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DOE OSTI2025

Stepwise impregnation of bimetallic catalysts for carbon nanotube synthesis

Supported bimetallic catalysts are widely used for carbon nanotube (CNT) synthesis, yet the effects of impregnation procedure remain underexplored. Here, we investigated how the sequence of metal impregnation affects CNT synthesis. We prepared cobalt-molybdenum (Co-Mo) bimetallic catalysts on alumina supports via co- and stepwise impregnation, then compared their CNT synthesis performance under identical conditions. Stepwise-impregnated catalysts exhibited higher carbon yields than those prepared by co-impregnation. Notably, impregnating Mo after Co achieved the highest yield despite the lowest BET surface area. Synchrotron X-ray diffraction and visible/UV-Raman spectroscopy revealed that only this catalyst contained Al 2 (MoO 4 ) 3 with a MoO 4 structure. X-ray photoelectron spectroscopy clarified the surface chemistry: the catalyst with the highest CNT productivity exposed Mo entirely as Mo 6+ in Al 2 (MoO 4 ) 3 and CoMoO 4 , whereas the others contained both Mo 4+ and Mo 6+ . The MoO x species like Al 2 (MoO 4 ) 3 is known to suppress Co sintering during CNT synthesis, delaying catalyst deactivation and enhancing the carbon yield. Moreover, an inverse relationship was observed between carbon yield and the CoMoO 4 content. This is attributed to the consumption of catalytically active Co during CoMoO 4 formation, which reduces active sites for CNT growth. ICP-OES further confirmed higher Co and Mo loadings for stepwise catalysts, contributing to superior catalyst performance. The extent of CoMoO 4 formation strongly depended on the metal introduction sequence. In conclusion, this trend is illustrated by considering the relationship between the point of zero charge of support and the pH of the metal precursor solutions.

36 MATERIALS SCIENCE↗

DOE OSTI2024

An active, stable cubic molybdenum carbide catalyst for the high-temperature reverse water-gas shift reaction

Although technologically promising, the reduction of carbon dioxide (CO 2 ) to produce carbon monoxide (CO) remains economically challenging owing to the lack of an inexpensive, active, highly selective, and stable catalyst. We show that nanocrystalline cubic molybdenum carbide (α-Mo 2 C), prepared through a facile and scalable route, offers 100% selectivity for CO 2 reduction to CO while maintaining its initial equilibrium conversion at high space velocity after more than 500 hours of exposure to harsh reaction conditions at 600°C. The combination of operando and postreaction characterization of the catalyst revealed that its high activity, selectivity, and stability are attributable to crystallographic phase purity, weak CO-Mo 2 C interactions, and interstitial oxygen atoms, respectively. Mechanistic studies and density functional theory (DFT) calculations provided evidence that the reaction proceeds through an H 2 -aided redox mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Hybrid HEFA-HDCJ Process for the Production of Jet Fuel Blendstocks

09 BIOMASS FUELS↗

DOE OSTI2025

Hybrid HEFA-HDCJ Process for the Production of Jet Fuel Blendstocks

The hydrotreatment of bio-oil derived from the pyrolysis and biocrude from hydrothermal liquefaction of lignocellulosic materials to produce hydrocarbons faces significant technological challenges, mainly due to the high reactivity and poor thermal stability of bio-oil, resulting in the formation of large quantities of coke. This problem has been addressed by existing PNNL patents with a two-step hydrotreatment technology in which the bio-oil is first stabilized with a noble hydrogenation metal (often Pt or Ru). Then, in the second step, the bio-oil is deoxygenated with a Ni-Mo or Co-Mo sulfide catalyst. The main problem with this approach is that the Pt/Ru catalysts deactivate easily in the presence of S or other impurities, which are commonly present in pyrolysis oils. In this project, we explored technological solutions to mitigate coke formation, avoiding the use of Pt/Ru catalysts. Our strategy is based on three actions: (1) Bio-oil stabilization in the presence of alcohols. In this project, we studied the stabilization with butanol. (2) the use of a cosolvent to solubilize the bio-oil. Because coke formation reactions are second-order reactions a reduction in the concentration of reactive bio-oil molecules. In this case, we used yellow greases as a co-solvent. (3) Separation of bio-oil reactive fractions. In this project, we studied the removal of water-soluble fractions. Our batch co-hydrotreatment studies confirmed that the addition of butanol and methanol and the blend with lipids effectively contributed to mitigating coke formation (reducing coke yield to about 1 wt.% %). The removal of sugars did not have a noticeable effect on the overall coke yield, suggesting that coke precursors are present in all bio-oil fractions. Our analytical work suggests that they may be concentrated in the water-insoluble/CH 2 Cl 2 insoluble fractions of pyrolysis oils. Although the technological strategies tested resulted in significant coke reductions, the levels achieved were not sufficiently low to ensure a reliable operation in continuous, fixed-bed trickle-bed reactors. Long runs of more than 100 hours (maximum: 255 h) of co-processing time on stream were achieved in a continuous 40 mL reactor. When the same test was conducted in a larger 400 mL reactor, pressure drop increases associated with coke formation were observed. This increase in coke formation could be due to larger temperature gradients in the bed. Hydrodeoxygenation tests in moving bed reactors and using more active hydrogenation catalysts (for example Ni) could lead to more reliable operations. Unfortunately, our team did not have access to such experimental setups. The technoeconomic analysis suggests that although alcohol use is an effective means to reduce coke formation, the use of alcohol increases production cost. Thus, its use needs to be minimized. A delicate balance needs to be found between the use of technological solutions that allow the reliable operation of the system (stabilization with Ni catalysts, use of small quantities of solvents, processing in moving bed reactors) with a tolerable level of coke formation for the hydrodeoxygenation reactor used and that result in minimum production costs.

