Cl-Free Ru Catalysts for Ammonia Decomposition Prepared by Chemical Reduction: Effects of Thermal Treatment

Abstract

Ru/Al2O3 catalysts were synthesized via a chemical reduction method using ruthenium chloride as the precursor and subsequently subjected to different calcination temperatures. The catalysts’ physicochemical properties were characterized, and their catalytic performance in ammonia decomposition was evaluated. For comparison, Ru/Al2O3 catalysts were also prepared via a wet impregnation method to assess the effectiveness of the chemical reduction approach in removing Cl residues. In the chemical reduction process, ruthenium precursor was fully converted to metallic ruthenium using a NaBH4 solution, which was subsequently dispersed onto an alumina support. Nevertheless, there was residual Cl on the catalysts prepared by wet impregnation even after calcination process, which has negative effect on the ammonia cracking reaction. As the calcination temperature increased, Ru dispersion decreased owing to the agglomeration of Ru particles. The uncalcined catalyst synthesized via chemical reduction exhibited excellent and sustained catalytic activity in the ammonia decomposition reaction. It consistently maintained an ammonia conversion rate of approximately 97% over 100 h at 550°C.