Importance of the Oxide-Ion Activity on the Hot Corrosion of Nickel at the Interface with Molten Borate-Based Sorbents During CO2 Capture
The Journal of Physical Chemistry C, 2024, 128, 39, 16813-16823
David Unnervik and Takuya Harada

The oxidation and subsequent dissolution of nickel was investigated in molten lithium–sodium orthoborate ((Li0.5Na0.5)3BO3) to assess the scaling-up potential of this modern sorbent for carbon capture through its compatibility with typical reactor materials used in processes involving molten salts. Results indicate the oxidation process to be diffusion-limited and to proceed through the chemical dissolution of oxygen in the melt via reaction with oxide ions, showcasing the decisive role of the oxide-ion activity on the oxidation rate. Additionally, an observed loss in carbon capture capacity over time is explained by the reaction of the sorbent with nickel oxide, thus encouraging reactor designs in which the ratio between the metal/melt interfacial area and the bulk volume is minimized. The dissolution of nickel appears to partially follow an acidic regime, with the upper solubility limits approaching 1000 ppm. These results mirror previously reported mechanisms on lithium–sodium carbonate and shed further light on the scale-up potential of this innovative class of sorbents for carbon capture.

 

High-throughput screening of nano-hybrid metal–organic-frameworks for photocatalytic CO2 reduction
Materials Horizons, 2024, 11, 18, 4311-4320
Moin Khwaja and Takuya Harada

Photocatalytic conversion of CO2 into fuel feed stocks is a promising method for sustainable fuel production. A highly attractive class of materials, inorganic-core@metal–organic-framework heterogeneous catalysts, boasts a significant increase in catalytic performance when compared to the individual materials. However, due to the ever-expanding chemical space of inorganic-core catalysts and metal–organic frameworks (MOFs), identification of these optimal heterojunctions is difficult without appropriate computational screening. In this work, a novel high-throughput screening method of nano-hybrid photocatalysts is presented by screening 65 784 inorganic-core materials and 20 375 MOF-shells for their ability to reduce CO2 based on their synthesizability, aqueous stability, visible light absorption, and electronic structure; the passing materials were then paired based on their electronic structure to create novel heterojunctions. The results showed 58 suitable inorganic-core materials and 204 suitable MOFs ranging from never-before-synthesized catalysts to catalysts that have been overlooked for their photocatalytic ability. These materials lay a new foundation of photocatalysts that have passed theoretical requirements and can significantly increase the rate of catalyst discovery.

 

Wetting Kinetics of Lithium–Sodium Orthoborate on Nickel and Stainless Steel under CO2-Lean and Saturated Conditions
Langmuir, 2024 , 40, 15, 8059-8066
David Unnervik and Takuya Harada

Contact angle measurements were conducted on lithium–sodium orthoborate, an alkali-metal borate-based high-temperature carbon capture sorbent, in contact with nickel and stainless steel under air, N2, and CO2 atmospheres at 600 °C in order to assess the compatibility of this innovative sorbent with packed-bed reactors, typically used in the commercial carbon capture industry. On nickel, the results reveal the melt to be wetting (contact angle θ ≤ 90°), albeit with a contact angle reaching an apparent equilibrium over the experimental time considered. It was found that θ was lower under N2 than under CO2, which was explained as a consequence of the oxide-ion activity difference between the CO2-lean and saturated melts. On stainless steel, however, the melt rapidly spreads, tending toward complete wetting of the metal sheet (θ = 0°) in all atmospheres. For the two metals investigated, the results indicate high to very high wettability, hence the adequacy of using lithium–sodium orthoborate in conventional gas–liquid contactors, further backing this sorbent as a potential alternative to existing sorbents for CO2 capture.

 

Carbonate-Induced Structural Transformation of Lithium-Sodium Orthoborate to a Low-Viscosity Metaborate via CO₂Capture
ACS Applied Materials & Interfaces, 2023, 15, 54667-54676
David Unnervik and Takuya Harada

This paper reports on the structural changes occurring within the lithium–sodium orthoborate crystal lattice during the solid-state absorption of CO2. Results derived from Fourier transform infrared measurements indicate that the CO2-saturated mixed-alkali metal orthoborate and its CO2-lean metaborate counterpart essentially present the same spectral profile, suggesting that CO2 capture results in a fundamental shift of the orthoborate composition to the metaborate one. The implications of such a structural transformation were examined in the molten state at elevated temperatures through rheological measurements, and although confirming that the CO2-lean metaborate exhibits a higher viscosity than the CO2-lean orthoborate, the results suggest that incorporation of CO2 in the orthoborate ionic lattice dilutes the melt, leading to a remarkable reduction in its overall viscosity, despite causing a structural transformation from the less viscous orthoborate form to the more viscous metaborate one.

