Effect of support acid-base properties on fe-catalyzed ammonia decomposition to hydrogen: a comparative study of boehmite-derived γ-Al2O3 and silica-alumina supports

Abstract

Ammonia is a promising hydrogen carrier, and its catalytic decomposition requires efficient and cost-effective catalysts. Here, we systematically investigated the effect of support's electron-donor properties on iron-catalyzed ammonia decomposition using commercially available boehmite-derived supports. PURAL SB (alumina) and the silica doped aluminas SIRAL10 and SIRAL40 with SiO2/Al2O3 = 10/90 and 40/60 w/w, respectively, were calcined at 700 °C and impregnated with a high Fe loading of 15 wt%. Catalytic tests revealed that the catalyst prepared on PURALSB calcined at 700 °C and reduced in H2 prior to reaction (Fe/PURALSB-C700-r) exhibited the highest activity, achieving 99.6% ammonia conversion at 700 °C and a space velocity of 30,000 ml NH3/(h×gcat), and sustained a stable 60% conversion over 140 h of time-on-stream at 200,000 ml NH3/(h×gcat). The catalytic activity decreased in the order Fe/PURALSB-C700-r > Fe/SIRAL10-C700-r > Fe/SIRAL40-C700-r, correlating with the support's basicity: the best-performing catalyst possessed the highest point of zero charge (7.8) and the lowest acidic-to-basic site ratio (1.15) from desorption measurements.