Poly(ethyleneimine)‐tethered Ir Complex Catalyst Immobilized in Titanate Nanotubes for Hydrogenation of CO₂ to Formic Acid

Abstract

Production of formic acid (FA) by hydrogenation of CO2 using a ternary hybrid catalyst, poly(ethyleneimine)‐tethered Ir‐iminophosphine complex (Ir‐PN‐PEI) immobilized in titanate nanotubes (TNTs), is reported. On the basis of comprehensive structural analyses, we show that Ir‐PN‐PEI is tightly immobilized within the cavity space of TNT without affecting the electronic/coordination states of Ir atoms. Liquid‐phase CO2 hydrogenation under pressurized CO2 and H2 demonstrates that the Ir‐PN‐PEI catalyst immobilized in Na+‐type TNT exhibits the highest FA yields (TON>1000 for 20 h under mild reaction conditions (2.0 MPa, 140 °C)) and improved reusability, which far outperform those of unimmobilized prototype Ir‐PN‐PEI. The improved catalytic performance is attributed to the ability of TNT to efficiently capture CO2 and to stabilize PEI, with Na+‐type TNT with higher basic property providing a more productive effect. The catalyst is reusable over multiple cycles with activity comparable to those of heterogeneous catalysts previously reported, rendering this material suitable for efficient transformation of CO2 into FA.

An In Situ Infrared Study of CO2 Hydrogenation to Formic Acid by Using Rhodium Supported on Titanate Nanotubes as Catalysts

“…Recent investigations, have described the effect of electronic interactions between poly(ethyleneimine)‐tethered complexes (PN‐PEI) with Ir atoms in the hydrogenation of CO 2 to give formic acid. It was proposed that the presence of the PN‐PEI ligands increase the reaction rate due to electronic interactions.…”

“…The calculated TOF value was equal to 7.2x10 −2 h −1 . The obtained TOF is lower than those reported by other authors (20 to 1190 h −1 ),,, for the synthesis of formic acid via heterogeneous hydrogenation of CO 2 .…”

“…Recently, Kuwahara et al., compared different poly(ethyleneimine)‐tethered Ir‐iminophosphine complex (Ir‐PN‐PEI) immobilized in titanate nanotubes as catalysts in the synthesis of formic acid through CO 2 hydrogenation. The catalytic tests were carried out in liquid phase at 2.0 MPa and 140 °C.…”

Controlled Pyrolysis of Ni‐MOF‐74 as a Promising Precursor for the Creation of Highly Active Ni Nanocatalysts in Size‐Selective Hydrogenation

“…Heterogeneous catalysts are essential materials for the industrial manufacture of many fine chemicals due to their recyclability. [1,2] In order to synthesize highly activeh eterogeneous catalysts, various approaches, such as controlling the shape of metal NPs, [3][4][5][6] utilizationo ft he synergetic effect between metal NPs andc atalyst supports, [7][8] and alloyingw ith second and third metals, [9][10][11] have been widely reportedo ver several decades. However,t he preparation of catalysts for size-selective hydrogenation of olefins with different molecular sizes is still ad ifficult problem.…”

Supported Porous Nanomaterials as Efficient Heterogeneous Catalysts for CO2 Fixation Reactions

“…[28] These metal complexes can be immobilized over the mesoporous supports to enhance the catalytic efficiency of FA or HCHO production.High recycling efficiency of the heterogeneous catalysts could be achieved by immobilizing these reactive homo-geneous metal complexes over high surface area mesoporous supports and this can offer highsustainabilityo fthesecatalytic systems. Yamashita and co-workers have designed ah ybrid catalystc omposed of ap oly(ethyleneimine)-functionalized Ir complex immobilized over titanate nanotubes, [29] whichc an achieve at urnover number (TON) of over 1000 in the liquid phase hydrogenation of CO 2 to FA under moderate pressure of CO 2 /H 2 mixture at 140 8C.…”