13 research outputs found
An overview of porous silica immobilized amines for direct air CO<sub>2</sub> capture
No full textAn increased level of CO2 in the atmosphere is identified as a threat to life on planet earth. Since hydrogenation of CO2 back to fuel is identified as a major solution for both decreasing the emission and meeting the energy demands, the energy-efficient capture of CO2 is recognized as an inevitably significant step. Small- and large-scale direct air capture (DAC) of CO2 is a viable solution to address CO2 discharge from industrial, automobile, and household activities (both point and mobile sources). The real challenge of DAC is to pick 400 molecules of CO2 for capture from a million gas molecules in the atmosphere. Thus, in this report, we focus on reviewing the literature dealing with the chemical interaction between the sorbate (CO2) and sorbent which is highly specific. Materials such as metal hydroxides and amine solutions are well discussed in other celebrated reviews and perspectives. Here we focus on inert porous silica immobilized amine materials emphasizing particularly on their advantages compared to other sorbent materials. Furthermore, amine functionalized novel silica materials such as bimodal porous silica and hierarchical silica are discussed highlighting the CO2 capture mechanism, desorption, and sorbent-regeneration. Both O2 and CO2-induced degradation pathways along with measures to retard sorbent degradation are presented. Finally, a brief overview of sustainability and future potential of amine-silica composite materials is presented to gain more insights
Revisiting Reaction Kinetics of CO Electroreduction to C<sub>2+</sub> Products in a Flow Electrolyzer
No full textThe identification of the rate-determining
step (RDS)
in the electrochemical
CO/CO2 reduction to multi-carbon (C2+) products
has been complicated by the deficiency of rigorous reaction kinetic
data. This work describes an experimental analysis of the key reaction
steps by exploring the effect of CO partial pressure on the activity
of C2+ products. With the aid of a flow electrolyzer integrated
with a gas diffusion electrode, the distinct reaction orders of CO
and reaction mechanisms in forming different C2+ products
were determined. Specifically, *CO dimerization is identified as the
RDS for ethylene and ethanol production, as evidenced by the gradual
transition of measured CO reaction order from second to zero as CO
partial pressure increases from 0.05 to 1 atm. The formation of n-propanol is suggested to proceed via the
*CO trimerization mechanism. The acetate generation mechanism might
involve a critical step of *CO hydrogenation before C–C coupling.
Kinetic studies reveal that product-specific active sites are responsible
for activity and selectivity toward specific C2+ products
over oxide-derived copper
Structural ordering enhances highly selective production of acetic acid from CO<sub>2</sub> at ultra-low potential
No full textElectrochemical reduction of CO2 to value-added chemicals and fuels using renewable energy technologies is known to facilitate the creation of an artificial carbon cycle. Although the practical use of most conventional electrocatalysts is curbed by the low efficiency and poor stability of the catalyst there is also the need of large input energy in the form of potential. In this work, a family of bismuth-based transition metal chalcogenides was designed to enable multi-electron transfer for selectively reducing CO2 to acetic acid at ultra-low potential of −0.1 V (vs. RHE). The structural design in AgBiS2, CuBiS2 and AgBiSe2 facilitated an optimized CO adsorption accounting for the production of acetic acid at low potential. The disordered arrangement of Ag and Bi in AgBiS2 also favors CO hydrogenation, which leads to the formation of a large amount of methanol in addition to acetic acid. However, an induced structural ordering of these atoms upon selected substitution enhanced the lattice strain in CuBiS2 and AgBiSe2 favoring only C–C coupling and 100% acetic acid is produced at lower potential with stability up to 100 hours. The origin of the CO2 reduced product has been validated by 13CO2 isotopic experiments and the mechanistic pathway has been proposed with the support of in situ IR experiments. Finally, a 4 times improvement in the current density of the best catalyst, AgBiSe2, was achieved in a flow cell configuration, which produced the highest ever acetic acid yield at lower potential with a faradaic efficiency of 49.81%. This work provides a novel strategy to improve electrochemical performance towards the formation of high value-added chemicals selectively at ultra-low potential
Unraveling the Role of Site Isolation and Support for Semihydrogenation of Phenylacetylene
No full textIntermetallic compounds (IMCs) composed of transition metals and post-transition metals function as superior heterogeneous catalysts in comparison to their monometallic and bimetallic alloy counterparts. Rendering IMCs in their nanomaterial iterations further enhances their efficiency. Herein, we demonstrate the role of PdIn as well-dispersed intermetallic nanoparticles (IMNPs) for the semihydrogenation of phenylacetylene selectively to styrene at ambient conditions. Higher selectivity of PdIn was explained with the help DOS calculations. We have explored the role of a few well-known silica-based supports such as SBA-15 and MCM-41, providing insight into how they affect catalysis. As an additional support we have explored previously reported JNC-1, a mesoporous carbon material obtained via a templated strategy using SBA-15. PdIn supported on SBA-15 and JNC-1 displayed the best dispersion, while also exhibiting the most catalytic activity due to the unique nature of the porous structure
Reduction Selectivity to Methanol at Ultralow Potential
