1,10-phenanthroline complexes derived N-doped Pd nanoparticle encapsulated in TS-1 zeolite for acetylene dialkoxycarbonylation

Abstract

Achieving stable heterogeneous catalysts remains a critical challenge in acetylene dialkoxycarbonylation. This study introduces a strategy to encapsulate Pd nanoparticles within TS-1 zeolite via a ligand-protection method, followed by N doping to enhance catalyst stability. It is verified that N doping onto Pd nanoparticles could modify its nanostructure and the coordination bonds, so that the thermal stability of which was significantly enhanced and the CO adsorption capability on it was improved. Moreover, the number of Lewis acid sites (LAS) or Brønsted acid sites (BAS) could be tuned by adjusting the amount of tetrapropylammonium hydroxide (TPAOH) in the synthesis process. The increased number of acid sites enhanced the adsorption capacity of the Pd-N@TS-1(1) catalyst for acetylene, thereby mitigating the deactivation of Pd sites by C₂H₂ under CO-rich conditions. Consequently, the optimized catalyst exhibited a high dialkoxycarbonylation selectivity of 97 % with a significantly improved cycling stability over five cycles. Density Functional Theory (DFT) calculations revealed that the Pd-N site was the primary active center for CO activation, N doping reduced the adsorption energy of CO, promoted its enrichment, and increased the insertion frequency of CO, thereby enhanced the catalytic activity. This approach to controlling the catalytic behavior of Pd sites provides a promising strategy for designing efficient catalysts with long-term stability for acetylene dialkoxycarbonylation.