Efficient hydrogenolysis of aryl ethers over Ce-MOF supported Pd NPs under mild conditions: mechanistic insight using density functional theoretical calculations

Abstract

Selective hydrogenolysis of lignin-derived aryl ethers under mild temperature and pressure conditions is an important milestone to be achieved to fulfill the future fuel demands from abundantly available biomass resources. Selective hydrogenolysis requires precise modulation of surface active sites of the catalyst to obtain the desired activity and selectivity. In this study, the selective hydrogenolysis of benzyl phenyl ether to phenol and toluene is achieved in methanol and water medium at a very low temperature and low H₂ pressure over a Pd nanoparticle decorated Ce-BTC metal–organic framework. The activity of the developed catalyst is two times higher than that of Pd decorated CeO₂. The structure–activity relationship is established using catalytic measurements, X-ray photoelectron spectroscopy, and transmission electron microscopy. The mechanistic insight into the hydrogenolysis of aryl ethers and the reasons behind the superior activity of Pd/Ce-BTC to that of Pd/CeO₂ are investigated using density functional theoretical (DFT) calculations. Spectroscopic measurements and DFT calculations suggest that the higher Pd⁰/Pd²⁺ ratio and higher adsorption of benzyl phenyl ether over Pd/Ce-BTC and the higher adsorption of phenol over Pd/CeO₂ are factors responsible for the higher activity of Pd/Ce-BTC than that of Pd/CeO₂. Efficient recyclability and hot filtration tests reveal that the catalyst exhibits no noteworthy loss in the activity after five consecutive cycles. The Pd/Ce-BTC catalyst displays a very high turnover frequency and low activation energy, which are very attractive from the industrial perspective and academic point of view.