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

摘要

Background: Presently worldwide manufacturing of formic acid follows the permutation of methanol and carbon monoxide in presence of a strong base. But due to the use of toxic CO molecule and easy availability of CO 2 molecule in the atmosphere, most of the research has been shifted from the conventional method of formic acid synthesis to direct hydrogenation of CO 2 gas using different homogenous and heterogeneous catalysts. Objective: To develop reaction protocol to achieve easy CO 2 hydrogenation to formic acid using Ionic liquid reaction medium. Methods: We used the sol-gel method followed by calcination (over 250°C for 5 hours) to synthesize two types of ruthenium metal-doped TiO 2 nanoparticles (with and without ionic liquids), namely Ru@TiO2@IL and Ru@TiO 2 . We are reporting the application NR 2 (R= CH 3 ) containing imidazolium- based ionic liquids not only to achieve a good reaction rate but also to get agglomeration free ruthenium metal-doped TiO 2 nanoparticles along with easy product isolation due to the presence of NR 2 (R= CH 3 ) functionality in ionic liquid structure. We synthesized various NR2 (R= CH 3 ) functionalized ionic liquids such as 1-Butyl-3-methylimidazolium Chloride, 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium trifluoromethanesulfonate ([DAMI][TfO]), 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium bis (trifluoromethylsulfonyl) imide ([DAMI][NTf2]) and 1-butyl-3-methylimidazolium chloride ionic liquids which were synthesized as per the reported procedure. Results: We easily developed two types of Ru metal-doped TiO 2 nanoparticles using the sol-gel method. After calcination, both Ru@TiO 2 @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@TiO 2 @IL (3.2 wt% Ru) and Ru@TiO 2 (1.7 wt% Ru) the materials as a catalyst for direct hydrogenation of CO 2 in the presence of water and functionalized [DAMI] [TfO] ionic liquid. Conclusion: Here we demonstrated the preparation and characterization of TiO 2 supported Ru nanoparticles with and without ionic liquid. After understanding the correct morphology and physiochemical analysis of Ru@TiO 2 @IL (3.2 wt% Ru), and Ru@TiO 2 (1.7 wt% Ru) catalysts, we examined their application in CO 2 reduction and formic acid synthesis. During the optimization, we also noticed the significant effect of functionalized [DAMI] [TfO] ionic liquid and water to improve the formic acid yield. Lastly, we also checked the stability of the catalyst by recycling the same till the 7th run.