Reaction pathways and kinetics governing the Rucatalyzed hydrogenation of levulinic acid (LA) in the aqueous phase to form γ-valerolactone (GVL) were considered in a packed bed reactor. GVL can be produced by two distinct hydrogenation pathways; however, over Ru/C at temperatures below 423 K, it forms exclusively via intramolecular esterification of 4-hydroxypentanoic acid (HPA). Over Ru/C, reasonable hydrogenation rates of LA to HPA were observed at near-ambient temperatures (e.g., 0.08 s −1 at 323 K), but GVL selectivities are poor (<5%) under these conditions. Apparent barriers for LA hydrogenation and HPA esterification are 48 and 70 kJ mol −1 , respectively, and GVL selectivity improves at higher temperatures alongside increasing mass transfer limitations in 45−90 μm catalyst particles. Reactivity and selectivity trends in LA hydrogenation below 343 K are well-described by an empirical kinetic model capturing sequential hydrogenation and esterification. Coupling stacked beds of Ru/ C and Amberlyst-15 delivers high GVL yields (∼80%) at near ambient temperatures (323 K) and practical residence times.

Acceleration of catalytic transformation of molecules via heterogeneous materials occurs through design of active binding sites to optimally balance the requirements of all steps in a catalytic cycle. In accordance with

Transformational catalytic performance in rate and selectivity is obtainable through catalysts that change on the time scale of catalytic turnover frequency. In this work, dynamic catalysts are defined in the context and history of forced and passive dynamic chemical systems, with classification of unique catalyst behaviors based on temporally-relevant linear scaling parameters. The conditions leading to catalytic rate and selectivity enhancement are described as modifying the local electronic or steric environment of the active site to independently accelerate sequential elementary steps of an overall catalytic cycle. These concepts are related to physical systems and devices that stimulate a catalyst using light, vibrations, strain, and electronic manipulations including electrocatalysis, back-gating of catalyst surfaces, and introduction of surface electric fields via solid electrolytes and ferroelectrics. These catalytic stimuli are then compared for capability to improve catalysis across some of the most important chemical challenges for energy, materials, and sustainability. File list (2) download file view on ChemRxiv Perspective_Manuscript_ChemRxiv.pdf (3.88 MiB) download file view on ChemRxiv Perspective_Supporting_Information_ChemRxiv.pdf (149.75 KiB)