Exsolved nickel nanoparticles acting as oxygen storage reservoirs and active sites for redox CH4 conversion

The growing demand for H2 and syngas requires the development of new, more efficient processes and materials for their production, especially from CH4 that is a widely available resource. One process that has recently received increased attention is chemical looping CH4 partial oxidation, which, however, poses stringent requirements on material design, including fast oxygen exchange and high storage capacity, high reactivity toward CH4 activation, and resistance to carbon deposition, often only met by composite materials. Here we design a catalytically active material for this process, on the basis of exsolution from a porous titanate. The exsolved Ni particles act as both oxygen storage centers and as active sites for CH4 conversion under redox conditions. We control the extent of exsolution, particle size, and population of Ni particles in order to tune the oxygen capacity, reactivity, and stability of the system and, at the same time, obtain insights into parameters affecting and controlling exsolution

Low temperature methane conversion with perovskite-supported exo/endo-particles

Lowering the temperature at which CH4 is converted to useful products has been long-sought in energy conversion applications. Selective conversion to syngas is additionally desirable. Generally, most of the current CH4 activation processes operate at temperatures between 600 and 900 °C when non-noble metal systems are used. These temperatures can be even higher for redox processes where a gas phase–solid reaction must occur. Here we employ the endogenous-exsolution concept to create a perovskite oxide with surface and embedded metal nanoparticles able to activate methane at temperatures as low as 450 °C in a cyclic redox process. We achieve this by using a non-noble, Co–Ni-based system with tailored nano- and micro-structure. The materials designed and prepared in this study demonstrate long-term stability and resistance to deactivation mechanisms while still being selective when applied for chemical looping partial oxidation of methane

Endogenous nanoparticles strain perovskite host lattice providing oxygen capacity and driving oxygen exchange and CH4 conversion to syngas

Particles dispersed on the surface of oxide supports have enabled a wealth of applications in electrocatalysis, photocatalysis, and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties analogous to substitutional doping of ions in crystal lattices. Here we demonstrate such a concept allowing extensive, controlled growth of metallic nanoparticles, at nanoscale proximity, within a perovskite oxide lattice as well as on its surface. By employing operando techniques, we show that in the emergent nanostructure, the endogenous nanoparticles and the perovskite lattice become reciprocally strained and seamlessly connected, enabling enhanced oxygen exchange. Additionally, even deeply embedded nanoparticles can reversibly exchange oxygen with a methane stream, driving its redox conversion to syngas with remarkable selectivity and long term cyclability while surface particles are present. These results not only exemplify the means to create extensive, self-strained nanoarchitectures with enhanced oxygen transport and storage capabilities, but also demonstrate that deeply submerged, redox-active nanoparticles could be entirely accessible to reaction environments, driving redox transformations and thus offering intriguing new alternatives to design materials underpinning several energy conversion technologies

Dielectric barrier plasma discharge exsolution of nanoparticles at room temperature and atmospheric pressure Dataset

The dataset that corresponds to the results reported in the paper are included within this record as an Excel file and with tabs corresponding to each figure. Additional results and raw data underlying this work (full set of microscopy images and size analysis and statistics, high resolution deconvoluted x-ray photoelectron spectra and control magnetic measurements) are available in the Supporting Information (in PDF format) or on request following instructions provided here. This work has been supported by EPSRC through the UK Catalysis Hub (EP/R027129/1) and the Emergent Nanomaterials-Critical Mass Initiative (EP/R023638/1, EP/R023921/1, EP/R023522/1, EP/R008841/1) as well as the Royal Society (IES\R2\212049). F.F. gratefully acknowledges support from the National Research Council of Italy (2020 STM program). I.S.M. acknowledges funding from the Royal Academy of Engineering through a Chair in Emerging Technologies Award entitled “Engineering Chemical Reactor Technologies for a Low-Carbon Energy Future” (Grant CiET1819\2\57). KK acknowledges funding from the Henry Royce Institute (EP/X527257/1)

Dielectric barrier plasma discharge exsolution of nanoparticles at room temperature and atmospheric pressure

Exsolution of metal nanoparticles (NPs) on perovskite oxides has been demonstrated as a reliable strategy for producing catalyst-support systems. Conventional exsolution requires high temperatures for long periods of time, limiting the selection of support materials. We report plasma direct exsolution at room temperature and atmospheric pressure of Ni NPs from a model A-site deficient perovskite oxide (La0.43Ca0.37Ni0.06Ti0.94O2.955). Plasma exsolution is carried out within minutes (up to 15 min) using a dielectric barrier discharge configuration both with He-only gas as well as with He/H2 gas mixtures, yielding small NPs (< 30 nm diameter). To prove the practical utility of exsolved NPs, we have carried out various experiments aimed at assessing their catalytic performance for methanation from synthesis gas, CO and CH4 oxidation. We successfully demonstrated low-temperature and atmospheric pressure plasma exsolution and suggest that this approach could contribute to the practical deployment of exsolution-based stable catalyst systems