15 research outputs found
Hydrogenation to Single Carbon Products: Scientific and Technological Challenges
No full textCatalytic conversion of CO2 to chemicals and fuels is a “two birds, one stone” approach toward solving the climate change problem and energy demand–supply deficit in the modern world. Recent advances in mechanistic insights and design of suitable catalysts for direct thermocatalytic hydrogenation of CO2 to C1 products are thoroughly discussed in this Review. The role of catalyst composition and process conditions in determining the selective pathways to various products like carbon monoxide, methanol, methane, and dimethyl ether has been overviewed in light of thermodynamic and kinetic considerations. After extensive elaboration of the main motivation of the reaction pathways, catalytic roles, and reaction thermodynamics, we summarize the most important macroscopic aspects of CO2 hydrogenation technology development, which include reactor innovations, industrial status of the technology, life cycle assessment and technoeconomic analysis. Finally, a critical perspective on the future challenges and opportunities in both the core fronts and overall technology development is provided
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
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
Influence of support textural property on CO2 to methane activity of Ni/SiO2 catalysts
No full textIn this work, we elucidated the role of physicochemical textural properties of inert support on the catalyst activity by impregnating Ni on ordered mesoporous silica (SBA-15 and MCM-41) and non-mesoporous silica (nMPS). The catalyst Ni/SBA-15 exhibited the best CO2 conversion (83%) and product selectivity (99.9 %) followed by Ni/MCM-41 and the least by Ni/nMPS. The difference in the nature of the catalyst, degree of nanoparticle distribution and nanoparticle encapsulation by different silica support were studied by N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) experiments. The Operando Diffused Reflectance Infrared Fourier Transform Spectroscopy were used to understand the variance in reaction pathway which is accredited to the textural properties of the support. The SBA-15 supported Ni catalyst followed dissociative CO pathway while MCM-41 and nMPS reacted through associative formate mechanism as major pathway. These findings provide a novel perspective on CO2 hydrogenation over Ni-silica, allowing us to tune both activity and selectivity
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
Tuning the acidity and textural properties of polyethyleneimine-supported adsorbents for enhanced economical CO<sub>2</sub> capture
No full textCO2 capture using amine-based porous solids is a promising field that has received tremendous research interest. Owing to high CO2 capture performance, fast uptake kinetics and easy regeneration, CO2 capture using amine-based sorbents has extensively been studied. Herein, polyethyleneimine (PEI)-based sorbents were developed using pseudoboehmite (PSB) and gamma alumina (γ-Al2O3) as supports, represented as PEI@PSB and PEI@γ-Al2O3, respectively. The dispersion, morphology and dynamics of PEI on a porous support play key roles in the CO2 capture performance of an adsorbent. The dispersion of PEI in an adsorbent is tuned by varying the nature of acidity of the supports. The acid-base interaction between PEI and a support enhances its dispersion in the adsorbent. It was observed that PEI@PSB with enhanced Brønsted acidic sites showed excellent PEI dispersion and consequently showed superior CO2 uptake performance compared to PEI@γ-Al2O3. In situ IR analysis majorly shows the formation of ammonium carbamates and negligible carbamic acid, confirming well-dispersed PEI on the PSB support. Among the series of adsorbents, 25% PEI@PSB exhibited the highest CO2 uptake performance of 4.9 mmol CO2 per g of the sorbent. Nitrogen sorption analysis revealed that 25 wt% of PEI is the loading optimum to retain the porosity of the material, facilitating better CO2 uptake. The long-term stability and regeneration studies confirmed that the PEI@PSB adsorbent was robust and could retain a similar adsorbent capacity of up to 100 recycles. Finally, life-cycle assessment (LCA) depicted a decrease of 19-21-fold in all the environmental impact categories per ton of carbon capture with renewable energy input, indicating the potential for decarbonizing hard-to-abate industrial emissions and achieving net-zero climate targets
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
Metal deficiency tuned charge transfer in intermetallic Ni<sub>2−<i>x</i></sub>Sn (<i>x</i> = 0.37–0.65) enhances selective conversion of furfural to furfuryl alcohol towards the theoretical limit
No full textHeterogeneous catalysis facilitated by intermetallic nanoparticles has recently been the subject of increased scrutiny, given the enhanced selectivity and stability they bestow on many chemical reactions compared to their monometallic components. This paper explores a series of Ni-Sn (Ni2-xSn, where x = 0.65, 0.5, 0.37) intermetallic compounds supported on a high-surface-area support, SBA-15, as catalysts for the selective hydrogenation of furfural to furfuryl alcohol. Rietveld refinements of the X-ray diffraction data show catalysts with mixed intermetallic phases that assist in the catalysis. At the same time, X-ray photoelectron spectroscopy (XPS) studies and X-ray absorption studies indicate the role played by charge transfer from Sn to Ni for the catalysis. Selectivity to the desired furfuryl alcohol in all the intermetallic samples was high (>97%), but Ni1.35Sn had a relatively lower conversion than the other intermetallic compounds
