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.