*3.2. Catalyst Characterisation*

N2 adsorption was used to measure the specific surface area. The sample (200 mg) was degassed at 200 ◦C overnight in VacPrep 061 Degasser (Norcross, GA, USA). Nitrogen adsorption was performed with a Miromeritics TriStar II 3020 Surface Area and Porosity Analyzer (Norcross, GA, USA) at −196 ◦C. The specific surface areas were calculated using the BET desorption branch of the isotherm [33].

Ex situ XRD patterns of as prepared samples were obtained with a Bruker D8 Advanced X-ray Diffractometer (Cambridge, United Kingdom) with a copper anode with an X-ray wavelength of 1.5418 Å. The measured angles (2θ) were scanned from 10◦ to 75◦ in 30 min; at a fixed divergence angle of 0.2◦. The PDF database was used for phase identification. The average crystallite sizes were calculated according to the Scherrer equation [34] assuming spherical crystals (K = 0.9) using the diffraction peak between 2θ = 45–50◦.

In situ powder XRD experiments were carried out at BM31 of the Swiss-Norwegian beam lines (SNBL) at the European Synchrotron Radiation Facility (ESRF). Catalyst sample (30mg, sieve fraction 53–90 μm) was fixed between two quartz wool plugs in a quartz capillary of 1 mm internal diameter (bed length: 10 mm). The capillary was then mounted in a custom cell [35] and exposed to X-rays for diffraction measurements. The temperature of the capillary reactor was controlled by a calibrated hot air blower. Powder X-ray diffraction patterns were collected with a 2D plate detector (Mar-345) using monochromatic radiation of wavelength 0.49324Å. Note that is different from the Cu Kα wavelength, which is used for acquiring ex situ XRD patterns. The instrumental peak broadening, wavelength calibration, and detector distance corrections were performed using a NIST 660a LaB6 standard. Mass flow controllers were used to feed NO, O2 and He in to produce the desired gas-feed composition (15 Ncm3/min; 1% NO, 6% O2, He balance). XRD patterns were recorded in situ during the

pretreatment step (flowing 15 Ncm3/min of 6% O2/He by heating at 10 ◦C/min from ambient to 500 ◦C and holding for 1 hr) and steady state NO oxidation (1%NO, 6% O2 and balance He) at 350 ◦C for 2 h. A lower concentration of NO (1%) was used for the in situ studies due to experimental constraints at the beamline.

The morphological analysis of as-synthesized perovskites was performed by using an in-lens cold field emission electron microscope FE-S(T)EM, (Hitachi S-5500) in scanning electron microscopy (SEM) mode.

Temperature programmed reduction by H2 was performed with an Altamira BenchCAT Hybrid 1000 HP (Pittsburgh, PA, USA). The samples (100 mg) were pretreated in 50 Ncm3/min flow of Ar at 150 ◦C for 30 min, with a heating rate of 10 ◦C. TPR was conducted by heating at a rate of 5 ◦C/min from 50 to 850 ◦C with a 50 Ncm3/min flow of 10% H2/Ar.
