The dehydroaromatization (DHA) reaction of methane under non-oxidative conditions is carried out over a molybdenum catalyst supported on HZSM-5 and boric acid (BA) treated HZSM-5 at 700 °C and atmospheric pressure.

Methane dehydrogenation and C–C coupling reactions to form ethylene on two different carbide clusters of molybdenum (Mo4C2 and Mo2C6) were studied. Density functional theory (DFT) calculations were performed to understand the reactivity of the two clusters, linking it to the overall methane dehydroaromatization (MDA) process. The electronic effect of catalyst reduction procedures and anchoring of the cluster on the zeolite framework was captured in simulations with varying positive charge on the cluster. In general, with one exception, DFT calculations suggested a reduction in dehydrogenation activation energies with more reduced (lesser positive charge) clusters. Similarly, activation barriers for the transfer of a H atom from the carbon to the neighboring Mo site were calculated to be lower on more reduced clusters. In contrast, the coupling reactions of the two CH3 and the two H atoms on the surface showed a reverse trend. The activation energies of the C–C and the H–H coupling steps were observed to be lower on less reduced (higher positive charge) clusters. On comparing the two (Mo4C2 and Mo2C6) clusters with similar charges, the activation energies for the first methane dehydrogenation were observed to be of similar value on both clusters for the neutral charge. However, second methane dehydrogenation was calculated to show a significantly higher barrier on the Mo2C6 cluster for both neutral and +1 charges. In addition, the CH3 coupling reaction was facilitated with a relatively lower activation barrier on the Mo2C6 cluster as compared to that on the Mo4C2 cluster. Thus, Mo2C6 sites in the vicinity of the Brønsted acid sites of the zeolite are likely to be more active for the coupling of the two CH3 species and helpful in MDA. This alluded to the operando experimental findings by Lezcano-González Lezcano-González Angew. Chem., Int. Ed.20165552155219], wherein it was suggested that methane might be activated on carbide and oxycarbide species; however, formation of MoC3-type species on stream was linked directly to MDA.

C–H bond activation steps in non-oxidative methane dehydroaromatization (MDA) play a key role in the functionalization of reactant and adsorbed species to form aromatics.

Methane catalytic pyrolysis, which is the reaction to produce hydrogen and carbon without emitting CO2, represents an approach for decarbonization using natural gas as an energy resource. The endothermic pyrolysis reaction was carried out under two heating scenarios: convective thermal heating and microwave-driven irradiative heating. The pyrolysis reaction was conducted at 550–600 °C over carbon nanotube (CNT)-supported Ni–Pd and Ni–Cu catalysts. On both catalysts, an enhanced methane conversion rate was observed under microwave irradiation. The enhanced catalytic activity was hypothetically caused by the presence of free electrons in the carbon atoms within the CNT that enabled the CNT support to absorb microwave energy effectively and to be heated efficiently by microwave. The microwave catalytic pyrolysis has shown improvement in kinetics, where the apparent activation energy dropped from 45.5 kJ/mol under conventional convective heating to 24.8 kJ/mol under microwave irradiation. When the methane conversion rate is increased by 37%, the microwave power consumption only changed by 10.8%. The research demonstrated the potential of transforming natural gas into clean hydrogen and value-added carbon in a more energy-efficient way. Process simulation and techno-economic analysis showed that potentially hydrogen minimum selling price of about $1/kg H2 could be achieved.