Double oxalates of Rh(III) with Ni(II) and Co(II) – Effective precursors of nanoalloys for hydrocarbons steam reforming

Abstract

Heteronuclear coordination compounds of d-metals are suitable single-source precursors for bimetallic nanoalloys, which often show extraordinary catalytic properties due to synergetic effect. In particular, Ni- and Rh-based catalysts are highly effective in low temperature steam reforming processes. Double oxalates of Rh with Ni and Co of the formula {[Rh(H2O)2(C2O4)μ-(C2O4)]2M(H2O)2}·6H2O (M = Ni, Co) were synthesized and structurally characterized. According to thermogravimetric analysis, the complexes decompose completely in He and H2 atmospheres to form corresponding nanoalloys at ∼300 °C. The calcination in O2 atmosphere leads to formation of spinel type mixed oxide. The supported Co–Rh/Al2O3 and Ni–Rh/Al2O3 catalysts were prepared by impregnation of double oxalate complexes in porous support with subsequent calcination and tested in propane low temperature steam reforming in CH4 excess. The Co-containing catalyst showed comparable activity regarding to pure Rh/Al2O3 sample, while bimetallic Ni–Rh/Al2O3 catalyst revealed to be appreciably more active, than monometallic catalysts with higher active component loadings. Rh–Ni catalyst allowed for complete propane conversion at T ≈ 350 °C, whereas for Rh catalyst the temperature was T ≈ 410 °C, and Rh–Co did not reach complete C3H8 conversion at all.