The New Ni Catalyst On The Ethylene Glycol Liquid Phase Reforming For Hydrogen Production Reaction

Aqueous phase reforming(APR) of ethylene glycol is a promising new route for the catalytic production of high-purity hydrogen for fuel cells and light alkanes.Since Ni shows high activities for C-C bond scission and methanation,moderate WGS activity,and is much less expensive than the noble Pt,Ni-based catalysts have been extensively studied in APR of ethylene glycol.In the present work,Ni catalysts prepared from a new method for the aqueous phase reforming of ethylene glycol were investigated.A non-pyrophoric Ni catalyst(NP Ni) was prepared by alkali leaching of a Ni₅₀Al₅₀ alloy using only～1/10 of the amount of NaOH required for the preparation of the conventional Raney Ni catalyst.Characterizations reveal that the as-prepared NP Ni catalyst can be looked as a Ni-Al(OH)₃ composite catalyst with Ni in the metallic state and Al(OH)₃ in forms of gibbsite and bayerite.After 100 h on stream in APR of ethylene glycol,phase transformation of gibbsite and bayerite to flake-like boehmite occurred,along with the growth of Ni crystallites and partial oxidation of metallic Ni to Ni(OH)₂.Under identical reaction conditions for APR of ethylene glycol,the NP Ni catalyst is about 40-52%more active than Raney Ni in terms of the conversion of ethylene glycol to gas products,which is attributed to the stabilizing effect of hydrated alumina on Ni crystallites.The higher selectivity toward H2 and the lower concentration of CO in the product gas on the NP Ni catalyst are attributed to the activation of water by hydrated alumina which is beneficial to the WGS reaction.The non-pyrophoric rapidly quenched Ni catalyst(NPRQ Ni) was prepared by alkali leaching of a rapidly quenched Ni₅₀Al₅₀(RQ Ni₅₀Al₅₀) alloy using the same method as the preparation of the NP Ni catalyst.In APR of ethylene glycol,the NPRQ Ni catalyst exhibited an catalytic activity doubled that of the RQ Ni catalyst due to its larger active surface area,and maintained～82%of its initial activity even after 100 h on stream due to its tolerance to oxidation and metal leaching.Sn-modified NP Ni catalysts(NP NiSn) were obtained by impregnating of NP Ni catalyst with SnCl₄.In APR of ethylene glycol,the addition of Sn facilitated the H₂ production.On the NP Ni₇Sn catalyst,H₂ selectivity of 85%was achieved at the steady state,which is about 80%higher than that on Raney Ni catalyst. Characterization by H₂-TPD has shown that new active sites were formed on the NP NiSn catalysts,and the increased H₂ selectivity may be ascribed to such active sites. H₂ without CO and CO₂ was produced through one-pot H₂ production from APR of ethylene glycol with KOH as the CO₂ absorbent.The formation of H₂ was enhanced by the addition of KOH to the ethylene glycol solution.Gas product composed of 98 mol%of H₂ and 2 mol%of methane obtained at high conversion of ethylene glycol when the concentration of KOH was up to 2 mol L^-1,and the H₂ yield was dramatically improved to 151%,which is closed to the theoretical yield(167%). The WGS reaction was promoted by potassium and the absorption of CO₂ with KOH, which leads to the higher H₂ selectivity.The presence of KOH also enhanced the stability of NP Ni catalyst.The conversion of ethylene glycol and the conversion of ethylene glycol to gas products on NP Ni catalyst were about 100%and 90%, respectively,even after 36 h on stream due to the suppressing of Ni sintering by potassium.