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

Abstract Utilizing near zero‐carbon NH 3 as fuel in engines is promising for carbon‐neutrality. However, the application of NH 3 into the engine suffers from the intrinsic poor combustion characteristics of NH 3 and the emission of harmful NO x exhausts. Herein, we proposed and successfully confirmed a novel scenario for converting a conventional “CH 4 ‐fueled” engine to “NH 3 ‐fueled” engine. Specifically, CH 4 was used to power the internal combustion engine and release CO 2 as the exhaust. Afterwards, we put forward two routes to convert the exhaust and NH 3 into N 2 and CH 4 for enclosing the carbon cycle. The first “spatially decoupled” route splits the exhaust treatment into NH 3 cracking over Ru clusters on the calcined Mg−Al hydrotalcite (Ru/MAO) and CO 2 methanation over a commercial Ni/Al 2 O 3 . Both NH 3 and CO 2 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 NH 3 and CO 2 into N 2 , CH 4 , and H 2 O. Due to the mismatch of reaction conditions and the competitive adsorption of reactants, the conversions of NH 3 and CO 2 were lowered to 80.1 % and 49.3 %, respectively, over Ru/MAO under 1 bar (CO 2 :NH 3 =3 : 8) at 550 °C.