*2.2. Catalytic Activity*

The activity of the pre-reduced catalysts towards the water gas shift (WGS) reaction was assessed by measuring CO conversion between 300 ◦C and 800 ◦C and the results are shown in Figure 3. Activities of the catalysts produced using Ni-free LST as a support are displayed in Figure 3a. Nickel was the most active among all metals and LST-5Ni exhibited CO conversion above 60% at 460 ◦C. The next best activities were shown by LST-5Fe followed by LST-5Mn and finally LST-5Mo and LST-5Cr, which showed only limited activities at reactions temperatures below 800 ◦C. The lack of activity of Cr and Mo is not surprising. Molybdenum was added with the specific intent to introduce an element with negligible WGS activity, but with significant sensitivity to sulfur to be used as a sacrificial agent. Chromium is mainly used in Fe/Cr-based WGS catalysts for its capability to stabilize the active Fe phase [22]. Since LST did not show any significant WGS activity (Figure 3a) it can be assumed that the catalytic activity of LST-Ni, LST-Fe and LST-Mn was due to the impregnated metal. The CO conversion of each catalyst after poisoning is shown by the dashed lines in Figure 3a. Only LST-5Ni suffered severely during catalyst poisoning using 50 ppm H2S under reaction conditions (800 ◦C, 1 h). The catalytic activity of LST-5Fe, LST-5Mn, LST-5Cr and LST-5Mo on the other hand, remained rather constant.

**Figure 3.** (**a**) WGS activity of LST impregnated with Cr (red), Fe (blue), Mn (orange), Mo (turquoise) and Ni (black) before (continuous lines) and after (dotted lines) catalyst poisoning with 50 ppm H2S. (**b**) WGS activity of LSTN (black), as well as LSTN impregnated with Cr (red), Fe (blue), Mn (orange) and Mo (turquoise).

Catalytic activities of impregnated LSTN-type catalysts are displayed in Figure 3b. LSTN exhibited the highest activity towards the WGS reaction, followed by LSTN-5Mn and LSTN-5Cr. LSTN-5Fe also exhibited higher activity than its Ni-free counterpart LST-5Fe, whereas the low activity of LSTN-5Mo remained unchanged by the presence of Ni in the sample. The catalytic results provide an indication for Ni alloying with the impregnated metals Cr, Fe and Mn. The fact that all LSTN-5Me (Me = Cr, Fe, Mn, Mo) catalysts exhibited lower catalytic activity than LSTN, while all metals showed at least some activity towards WGS on Ni-free LST, provides evidence for close interaction between segregated Ni and Me in LSTN-5Me or coverage of the active Ni phase with the less active Me. This interaction was found to be less beneficial for WGS activity under sulfur-free conditions. However, catalytic tests after sulfur poisoning showed a stabilizing effect of the metals on WGS activity. Especially LSTN-5Fe was able to maintain comparably high levels of catalytic activity after poisoning by H2S. It should be noted that the activity of LSTN-5Fe after poisoning did not exceed the one of LST-5Fe, which could indicate that Ni is still poisoned. Nevertheless, the improved activity of LSTN-5Fe in sulfur-free conditions compared to LST-5Fe demonstrates a potential benefit of a bimetallic catalyst.
