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428 results on '"Pérez-Ramírez, J."'

12. Catalytic Synergies in Bimetallic Ru-Pt Single-Atom Catalysts via Speciation Control

Author

Química Física i Inorgànica, Universitat Rovira i Virgili, Giulimondi V; Ruiz–Ferrando A; Clark AH; Kaiser SK; Krumeich F; Martín AJ; López N; Pérez–Ramírez J, Química Física i Inorgànica, Universitat Rovira i Virgili, and Giulimondi V; Ruiz–Ferrando A; Clark AH; Kaiser SK; Krumeich F; Martín AJ; López N; Pérez–Ramírez J

Abstract

Bimetallic single-atom catalysts (b-SACs) have recently gained prominence by virtue of the unique catalytic cooperative interactions they can exhibit, intertwining electronic and geometric effects. To date, research efforts have exclusively focused on direct mechanisms such as electron density transfer or sequential reactivity. Herein, the first study on indirect, coordination-induced catalytic synergies in carbon-supported Ru-Pt SACs is conducted. To this end, a holistic approach is developed, combining i) precision synthesis, ii) advanced characterization, iii) exploration of single-site adsorption properties via the hydrogen evolution reaction, and iv) modeling through density functional theory. Despite the lack of both intermetallic coordination in the first or second shell and charge redistribution effects, the Ru-Pt SACs exhibit a H-2 formation rate enhanced up to 15-fold compared with their monometallic counterparts. To unfold the origin of the intermetallic cooperativity, modifications of the structural and catalytic properties induced by the integration of a second metal species are investigated. Thus, Pt atoms are found to selectively occupy the most energeticallyfavorable cavities in the support, prompting Ru atoms to assume a distinct, more active, configuration. This contribution unveils a novel principle of bimetallic cooperativity, demonstrating the key role of integrative experimental and computational analyses in studying b-SACs.

Published
2022

15. Sustainability Assessment of Thermocatalytic Conversion of CO2 to Transportation Fuels, Methanol, and 1-Propanol

Author

Vo, C., Mondelli, C., Hamedi, H., Pérez-Ramírez, J., Farooq, S., and Karimi, I.

Abstract

Using captured CO2 as a chemical feedstock is widely considered toward establishing low carbon technologies to mitigate climate change. Process systems engineering analyses can help increase the chances of success by identifying attractive targets at early stages. Here, a comparative techno-economic and environmental analysis of three thermocatalytic CO2-based plants individually producing liquid hydrocarbon transportation fuels (LHTF), methanol, and 1-propanol is introduced. While the 1-propanol plant generates a remarkable profit, the LHTF and methanol plants are not economically viable, mainly due to the CO2 and H2 input cost. Sensitivity analysis shows that the feedstock prices need to drop by 80% for these two plants to break even. A tax structure is not a sensible option since it would be more than 4 times the highest carbon tax currently implemented in the country. In terms of the environmental performance, the CO2 utilization efficiencies are 45.5, 60.1, and −33.8% for LHTF, methanol, and 1-propanol syntheses, respectively. The negative utilization efficiency in the 1-propanol plant highlights the need of a greener production of its raw material ethylene. When the entire life cycles of the products are considered, these emerging plants emit 85.9, 77.4, and 35.9% less CO2 than their conventional counterparts for the same output. Our study provides the first evaluation of CO2-based 1-propanol synthesis, highlighting its potential, underscores gaps in the CO2-based LHTF, methanol, and 1-propanol by comparing them on a uniform common basis, and sets future research directions.

Published
2021

17. Structure Sensitivity and Evolution of Nickel-Bearing Nitrogen-Doped Carbons in the Electrochemical Reduction of CO2

Author

Büchele, S, Martín, AJ, Mitchell, S, Krumeich, F, Collins, SM, Xi, S, Borgna, A, and Pérez-Ramírez, J

Subjects
inorganic chemicals
Abstract

The emergence of nickel single atoms on nitrogen-doped carbons as high-performance catalysts amenable to rationalization due to their well-defined structure could lead to applicable technologies for the electrocatalytic CO2 reduction reaction (eCO2RR). However, real materials are unlikely to display a uniform site structure, which limits the scope of current efforts focused on idealized models for future implementation. Here, we prepare distinct nickel entities (single atoms or nanoparticles) on nitrogen-doped carbons and evaluate them in eCO2RR. Single atoms demonstrate a characteristic high selectivity to CO. However, this is not altered by the presence of metal nanoparticles formed upon reducing the nitrogen content of the carrier. In contrast, nanoparticles incorporated via a colloidal route promote the parasitic hydrogen evolution reaction. In these systems, the CO selectivity evolves upon repeated exposure to potential, reaching values comparable to single atoms. By introducing CO stripping voltammetry as a characterization tool for this class of materials, we identify a decreased metallic surface, suggesting that the nanoparticle surface is altered by CO. The findings highlight the critical role of dynamic effects in catalyst design for eCO2RR.

Published
2020

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