Ni-Based SBA-15 Catalysts Modified with CeMnO x for CO 2 Valorization via Dry Reforming of Methane: Effect of Composition on Modulating Activity and H 2 /CO Ratio.

Dry reforming of methane with ratio CH 4 /CO 2 = 1 is studied using supported Ni catalysts on SBA-15 modified by CeMnO x mixed oxides with different Ce/Mn ratios (0.25, 1 and 9). The obtained samples are characterized by wide-angle XRD, SAXS, N 2 sorption, TPR-H 2 , TEM, UV-vis and Raman spectroscopies. The SBA-15 modification with CeMnO x decreases the sizes of NiO nanoparticles and enhances the NiO-support interaction. When Ce/Mn = 9, the NiO forms small particles on the surface of large CeO 2 particles and/or interacts with CeO 2 , forming mixed phases. The best catalytic performance (at 650 °C, CH 4 and CO 2 conversions are 51 and 69%, respectively) is achieved over the Ni/CeMnO x /SBA-15 (9:1) catalyst. The peculiar CeMnO x composition (Ce/Mn = 9) also improves the catalyst stability: In a 24 h stability test, the CH 4 conversion decreases by 18 rel.% as compared to a 30 rel.% decrease for unmodified catalyst. The enhanced catalytic stability of Ni/CeMnO x /SBA-15 (9:1) is attributed to the high concentration of reactive peroxo (O - ) and superoxo (O 2 - ) species that significantly lower the amount of coke in comparison with Ni-SBA-15 unmodified catalyst (weight loss of 2.7% vs. 42.2%). Ni-SBA-15 modified with equimolar Ce/Mn ratio or Mn excess is less performing. Ni/CeMnO x /SBA-15 (1:4) with the highest content of manganese shows the minimum conversions of reagents in the entire temperature range (X(CO 2 ) = 4-36%, X(CH 4 ) = 8-58%). This finding is possibly attributed to the presence of manganese oxide, which decorates the Ni particles due to its redistribution at the preparation stage.