Improving the coking resistance of Ni/Al2O3 modified by promoter (Ce, Zr, or Mg) under ethanol steam reforming: Perspective from growth sites of coking

A series of nickel catalysts supported on Al 2 O 3 that modified with Ce-, Zr-, and Mg-promoter were prepared via a sol-gel method and a subsequent impregnation method for the ethanol steam reforming reaction (ESR). The effect of promoters on the carbon deposition was focused. Compared with Ni/Al 2 O 3 catalyst, the introduction of different promoters decreased the selectivity for CH 2 CH 2 to different extent, especially, Ce-, Mg- containing catalysts completely suppressed the production of CH 2 CH 2 for 30 h tested at 500 °C. And the medium and strong acid sites were confirmed as the major sites for CH 2 CH 2 production. Encapsulation carbon derived from ethylene takes the primary responsibility for carbon deposition, and the formation of metal carbide is the other reason for causing carbon deposition. Among the tested catalysts, Ni/Mg–Al 2 O 3 exhibited a better performance for anti-carbon, which was attributed to the blockage of medium and strong acid sites as well as the high Ni crystallinity. The state of Ni particles：I. Ni crystal; II. solid solution; III. amorphous Ni cluster. A. ESR occurs on crystalline Ni; B. Ethanol dehydrogenates on the support; C. Adsorbed C atoms diffuse into the interior of the Ni cluster. • Ni catalysts supported on honeycomb modified alumina were prepared. • The cause of coking was studied from the perspective of growth sites. • The mechanism of anti-coking by introduction of Mg was identified.