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The increasing interest in utilizing methane, the primary component of natural gas, for chemical production has spurred research into methane partial oxidation (MPO) as an alternative to traditional steam methane reforming (SMR). MPO has lower energy requirements and potential for carbon capture, making it an attractive option for hydrogen production. Challenges remain, however, such as carbon deposition leading to degradation and achieving high hydrogen selectivity. Here, the impact of periodic reactor operation on MPO over a Pt/Al2O3 catalyst was studied, primarily via varying reactor inlet compositions. Experiments were conducted using periodic operation strategies to assess the influence of changing reactant inlet concentrations on hydrogen formation during MPO. The results suggest that cycling between mixtures with low and high oxygen content can lead to transient hydrogen formation rates that surpass those achieved at steady state. Control experiments and density functional theory (DFT) calculations show that enhanced hydrogen formation can be attributed to the reaction between CO with hydroxyl groups at the metal and alumina support interface. This work underscores the critical role of surface coverages at the metal support interface and suggests avenues for future exploration, including alternative support materials with higher OH mobility and changes in the cycling scheme to enhance catalyst performance under periodic conditions. 

The viability of alkane oxidative dehydrogenation (ODH) processes specifically, and catalytic partial oxidation reactions more generally, are oftentimes limited by the formation of undesired deep oxidation products such as CO and CO2. The forced dynamic operation (FDO) of catalytic reactors has been proposed as a means for enhancing desired olefin or oxygenate selectivity and yield over those of CO and CO2, but an elucidation of the precise mechanistic bases for the dynamic enhancement observed continues to remain evasive. In this work, we provide an explanation of the extent of dynamic enhancement noted during ethane ODH over supported MoOx catalysts but not VOx ones─an explanation grounded in a quantitative analysis of the density and reactivity of chemisorbed and lattice oxygen species on these two classes of catalysts. Supported vanadia catalysts, unlike molybdena ones, carry oxygen species with similar reducibilities, resulting in highly contrasting trends in dynamic and steady state ODH properties for the two catalysts. Whereas in the case of VOx/Al2O3, oxygen speciation affects the nature of the hydrocarbon activated (ethane or ethylene), in the case of MoOx/Al2O3, it affects the type of product formed (ethylene or COx). Metal oxide loading is shown to be a key parameter impacting dynamic enhancement, with the FDO enhancement of higher loading molybdena samples converging toward that of the vanadia catalyst. The preferential depletion of chemisorbed oxygens is revealed to be a key determinant of the extent of dynamic enhancement, with an asymmetry in modeled O*/OL ratios under dynamic conditions relative to SS ones helping rationalize the effect that modulation frequency has on FDO enhancement. Collectively, the results presented here establish a quantitative, molecular-level basis for dynamic enhancement noted during the ODH of ethane, and point to considerations relating to the reactivity of chemisorbed and lattice oxygens as well as their dynamic and steady state ratios as levers for mitigating side-product formation through FDO. 

Transient reaction modulation has found its place in many branches of chemical reaction engineering over the past hundred years. Historically, catalytic reactions have been dominated by the impulse to reduce spatial and temporal perturbations in favor of steady, static systems due to their ease of operation and scalability. Transient reactor operation, however, has seen remarkable growth in the past few decades, where new operating regimes are being revealed to enhance catalytic reaction rates beyond the statically achievable limits classically described by thermodynamics and the Sabatier principle. These theoretical and experimental studies suggest that there exists a resonant frequency which coincides with its catalytic turnover that can be exploited and amplified for a given reaction to overcome classical barriers. This review discusses the evolution of thought from thermostatic (equilibrium), to thermodynamic (dynamic equilibrium), and finally dynamic (non-equilibrium) catalysis. Natural and forced dynamic oscillations are explored with periodic reactor operation of catalytic systems that modulate energetics and local concentrations through a multitude of approaches, and the challenges to unlock this new class of catalytic reaction engineering is discussed.