Ultrathin Washcoat and Very Low Loading Monolithic Catalyst with Outstanding Activity and Stability in Dry Reforming of Methane.
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ABSTRACT:
SUBMITTER: Agueniou F
PROVIDER: S-EPMC7152993 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The carbon dioxide reforming of methane has attracted attention from researchers owing to its possibility of both mitigating the hazards of reactants and producing useful chemical intermediates. In this framework, the activity of the nickel-based catalysts, supported by yttria-stabilized zirconia and promoted with holmium oxide (Ho2O3), was assessed in carbon dioxide reforming of methane at 800 °C. The catalysts were characterized by N2-physisorption, H2 temperature-programmed reduction, temperature-programmed desorption of CO2, X-ray diffraction, scanning electron microscopy (SEM) together with energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) techniques. The effect of holmium oxide weight percent loading (0.0, 1.0, 2.0, 3,0, 4.0, and 5.0 wt %) was examined owing to its impact on the developed catalysts. The optimum loading of Ho2O3 was found to be 4.0 wt %, where the methane and carbon dioxide conversions were 85 and 91%, respectively. The nitrogen adsorption-desorption isotherms specified the mesoporous aspect of the catalysts, while the SEM images displayed a morphology of agglomerated, porous particles. The TEM images of the spent catalyst displayed the formation of multiwalled carbon nanotubes. TGA of the 4.0 wt % of Ho2O3 catalyst, experimented over 7-hour time-on-stream, displayed little weight loss (<14.0 wt %) owing to carbon formation, indicating the good resistance of the catalyst to carbon accumulation due to the enhancing ability of Ho2O3 and its adjustment of the support.
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Project description:The development of efficient catalysts with high activities and durabilities for use in the dry reforming of methane (DRM) is desirable but challenging. We report the development of a nanoporous nickel composite (nanoporous Ni/Y2O3) via a facile one-step dealloying technique, for use in the DRM. Focusing on the low-temperature DRM, our composite possessed remarkable activity and durability against coking compared with conventional particle-based Ni catalysts. This was attributed to the aluminum oxides present on the Ni surface, which suppress pore coarsening. In addition, the inert bundled Y2O3 nanowires are suitable for use as substrates for nanoporous Ni.
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Project description:A highly active and stable nano structured Pt/Mg1-xNixO catalysts was developed by a simple co-precipitation method. The obtained Pt/Mg1-xNixO catalyst exhibited cubic structure nanocatalyst with a size of 50-80 nm and realized CH4 and CO2 conversions as high as 98% at 900°C with excellent stability in the dry reforming of methane. The characterization of catalyst was performed using various kinds of analytical techniques including XRD, BET, XRF, TPR-H2, TGA, TEM, FESEM, FT-IR, and XPS analyses. Characterization of spent catalyst further confirms that Pt/Mg1-xNixO catalyst has high coke-resistance for dry reforming. Thus, the catalyst demonstrated in this study, offers a promising catalyst for resolving the dilemma between dispersion and reducibility of supported metal, as well as activity and stability during high temperature reactions.
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Project description:The generation of synthesis gas (hydrogen and carbon monoxide mixture) from two global warming gases of carbon dioxide and methane via dry reforming is environmentally crucial and for the chemical industry as well. Herein, magnesium-promoted NiO supported on mesoporous zirconia, 5Ni/xMg-ZrO2 (x = 0, 3, 5, 7 wt%) were prepared by wet impregnation method and then were tested for syngas production via dry reforming of methane. The reaction temperature at 800 °C was found more catalytically active than that at 700 °C due to the endothermic feature of reaction which promotes efficient CH4 catalytic decomposition over Ni and Ni-Zr interface as confirmed by CH4-TSPR experiment. NiO-MgO solid solution interacted with ZrO2 support was found crucial and the reason for high CH4 and CO2 conversions. The highest catalyst stability of the 5Ni/3Mg-ZrO2 catalyst was explained by the ability of CO2 to partially oxidize the carbon deposit over the surface of the catalyst. A mole ratio of hydrogen to carbon monoxide near unity (H2/CO ~ 1) was obtained over 5Ni/ZrO2 and 5Ni/5Mg-ZrO2, implying the important role of basic sites. Our approach opens doors for designing cheap and stable dry reforming catalysts from two potent greenhouse gases which could be of great interest for many industrial applications, including syngas production and other value-added chemicals.
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Project description:Herein, we report the synthesis of a ?-Al2O3-supported NiCo catalyst for dry methane reforming (DMR) and study the catalyst using in situ scanning transmission X-ray microscopy (STXM) during the reduction (activation step) and under reaction conditions. During the reduction process, the NiCo alloy particles undergo elemental segregation with Co migrating toward the center of the catalyst particles and Ni migrating to the outer surfaces. Under DMR conditions, the segregated structure is maintained, thus hinting at the importance of this structure to optimal catalytic functions. Finally, the formation of Ni-rich branches on the surface of the particles is observed during DMR, suggesting that the loss of Ni from the outer shell may play a role in the reduced stability and hence catalyst deactivation. These findings provide insights into the morphological and electronic structural changes that occur in a NiCo-based catalyst during DMR. Further, this study emphasizes the need to study catalysts under operating conditions in order to elucidate material dynamics during the reaction.
