Direct Synthesis of Formic acid from Carbon Dioxide by Hydrogenation over Ruthenium Metal Doped Titanium Dioxide Nanoparticles in Functionalized Ionic Liquid

Abstract

Presently worldwide manufacturing of formic acid follows the permutation of methanol and carbon monoxide in the presence of a strong base. But due to the use of toxic CO molecules and easy availability of CO2 molecules in the atmosphere, most of the research has been shifted from the conventional method of formic acid synthesis to direct hydrogenation of CO2 gas using different homogenous and heterogeneous catalysts. The study aims to develop a reaction protocol to achieve easy CO2 hydrogenation to formic acid using an Ionic liquid reaction medium. We used the sol-gel method followed by calcination (over 250oC for 5 hours) to synthesize two types of ruthenium metal-doped TiO2 nanoparticles (with and without ionic liquids) Ru@TiO2@IL and Ru@TiO2. We report the application NR2 (R= CH3) containing imidazolium-based ionic liquids to achieve a good reaction rate and get agglomeration free ruthenium metal-doped TiO2 nanoparticles along with easy product isolation due to the presence of NR2 (R= CH3) functionality in ionic liquid structure. We synthesized various NR2 (R= CH3) functionalized ionic liquids such as 1-Butyl-3-methylimidazolium Chloride, 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium trifluoromethane sulfonate ([DAMI][TfO]), 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium bis (trifluoromethylsulfonyl) imide ([DAMI][NTf2]) and 1-butyl-3-methylimidazolium chloride ionic liquids were synthesized as per the reported procedure. We quickly developed two typed of Ru metal-doped TiO2 nanoparticles using the sol-gel method. After calcination, both Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) materials were characterized by XRD, FTIR, TEM, ICP-AES, EDS, and XANES analysis. After understanding the correct structural arrangement of Ru metal over TiO2 support, we utilized both Ru@TiO2@IL (3.2 wt% Ru) and Ru@TiO2 (1.7 wt% Ru) the materials as a catalyst for direct hydrogenation of CO2 in the presence of water. We functionalized [DAMI] [TfO] ionic liquid. After understanding the correct morphology and physiochemical analysis of Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) catalysts, we examined their application in CO2 reduction and formic acid synthesis. Here we demonstrated the preparation and characterization of TiO2 supported Ru nanoparticles with and without ionic liquid. We also noticed the significant effect of functionalized [DAMI] [TfO] ionic liquid and water to improve the formic acid yield during the optimization. Last, we also checked the stability of the catalyst by recycling the same till the 7th run.