High performance Pd single atomic catalyst based on cellulose elementary crystals

Author: ZHANG Jinsong , YAN Yukun , LIU Zhiyu

Suzuki coupling reaction is an important reaction in the organic synthesis industry and plays an important role in the pharmaceutical industry. The Pd catalyst is the core of the suzuki reaction. However, the excessive use of Pd in the existing commercial Pd catalysts not only causes excessive use costs, but also the Pd lost from the catalyst will also cause product pollution. It has been reported in the literature that these reactions can become more economically attractive and safer only if the palladium loading of the catalyst is reduced to a level below 100 ppm. To this end, we have selected independently developed cellulose element crystals (CECs) as the support for Pd catalysts. Pd atoms close to 0 valence are fixed in situ on a specific crystal plane with a low coordination number, and a kind of Pd-CECs monoatomic catalyst with high activity and high stability. The X-ray absorption spectrum was used to determine the coordination mode and valence information of Pd. By studying the intermediate information of Pd-CECs and reactants, it was confirmed that the catalyst can be used as a catalytic platform for suzuki reaction. Through the characterization of oxidative addition intermediates by EXAFS, it can be confirmed that the activation of halogenated hydrocarbons can occur in situ on Pd-CECs, which prevents the loss of Pd during the reaction. At the same time, CECs as a carrier can activate phenylboronic acid intermediates and further improve the conversion rate of the reaction. The catalyst can be applied to multiple types of reactants, and can realize kilogram-scale catalytic reaction applications. Under a 20-L small-scale reaction system, it reached the high reaction rate along with high turnover number at the level of 300,000 h-1 TOF and 15,000,000 TON in kg scale.

Fig.1: a) Scheme of stabilization single Pd atoms; b) HAADF-STEM image of Pd/CECs on MXene; c) Normalized Pd Kedge XANES spectra of Pd1/CEC and Pd foil(inset: calculated first derivative curves); d) EXAFS spectra of Pd1/CEC( blue line) and Pd foil(red line) at the Pd R-space.