Utilising unexploited methane through its reaction with CO2 via the dry reforming of methane (DRM) has attracted attention. However, there are challenges related to catalyst deactivation and energy consumption due to the highly endothermic nature of the DRM; thus, microwave activation has been proposed to increase energy efficiency by directly heating the catalyst while minimising the heating of the reactor. In this study, we clarify the advantages of microwave heating in terms of more reactive coke formation during the reaction and enhanced reactivity under microwave conditions compared with conventional resistive heating. For the latter, steady-state isotopic transient kinetic analysis (SSITKA) was conducted to gain mechanistic insights, which suggested that microwave heating accelerated CO generation steps. This study shows that microwave activation can be advantageous in terms of reaction kinetics for the DRM.

Dry reforming of methane (DRM) was investigated using nanostructured core@shell materials, thermally activated with two different heating methods, namely conventional resistive heating and microwave. The core@shell catalysts were composed of β-SiC nanoparticles, with a mean particle size below 100 nm, coated by a uniform SiO2 shell of ca. 30 nm thickness. Highly dispersed Rh nanoparticles, with a mean particle size of 2.5 nm, were present on the surface of the SiO2 shell. Operation under microwave heating conditions enhanced the reverse water gas shift reaction activity, which takes place in parallel with the DRM process, as compared to the operation under resistive heating conditions. Moreover, stable long-term operation was achieved under microwaved-assisted conditions, due to the unique spatial arrangement of the phases composing the nanostructured catalytic system, together with the suppression of irreversible coke deposition.

To introduce promotional H₂O effects for both CH₄ rate and C₂ selectivity, the OH radical formation, catalyzed through H₂O activation with O₂ surface species, was critical for modeling selective Mn-K₂WO₄/SiO₂ catalysts. Based on our reported experimental evidence, which demonstrates the formation of H₂O₂ through surface alkali peroxide intermediate, the elementary reactions that account for the OH-mediated pathway were added into the microkinetic model. The advanced model adeptly replicated the promotional H₂O effects on both OCM rate and selectivity. The data from a low-pressure microkinetic study were treated isothermally, and extended for near-industrially relevant pressures up to 901 kPa. Thermal visualization using an infrared camera found substantial temperature increases at undiluted high-pressure conditions which caused C₂ selectivity to drop significantly. When the furnace temperatures were decreased after ignition, side reactions after O₂ depletion (e.g., hydrocarbon reforming) were suppressed, obtaining 13.7 (11.8) % yields at 19.9 % CH₄ conversion with 68.6 (59.1) % selectivities for C_2-4 (C₂) at 901 kPa. The temperature was found to be the determining factor of C₂ yield which was perturbed by varying space velocity or CH₄/O₂ ratios. The optimum temperature for high-pressure conditions was predicted as 885 °C at 901 kPa. The study provides mechanistic and industrially relevant understandings for further OCM catalyst design and system application.

The oxidative coupling of methane (OCM) was investigated using a catalyst with a core@shell structure or a physical mixture comprised of MgO and SiC or Fe₃O₄, which was thermally activated via two different heating methods, namely, conventional resistive heating and microwave heating. The use of microwave radiation together with the catalyst structure was essential to achieve high reaction efficiency. The C₂ selectivity and yield were correlated with the presence of temperature gradients in the catalytic bed under microwave radiation. These thermal gradients and their distribution were experimentally evaluated using operando thermal visualization. Hotspots and thermal gradients were beneficial to achieve a higher CH₄ conversion; however, it was found that a uniform reactor temperature was crucial to attain a high C₂ yield in OCM and the core@shell structure is beneficial. The hypothesis that an enhanced OCM performance can be achieved by keeping the catalyst material hot and the gas cold, using microwave to prevent uncontrolled gas-phase reactions was supported by a kinetic study and experimentally demonstrated.