No full textElectrochemical CO reduction reaction (eCORR) is performed on two intermetallic compounds formed by copper and gallium metals (CuGa and CuGa). Among them, CuGa selectively converts CO to methanol with remarkable Faradaic efficiency of 77.26% at an extremely low potential of −0.3 V vs RHE. The high performance of CuGa compared to CuGa is driven by its unique 2D structure, which retains surface and subsurface oxide species (GaO) even in the reduction atmosphere. The GaO species is mapped by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) techniques and electrochemical measurements. The eCORR selectivity to methanol are decreased at higher potential due to the lattice expansion caused by the reduction of the GaO, which is probed by in situ XAFS, quasi in situ powder X-ray diffraction, and ex situ XPS measurements. The mechanism of the formation of methanol is visualized by in situ infrared (IR) spectroscopy and the source of the carbon of methanol at the molecular level is confirmed from the isotope-labeling experiments in presence of CO. Finally, to minimize the mass transport limitations and improve the overall eCORR performance, a poly(tetrafluoroethylene)-based gas diffusion electrode is used in the flow cell configuration
Lattice charge tuning-driven multi-carbon products from carbon dioxide
No full textMitigating global CO2 concentrations from anthropogenic sources through electrochemical conversion to value-added chemicals is the need of the hour. In this work, the fundamental concept of "Lattice Charge" has been strategically manipulated in materials to selectively produce multi-carbon products from greenhouse CO2 gas. To achieve this, a series of catalysts within a well-known ABX2 family (A = Ag, Cu; B = In, Ga, Fe; X = S, Se) have been explored, which exhibit significant activity toward the electrochemical CO2 reduction reaction (eCO2RR) and results in the formation of higher carbon chemicals including C3 products, acetone, and energy-dense isopropanol (FE = 24.5 ± 2.5%). The Hirshfeld charge analysis technique highlighted the structure-activity correlation and the importance of the optimized lattice charge distribution as a crucial tool to manipulate the eCO2RR product in electrocatalyst designs, and the real-time in situ ATR-FTIR technique probes the crucial intermediate species adsorbed during the CO2 reduction process
Unraveling the cooperative mechanisms in ultralow copper-loaded WC@NGC for enhanced CO<sub>2</sub> electroreduction to acetic acid
No full textElectrochemical CO2 reduction reaction (eCO2RR) has been explored on tungsten carbide (WC) nanoparticles embedded on N-doped graphitic carbon (NGC), demonstrating excellent activity toward the formation of acetic acid at an extremely lower potential. The activity has been further enhanced by loading ultralow copper sites into the catalyst system, exhibiting 80.02% Faradaic efficiency (FE) toward acetic acid at an applied potential of -0.3 V (vs RHE). Potential-dependent in situ infrared (IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, ex situ extended X-ray absorption fine structure (EXAFS) studies, and computational analysis confirm that synergy between uniformly dispersed Cu atoms and WC lattice plays a crucial role in the formation of acetic acid with high FE at a lower potential. It has been observed that the W atom of WC strongly chemisorbs CO2 with a significant change in the C-O bond length and the O-C-O bond angle, in contrast to weaker adsorption on Cu-based catalyst surfaces. The presence of a Cu site enhances the adsorption of CO2, thereby increasing the possibility of C-C coupling kinetically. Most importantly, hydrogen evolution predominates on the catalyst’s surface at higher applied potentials (-0.5 to -1.1 V vs RHE), elucidating the mechanism underlying enhanced charge transfer between copper and WC, a phenomenon ascertained through in situ IR spectroscopy and ex situ XPS analysis
Operando generated ordered heterogeneous catalyst for the selective conversion of CO2 to methanol
No full textThe discovery of new materials for efficient transformation of carbon dioxide (CO2) into desired fuel can revolutionize large-scale renewable energy storage and mitigate environmental damage due to carbon emissions. In this work, we discovered an operando generated stable Ni–In kinetic phase that selectively converts CO2 to methanol (CTM) at low pressure compared to the state-of-the-art materials. The catalytic nature of a well-known methanation catalyst, nickel, has been tuned with the introduction of inactive indium, which enhances the CTM process. The remarkable change in the mechanistic pathways toward methanol production has been mapped by operando diffuse reflectance infrared Fourier transform spectroscopy analysis, corroborated by first-principles calculations. The ordered arrangement and pronounced electronegativity difference between metals are attributed to the complete shift in mechanism. The approach and findings of this work provide a unique advance toward the next-generation catalyst discovery for going beyond the state-of-the-art in CO2 reduction technologies
Unraveling the Cooperative Mechanisms in Ultralow Copper-Loaded WC@NGC for Enhanced CO<sub>2</sub> Electroreduction to Acetic Acid
No full textElectrochemical CO2 reduction reaction (eCO2RR) has been explored on tungsten carbide (WC) nanoparticles
embedded
on N-doped graphitic carbon (NGC), demonstrating excellent activity
toward the formation of acetic acid at an extremely lower potential.
The activity has been further enhanced by loading ultralow copper
sites into the catalyst system, exhibiting 80.02% Faradaic efficiency
(FE) toward acetic acid at an applied potential of −0.3 V (vs
RHE). Potential-dependent in situ infrared (IR), X-ray photoelectron
spectroscopy (XPS), Raman spectroscopy, ex situ extended X-ray absorption
fine structure (EXAFS) studies, and computational analysis confirm
that synergy between uniformly dispersed Cu atoms and WC lattice plays
a crucial role in the formation of acetic acid with high FE at a lower
potential. It has been observed that the W atom of WC strongly chemisorbs
CO2 with a significant change in the C–O bond length
and the O–C–O bond angle, in contrast to weaker adsorption
on Cu-based catalyst surfaces. The presence of a Cu site enhances
the adsorption of CO2, thereby increasing the possibility
of C–C coupling kinetically. Most importantly, hydrogen evolution
predominates on the catalyst’s surface at higher applied potentials
(−0.5 to −1.1 V vs RHE), elucidating the mechanism underlying
enhanced charge transfer between copper and WC, a phenomenon ascertained
through in situ IR spectroscopy and ex situ XPS analysi
Operando Generated Ordered Heterogeneous Catalyst for the Selective Conversion of CO2 to Methanol
No full text
