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

摘要

Skeletal Ni(RQ Ni)catalyst was prepared by alkali leaching of rapidly quenched Ni_(50)Al_(50)alloy.By impregnating RQ Ni with SnCl_4 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 Ni_3Sn alloy segregated on the catalyst surface.In aqueous-phase reforming of ethylene glycol,the RQ Ni catalyst was less selective in producing H_2 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 H_2.Moreover,the structural difference influences the reaction pathway,with the undesired C-O cleavage pathway obstructed on RQ Ni.Modification of RQ Ni with Sn drastically improves the H_2 selectivity.On the RQ Ni_(80)Sn_(20)catalyst,alkane production was virtually retarded,whereas H_2 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 H_2O dissociation while neighboring Ni adsorbs CO,thus promoting the desired water-gas shift reaction,leading to more H_2.