(492e) An Examination of the Intrinsic Activity and Stability of Various Solid Acids during the Catalytic Decarboxylation of γ-Valerolactone
In this study, we have considered the catalytic decarboxylation of γ-valerolactone (GVL), which occurs over solid acids to yield 1-butene and carbon dioxide. To arrive at a set of governing design parameters for decarboxylation catalysts, we have examined the roles of Brønsted:Lewis site distribution, Brønsted site deprotonation energy, and catalyst morphology in defining the activity and stability of materials employed for GVL decarboxylation. Decarboxylation rates were measured in a gas-phase reactor from 523 – 723K over a series of solid acids including amorphous silica alumina, MFI zeolites, supported phosphotungstic acid, and γ-Al2O3. In aluminosilicates, Brønsted sites associated with framework aluminum contribute the majority of decarboxylation activity. Relative to bridging hydroxyls, coordinatively unsaturated aluminum sites are substantially less active, and they do not contribute significantly to butene production rates in materials having both framework and extraframework aluminum. Through comparison of aluminosilicates with supported heteropolyacids, decarboxylation barriers were found to scale with the deprotonation energy of Brønsted acid sites; however, the intrinsic decarboxylation activity of a Brønsted site is not necessarily anticipated by its deprotonation energy. Catalyst deactivation in this system is attributed to coke deposition, and catalyst stability correlates most strongly with pore size such that microporous zeolites deactivate quickly compared to mesoporous analogs.