09 BIOMASS FUELS↗

DOE OSTI2020

Materials Data on Co3Mo by Materials Project

Co3Mo is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mo is bonded to twelve Co atoms to form MoCo12 cuboctahedra that share corners with six equivalent MoCo12 cuboctahedra, corners with twelve CoCo8Mo4 cuboctahedra, edges with eighteen CoCo8Mo4 cuboctahedra, faces with eight equivalent MoCo12 cuboctahedra, and faces with twelve CoCo8Mo4 cuboctahedra. There are six shorter (2.55 Å) and six longer (2.56 Å) Mo–Co bond lengths. There are two inequivalent Co sites. In the first Co site, Co is bonded to four equivalent Mo and eight Co atoms to form distorted CoCo8Mo4 cuboctahedra that share corners with four equivalent MoCo12 cuboctahedra, corners with fourteen CoCo8Mo4 cuboctahedra, edges with six equivalent MoCo12 cuboctahedra, edges with twelve CoCo8Mo4 cuboctahedra, faces with four equivalent MoCo12 cuboctahedra, and faces with sixteen CoCo8Mo4 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.48–2.63 Å. In the second Co site, Co is bonded to four equivalent Mo and eight equivalent Co atoms to form distorted CoCo8Mo4 cuboctahedra that share corners with four equivalent MoCo12 cuboctahedra, corners with fourteen CoCo8Mo4 cuboctahedra, edges with six equivalent MoCo12 cuboctahedra, edges with twelve equivalent CoCo8Mo4 cuboctahedra, faces with four equivalent MoCo12 cuboctahedra, and faces with sixteen CoCo8Mo4 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Co7Mo6 by Materials Project

Co7Mo6 is Frank-Kasper $\mu$ Phase structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to nine Mo and six equivalent Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.74–3.03 Å. There are three shorter (2.65 Å) and three longer (2.69 Å) Mo–Co bond lengths. In the second Mo site, Mo is bonded in a 6-coordinate geometry to four Mo and twelve Co atoms. There are one shorter (2.63 Å) and three longer (2.83 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.70–2.87 Å. In the third Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Co atoms. The Mo–Mo bond length is 2.54 Å. All Mo–Co bond lengths are 2.59 Å. There are two inequivalent Co sites. In the first Co site, Co is bonded to seven Mo and five Co atoms to form a mixture of corner, edge, and face-sharing CoCo5Mo7 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.37–2.40 Å. In the second Co site, Co is bonded to six equivalent Mo and six equivalent Co atoms to form CoCo6Mo6 cuboctahedra that share corners with twelve equivalent CoCo5Mo7 cuboctahedra, edges with six equivalent CoCo6Mo6 cuboctahedra, and faces with eighteen equivalent CoCo5Mo7 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Co3Mo by Materials Project

