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Calcium-looping reforming of methane realizes in situ CO₂ utilization with improved energy efficiency.

ABSTRACT: Closing the anthropogenic carbon cycle is one important strategy to combat climate change, and requires the chemistry to effectively combine CO₂ capture with its conversion. Here, we propose a novel in situ CO₂ utilization concept, calcium-looping reforming of methane, to realize the capture and conversion of CO₂ in one integrated chemical process. This process couples the calcium-looping CO₂ capture and the CH₄ dry reforming reactions in the CaO-Ni bifunctional sorbent-catalyst, where the CO₂ captured by CaO is reduced in situ by CH₄ to CO, a reaction catalyzed by catalyzed by the adjacent metallic Ni. The process coupling scheme exhibits excellent decarbonation kinetics by exploiting Le Chatelier's principle to shift reaction equilibrium through continuous conversion of CO₂, and results in an energy consumption 22% lower than that of conventional CH₄ dry reforming for CO₂ utilization. The proposed CO₂ utilization concept offers a promising option to recycle carbon directly at large CO₂ stationary sources in an energy-efficient manner.

SUBMITTER: Tian S

PROVIDER: S-EPMC6461455 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Calcium-looping reforming of methane realizes in situ CO2 utilization with improved energy efficiency.

Tian Sicong S Yan Feng F Zhang Zuotai Z Jiang Jianguo J

Science advances 20190412 4

Closing the anthropogenic carbon cycle is one important strategy to combat climate change, and requires the chemistry to effectively combine CO2 capture with its conversion. Here, we propose a novel in situ CO2 utilization concept, calcium-looping reforming of methane, to realize the capture and conversion of CO2 in one integrated chemical process. This process couples the calcium-looping CO2 capture and the CH4 dry reforming reactions in th ...[more]

PMID: 30993203

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Project description:The influence of A- and/or B-site doping of Ruddlesden-Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A2BO4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La2NiO4 with Cu stabilizes the orthorhombic structure (Fmmm) of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La2Ni0.9Cu0.1O4 and La2Ni0.8Cu0.2O4, slightly higher than for undoped La2NiO4. Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C-600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH4:CO2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La2O3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La2O2CO3, BaCO3). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni-Cu alloy phases (in a composition of >7:1 = Ni:Cu) for La2Ni0.9Cu0.1O4, La2Ni0.8Cu0.2O4, and La1.8Ba0.2Ni0.9Cu0.1O4, (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii) the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity, the latter decreases in the order of La2Ni0.9Cu0.1O4 ∼ La2Ni0.8Cu0.2O4 ≥ La1.8Ba0.2Ni0.9Cu0.1O4 > La2NiO4 > La1.8Ba0.2NiO4. Simple A-site doped La1.8Ba0.2NiO4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the A site of the respective Ruddlesden-Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can, however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La2NiO4 based systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La2NiO4 structure less stable and suppressing coking by efficiently removing surface carbon) and Ba (rendering the La2NiO4 structure more stable and forming unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.

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Calcium-looping reforming of methane realizes in situ CO₂ utilization with improved energy efficiency.

Publications

Calcium-looping reforming of methane realizes in situ CO<sub>2</sub> utilization with improved energy efficiency.

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