A monopropellant consisting of 59% hydroxylammonium nitrate and 41% 1-ethyl-3-methylimidazolium ethyl sulfate by mass is tested for decomposition on heated platinum, rhenium, and titanium surfaces. It was found that the propellant decomposes at 165 °C on titanium, which is the decomposition temperature of HAN. The onset temperature for decomposition on platinum was 85 °C and on rhenium it was 125 °C. This suggests that platinum and rhenium act as catalysts for the decomposition of the monopropellant. From the experimental data, Arrhenius-type reaction rate parameters were calculated. The activation energy for platinum was 3 times less than that of titanium suggesting it could be a prime choice for catalyst material in further thruster development.