Molecular Rh(III) and Ir(III) Catalysts Immobilized on Bipyridine-Based Covalent Triazine Frameworks for the Hydrogenation of CO2 to Formate

Gunniya Gunasekar,Sungho Yoon,Kwangho Park,Hyeonseok Jeong,Kwang-Deog Jung,Kiyoung Park

doi:10.3390/catal8070295

Abstract

The catalytic reactivity of molecular Rh(III)/Ir(III) catalysts immobilized on two- and three-dimensional Bipyridine-based Covalent Triazine Frameworks (bpy-CTF) for the hydrogenation of CO2 to formate has been described. The heterogenized Ir complex demonstrated superior catalytic efficiency over its Rh counterpart. The Ir catalyst immobilized on two-dimensional bpy-CTF showed an improved turnover frequency and turnover number compared to its three-dimensional counterpart. The two-dimensional Ir catalyst produced a maximum formate concentration of 1.8 M and maintained its catalytic efficiency over five consecutive runs with an average of 92% in each cycle. The reduced activity after recycling was studied by density functional theory calculations, and a plausible leaching pathway along with a rational catalyst design guidance have been proposed.

Highlights

The burgeoning interest of CO2 as an energy vector for renewable fuel storage and as a C1 building block for chemical production has renewed attention on CO2 hydrogenation into formic acid [1,2,3,4,5,6,7,8].Formic acid and its salts are used as basic chemicals in various industries [9], and are regarded as a liquid form of hydrogen, which is strongly viewed as an ultimate renewable fuel by the scientific and technological community [10]
Ageneral synthetic strategy for the preparation of bpy-Covalent Triazine Frameworks (CTFs)-based Rh and Ir complexes has been presented in Scheme 2
These results clearly indicate that the catalytic efficiency of Ir4.7@bpy-CTF400 is1.7superior to that in of contrast to the trend of the homogeneous catalysts

Summary

Introduction

The burgeoning interest of CO2 as an energy vector for renewable fuel storage and as a C1 building block for chemical production has renewed attention on CO2 hydrogenation into formic acid [1,2,3,4,5,6,7,8].Formic acid and its salts are used as basic chemicals in various industries [9], and are regarded as a liquid form of hydrogen, which is strongly viewed as an ultimate renewable fuel by the scientific and technological community [10]. The burgeoning interest of CO2 as an energy vector for renewable fuel storage and as a C1 building block for chemical production has renewed attention on CO2 hydrogenation into formic acid [1,2,3,4,5,6,7,8]. Formic acid production by CO2 hydrogenation is one exemplary approach to generate renewable fuels in a fully sustainable carbon-neutral economy. While the reported homogeneous catalysts exhibit excellent activity and selectivity, the challenges encountered for this catalysis are related to the recyclability of catalysts and product isolation (formic acid). The latter is more complicated because the catalysts

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