NiCoCe-LDO catalysts for low-temperature SCR of NOX with C3H6: Trimetallic synergy and reaction mechanism

To advance hydrocarbon-selective catalytic reduction (HC-SCR) of NOx, ternary mixed metal oxide catalysts (Ni x Co y Ce z -LDO) were synthesized through calcination of layered double hydroxide (LDH) precursors prepared via urea-assisted homogeneous precipitation. The trimetallic catalysts demonstrated enhanced low-temperature activity, improved redox properties, and superior sulfur resistance, attributed to synergistic interactions among Ni, Co, and Ce. In particular, Ni 0.48 Co 0.24 Ce 0.28 -LDO exhibited optimal performance, attaining 96.6% NO conversion with 98.25% N 2 selectivity at 225 °C, while maintaining high stability under 5% O 2 and 0.02% SO 2 . Characterization (XRD, ICP, SEM and BET) confirmed the formation of highly dispersed nanocrystallites with uniformly distributed metals and identified CeO 2 as the dominant crystalline phase, which provided abundant Lewis acid sites for C 3 H 6 activation. XPS and H 2 -TPR results indicated that the incorporation of Ce increased the Ni 3+ /Ni 2+ and Co 3+ /Co 2+ ratios, promoted oxygen vacancy formation, and enhanced catalyst reducibility, while the presence of Ni facilitated the generation of mobile surface oxygen species (O β ). Py-FTIR analysis further revealed that the synergistic interaction between Ni and Co enhanced Lewis acidity by increasing the density of unsaturated cationic sites, explaining why the trimetallic Ni 0.48 Co 0.24 Ce 0.28 -LDO catalyst exhibited the highest Lewis acid content. In-situ DRIFTS demonstrated that both Lewis and Brønsted acid sites promoted the formation of reactive nitrate species, while C 3 H 6 oxidation to formate and acetate intermediates drove the NO X reduction pathway. Based on these results, a reaction mechanism was proposed. Overall, this study provides valuable insights for designing efficient and low-cost catalysts for HC-SCR applications.