Synthesis of High-Performance and High-Stability Pd(II)/NaY Catalyst for CO Direct Selective Conversion to Dimethyl Carbonate by Rational Design

Abstract

Direct selective catalytic conversion of CO to C2+ oxygenates with high performance and high stability is challenging. Generating dimethyl carbonate (DMC), a high added-value oxygenate, by CO direct catalytic conversion with Pd-based catalyst is of particular interest as an economic and environmentally friendly potential alternative of the traditional transesterification route. Pd(II)-based catalysts were often used in this route to selectively generate DMC. However, Pd(II) easily reduces to Pd(0) in the presence of CO, which leads to the byproduct of dimethyl oxalate (DMO). A high-performance and high-stability catalytic system selective toward DMC is thus hard to achieve. We herein reveal, by density functional theory calculations, that the mononuclear-isolated nature of Pd(II) centers is critical for the selectivity toward DMC while the aggregation of Pd(0) centers leads to the selective generation of DMO. Inspired by this picture, heterogeneous catalyst with mononuclear-isolated Pd(II) centers anchored on Y-type silico-alumina zeolite was produced experimentally using an ultrasonic-assisted ammonia evaporation approach. This catalyst demonstrates a high selectivity (>99.5%) to target DMC over 100 h, a stability beyond any other reported results. Characterization of the catalyst structure as well as the reaction intermediates and kinetics further verified the computational mechanism. Current work provides a high-performance catalytic system to selectively produce DMC with high-stability through rational design and controlled synthesis, and sheds the light on how to synthesize high-performance and long-lived catalysts for the future industrialization of this process route.