Flexible Chain Tunning of Metalloporphyrin Ionic Framework: Spatial Microenvironment Construction for Enhancing Urea Alcoholysis

Abstract

Urea alcoholysis is a key industrial sustainable process in CO2-based chemical production and hydrogen energy storage, but current approaches based on catalytic materials are limited due to their lack structural accuracy and customizability nature. For a sustainable supply of catalytic materials, considerable effort from the scientific aspect for developing functional organic-designable-heterogeneous (metalloporphyrin ionic framework) catalysts have been made by combining metal ions and ionic liquids (ILs) for the transformation of urea and biobased diols into cyclic carbonates. As expected, benefiting from fine tuning of metalloporphyrin ionic framework spatial microenvironment by flexible chains, which effectively regulates the charge distribution of porphyrin coordinated metal ions and in situ synthesized ILs. Meanwhile, the medium flexible chain of Zn-TPyP-Bu-Br ensures consistency in the direction of porphyrin monomer and abundance of active sites, promoting the catalytic conversion of urea and intermediate substance for higher yield of cyclic carbonates with remarkable stability and less catalyst dosage. Based on detailed experiments and molecular dynamics simulations, this catalytic microenvironment effects can be explained by the influence of porphyrin flexible linking chains on the charge regulation of active sites. This work suggests a strategy to be extended to the rational design of a large family of functional organic polymer catalysts that could fulfil the vast promise of urea and biobased diols to fuel a reliable and potentially sustainable energy source.

Keywords: Metalloporphyrin ionic framework, Ionic liquids, Flexible chains, Spatial microenvironment, Cyclic carbonates