mahikal

• Luthra, Mahika; Castro, Abril C; Badia, David Balcells; Daasbjerg, Kim & Flores, Ainara Nova (2024). Metal-Dependent Mechanism of the Electrocatalytic Reduction of CO<inf>2</inf> by Bipyridine Complexes Bearing Pendant Amines: A DFT Study. ACS Organic & Inorganic Au. doi: 10.1021/acsorginorgau.4c00046. Full text in Research Archive Show summary

  In this study, the electrocatalytic reduction of carbon dioxide by MnI, ReI, and RuII bipyridine complexes bearing pendant amines is evaluated by DFT methods. Prior experimental studies showed that introducing pendant amines in the secondary coordination sphere of the catalyst shifts product selectivity from CO to HCOO– (in the presence of a proton source) in the case of Mn. In contrast, CO is the major product with Re and Ru. This work includes a comprehensive study of the pathways leading to CO, HCOO–, and H2 to elucidate the energetic preferences that underlie product selectivity. Our results show that switching the metal center leads to changes in the preferred mechanism. While with Mn, the reaction is preferred in an endo configuration, allowing the participation of amines in the hydride formation, reactivity on the exo configuration is preferred with Re. In addition, the distinct redox properties of Re allow for the formation of Re OCOCO2-bridged adducts that lead to CO without a proton source. Further, the ability of Ru to exchange the two Cl– anions changes the preferred coordination number of Ru compared to Mn and Re and, consequently, its reaction mechanism. Overall, this study provides the structure and reactivity insight needed for further catalyst design.

• Hong, Wanwan; Luthra, Mahika; Jakobsen, Joakim B.; Madsen, Monica R.; Castro, Abril C & Hammershøj, Hans Christian D. [Show all 11 contributors for this article] (2023). Exploring the Parameters Controlling Product Selectivity in Electrochemical CO<inf>2</inf> Reduction in Competition with Hydrogen Evolution Employing Manganese Bipyridine Complexes. ACS Catalysis. p. 3109–3119. doi: 10.1021/acscatal.2c05951. Full text in Research Archive Show summary

  Selective reduction of CO2 is an efficient solution for producing nonfossil-based chemical feedstocks and simultaneously alleviating the increasing atmospheric concentration of this greenhouse gas. With this aim, molecular electrocatalysts are being extensively studied, although selectivity remains an issue. In this work, a combined experimental–computational study explores how the molecular structure of Mn-based complexes determines the dominant product in the reduction of CO2 to HCOOH, CO, and H2. In contrast to previous Mn(bpy-R)(CO)3Br catalysts containing alkyl amines in the vicinity of the Br ligand, here, we report that bpy-based macrocycles locking these amines at the side opposite to the Br ligand change the product selectivity from HCOOH to H2. Ab initio molecular dynamics simulations of the active species showed that free rotation of the Mn(CO)3 moiety allows for the approach of the protonated amine to the reactive center yielding a Mn-hydride intermediate, which is the key in the formation of H2 and HCOOH. Additional studies with DFT methods showed that the macrocyclic moiety hinders the insertion of CO2 to the metal hydride favoring the formation of H2 over HCOOH. Further, our results suggest that the minor CO product observed experimentally is formed when CO2 adds to Mn on the side opposite to the amine ligand before protonation. These results show how product selectivity can be modulated by ligand design in Mn-based catalysts, providing atomistic details that can be leveraged in the development of a fully selective system.

• Bai, Yunfei; Taarning, Esben; Luthra, Mahika; Lundegaard, Lars F.; Katerinopoulou, Anna & Falsig, Hanne [Show all 8 contributors for this article] (2023). Tracking Lattice Distortion Induced by Defects and Framework Tin in Beta Zeotypes. Journal of Physical Chemistry C. ISSN 1932-7447. 127(38), p. 19278–19289. doi: 10.1021/acs.jpcc.3c04751. Full text in Research Archive Show summary

  The use of powder X-ray diffraction (PXRD) coupled with lattice parameter refinement is used to investigate the crystal structure of Sn-Beta materials. A newly developed semiempirical PXRD model with a reduced tetragonal unit cell is applied to obtain the characteristic crystallographic features. There is a robust correlation between lattice parameters and the concentration of tin and defects for materials prepared via hydrothermal (HT) and postsynthetic (PT) methods. With tin incorporation, PT Sn-Beta samples, which possess a more defective structure, exhibit an extended interlayer distance in the stacking sequence and expansion of the translation symmetry within the layers, leading to larger unit cell dimensions. In contrast, HT Sn-Beta samples, having fewer defects, show a minimal effect of tin site density on the unit cell volume, whereas lattice distortion is directly correlated to the framework tin density. Furthermore, density functional theory (DFT) studies support an identical trend of lattice distortion following the monoisomorphous substitution of T sites from silicon to tin. These findings highlight that PXRD can serve as a rapid and straightforward characterization method to evaluate both framework defects and heteroatom density, offering a novel approach to monitor structural changes and the possibility to evaluate the catalytic properties of heteroatom-incorporated zeotypes.

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• Luthra, Mahika; Nova, Ainara; Balcells, David & Castro, Abril C (2022). Mechanistic Insight into Electrocatalytic CO2 Reduction with Mn Bipyride complexes using Ab-Initio MD and Static DFT. Full text in Research Archive
• Luthra, Mahika; Nova, Ainara; Castro, Abril C & Balcells, David (2021). Mechanistic Insight into the Electrochemical Reduction of CO2 using Homogenous Molecular Catalysts. Full text in Research Archive

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