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This work investigates selective Ni locations over Ni/CeZrO x –Al 2 O 3 catalysts at different Ni loading contents and their influences on reaction pathways in ethanol steam reforming (ESR). Depending on the Ni loading contents, the added Ni selectively interacts with CeZrO x –Al 2 O 3 , resulting in the stepwise locations of Ni over CeZrO x –Al 2 O 3. This behavior induces a remarkable difference in hydrogen production and coke formation in ESR. The selective interaction between Ni and CeZrO x for 10-wt.% Ni generates more oxygen vacancies in the CeZrO x lattice. The Ni sites near the oxygen vacancies enhance reforming via steam activation, resulting in the highest hydrogen production rate of 1863.0 μmol/g cat ·min. In contrast, for 15 and 20-wt.% Ni, excessive Ni is additionally deposited on Al 2 O 3 after the saturation of Ni–CeZrO x interactions. These Ni sites on Al 2 O 3 accelerate coking from the ethylene produced on the acidic sites, resulting in a high coke amount of 19.1 mg c /g cat·h (20Ni/CZ-Al). [Display omitted] • Ni/CeZrO x –Al 2 O 3 for ethanol steam reforming are prepared at different Ni contents. • Depending on the Ni amounts, Ni selectively interacts with the CeZrO x –Al 2 O 3 support. • Stepwise Ni locations over CeZrO x –Al 2 O 3 remarkably affect the ESR reaction pathways. • Ni sites near the oxygen vacancies on CeZrO x enhance reforming via steam activation. • Ni sites on Al 2 O 3 accelerate coking from the ethylene produced on the acidic sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Manipulating metal-support interactions in Ni/CZA catalysts were investigated. • 20Ni/40CZA contained highly dispersed Ni nanoparticles and abundant oxygen vacancies. • 20Ni/40CZA exhibited the highest H 2 production rate and the lowest coke formation. • Coke precursor gasification was promoted by the efficient delivery of active oxygen. Understanding coke formation routes over Ni-based catalysts is essential in determining the catalytic performance in ethanol steam reforming. In this study, we focused on optimizing the active sites distribution via the metal-support interactions and understanding the coke precursor gasification in Ni/Ce x Zr 1-x O 2 –Al 2 O 3 (CZA) catalysts for ethanol steam reforming. We found that the optimized active sites distribution could minimize coke formation by enabling efficient gasification of a coke precursor on Ni. In the 20Ni/40CZA catalyst, the crystalline CZ exhibited a strong interaction with Ni, maintaining a uniform distribution of highly dispersed Ni nanoparticles and creating abundant oxygen vacancies on CZ, even at 20 wt% of Ni loading. Consequently, the resistance to coking over 20Ni/40CZA was significantly enhanced due to the efficient delivery of active oxygen atoms from steam on the abundant oxygen vacancies to the coke precursor on the Ni surface, resulting in fast gasification of the coke precursor. [ABSTRACT FROM AUTHOR]