Characterization and catalytic properties of Sn-modified rapidly quenched skeletal Ni catalysts in aqueous-phase reforming of ethylene glycol

Skeletal Ni (RQ Ni) catalyst was prepared by alkali leaching of rapidly quenched Ni50Al50 alloy. By impregnating RQ Ni with SnCl4 followed by thermal treatment in inert atmosphere, homogeneous Sn-modified skeletal Ni (RQ Ni–Sn) catalysts were obtained. It was found that thermal treatment induces alloying of the deposited metallic Sn with Ni, forming Ni3Sn alloy segregated on the catalyst surface. In aqueous-phase reforming of ethylene glycol, the RQ Ni catalyst was less selective in producing H2 but more selective in producing alkanes than the Raney Ni catalyst described in the literature. This is attributed to the expansion of the lattice of RQ Ni favoring the dissociation of CO and, consequently, the methanation reaction consuming H2. Moreover, the structural difference influences the reaction pathway, with the undesired CO cleavage pathway obstructed on RQ Ni. Modification of RQ Ni with Sn drastically improves the H2 selectivity. On the RQ Ni80Sn20 catalyst, alkane production was virtually retarded, whereas H2 selectivity as high as 98 mol% was achieved at high conversion. Based on the characterizations and previous findings, it is suggested that Sn may block the active sites for CO adsorption and/or dissociation, thus suppressing the undesired methanation reaction. On the other hand, bifunctional Ni–Sn ensembles may form, in which Sn facilitates H2O dissociation while neighboring Ni adsorbs CO, thus promoting the desired water–gas shift reaction, leading to more H2.