The catalytic adsorption and dissociation of carbon dioxide on a double icosahedral Ru19 nanocluster – A theoretical study

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

Adsorption and Activation of CO2 on Small-Sized Cu-Zr Bimetallic Clusters

Adsorption and activation of CO₂ is a key step in any chemical reaction, which aims to convert it to other useful chemicals. Therefore, it is important to understand the factors that drive the activation process and also search for materials that promote the process. We employ the density functional theory to explore the possibility of using small-sized bimetallic Cu-Zr clusters, Cu_4-nZr_n, with n = 1-3 for the above-mentioned key step. Our results suggest that after adsorption, a CO₂ molecule preferably resides on Zr atoms or at the bridge and triangular faces formed by Zr atoms in bimetallic Cu-Zr clusters accompanied with its high degree of activation. Importantly, maximum activation occurs when CO₂ is adsorbed on the CuZr₃ cluster. Interestingly, we find that the adsorption energy of CO₂ can be tuned by varying the extent of the Zr atom in Cu-Zr clusters. We rationalize the high adsorption of CO₂ with the increase in the number of Zr atoms using the d-band center model and the concept of chemical hardness. The strong chemisorption and high activation of CO₂ are ascribed to charge migration between Cu-Zr clusters and the CO₂ molecule. We find an additional band in the infrared vibrational spectra of CO₂ chemisorbed on all of the clusters, which is absent in the case of free CO₂. We also observe that the energy barriers for the direct dissociation of the CO₂ molecule to CO and O decrease significantly on bimetallic Cu-Zr clusters as compared to that on pure Cu₄. In particular, the barrier heights are considerably small for Cu₃Zr and CuZr₃ clusters. This study demonstrates that Cu₃Zr and CuZr₃ clusters may serve as good candidates for activation and dissociation of the CO₂ molecule.

Role of metcar on the adsorption and activation of carbon dioxide: a DFT study

Metallocarbohedrenes or metcars belong to one of the classes of stable nanoclusters having a specific stoichiometry. In spite of the available theoretical and experimental studies, the structure of pristine Ti8C12 metcar is still uncertain. We study the geometric structure of a titanium metcar, Ti8C12, together with its electronic properties and chemical activity towards adsorption and activation of CO2 molecule by means of density functional theory. Our results suggest that the CO2 molecule is strongly adsorbed and undergoes a significantly high degree of activation onto the Ti8C12 metcar. The migration of charge from titanium metcar to CO2 molecule attributes the high degree of activation of this molecule. In the infrared vibrational spectra for CO2 molecule adsorbed onto Ti8C12, we find a new signal which is absent in the corresponding spectra for gaseous CO2. In addition to adsorption energy, we also estimate the energy barrier for the dissociation of CO2 molecule to CO and O fragments on a Ti8C12 cluster. As a whole, this work reveals the ground state geometry of Ti8C12 metcar and highlights the role of this metcar in CO2 adsorption and activation, which are the key steps in designing potential catalysts for CO2 capture and its conversion to industrially valuable chemicals.

Adsorption and activation of CO2 on Zrn (n = 2-7) clusters

The first step in the conversion of CO2 to useful chemicals involves the adsorption of this molecule on a catalyst accompanied with its high degree of activation. In this paper, we explore the efficacy of small sized zirconium clusters, Zrn (n = 2-7), in the adsorption and activation of the CO2 molecule by using the density functional theory based ab initio method. The results of our calculations provide compelling evidence for the chemisorption and very high degree of activation of CO2 with the elongation of the C-O bond in the range of 1.27-1.42 Å compared to 1.16 Å for free CO2 and the deformation of the O-C-O bond angle from linear to 115-136°. This activation takes place through a charge migration from the Zrn cluster to the CO2 molecule resulting in the formation of CO2δ- species. To assess the catalytic potential of Zr-clusters for CO2 conversion, we also analyse the reaction pathways and the transition barrier heights for the dissociation of CO2 (CO2 → CO + O) on all the Zrn clusters. Our results for the dissociation of CO2 to CO and O fragments reveal that the transition barrier is small for all the Zrn clusters except for Zr2 and Zr4 and it attains a minimum value of 0.11 eV for an isomer of the Zr6 cluster. The present work clearly demonstrates that small-sized monometallic Zr-clusters are highly efficient in activating and dissociating a CO2 molecule adsorbed on these clusters.

Highly effective catalysis of the double-icosahedral Ru(19) cluster for dinitrogen dissociation - a first-principles investigation

The N2 bond cleavage is the rate-limiting step in the synthesis of ammonia, and ruthenium is a catalyst well known for this reaction. The double-icosahedral (D5h) Ru19 cluster is famous as an active catalyst, and has a remarkable stability towards the adsorption of H2, N2 and CO. Using first-principles calculations, we have investigated the adsorption and dissociation of dinitrogen on a double-icosahedral Ru19 cluster. Our results show that the hollow site in the rhombus region (BHB site) of the Ru19 cluster possesses the greatest catalytic activity to dissociate N2, with the reaction barrier of 0.89 eV and an exothermicity of -1.45 eV. Multiple coadsorption of N2 on the cluster (i.e. coadsorption of 2N2 and 3N2 on a single Ru19 cluster) causes the barrier to dissociate N2 to be less on a BHB site than for adsorption of a single N2. To understand the catalytic properties of a Ru19 cluster towards N2 bond cleavage, we calculated the electron population, vibrational wavenumbers and local densities of states; the results are explicable.

Highly efficient Pd-based core–shell nanowire catalysts for O2 dissociation

With the consideration of the stability and cost, we found that the Fe, Co, Ni, Cu, Ru, Ir atoms have lower price than the Pd and favor at the core even with O adatom at the surface. The formed M@Pd core–shell nanowires are active for O₂ dissociation with activation barriers no larger than 0.25 eV.