A Scenario for a Carbon‐Neutral Ammonia‐Fueled Engine Mediated by Catalytic NH₃ Cracking and CO₂ Hydrogenation

Abstract

Utilizing near zero‐carbon NH3 as fuel in engines is promising for carbon‐neutrality. However, the application of NH3 into the engine suffers from the intrinsic poor combustion characteristics of NH3 and the emission of harmful NOx exhausts. Herein, we proposed and successfully confirmed a novel scenario for converting a conventional "CH4‐fueled" engine to “NH3‐fueled” engine. Specifically, CH4 was used to power the internal combustion engine and release CO2 as the exhaust. Afterwards, we put forward two routes to convert the exhaust and NH3 into N2 and CH4 for enclosing the carbon cycle. The first "spatially decoupled" route splits the exhaust treatment into NH3 cracking over Ru clusters on the calcined Mg‐Al hydrotalcite (Ru/MAO) and CO2 methanation over a commercial Ni/Al2O3. Both NH3 and CO2 were almost completely converted into the target products under their respective optimal conditions. The second “spatially coupled” route refers to an one‐pot reaction of NH3 and CO2 into N2, CH4, and H2O. Due to the mismatch of reaction conditions and the competitive adsorption of reactants, the conversions of NH3 and CO2 were lowered to 80.1% and 49.3%, respectively, over Ru/MAO under 1 bar (CO2:NH3 = 3:8) at 550 °C.