Co3Mo is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Mo is bonded to twelve equivalent Co atoms to form MoCo12 cuboctahedra that share corners with twelve equivalent MoCo12 cuboctahedra, edges with twenty-four equivalent CoCo8Mo4 cuboctahedra, faces with six equivalent MoCo12 cuboctahedra, and faces with twelve equivalent CoCo8Mo4 cuboctahedra. All Mo–Co bond lengths are 2.54 Å. Co is bonded to four equivalent Mo and eight equivalent Co atoms to form CoCo8Mo4 cuboctahedra that share corners with twelve equivalent CoCo8Mo4 cuboctahedra, edges with eight equivalent MoCo12 cuboctahedra, edges with sixteen equivalent CoCo8Mo4 cuboctahedra, faces with four equivalent MoCo12 cuboctahedra, and faces with fourteen equivalent CoCo8Mo4 cuboctahedra. All Co–Co bond lengths are 2.54 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Co2Mo3 by Materials Project

Mo3Co2 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are twelve inequivalent Mo sites. In the first Mo site, Mo is bonded to six Mo and six Co atoms to form distorted MoCo6Mo6 cuboctahedra that share corners with ten CoCo3Mo9 cuboctahedra, edges with six MoCo6Mo6 cuboctahedra, edges with six CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with eight CoCo3Mo9 cuboctahedra. There are a spread of Mo–Mo bond distances ranging from 2.61–2.67 Å. There are a spread of Mo–Co bond distances ranging from 2.64–2.84 Å. In the second Mo site, Mo is bonded to six Mo and six Co atoms to form distorted MoCo6Mo6 cuboctahedra that share corners with ten CoCo3Mo9 cuboctahedra, edges with six MoCo6Mo6 cuboctahedra, edges with six CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with eight CoCo3Mo9 cuboctahedra. There are a spread of Mo–Mo bond distances ranging from 2.62–2.67 Å. There are a spread of Mo–Co bond distances ranging from 2.64–2.84 Å. In the third Mo site, Mo is bonded in a 12-coordinate geometry to five Mo and seven Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.61–3.01 Å. There are a spread of Mo–Co bond distances ranging from 2.57–2.84 Å. In the fourth Mo site, Mo is bonded in a 12-coordinate geometry to five Mo and seven Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.61–3.02 Å. There are a spread of Mo–Co bond distances ranging from 2.57–2.82 Å. In the fifth Mo site, Mo is bonded to six Mo and six Co atoms to form distorted MoCo6Mo6 cuboctahedra that share corners with ten CoCo3Mo9 cuboctahedra, edges with six MoCo6Mo6 cuboctahedra, edges with six CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with eight CoCo3Mo9 cuboctahedra. There are one shorter (2.61 Å) and two longer (2.66 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.64–2.84 Å. In the sixth Mo site, Mo is bonded to six Mo and six Co atoms to form distorted MoCo6Mo6 cuboctahedra that share corners with ten CoCo3Mo9 cuboctahedra, edges with six MoCo6Mo6 cuboctahedra, edges with six CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with eight CoCo3Mo9 cuboctahedra. There are one shorter (2.62 Å) and two longer (2.66 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.65–2.84 Å. In the seventh Mo site, Mo is bonded in a 12-coordinate geometry to five Mo and seven Co atoms. There are one shorter (2.61 Å) and one longer (3.01 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.56–2.83 Å. In the eighth Mo site, Mo is bonded in a 12-coordinate geometry to four Mo and seven Co atoms. The Mo–Mo bond length is 2.61 Å. There are a spread of Mo–Co bond distances ranging from 2.57–2.82 Å. In the ninth Mo site, Mo is bonded in a 12-coordinate geometry to seven Mo and five Co atoms. Both Mo–Mo bond lengths are 2.89 Å. There are a spread of Mo–Co bond distances ranging from 2.57–2.95 Å. In the tenth Mo site, Mo is bonded in a 12-coordinate geometry to seven Mo and five Co atoms. There are a spread of Mo–Co bond distances ranging from 2.57–2.95 Å. In the eleventh Mo site, Mo is bonded in a 12-coordinate geometry to six Mo and five Co atoms. Both Mo–Mo bond lengths are 2.90 Å. There are a spread of Mo–Co bond distances ranging from 2.57–2.96 Å. In the twelfth Mo site, Mo is bonded in a 12-coordinate geometry to seven Mo and five Co atoms. There are a spread of Mo–Co bond distances ranging from 2.57–2.94 Å. There are eight inequivalent Co sites. In the first Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with four equivalent MoCo6Mo6 cuboctahedra, edges with ten CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with seven CoCo3Mo9 cuboctahedra. There are two shorter (2.60 Å) and one longer (2.63 Å) Co–Co bond lengths. In the second Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with four equivalent MoCo6Mo6 cuboctahedra, edges with ten CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with seven CoCo3Mo9 cuboctahedra. There are two shorter (2.60 Å) and one longer (2.62 Å) Co–Co bond lengths. In the third Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with two equivalent MoCo6Mo6 cuboctahedra, edges with eight CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with nine CoCo3Mo9 cuboctahedra. There are one shorter (2.62 Å) and two longer (2.68 Å) Co–Co bond lengths. In the fourth Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with two equivalent MoCo6Mo6 cuboctahedra, edges with eight CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with nine CoCo3Mo9 cuboctahedra. There are one shorter (2.62 Å) and two longer (2.68 Å) Co–Co bond lengths. In the fifth Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with four equivalent MoCo6Mo6 cuboctahedra, edges with ten CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with seven CoCo3Mo9 cuboctahedra. In the sixth Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with four equivalent MoCo6Mo6 cuboctahedra, edges with ten CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with seven CoCo3Mo9 cuboctahedra. In the seventh Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with two equivalent MoCo6Mo6 cuboctahedra, edges with eight CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with nine CoCo3Mo9 cuboctahedra. In the eighth Co site, Co is bonded to nine Mo and three Co atoms to form distorted CoCo3Mo9 cuboctahedra that share corners with four CoCo3Mo9 cuboctahedra, corners with five MoCo6Mo6 cuboctahedra, edges with two equivalent MoCo6Mo6 cuboctahedra, edges with eight CoCo3Mo9 cuboctahedra, faces with four MoCo6Mo6 cuboctahedra, and faces with nine CoCo3Mo9 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on CoMo by Materials Project

