Supplementary information
A Combined Multi-technique In situ Approach used to Probe the Stability of Iron Molybdate Catalysts during
Redox Cycling
Matthew G. O’Brien, Andrew M. Beale, Simon D. M. Jacques, Bert M. Weckhuysen*
S1: Characterization of the known phases present in the redox process
From the WAXS data in figure 1 ( and repeated below for convenience) the initial Fe2(MoO4)3 phase can be
identified by the six strongest characteristic peaks at 11.35, 11.65, 12.46, 13.60, 15.34 and 23.47 ˚which
are indexed to the Miller indices (2 1 2)/(4 1 2), (1 2 2)/(3 2 -2), (2 2 -1), (2 0 -6)/(4 0 -6), (1 1 -16)/(4 2 0) and (4
4 -7)/(7 3 -2) respectively1 (note that although only displayed to 20º2 data was available to 30º2). Then, as
expected, during the first reduction -FeMoO4 begins to form as characterized by peaks at 11.85, 14.27 and
15.09 ˚and indexed to the (2 2 0), (1 1 2) and (2 2 -2)/(3 1 -2) indices respectively.2 At the same time MoO2
is observed forming, as characterized by the three prominent peaks at 11.85, 16.61 and 23.68 ˚ , indexed to
(1 1 -1), (1 1 1)/(0 2 0) and (2 2 -2)/(0 2 2) irrespectively.
P2
P1
Figure S1: Reproduction of the WAXS data from figure 1 with the dashed lines representing reduction and
solid oxidation. The two unidentified phases P1 and P2 are labeled.
S2: Contour plot of the WAXS data
Figure S2: A contour plot of the WAS data highlighting the P1 and P2 formation and indicating they are not due to shifts
in peak positions of known phases.
S3: Initial plot of UV-Vis data
Figure S3: The initial UV-Vis scan of the catalyst, indicating the ligand to metal charge transfer band (350 nm) and the
unidentified band (463 nm) (a) and a time resolved stack plot the data during the redox cycles. The red arrows represent
reducing conditions, the blue arrows oxidizing conditions (b). Note that the two bands at 580 and 608 nm do not change
throughout the experiment and therefore most likely do not represent significant components of the catalyst
composition and may even be due to some instrument or sample cell induced effect.
S4: XAS scans at the beginning and end of reduction
Normalised Intensity (a.u.)
1.4
1.2
1.0
2
0.8
1
0.6
0.4
0.2
0.0
20000
20050
20100
Energy (eV)
20150
20200
Figure S4: Comparison of the edge position (1) and first oscillation in the EXAFS (2) at the beginning of reduction (solid
line) and at the end of reduction, when phase P2 is present (dashed line).
S5: Close up of the formaldehyde GC data during oxidation to reduction switch of gas
Ion current (A)
8.0x10
-12
6.0x10
-12
4.0x10
-12
2.0x10
-12
140
142
144
146
Time (min)
148
150
152
Figure S5: The increased formaldehyde production during the oxidation to reduction gas switch reveals tow maxima in
output (arrows).
S5: XAS Comparison of the WAXS data at the beginning an end of oxidation
Intensity (a.u.)
2000
134 min
84 min
MoO3
1500
1000
500
0
10
12
14
16
Angle (2)
18
20
Figure S5: The appearance of a peak at 12.36o 2 upon oxidation of the catalyst, indicating the possible formation of
MoO3.
References
(1)
Rapposch, M. H.; Anderson, J. B.; Kostiner, E. Inorg. Chem. 1980, 19, 3531.
(2)
Sleight, A. W.; Chamberland, B. L.; Weiher, J. F. Inorg. Chem. 1968, 7, 1093.
(3)
Kim, Y. H.; Borry, R. W.; Iglesia, E. Microporous Mesoporous Mat. 2000, 35-6, 495.