Methane‐to‐methanol conversion (MMC) can be facilitated with high methanol selectivities by copper‐exchanged zeolites. There are however two open questions regarding the use of these zeolites to facilitate the MMC process. The first concerns the possibility of operating the three cycles in the stepwise MMC process by these zeolites in an isothermal fashion. The second concerns the possibility of improving the methanol yields by systematic substitution of some copper centers in these active sites with other earth‐abundant transition metals. Quantum‐mechanical computations can be used to compare methane activation by copper oxide species and analogous mixed‐metal systems. To carry out such screening, it is important that we use theoretical methods that are accurate and computationally affordable for describing the properties of the hetero‐metallic catalytic species. We have examined the performance of 47 exchange‐correlation density functionals for predicting the relative spin‐state energies and chemical reactivities of six hetero‐metallic [M‐O‐Cu]2+and [M‐O2‐Cu]2+, (where MCo, Fe, and Ni), species by comparison with coupled cluster theory including iterative single, double excitations as well as perturbative treatment of triple excitations, CCSD(T). We also performed multireference calculations on some of these systems. We considered two types of reactions (hydrogen addition and oxygen addition) that are relevant to MMC. We recommend the use of τ‐HCTH and OLYP to determine the spin‐state energy splittings in the hetero‐metallic motifs. ωB97, ωB97X, ωB97X‐D3, and MN15 performed best for predicting the energies of the hydrogen and oxygen addition reactions. In contrast, local, and semilocal functionals do poorly for chemical reactivity. Using [Fe‐O‐Cu]2+as a test, we see that the nonlocal functionals perform well for the methane CH activation barrier. In contrast, the semilocal functionals perform rather poorly. © 2018 Wiley Periodicals, Inc.
Chemical looping combustion is a clean combustion technology for fossil or renewable fuels. We have previously shown that the process can also be used to enable CO2activation through reduction to CO with Fe oxygen carriers in so‐called “chemical looping dry reforming” (CLDR). Although Fe shows good reactivity with CO2, its reactivity with methane as a fuel is low. In contrast, Ni is highly reactive for methane conversion but cannot be oxidized with CO2. Here, we demonstrate that Fe–Ni alloys combine the reactivities of each metal synergistically. By combining materials synthesis and characterization with reactive evaluation in multicycle CLDR operation, we demonstrate that relatively low amounts of Ni suffice to activate the carrier for methane conversion and that the presence of Fe enables the reoxidation of Ni with CO2. Moreover, the weak oxidant CO2allows the controlled oxidation of the Fe–Ni alloy, which enables CH4upgrading through syngas (CO+H2) production.
more » « less- NSF-PAR ID:
- 10238525
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Energy Technology
- Volume:
- 4
- Issue:
- 10
- ISSN:
- 2194-4288
- Page Range / eLocation ID:
- p. 1147-1157
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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