CoMo is Frank-Kasper $\mu$ Phase-like structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are seven inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to four Mo and twelve Co atoms. There are one shorter (2.65 Å) and three longer (2.85 Å) Mo–Mo bond lengths. There are a spread of Mo–Co bond distances ranging from 2.70–2.88 Å. In the second Mo site, Mo is bonded in a 10-coordinate geometry to seven Mo and nine equivalent Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.69–2.85 Å. There are three shorter (2.75 Å) and six longer (2.91 Å) Mo–Co bond lengths. In the third Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Co atoms. There are a spread of Mo–Mo bond distances ranging from 2.52–3.04 Å. All Mo–Co bond lengths are 2.60 Å. In the fourth Mo site, Mo is bonded in a 8-coordinate geometry to eight Mo and six equivalent Co atoms. There are three shorter (3.02 Å) and three longer (3.05 Å) Mo–Mo bond lengths. All Mo–Co bond lengths are 2.60 Å. In the fifth Mo site, Mo is bonded in a 6-coordinate geometry to six Mo and six Co atoms. There are three shorter (2.63 Å) and three longer (2.69 Å) Mo–Co bond lengths. In the sixth Mo site, Mo is bonded in a 6-coordinate geometry to six Mo and six Co atoms. There are three shorter (2.65 Å) and three longer (2.69 Å) Mo–Co bond lengths. In the seventh Mo site, Mo is bonded to six equivalent Mo and six equivalent Co atoms to form distorted MoCo6Mo6 cuboctahedra that share corners with twelve equivalent CoCo4Mo8 cuboctahedra, edges with six equivalent MoCo6Mo6 cuboctahedra, and faces with eighteen equivalent CoCo4Mo8 cuboctahedra. All Mo–Co bond lengths are 2.47 Å. There are three inequivalent Co sites. In the first Co site, Co is bonded to eight Mo and four equivalent Co atoms to form distorted CoCo4Mo8 cuboctahedra that share corners with two equivalent MoCo6Mo6 cuboctahedra, corners with thirteen CoCo4Mo8 cuboctahedra, edges with five CoCo4Mo8 cuboctahedra, faces with three equivalent MoCo6Mo6 cuboctahedra, and faces with ten equivalent CoCo4Mo8 cuboctahedra. There are two shorter (2.34 Å) and two longer (2.43 Å) Co–Co bond lengths. In the second Co site, Co is bonded to seven Mo and five Co atoms to form CoCo5Mo7 cuboctahedra that share corners with fifteen CoCo4Mo8 cuboctahedra, edges with five CoCo5Mo7 cuboctahedra, and faces with thirteen CoCo5Mo7 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.38–2.41 Å. In the third Co site, Co is bonded to six equivalent Mo and six equivalent Co atoms to form CoCo6Mo6 cuboctahedra that share corners with twelve equivalent CoCo5Mo7 cuboctahedra, edges with six equivalent CoCo6Mo6 cuboctahedra, and faces with eighteen equivalent CoCo5Mo7 cuboctahedra.

36 MATERIALS SCIENCE↗