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Methane, abundant but inert, contributes significantly to greenhouse gases, primarily through combustion, which emits vast amounts of CO 2. Photocatalytic methane coupling at ambient temperature offers a method to convert it into ethane, a more versatile hydrocarbon. This study examines selective methane-to-ethane coupling using heterogeneous photocatalysts comprising silver and palladium salts dispersed on titania. Through a combination of ex-situ and in-situ techniques along with DFT simulations, distinct mechanisms and active phases in these catalysts are revealed. In silver catalysts, dispersed cationic Ag+ species are crucial for methane activation, while in palladium catalysts, palladium primarily exists in metallic form during coupling. Water strongly enhances coupling rates with both catalysts. DFT modeling identified methane adsorption sites, suggesting methane activation via •OH radicals, experimentally supported by EPR under in-situ conditions. [Display omitted] • Selective methane coupling on metal salts of heteropolyacid dispersed on titania. • Strong promoting effect of water on methane photocatalytic coupling. • In-situ identification of reaction mechanisms and intermediates. • Methane activation on cationic silver and metallic palladium. [ABSTRACT FROM AUTHOR]

[Display omitted] • The structure and surface composition of Cu- and Mn-doped La 0.7 FeO 3 was refined using both bulk and surface characterization techniques • The CuO segregated phase plays the role of redox-active center in Cu-LaFeO 3 material. • Mn 3 + cations embedded at B-site of the perovskite lattice are the major redox-active centers in Mn-doped La 0.7 FeO 3. The present work aims at presenting our investigations on the redox behaviour of Cu- or Mn-doped LaFeO 3 -based perovskite powders under three-way catalysis (TWC) relevant conditions. Two distinct La-deficient catalysts of generic formula La 0.67 Fe 0.8 Mn 0.2 O 3 and La 0.67 Fe 0.8 Cu 0.2 O 3 denoted as Mn-dLFO and Cu-dLFO, respectively, were prepared based on the conventional citrate complexation route and systematically investigated using complementary characterisation techniques. This study has made it possible to highlight fundamentally different structures. In Cu-dLFO, most Cu 2 + cations are expelled from the LaFeO 3 perovskite lattice in the form of a segregated CuO phase. On the other hand, in the case of Mn-dLFO, majority of Mn 3 + cations are stabilised within the perovskite solid solution, while substantial iron exsolution in the form of an additional α -Fe 2 O 3 phase was evidenced. The evolution of both catalysts during CO-TPR using operando Raman revealed the formation of polycyclic aromatic hydrocarbons (PAHs) besides the relative structural stability of the LaFeO 3 lattice. The reduction of Mn 3 + to Mn 2 + , indirectly suggested by Raman analysis, is further supported by a quasi- in situ XPS study. The latter also evidenced the reduction of CuO to metal copper to a large extent in Cu-dLFO. In addition, a share of the α -Fe 2 O 3 phase present in Mn-dLFO is reduced to metal Fe 0 during CO oxidation, and is fully re-oxidised upon NO reduction. Our investigation thus evidences that both copper and manganese sites in Cu-dLFO and Mn-dLFO, respectively, are redox-active centres upon CO oxidation/NO reduction with, however, varying operating modes underpinned by their fundamentally different structures. [ABSTRACT FROM AUTHOR]