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Pretreatment under specific atmosphere is a general strategy to activate catalysts. How physicochemical properties of supports are modulated during activation process and their influence on active sites are still the ongoing topic. Herein, the effect of reaction gas treatment on performance of phosphorus modified Pd/Al 2 O 3 catalysts in lean methane oxidation was studied. The pretreated Pd/P-doped Al 2 O 3 catalyst exhibited a full conversion of CH 4 at ∼400 °C, excellent stability under both dry and wet conditions. Characterization results reveal that the uniform and stable P species in Al 2 O 3 enhanced the metal-support interaction and availability of oxygen in support. Under reaction gas condition, PdO-support connection was further promoted to favor generation of oxygen vacancies on support with the help of CH 4 , leading to weakened Pd–O bond, facile reformation and increased fraction of PdO. These facilitated formation of intermediates and surface dehydroxylation and mitigated the deactivation caused by thermodynamic decomposition of PdO. [Display omitted] • The P species kept homogeneous and stable during reaction gas treatment. • Activity of PdO for CH 4 activation is improved due to reaction gas treatment. • Reactivity of oxygen in P-modified Al 2 O 3 support is promoted. • Thermodynamic decomposition of PdO at high temperatures is prevented. • The rate of surface dehydroxylation is accelerated. [ABSTRACT FROM AUTHOR]

[Display omitted] • The K-mediated ultrasmall Ru nanoclusters show excellent NH3 synthesis activity. • Avoiding hydrogen poisoning on ultrasmall Ru nanoclusters through K mediation. • The addition of K could mediate the H-spillover and d-band center. • K addition significantly affects the electronic structure of Ru and oxygen vacancies. The effects of promoters on Ru nanoparticles (≥2 nm) catalysts for NH 3 synthesis have been extensively elaborated, but their roles on ultrasmall Ru nanoclusters (NCs, 1–2 nm) remain largely unknown and need to be further uncovered. Herein, a series of K-promoted MgO supported Ru NCs were synthesized and investigated for NH 3 synthesis. The addition of 5wt.%K onto Ru/MgO NCs leads to a significantly high NH 3 synthesis rate of 21.7 mmol NH3 g cat −1h−1 at 400 °C and 0.2 MPa, close to the thermodynamic equilibrium. Out studies reveal that anchoring K onto Ru NCs can increase the electron density and cause an upshift of the d -band center of Ru entities. Moreover, the addition of K regulates the hydrogen affinity and accelerates the migration of hydrogen from the Ru NCs surface to MgO support, which is crucial in avoiding the hydrogen poisoning effect on Ru NCs. With the synergistic effect of the Ru NCs sites bridged by H-spillover, makes the K-mediated Ru/MgO NCs catalysts efficient for NH 3 synthesis at mild conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • For the first time, we report a new strategy of colloid carbonization to synthesize highly active and stable Ru catalyst for NH 3 synthesis. • The developed Ru2.1-CC exhibits a NH 3 synthesis rate 9.4-fold that of Ru2.2-IM synthesized by impregnation method. • Ru2.1-CC catalyst displays high stability without aggregation of Ru nanoparticles after 100 h stability test. • The formation of ample B5 active sites and Ru-C interaction via colloid carbonization account for high reactivity and stability. Ruthenium-based catalysts are widely used in ammonia (NH 3) synthesis because of a high affinity for N 2 activation, while confronting the challenge of facile deactivation due to sintering. Herein, for the first time, we develop a highly active and sintering-resistant Ru2.1-CC catalyst via colloid carbonization (CC) for NH 3 synthesis. It exhibits a superior NH 3 synthesis rate around 9.4-fold that of Ru catalyst synthesized by impregnation method, displaying extremely high stability without aggregation of Ru nanoparticle after 100 h stability test. Our studies show that Ru2.1-CC possesses the average Ru particle size of 2.1 nm with narrow size distribution and thus exposes more active sites for N 2 activation. Moreover, the formation of Ru-C interaction via colloid carbonization over Ru2.1-CC can stabilize Ru particle size to realize high stability, meanwhile reduce work function and upshift the d-band center of Ru metal to accelerate its electron transfer for N 2 activation and NH 3 synthesis. This study provides a new strategy for simple synthesis of noble metal-based catalysts that are highly active and stable for NH 3 synthesis. [ABSTRACT FROM AUTHOR]