Recent Submissions

  • Activating the Fe(I) State of Iron Porphyrinoid with Second-Sphere Proton Transfer Residues for Selective Reduction of CO2 to HCOOH via Fe(III/II)?COOH Intermediate(s)

    Amanullah, Sk (2022-05-16) [Poster]
    Reduction of CO2 to value-added chemicals is a logical way to store solar energy and address the increasing concerns about the higher abundance of the greenhouse gas, CO2, in the atmosphere.1 An important issue in CO2 reduction is selectivity as CO2 can be reduced to CO, HCOOH, CH3OH, CH4, or other C2 and C3 hydrocarbons, all of which have commercial values. However, for practical implementation of any of these carbon fixation strategies, the reduction should be selective. A key pursuit arising from the previous investigations of CO2 reduction is the possibility of obtaining the desired selectivity in CO2 reduction by incorporating second-sphere interactions in the ligand design.2 In fact, installing second-sphere hydrogen-bonding interactions has allowed fast reduction of CO2 to CO, but selectivity for the formation of HCOOH has yet to be demonstrated. Although frequently used to explain the observed reactivities, only rarely have the intermediates been experimentally observed and characterized.3 As a result, there is a lack of insight into the electronic structure of the M-COOH intermediates, which is key to understanding their reactivities. After CO2 binding to the metal-centre followed by the protonation, the M-COOH intermediate, can lead to either CO or HCOOH depending on the site of protonation on this M-COOH intermediate. When the O-center is protonated, CO is released, while when the C-center is protonated, HCOOH is formed. The fate of this protonation can be determined either by controlling the pKa of the C or O centers or by using second sphere interactions to direct the protonation. Alternatively, the pKa of the C and/or O centers can be tuned by controlling the Lewis acidity of the metal center via ligand design or choice of metal.4 Despite being attractive catalysts, iron porphyrins inevitably favor the reduction of CO2 to CO and not HCOOH. Additionally, the Fe center has to be reduced to its formal Fe(0) state to bind CO2, and the reduction requires proton sources like, PhOH, which considering its pernicious environmental effects, may be detrimental to the practical utilization of these complexes for CO2 reduction. Generally, over-potential can be lowered by installing electron-withdrawing groups around the porphyrin ring. Unfortunately, no known iron porphyrin or their analogues (without auxiliary ligands) are known to reduce CO2 selectively to HCOOH until date.1-2 \r\n We demonstrate that an iron chlorin, a saturated analogue of porphyrin, having four electron-withdrawing groups and a pendant amine second sphere residue reduces CO2 selectively to HCOOH under both electrochemical and chemical conditions in its Fe(I) state using H2O as a proton source.5 The solid-state structure and solution 1D and 2D NMR data of an analogous Ni(II) complex confirm the presence of the pendant amine group near the active site. Two intermediates involved in the reduction are identified using a combination of FTIR, resonance Raman, and Mössbauer spectroscopy. The ligand design is envisaged to place the second sphere residue closer to the active site, and this helps shuttle protons to the catalytic center, which (a) allow CO2 binding to the Fe(I) state resulting in only a meager overpotential, (b) stabilize both Fe(III)COOH and Fe(II) COOH intermediates, and (c) result in electrocatalytic CO2 reduction to HCOOH with 88% selectivity under chemical and 97% under electrochemical conditions. References: 1. a) Appel et al, Chem. Rev. 2013, 113, 6621-6658; b) Francke et al, Chem. Rev. 2018, 118, 4631-4701 2. Amanullah et al, Chem. Soc. Rev. 2021, 50, 3755-3823 3. Mondal et al, J. Am. Chem. Soc. 2015, 137, 11214 11217 4. Saha et al, Acc. Chem. Res. 2022, 55, 134-144 5. Amanullah et al, J. Am. Chem. Soc. 2021, 143, 13579-13592"
  • An Efficient Metal-Organic Framework-Derived Nickel Catalyst for the Light-Driven Methanation of CO2

    Mateo, Diego (2022-05-16) [Poster]
    We report the synthesis of a highly active and stable metal-organic framework derived Ni-based catalyst for the photo-thermal reduction of CO2 to CH4. Through the controlled pyrolysis of MOF-74 (Ni), the nature of the carbonaceous species and therefore photo-thermal performance can be tuned. CH4 production rates as high as 488 mmol g-1 h-1 under UV visible-IR irradiation are achieved under optimal conditions. Mechanistic studies suggest that reaction proceeds through a thermal pathway thanks to an effective light-to-heat conversion of the catalyst. No significant loss of activity was observed after more than 12 hours of consecutive reaction under continuous flow configuration.
  • Synthesis of Naphthalene-Based Polyaminal-Linked Porous Polymers for Highly Effective Uptake of CO2 and Heavy Metals

