Cr3+–Co0.054Ni0.018Mg0.93O Solid-Solution Catalysts for High-Pressure Syngas Production: Effect of Chromium on the Reduction and Catalysis

Abstract

Adding Cr to heat-tolerant Co0.054Ni0.018Mg0.93O solid-solution catalysts for CH4/CO2/H2O reforming at 2.1 MPa allowed us to control the key properties determining the behavior of the supported catalysts, such as the reduction degree of the metal, metal particle size, and amount of exposed zerovalent metals. A small load of Cr [Cr/(Co + Ni) = 0.11 mol %] efficiently catalyzed Co2+ and Ni2+ reduction. This catalyst, which had abundant small alloy particles on the support material, resisted coking and oxidative deactivation, even under accelerated deterioration conditions. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, extended X-ray absorption fine structure, and scanning transmission electron microscopy–energy-dispersive X-ray measurements indicated that Cr existed as a trivalent cation in a CrxCo0.054Ni0.018Mg0.93O1+1.5x solid solution, leading to the formation of a divalent cation vacancy and that Cr3+ was abundant on the surface of the catalyst particles after calcination at 1373 K. The Cr3+ destabilized Co2+ and Ni2+ in the solid solution, especially on the surface of the catalyst particles and, thus, promoted Co2+ and Ni2+ reduction. However, excess Cr3+ induced sintering of the catalyst particles, resulting in aggregation of alloy particles and, thus, in an increased risk of coking.