Evaluating the performance of non-precious metal based catalysts for sulfur-tolerance during the dry reforming of biogas

• Evaluation of active, stable non-precious metals catalysts for sulfur tolerance for dry reforming of biogas.
• The bimetallic catalysts consisting of cobalt and nickel produced a highly stable activity.
• A bimetallic catalyst in which cobalt was impregnated before nickel gave the best overall performance.
• Statistical structure-activity relations have been designed to help explain differences in activity of various catalysts.
• Increase in pore volume/surface area ratio, metal dispersion, reducibility and support basicity increase catalyst activity.

A portfolio of catalysts with a nominal composition 15 wt.%Ni + (0/5 wt.%)Co/MaOx–NaOx–Al2O3 (where M = Mg, Ca, La, Y, Gd; N = Al, Zr) were synthesized and evaluated for biogas reforming application. Structure activity relations (SARs) were designed to help explain the significant difference in activity observed among the catalysts containing monometallic (Ni) and bimetallic species (Ni–Co) and among the bimetallic catalysts impregnated by altering the sequence of impregnation. The order of activity observed among the various catalyst formulations was: bi-metallic (reverse stepwise Co → Ni) > bi-metallic (simultaneous Ni + Co) > mono-metallic > bi-metallic (stepwise Ni → Co). From SARs it is established that high pore volume to surface area ratio, high metal dispersion, high reducibility and high support basicity are the essential traits of an active and stable catalyst. Analysis of variability (ANOVA) was performed to identify the main and interaction effects of various factors on both catalyst activity and catalyst textural properties. Impregnation sequence and promoter composition are found to have significant effects on both catalysts activity and its textural properties. Also, an empirical model equation that establishes a statistical relationship between the factors and the response variable was developed. In addition, a sensitivity analysis was performed to study the effect of surfactant to metal ratio, CH4-to-CO2 ratio, operating temperature, H2S concentration, cobalt amount, and support basicity on catalyst performance.