve high Mo selectivity under harsh conditions. Acid-stable TiO₂ was employed as a suitable platform, and its adsorption energetics were enhanced by increasing the exposure of high-energy {001} facets, enhancing Mo adsorption independent of surface area. However, intrinsic Mo/V selectivity remained limited due to similar adsorption behavior. To overcome this, vanadium was introduced as a surface modifier, forming anchored VOₓ species that block V-reactive sites while preserving reversible Mo adsorption. Repeated adsorption–desorption cycles induced progressive surface reconstruction and self-limiting passivation, suppressing V uptake while maintaining Mo capacity. Consequently, Mo/V selectivity increased to approximately 168 after the third cycle and remained above 148 throughout ten consecutive adsorption–desorption cycles. The system showed rapid kinetics, stability in 1.0 M H₂SO₄, and efficient regeneration, enabling >95% Mo recovery with 99.6% purity. Moreover, validation with industrial spent HDS catalysts confirmed its practical applicability. This work demonstrates a separation principle that repurposes an interfering species as a functional modifier, dynamically amplifying selectivity beyond electrostatic limits for scalable metal recovery from acidic streams.

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