CO<sub>2</sub> Reforming of Ethanol over Ni/Al<sub>2</sub>O<sub>3</sub>-(Zr–Yb)O<sub>2</sub> Catalysts: The Effect of Zr:Al Ratio on Nickel Activity and Carbon Formation
Anna Zhukova, Yuri A. Fionov, Sofia G. Chuklina, И. И. Михаленко, A. V. Fionov, O. Ya. Isaikina, D. Yu. Zhukov, Alice Medeiros de Lima
Abstract
Ni-based catalysts supported on x Al 2 O 3 –(100 – x )(Zr–Yb)O 2 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 CO 2 /Ethanol feed molar ratios. The fresh and spent catalysts were characterized via X-ray diffraction (XRD), H 2 -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 Ni 0 particles formed during the reduction of oxide forms of nickel with moderate metal–support interaction. The higher Zr content in support composition increases the Ni 2+ reducibility and the Ni 0 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 CO 2 /Ethanol = 1:1 reagent mixture ratio, Ni/35AZ-1:1 was more active at 600 °C (43% H 2 yield, 38% CO yield), the best H 2 /CO ratio was achieved at 750 °C, and was at 1.2 regardless of the sample composition. Increasing the CO 2 concentration at CO 2 /Ethanol = 1.4:1 increased the activity of the Ni/35AZ-1:1.4 sample (47% H 2 yield, 44% CO yield at 600 °C), and the best H 2 /CO ratio was 1 at T = 750 °C.