Methane and methanol have emerged as chemical platforms that link the past, present, and future of the chemical industry. Methane, a primary fuel for power generation, and, methanol, a platform chemical, will likely serve as a bridge to a low-carbon energy future. We illustrate the kinetic and thermodynamic challenges in directing catalytic routes for the conversion of these critical feedstocks to products of higher value in the context of two case studies.

The dehydrative condensation of methanol to hydrocarbons (MTH) over zeotype catalysts is a versatile route for the commercial-scale valorization of abundant carbon feedstocks to fuels and chemicals. The identity and distribution of hydrocarbon products is largely influenced by the catalyst topology. For example, methanol conversion in medium-pore MFI zeolites yields a broad distribution of light olefins, gasoline-range hydrocarbons, and methyl-substituted benzenes, while the product distribution in small-pore CHA zeotypes is restricted to light olefins. We clarify the distinct reactivity within small- and medium-pore zeotype catalysts in the context of an autocatalytic hydrocarbon pool mechanism that succinctly describes MTH catalysis. In particular, we identify key molecular intermediates and reaction pathways that lead to both desired products and deactivating side paths. From this molecular-level understanding, we demonstrate the efficacy of inorganic modifiers and sacrificial hydrogen donors in mitigating catalyst deactivation in MTH catalysis and extend catalyst lifetimes indefinitely.

Strong, apolar C-H bonds in methane confer significant thermodynamic barriers for non-oxidative conversion of methane to aromatics. Medium pore MFI zeolites modified by well-dispersed carbidic molybdenum aggregates (MoCx/ZSM-5) reduce kinetic barriers to methane pyrolysis and catalyze dehydroaromatization (DHA) reactions with high benzene (≳ 70%) and aromatic (≳ 95%) selectivity at conversions near the ~10% equilibrium limit at ~950 K. We synthesize learnings from thermodynamics, reaction kinetics, and mass transport to clarify mechanistic observations and ascertain the identity of molecular events, species, and catalytic moieties that determine the activity of benchmark DHA catalysts. In doing so, we illustrate the significance of dispersive hydrogen transport at catalyst-bed length scales during DHA catalysis and we leverage this understanding to develop polyfunctional catalytic formulations that alleviate thermodynamic constraints on maximum single-pass conversion in DHA catalysis.