Thermochemical CO2 reduction catalyzed by homometallic and heterometallic nanoparticles generated from the thermolysis o supramolecularly assembled porous metal-adenine precursors

A family of unprecedented supramolecularly assembled porous metal–organic compounds (SMOFs), based on [Cu6M(μ-adeninato)6(μ3-OH)6(μ-H2O)6]2+ cations (MII: Cu, Co, Ni, and Zn) and different dicarboxylate anions (fumarate, benzoate, and naphthalene-2,6-dicarboxylate), have been employed as precursors of catalysts for the thermocatalytic reduction of CO2. The selected metal–organic cation allows us to tune the composition of the SMOFs and, therefore, the features and performance of the final homometallic and bimetallic catalysts. These catalysts were obtained by thermolysis at 600 °C under a N2 atmosphere and consist of big metal particles (10–20 μm) placed on the surface of the carbonaceous matrix and very tiny metal aggregates (<10 nm) within this carbonaceous matrix. The latter are the most active catalytic sites for the CO2 thermocatalytic reduction. The amount of this carbonaceous matrix correlates with the organic content present in the metal–organic precursor. In this sense, CO2 thermocatalytic reduction experiments performed over the homometallic, copper only, catalysts with different carbon contents indicate that above a certain value, the increase of the carbonaceous matrix reduces the overall performance by encapsulating the nanoparticles within this matrix and isolating them from interacting with CO2. In fact, the best performing homometallic catalyst is that obtained from the precursor containing a small fumarate counterion. On the other hand, the structural features of these precursors also provide a facile route to work with a solid solution of nanoparticles as many of these metal–organic compounds can replace up to 1/7 of the copper atoms by zinc, cobalt, or nickel. Among these heterometallic catalysts, the best performing one is that of copper and zinc, which provides the higher conversion and selectivity toward CO. XPS spectroscopy and EDX mappings of the latter catalyst clearly indicate the presence of Cu1–xZnx nanoparticles covered by small ZnO aggregates that provide a better CO2 adsorption and easier CO release sites.Eusko Jaurlaritza/Gobierno Vasco (IT1291-19; IT1722-22 and Investigo program for S.M.G. funded by the European Union-Next Generation EU). Universidad del País Vasco/Euskal Herriko Unibertsitatea (predoctoral fellowship for J.P.C. 17/051), Ministerio de Ciencia e Innovación (project PID2019-108028GB-C21 funded by MCIN/AEI/10.13039/501100011033; PID2022-138968NB-C22 funded by MCIN/AEI/10.13039/501100011033/FEDER/FEDER, and TED2021-129810B-C22 funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGeneration EU/PRTR)

Overcoming the kinetic and deactivation limitations of Ni catalyst by alloying it with Zn for the dry reforming of methane

Stimulated by the capacity of Zn to improve the adoption of CO2 and CH4, we doped a Ni-supported ZrO2 catalyst with Zn to enhance its performance and stability in the dry reforming of methane. We prepared a set of catalysts with different Ni:Zn:Zr proportions and conducted extensive ex situ and in situ characterizations to prove that a Ni–Zn alloy was formed at 750 °C under reductive conditions. Combining a tailored morphology of the alloy nanoparticles, strong metal–support (ZnO–ZrO2) interactions, and additional oxygen vacancies created by Zn inclusion resulted in an enhanced catalyst with 15% higher initial activity and higher stability for over 100 h on stream than Zn-free catalyst. Our experimental and modeling results demonstrated that the catalyst with adjusted Ni:Zn:Zr proportion improves the adsorption and reaction rates of CH4 and CO2 while extending its lifetime through enhanced coke precursor gasification compared to its Zn-free counterpart