| S-EPMC7295368 | biostudies-literature
Project description:5Ni/MgO and 5Ni/γAl2O3 are pronounced in the line of cheap catalyst systems for the dry reforming of methane. However, the lower reducibility of 5Ni/MgO and the significant coke deposition over 5Ni/γAl2O3 limit their applicability as potential DRM catalysts. The mixing capacity of MgO and Al2O3 may overcome these limitations without increasing the catalyst cost. Herein, a 5Ni/xMg(100 - x)Al (x = 0, 20, 30, 60, 70, and 100 wt. %) catalyst system is prepared, investigated, and characterized with X-ray diffraction, surface area and porosity measurements, H2-temperature programmed reduction, UV-Vis-IR spectroscopy, Raman spectroscopy, thermogravimetry, and transmission electron microscopy. Upon the addition of 20 wt. % MgO into the Al2O3 support, 5Ni/20Mg80Al is expanded and carries both stable Ni sites (derived through the reduction of NiAl2O4) and a variety of CO2-interacting species. CH4 decomposition at Ni sites and the potential oxidation of carbon deposits by CO2-interacting species over 5Ni/20Mg80Al results in a higher 61% H2-yield (against ~55% H2-yield over 5Ni/γAl2O3) with an excellent carbon-resistant property. In the major magnesia support system, the 5Ni/60Mg40Al catalyst carries stable Ni sites derived from MgNiO2 and "strongly interacted NiO-species". The H2-yield over the 5Ni/60Mg40Al catalyst moves to 71%, even against a high coke deposition, indicating fine tuning between the carbon formation and diffusion rates. Ni dispersed over magnesia-alumina with weight ratios of 7/3 and 3/7 exhibit good resistance to coke. Weight ratios of 2/8 and 7/3 contain an adequate amount of reducible and CO2-interactive species responsible for producing over 60% of H2-yield. Weight ratio 6/4 has a proper coke diffusion mechanism in addition to achieving a maximum of 71% H2-yield.
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Project description:Dry reforming of methane can be used for suppressing the rapid growth of greenhouse gas emissions. However, its practical implementation generally requires high temperatures. In this study, we report an optimal catalyst for low-temperature dry reforming of methane with high carbon coking resistance synthesized from NiYAl alloy. A facile two-step process consisting of preferential oxidation and leaching was utilized to produce structurally robust nanoporous Ni metal and Y oxides from NiYAl4. The catalyst exhibited an optimal carbon balance (0.96) close to the ideal value of 1.0, indicating the optimized dry reforming pathway. This work proposes a facile route of the structural control of active metal/oxide sites for realizing highly active catalysts with long-term durability.
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Project description:Natural gas is a robust and environmentally friendlier alternative to oil resources for energy and chemicals production. However, gas is distributed globally within shales and hydrates, which are generally remote and difficult reserves to produce. The accessibility, transportation, and distribution, therefore, bring major capital costs. With today's low and foreseen low price of natural gas, conversion of natural gas to higher value-added chemicals is highly sought by industry. Dry reforming of methane (DRM) is a technology pathway to convert two critical greenhouse gas components, CH4 and CO2, to syngas, a commodity chemical feedstock. To date, the challenges of carbon deposition on the catalyst and evolution of secondary gas-phase products have prevented the commercial application of the DRM process. The recent exponential growth of renewable electricity resources, wind and solar power, provides a major opportunity to activate reactions by harnessing low-cost carbon-free energy via microwave-heating. This study takes advantage of differences in dielectric properties of materials to enable selective heating by microwave to create a large thermal gradient between a catalyst surface and the gas phase. Consequently, the reaction kinetics at the higher temperature catalyst surface are promoted while the reactions of lower temperature secondary gas-phase are reduced.
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Project description:The high reaction temperatures during steam and dry reforming of methane inevitably entail catalyst deactivation. Evaluation of the feasibility or potentially relevant mechanisms at play is of utmost importance to develop highly active and stable catalysts. Herein, various oxidation reactions of bulk-sized nickel and cobalt to the corresponding metal oxide or in the presence of a metal oxide carrier are evaluated thermodynamically and linked to approximated conditions during methane reforming. In particular cobalt aluminate, as well as cobalt or nickel titanates are likely to form. As oxidation to bulk-sized metal oxide is unlikely, a thermodynamic analysis of metallic nanoparticles was performed to calculate the size dependent stability against oxidation to nickel oxide or cobalt oxide in water and carbon dioxide-rich environments. The calculations indicate that nickel nanoparticles >3 nm and cobalt nanoparticles >10 nm are expected to withstand oxidation during steam and dry reforming of methane with stoichiometric feed compositions and methane conversion levels >10% at temperatures up to 1100 and 900 °C, respectively. Lastly, the reduced thermal stability of nanoparticles due to melting point suppression was assessed, leading to similar recommendations concerning minimum particle sizes.
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Project description:Three morphology-controlled CeO?, namely nanorods (NRs), nanocubes (NCs), and nanopolyhedra (NPs), with different mainly exposed crystal facets of (110), (100), and (111), respectively, have been used as supports to prepare Ru (3 wt.%) nanoparticle-loaded catalysts. The catalysts were characterized by H?-temperature programmed reduction (H?-TPR), CO? temperature programmed desorption (CO-TPD), N? adsorption?desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (XDS). The characterization results showed that CeO?-NRs, CeO?-NCs, and CeO?-NPs mainly expose (110), (100) and (111) facets, respectively. Moreover, CeO?-NRs and CeO?-NCs present higher oxygen vacancy concentration than CeO?-NPs. In the CO? reforming of methane reaction, Ru/CeO?-NR and Ru/CeO?-NC catalysts showed better catalytic performance than Ru/CeO?-NPs, indicating that the catalysts with high oxygen vacancy concentration are beneficial for promoting catalytic activity.
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