CO₂ Capture and Conversion with a Multifunctional Polyethyleneimine‐Tethered Iminophosphine Iridium Catalyst/Adsorbent

Abstract

Tunable, multifunctional materials able to capture CO2 and subsequently catalyze its conversion to formic acid were synthesized by the modification of branched polyethyleneimine (PEI) with an iminophosphine ligand coordinated to an Ir precatalyst. The molecular weight of the PEI backbone was an important component for material stability and catalytic activity, which were inversely related. The amine functionalities on PEI served three roles: 1) primary amines were used to tether the ligand and precatalyst, 2) amines were used to capture CO2 , and 3) amines served as a base for formate stabilization during catalysis. Ligand studies on imine and phosphine based ligands showed that a bidentate iminophosphine ligand resulted in the highest catalytic activity. X-ray photoelectron spectroscopy revealed that an increase in Ir 4f binding energy led to an increase in catalytic activity, which suggests that the electronics of the metal center play a significant role in catalysis. Catalyst loading studies revealed that there is a critical balance between free amines and ligand-metal sites that must be reached to optimize catalytic activity. Thus, it was found that the CO2 capture and conversion abilities of these materials could be optimized for reaction conditions by tuning the structure of the PEI-tethered materials.

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

“…Figure A shows the IR spectra of PEI, PN‐PEI, Ir‐PN‐PEI and Ir‐PN‐PEI@TNT. The pristine PEI showed several weak bands at 1478 cm −1 and 1568 cm −1 which are characteristic of CH 2 deformation and N‐H bending vibrations, respectively . After the modification of PEI with DPPB, no peaks attributable to aldehyde groups of DPPB (typically seen at 1680 and 1700 cm −1 as doublet peaks) were observed, but instead characteristic peaks assignable to C=N stretching vibration and C=C stretching vibration of aromatic rings appeared at 1639 and 1436 cm −1 , respectively, suggesting that DPPB is fully connected to the primary amine sites on chain ends by C=N bond formation.…”

“…Branched poly(ethyleneimine) (PEI) is a typical aminopolymer containing a large number of primary, secondary, and tertiary amines, which allow it to directly capture CO 2 in dry or wet environments . With its flexible tunability and potential functionality, PEI has been utilized not only as a CO 2 adsorbent but also as a scaffold for metal complex and metal nanoparticles . Li et al.…”

“…Hicks et al. demonstrated the direct conversion of CO 2 to FA by using a PEI‐tethered electron‐donating bidentate iminophosphine (PN) ligand metallated with Ir, which afforded FA in an aqueous solution containing trimethylamine (NEt 3 ) under a total pressure of 40 bar (CO 2 :H 2 =1:1); however, solubility of polymer at high temperature (∼150 °C), aggregation of active metals and the resulting deactivation of catalyst still remain problems to be solved.…”

Aminosilanes Grafted to Basic Alumina as CO2 Adsorbents—Role of Grafting Conditions on CO2 Adsorption Properties

“…The formation of stable, strained Al sites in the presence of water and aminosilane and their effect on CO 2 capture have not been observed or reported previously. Moreover, such materials can be useful in catalytic applications coupled with CO 2 capture [96,97] or by combining amines and acid or base sites associated with a silica support. Indeed, we have shown previously how the alteration of the acid-base properties of the surface of metallosilicate supports can cause the amine sites in class 1 [54] PEI-impregnated materials to bind CO 2 more efficiently.…”

Triazine containing N-rich microporous organic polymers for CO 2 capture and unprecedented CO 2 /N 2 selectivity

“…From the inorganic platform, functionalized materials such as polyethylene amine tethered periodic MCM-41, polyaziridine coated silica, iridium complex etc. shows excellent efficiency for CO2 uptake [7], but lack of stability is the key issue for this class of materials. Metal organic frameworks (MOFs) are known as the predominant member for the CO2 storage material [8] because of their two or three dimensional porous framework with large accessible surface areas and huge pore volume.…”