X-ray diffraction (XRD) measurements were carried out on
a Panalytical X’pert Pro Super X-ray diffractometer with Cu-K
radiation (40 kV and 30 mA). For in situ XRD measurements, the
powdery sample was loaded into an XRK-900 cell, which was
directly attached with the X-ray diffractometer. The XRD pattern
for the fresh sample was first recorded. Then, a H2 gas flow with
a flow rate of 50 mL min−1 was introduced into the XRK-900 cell
and the temperature was raised at a rate of 10K min−1. When the
desired temperature was reached,the catalyst was kept atthattemperature
for 5 min, and the XRD pattern was recorded. 25 min were
typically required for the collection of one pattern with 2 ranging
from 20◦ to 50◦. Before the appearance of the characteristic peaks
ascribed to Fe species (32◦–45◦), the catalyst had been kept at the
desired temperature for >15 min. The in situ XRD patterns under
the reactant gas mixture of (H2 + CO2) were also recorded at 618K.
For these measurements, the sample was first reduced in the in situ
XRK-900 cell with H2 gas flow with a rate of 50 mL min−1 at 673K.
After being cooled down to 618K, the reactant gas mixture was
introduced to the in situ XRK-900 cell, and then the XRD pattern
was recorded after a certain time.