    alkayal, Nazeeha (2022-05-16) [Poster]
    Studying the effect of functional groups on the porosity structure and adsorption efficiency of polymer materials is becoming increasingly interesting. In this work, a novel porous polyaminal-linked polymer, based on naphthalene and melamine (PAN-NA) building blocks, was successfully synthesized by a one-pot polycondensation method, and used as an adsorbent for both CO2 and heavy metals. Fourier transform infrared spectroscopy, solid-state 13 C NMR, powder X-ray diffraction, and thermogravimetry were used to characterize the prepared polymer. The porous material structure was established by field-emission scanning electron microscope and N2 adsorption desorption methods at 77 K. The polymer exhibited excellent uptake of CO2, 133 mg/g at 273 K and 1 bar. In addition, the adsorption behavior of PAN-NA for different metal cations, including Pb(II), Cr(III), Cu(II), Cd(II), Ni(II), and Ba(II), was investigated; a significant adsorption selectivity toward the Pb(II) cation was detected. The influence of pH, adsorbent dose, initial concentrations, and contact time was also assessed. Our results prove that the introduction of naphthalene in the polymer network improves the porosity and, thus, CO2 adsorption, as well as the adsorption of heavy metals.

    Hengne, Amol (2022-05-16) [Poster]
    The catalytic conversion of abundant, inexpensive, renewable, and nontoxic carbon dioxide (CO2) into valuable fuels and chemicals is one of the most practical routes for reducing CO2 emission, and from an economic point of view. Here, the set of catalysts systems explored for selective CO2 hydrogenation to oxygenates [methanol and di-methyl ether (DME)] using Ga in combination and as a promoter in Cu supported catalysts. Copper (Cu) nanocomposite catalysts with gallium (Ga) and aluminum (Al) were prepared using the simultaneous co-precipitation digestion method. With the CuGa nanocomposite formation, the catalyst showed a sequential reduction of CuO, for example, Cu+2 to Cu+ to Cu0, and the Cu surface area was high in comparison with CuAl. CO2- temperature-programmed desorption (TPD) results suggests, the use of Ga in Cu catalysts enhanced the weak basic sites more than the Cu catalysts with Al. These findings confirmed that both the Cu surface area and CuO reducibility in the catalyst helped to boost the conversion of CO2. CuAl catalysts showed very poor selectivity to methanol despite CO formation, which could be due to the weak interaction of the CuAl nanocomposite catalysts compared to the CuGa nanocomposite catalysts. In another catalyst system, the Cu and Cu-Ga nanocomposite catalysts were prepared by wet impregnation and urea deposition method with the combination of mesoporous silica (SBA-15). The catalysts were characterized by using XRD, TEM with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and H2 temperature-programmed reduction. In comparison with Cu-SBA-15 based catalysts, the Ga-promoted catalyst prepared by the urea deposition method (Cu-Ga/SBA-15-UDP) was more active and selective for CO2 hydrogenation to oxygenates. The use of Ga as the promoter led to increased acidic sites, which was confirmed by using NH3 temperature-programmed desorption and IR spectroscopy with pyridine and 2,6-lutidine as probe molecules. The favorable effect of Ga on the CO2 conversion and selectivity to oxygenates may come from the strong interaction of Ga with silica, which is responsible for the enhanced metal surface area, the formation of the nanocomposite, and the metal dispersion. Notably, the incorporation of Ga into Cu/SiO2 led to a several-fold higher rate for methanol formation (13.12 µmolgCu-1s-1) with a reasonable rate for DME formation (2.15 µmolgCu-1s-1) compared to Cu/SiO2 catalysts.
  • Recovering carbon losses in CO2 electrolysis using a solid electrolyte reactor

    Chen, Feng-Yang (2022-05-16) [Poster]
    The practical implementation of electrochemical CO2 reduction technology is greatly challenged by notable CO2 crossover to the anode side, where the crossed-over CO2 is mixed with O2, via interfacial carbonate formation in traditional CO2 electrolysers. Here we report a porous solid electrolyte reactor strategy to efficiently recover these carbon losses. By creating a permeable and ion-conducting sulfonated polymer electrolyte between cathode and anode as a buffer layer, the crossover carbonate can combine with protons generated from the anode to re-form CO2 gas for reuse without mixing with anodic O2. Using a silver nanowire catalyst for CO2 reduction to CO, we demonstrated up to 90% recovery of the crossover CO2 in an ultrahigh gas purity form (>99%), while delivering over 90% CO Faradaic efficiency under a 200?mA?cm?2 current. A high continuous CO2 conversion efficiency of over 90% was achieved by recycling the recovered CO2 to the CO2 input stream.

View more