Preparation of alumina-supported intermetallic compounds

Abstract

A series of alumina-supported intermetallic compounds, Pt₃Co/Al₂O₃, PtCu/Al₂O₃, Pt₃Sn/Al₂O₃ and Pd₃Pb/Al₂O₃, being promising materials as catalysts, were prepared by reduction of two metal precursors co-impregnated on γ-Al₂O₃. As a Pt precursor, [Pt(NH₃)₄]²⁺ or PtCl₆²⁻ was used coupled with the second metal precursors. Two different reduction procedures, gaseous H₂ and LiBH₄ in liquid phase, were also employed and compared. Using PtCl₆²⁻ which possesses a more negative reduction potential than [Pt(NH₃)₄]²⁺ strongly enhanced formation of the desired Pt-based intermetallic nanoparticles regardless of the reduction procedure. A similar trend was observed in preparation of Pd₃Pb/Al₂O₃ with PdCl₄²⁻ compared to Pd²⁺. A strong reduction agent LiBH₄ gave higher contents of the corresponding intermetallic phases than H₂ in all cases. Single-phase intermetallic compounds supported on alumina were synthesized by employing the chloro-complexes and LiBH₄ reduction. A systematic investigation indicates that the degree of intermetallic formation intrinsically depends on the difference in reduction potentials (ΔE) of the two metal precursors. Bimetallic combinations with small ΔE such as PdCl₄²⁻/Bi³⁺, Co²⁺/SnCl₆²⁻ and Ni²⁺/SnCl₆²⁻ also allow syntheses of PdBi/Al₂O₃, Co₃Sn₂/Al₂O₃, Ni₃Sn/Al₂O₃ and Ni₃Sn₂/Al₂O₃ by H₂ reduction, respectively. An appropriate choice of the metal precursor to reduce ΔE is an effective strategy to synthesize an alumina-supported intermetallic compound.