Adjustment of Molecular Sorption Equilibrium on Catalyst Surface for Boosting Catalysis

ConspectusFor chemical reactions with complex pathways, it is extremely difficult to adjust the catalytic performance. The previous strategies on this issue mainly focused on modifying the fine structures of the catalysts, including optimization of the geometric/electronic structure of the metal nanoparticles (NPs), regulation of the chemical composition/morphology of the supports, and/or adjustment of the metal-support interactions to modulate the reaction kinetics on the catalyst surface. Although significant advances have been achieved, the catalytic performance is still unsatisfactory.It is accepted that the chemical equilibrium of a reaction can be disturbed by changing the concentration of the reactants or products, and the equilibrium will shift to another side to offset the perturbation until a new equilibrium is established. This is known as Le Chatelier's principle. Following this understanding, we show that the catalytic performance can be significantly modulated by adjusting the molecular sorption equilibrium on the catalyst surface. For example, enriching the reactants and/or intermediates on the catalyst surface pushes the reaction forward, thus increasing the catalytic conversion; removing the product away from the catalyst surface improves the catalytic conversion and product selectivity; and inhibiting the side reactions enhances the product selectivity and catalyst durability. Using these strategies has successfully enhanced the catalytic performances in many challenging reactions, such as increasing H₂O₂ concentration around the metal active sites to enhance methane oxidation, enriching olefin on the catalyst surface to boost hydroformylation, selective combustion of H₂ to shift the reaction equilibrium and improve ethane conversion in ethane dehydrogenation, and removing water from the reaction system to enhance Fischer-Tropsch synthesis. The key to these successes is effectively shifting the molecular sorption equilibrium under the working conditions.In this Account, we briefly summarize recent advances in adjusting molecular sorption equilibrium for boosting catalysis, with a focus on the equilibrium shift for a desired pathway by the unique functions of zeolites and polymers such as silanol nests on zeolite for olefin adsorption, the "molecular fence" effect of zeolite for H₂O₂ enrichment, MFI zeolite nanosheets for olefin diffusion, and the hydrophobic zeolite sheath and polymer for water separation/diffusion. We report the adjustment of the molecular sorption equilibrium on the catalyst surface via enriching the reactants and intermediates, removing the products, and inhibiting the side reactions to enhance the catalytic performance. As a result, high activity, excellent selectivity, and outstanding durability of the catalysts were achieved. In addition, current challenges and perspectives of applying this strategy to more important industrial reactions are discussed. Applications of advanced characterization tools, machine learning, and artificial intelligence for monitoring the dynamic structural changes of the catalyst and predicting the structural evolutions under working conditions are anticipated to continuously play important roles in catalyst design. We believe that this strategy will open a door for the development of highly efficient catalysts with potential applications in the future.