Research on Catalysts for Online Ammonia Hydrogen Production in Marine Engines: Performance Evaluation and Reaction Kinetic Modeling

One viable technical approach for achieving hydrogen-blended combustion in marine ammonia-fueled engines is to utilize online ammonia decomposition to produce hydrogen, which is then introduced into the engine for combustion. This work carried out ammonia decomposition experiments using various catalysts, examining the effects of temperature and space velocity on Ru/Ce0.33Zr0.58La0.03Nd0.03Pr0.03O2.09 and Ni/Ce0.36Zr0.64O2 catalysts. Based on the experimental data obtained, the kinetic parameters of ammonia decomposition were fitted using four different models: mass action law, first-order reaction, Langmuir, and Temkin–Pyzhev kinetics across two catalysts, with the subsequent mechanistic analysis of catalytic reaction processes within the reactor. The results revealed that the NH3 conversion rate of the Ru/Ce0.33Zr0.58La0.03Nd0.03Pr0.03O2.09 catalyst was superior to that of the Ni/Ce0.36Zr0.64O2 catalyst, with temperature activity windows of 250–450 °C and 400–600 °C, respectively. Within the range of 2000–32,000 mL·g−1·h−1), an increase in space velocity led to a decrease in NH3 conversion rate by approximately half. All four models were able to predict NH3 conversion rates for the different catalysts with reasonable accuracy. The activation energies for Ru/Ce0.33Zr0.58La0.03Nd0.03Pr0.03O2.09 and Ni/Ce0.36Zr0.64O2 catalysts were found to be 37.7 kJ·mol−1 and 66 kJ·mol−1, respectively. Targeting hydrogen requirements of 10–40% vol for ammonia engines, the corresponding catalytic temperatures for Ru/Ce0.33Zr0.58La0.03Nd0.03Pr0.03O2.09 and Ni/Ce0.36Zr0.64O2 were above 267 °C and 500 °C, respectively.