Engineering exsolved catalysts for CO2 conversion

Abstract

Introduction: Innovating technologies to efficiently reduce carbon dioxide (CO2) emission or covert it into useful products has never been more crucial in light of the urgent need to transition to a net-zero economy by 2050. The design of efficient catalysts that can make the above a viable solution is of essence. Many noble metal catalysts already display high activity, but are usually expensive. Thus, alternative methods for their production are necessary to ensure more efficient use of noble metals.Methods: Exsolution has been shown to be an approach to produce strained nanoparticles, stable against agglomeration while displaying enhanced activity. Here we explore the effect of a low level of substitution of Ni into a Rh based A-site deficienttitanate aiming to investigate the formation of more efficient, low loading noblemetal catalysts.Results: We find that with the addition of Ni in a Rh based titanate exsolution is increased by up to ∼4 times in terms of particle population which in turn results in up to 50% increase in its catalytic activity for CO2 conversion.Discussion: We show that this design principle not only fulfills a major research need in the conversion of CO2 but also provides a step-change advancement in the design and synthesis of tandem catalysts by the formation of distinct catalytically active sites.

Enhanced Stability of Iridium Nanocatalysts via Exsolution for the CO2 Reforming of Methane

“…Examples of studies using ∼2−4 wt % active metal resulted in conversions ranging between 45% and 80% CH 4 and 70%−93% CO 2 ; however, deactivation, mainly due to coke formation, was always observed. 28,39,50,51 Our system, doped with only 0.4 wt % Ir, showed conversions of 82% CH 4 and 86% CO 2 , without any coke deposition. Therefore, the use of a very dilute amount of Ir proved to be more effective than using Ni alone or combining Ni with another noble metal.…”

“…The most commonly studied metals for the DRM reaction are Ni and Co, mainly due to their low cost and high activity for this specific reaction. ,, However, these are both highly prone to deactivation by sintering and carbon deposition. ,, A partial solution to such issues would be in the use of noble metals, which have improved resistance to coke formation as well as activity and selectivity to syngas production. − However, the high temperatures required to reach an appreciable activity and conversion often cause mobility and sintering of the active species on the support surface, especially when catalysts are developed via traditional synthesis methods such as vapor deposition or chemical infiltration. , Therefore, a promising approach called “exsolution” has recently gathered interest due to its intrinsic characteristics of ease of synthesis and stability of the produced nanoparticles during catalytic application. − In such a method, instead of having the catalytic nanoparticles deposited on the surface of the support, the catalytic species is incorporated into the structure of a host during initial materials synthesis, to then diffuse from the solid solution to the surface of the support via a reduction treatment (or through the application of an electrical potential or plasma treatment) ,− in the form of “socketed” metallic nanoparticles. This results in the often observed exsolved materials’ unique stability to carbon deposition and sintering. , Moreover, recent studies have also highlighted the role of the socketing, and consequent strain achieved between exsolved NPs and the support, in the enhanced catalytic activities measured for several processes, such as CO oxidation, CO 2 reduction in solid oxide cells, and also CH 4 /CO 2 conversion. ,,,− Moreover, exploring the use of alkaline earth A-site perovskite oxides as supports might be beneficial due to their structural stability, the introduction of basic sites, which is known to promote surface reactions, and their lattice oxygen mobility, which could lead to the possible introduction of oxygen vacancies. These factors are all regarded as important in the activity observed for the DRM reaction. ,, …”

Co-Exsolution of Ni-Based Alloy Catalysts for the Valorization of Carbon Dioxide and Methane

“…In the field of catalysis, exsolution is being explored to create “smart” or “intelligent” nanocatalysts with improved sinter resistance, coke resistance, and impurity resistance. ,− The exsolved catalyst nanoparticles are formed under a reducing environment (Figure a) and can regenerate after exposure to an oxidizing environment, making them highly advantageous in energy-intensive reactions. − ,, Their unique properties of improved dispersion, thermal stability, and compositional malleability compared to those of conventional synthesis strategies (Figure b) are particularly useful for valorizing CO 2 into chemical commodities and fuels. Further advancement in knowledge to control the properties of exsolution catalyst nanoparticles can potentially revolutionize approaches to the optimization of chemical reactions and lead to significant advancements for carbon utilization. − …”