Controlling Reaction Routes in Noble‐Metal‐Catalyzed Conversion of Aryl Ethers

Abstract

Hydrogenolysis and hydrolysis of aryl ethers in the liquid phase are important reactions for accessing functionalized cyclic compounds from renewable feedstocks. On supported noble metals, hydrogenolysis is initiated by a hydrogen addition to the aromatic ring followed by CÀ O bond cleavage. In water, hydrolysis and hydrogenolysis proceed by partial hydrogenation of the aromatic ring prior to water or hydrogen insertion. The mechanisms are common for the studied metals, but the selectivity to hydrogenolysis increases in the order Pd < Rh < Ir < Ru � Pt in decalin and water; the inverse was observed for the selectivity to hydrolysis in water. Hydrogenolysis selectivity correlates with the Gibbs free energy of hydrogen adsorption. Hydrogenolysis has the highest standard free energy of activation and a weak dependence on H 2 pressure, thus, the selectivity to hydrogenolysis is maximized by increasing temperature and decreasing H 2 pressure. Selectivity to CÀ O bond cleavage reaches > 95 % in water and alkaline conditions.

Boosting the Catalytic Activity and Stability of Ru Metal Clusters in Hydrodeoxygenation of Guaiacol through MWW Zeolite Pore Constraints

“…Note that HAL products first reached maxima in concentration at about 40 min and then decreased along with the reaction time (Figure c). The decrease of HAL products was mainly caused by the O-alkylates (i.e., aryl ethers), which can be reversibly converted over BAS through hydrolysis or elimination, or on Ru metal clusters through hydrogenolysis. ,, Based on the experimental observations, the reaction networks for HDO of guaiacol over mono- and bifunctional Ru-containing MWW zeolite catalysts are proposed in Scheme S1, and the detailed pathways are discussed accordingly in the Supporting Information.…”