Evaluating bimetallic Ni-Co oxygen carriers for their redox behavior and catalytic activity toward steam methane reforming

This work deals with the synthesis of bimetallic Ni-Co oxygen carriers with ZrO2 as structure stabilizer via a one -pot sol-gel auto-combustion method and the evaluation of their redox properties and catalytic activity of their reduced state for steam methane reforming. Fresh materials were composed of Ni-Co mixed monoxides, which could be reduced to form a Ni-Co alloy. Conducting reforming experiments for 10 h time-on-stream at 650 degrees C showed that Ni-Co alloy sites of reduced bimetallic materials, in addition to the high reforming activity, can improve the stability compared to Ni sites of a monometallic material, due to a higher tendency of the latter toward sintering and coke formation. Redox behavior was tested via CH4 reduction and air oxidation cycles in a thermogravimetric analyzer. Increasing the Co content led to a slight decrease of reduction degree, which, however, was not altered over cycles. Both reduction and oxidation steps were found to proceed via a nucleation and nuclei growth reaction mechanism, with Co addition promoting the oxidation kinetics. Ultimately, addition of Co with low Co/(Ni + Co) ratios (<= 0.20) could balance adequate degree of reduction (>= 80 %) and oxygen transfer capacity (>= 0.07 g O/g material) in tandem with stable catalytic activity for steam methane reforming in the reduced state of oxygen carrier.

Automated summary

This study successfully synthesized bimetallic Ni-Co oxygen carriers with ZrO2 as a structure stabilizer using a one-pot sol-gel auto-combustion method. The redox properties and catalytic activity of the reduced state were evaluated, showing that the reduced bimetallic materials exhibited higher reforming activity and stability compared to monometallic materials, with Co addition promoting the oxidation kinetics.