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

Dry reforming of methane with ratio CH/CO = 1 is studied using supported Ni catalysts on SBA-15 modified by CeMnO mixed oxides with different Ce/Mn ratios (0.25, 1 and 9). The obtained samples are characterized by wide-angle XRD, SAXS, N sorption, TPR-H, TEM, UV-vis and Raman spectroscopies. The SBA-15 modification with CeMnO 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 particles and/or interacts with CeO, forming mixed phases. The best catalytic performance (at 650 °C, CH and CO conversions are 51 and 69%, respectively) is achieved over the Ni/CeMnO/SBA-15 (9:1) catalyst. The peculiar CeMnO composition (Ce/Mn = 9) also improves the catalyst stability: In a 24 h stability test, the CH conversion decreases by 18 rel.% as compared to a 30 rel.% decrease for unmodified catalyst. The enhanced catalytic stability of Ni/CeMnO/SBA-15 (9:1) is attributed to the high concentration of reactive peroxo (O) and superoxo (O) 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/SBA-15 (1:4) with the highest content of manganese shows the minimum conversions of reagents in the entire temperature range (X(CO) = 4-36%, X(CH) = 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.