Activation of two highly stable molecules – nitrogen and methane to co-produce ammonia and ethylene

•Microwave irradiation is capable of simultaneously activating highly stable molecules – nitrogen and methane.•The catalyst surface plays integral roles in production trend and selectivity of ethylene and ammonia.•DFT and MKM modelling elucidate the role of step sites and terrae sites of the catalyst in product formation.•Both the thermal and non-thermal effects of microwave irradiation are prevalent.•The catalyst coking and in-situ regeneration is demonstrated experimentally and explained theoretically using surface science. Two highly stable molecules, CH4 and N2 were simultaneously activated in a single-stage microwave-heated catalytic reactor to form ammonia, ethane, ethylene, and acetylene at atmospheric pressure. Density functional calculations and micro-kinetics modelling were used to predict the reaction behavior at temperatures ranging from 573 K to 973 K and validated with experimental analysis. The influences of terrace (111) and step (211) sites on K promoted Ru crystals were established in product formation and catalyst coking. NH3 formation occurs predominantly on the step (211) sites while C2 product formation can occur on both the sites. It was found that the elementary reaction steps leading to NH3 synthesis occurs due to the non-thermal effects of microwave irradiation while C2 products formed simultaneously are due to the thermal effects only. A reaction mechanism is postulated on the catalyst coking and validated experimentally by in-situ regeneration using H2 and O2.