The small pore zeolite Cu-SSZ-13 is an efficient material for the standard selective catalytic reduction of nitrogen oxides (NO_x) by ammonia (NH₃). In this work, Cu-SSZ-13 has been studied at 250 °C under high conversion using a modulation excitation approach and analysed with phase sensitive detection (PSD). While the complementary X-ray absorption near edge structure (XANES) spectroscopy measurements showed that the experiments were performed under cyclic Cu⁺/Cu²⁺ redox, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments provide spectroscopic evidence for previously postulated intermediates Cu–N(O)–NH₂ and Cu–NO₃ in the NH₃-SCR deNO_x mechanism and for the role of [Cu²⁺(OH⁻)]⁺. These results therefore help in building towards a more comprehensive understanding of the reaction mechanism which to date has only been postulated in silico.

Mo/H‐ZSM‐5 has been studied using a combination of operando X‐ray absorption spectroscopy and High Resolution Powder Diffraction in order to study the evolution of Mo species and their location within the zeolite pores. The results indicate that after calcination the majority of the species present are isolated Mo‐oxo species, attached to the zeolite framework at the straight channels. During reaction, Mo is first partially carburized to intermediate MoC_xO_y species. At longer reaction times Mo fully carburizes detaching from the zeolite and aggregates forming initial Mo_1.6C₃ clusters; this is coincident with maximum benzene production. The Mo_1.6C₃ clusters are then observed to grow, predominantly on the outer zeolite surface and this appears to be the primary cause of catalyst deactivation. The deactivation is not only due to a decrease in the amount of active Mo surface but also due to a loss in shape‐selectivity which leads to an increased carbon deposition at the outer shell of the zeolite crystals and eventually to pore blockage.

In situ XRD-CT and post-reaction SEM/EDX were used to study the solid-state chemistry and structural changes of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membrane reactors during the oxidative coupling of methane reaction.