CO₂ Reforming of Ethanol over Ni/Al₂O₃-(Zr–Yb)O₂ Catalysts: The Effect of Zr:Al Ratio on Nickel Activity and Carbon Formation

Ni-based catalysts supported on xAl2O3–(100 – x)(Zr–Yb)O2 mixed oxides xerogel matrix with various mole ratios (x = 35 and 65% alumina), prepared by a sol–gel method, were used as catalysts (Ni/xAZ) in the ethanol dry reforming (EDR) reaction in the temperature range 600–750 °C with different CO2/Ethanol feed molar ratios. The fresh and spent catalysts were characterized via X-ray diffraction (XRD), H2-TPR, Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), small angle X-ray scattering (SAXS), and Raman techniques. The results pointed to the key role of support composition (Zr:Al ratio) in the strength of metal–support interactions and natural carbon deactivation. Differences in the catalytic activity and stability of the samples are associated with different ratios of weakly and strongly interacting forms of nickel and their amounts depending on the Al/Zr ratio. The highest catalytic activity and stability of Ni/35AZ is due to the presence of ferromagnetic Ni0 particles formed during the reduction of oxide forms of nickel with moderate metal–support interaction. The higher Zr content in support composition increases the Ni2+ reducibility and the Ni0 formation due to its coordination in the form of the NiO with high metal–support interaction and defective spinel-type phase, improving resistance to graphite and carbonyl-type carbon formation under EDR reaction media. At the CO2/Ethanol = 1:1 reagent mixture ratio, Ni/35AZ-1:1 was more active at 600 °C (43% H2 yield, 38% CO yield), the best H2/CO ratio was achieved at 750 °C, and was at 1.2 regardless of the sample composition. Increasing the CO2 concentration at CO2/Ethanol = 1.4:1 increased the activity of the Ni/35AZ-1:1.4 sample (47% H2 yield, 44% CO yield at 600 °C), and the best H2/CO ratio was 1 at T = 750 °C.