Molten ionic oxides for CO₂capture at medium to high temperatures
Journal of Materials Chemistry A, 2019, 7, 21827-21834
Takuya Harada, Cameron Halliday, Aqil Jamal, and T. Alan Hatton

Nonvolatile Colloidal Dispersion of MgO Nanoparticles in Molten Salts for Continuous CO₂Capture at Intermediate Temperatures
ACS Sustainable Chemistry and Engineering, 2019, 7, 7979-7986
Takuya Harada, Paul Brown, and T. Alan Hatton

The establishment of advanced CO₂ capture, utilization, and storage (CCUS) technology is a crucial challenge for the mitigation of serious ongoing climate change. Herein, we report nonaqueous colloidal dispersions of MgO nanoparticles in molten salts as a new class of fluid absorbents for continuous CO₂ capture at intermediate temperatures ranging from 200 to 350 °C. The colloidal absorbents were developed by dispersion of the nanoparticles in three different types of thermally stable low-melting point salts: ternary-eutectic alkali-metal nitrates ((Li–Na–K)NO₃), tetraphenylphosphonium bis(trifluoromethane)sulfonimide ([P(Ph)₄][NTf₂]), and their mixtures. The new absorbents show high CO₂ uptake performance with acceptable rheological properties at the target temperatures. The analysis of reaction rate kinetics in the uptake of CO₂ revealed that CO₂ can diffuse quickly into the molten salts to initiate the rapid formation of carbonates on the surfaces of MgO nanoparticles dispersed in these molten salts. These results demonstrate that the new colloidal dispersions could be used as fluid absorbents for advanced continuous CO₂capture processes at the temperatures of exhausts from fossil fuel combustion reactors without the energy losses incurred upon cooling of the gases as required for traditional absorption systems.

Tri-lithium borate (Li₃BO₃); a new highly regenerable high capacity CO₂adsorbent at intermediate temperature
Journal of Materials Chemistry A, 2017, 5, 22224-22233
Takuya Harada, T. Alan Hatton

A lithium-borate oxide, Li₃BO₃, is proposed as a next generation high capacity CO₂ adsorbent operative over the intermediate temperature range of 500 to 650 °C. This adsorbent shows high CO₂ uptake capacity (e.g., 11.3 mmol g−1 at 520 °C) with excellent cyclic regenerability in the presence of alkali-metal nitrite salts as a reaction facilitator. The high CO₂ uptake is attributed to the dissociative formation of lithium carbonate (Li₂CO₃) and different compositions of lithium borates (Li₆B₄O₉, LiBO₂ and Li₂B₄O₇) during the reaction of Li₃BO₃ with CO₂. The excellent performance of the new CO₂ adsorbents is discussed in terms of rapid gas–solid reactions on Li₃BO₃ mediated by the molten nitrite salts and pinning effects that prevent the sintering of particle grains.

 

Alkali Metal Nitrate-Promoted High-Capacity MgO Adsorbents for Regenerable CO₂Capture at Moderate Temperatures
(*This work was press released as ACS News by American Chemical Society, and featured in Phys. Org. Science Daily, and others.)
Chemistry of Materials, 2015, 27, 1943-1949
Takuya Harada, Fritz Simeon, Esam Z. Hamad, and T. Alan Hatton

Regenerable high capacity CO₂sorbents are desirable for the establishment of widespread carbon capture and storage (CCS) systems to reduce global CO₂emissions. We report on the marked effects of molten alkali metal nitrates on CO₂uptake by MgO particles and their impact on the development of highly regenerable CO₂adsorbents with high capacity (>10.2 mmol g^–1) at moderate temperatures (∼300 °C) under ambient pressure. The molten alkali metal nitrates are shown to prevent the formation of a rigid, CO₂-impermeable, unidentate carbonate layer on the surfaces of MgO particles and promote the rapid generation of carbonate ions to allow the high rate of CO₂uptake.

Formation of magnetic nanotubes by the cooperative self-assembly of chiral amphiphilic molecules and Fe₃O₄nanoparticles
Physical Chemistry Chemical Physics (PCCP), 2010, 12, 11938-11943
Takuya Harada, Fritz Simeon, John B. Vander Sande, and T. Alan Hatton

Formation of Highly Ordered Rectangular Nanoparticle Superlattices by the Cooperative Self-Assembly of Nanoparticles and Fatty Molecules.
Langmuir, 2009, 25, 6407-6412
Takuya Harada, T. Alan Hatton

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