Micro-kinetic modeling of OCM reactions over Mn/Na2WO4/SiO2 catalyst

Ahari, Jafar Sadeghzadeh; Zarrinpashne, Saeed; Sadeghi, Mohammad Taghi

doi:10.1016/j.fuproc.2013.04.006

Cited by 26 publications

(21 citation statements)

References 26 publications

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“…5,6 The involvement of both solid-catalyzed gas phase heterogeneous reactions and gas phase homogeneous reactions poses additional complications. 7 Nonetheless, the discovery of a highly C 2 -selective catalyst that can make the process economically (>30% C 2 yield) viable is the biggest limitation that the OCM is facing at the moment. 8 Silica-supported alkali oxide, manganese and tungsten-based trimetallic catalysts are the most widely reported in the OCM for their remarkable methane conversion (20−30%) and C 2 selectivity (60−80%) for long times on stream.…”

Section: Introductionmentioning

confidence: 99%

Engineering Thermally Resistant Catalytic Particles for Oxidative Coupling of Methane Using Spray-Drying and Incorporating SiC

Lezcano

Velisoju

Kulkarni

et al. 2021

Ind. Eng. Chem. Res.

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Oxidative coupling of methane (OCM) is a promising single-step route to convert natural gas to high-valued chemicals. It is generally agreed that Mn–Na–W catalysts offer a balanced conversion–selectivity trade-off. The present work outlines a novel SiC–SiO2 support synthesized by spray drying to extend the lifetime of the catalyst. Incorporating SiC into the support enables the exothermic reaction heat to be effectively dissipated, avoiding hotspots and thermal shocks, and increasing the thermal resistance. The spray drying technique yields particles with a consistent distribution of SiC inside the particles, amplifying the thermal resistance of the catalyst. Our kinetic results show that the spray dried catalyst with SiC has significantly higher stability at high C2 selectivity compared to the benchmark SiO2-supported catalyst prepared by wetness impregnation. This result is due to (1) the more uniform distribution of active phases and SiC provided by the spray drying methodology and (2) the greater thermal resistance provided by SiC, which avoids thermal shocking and stabilizes the Mn–Na–W phases during the long-term (70 h) stability test for OCM.

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Section: Introductionmentioning

confidence: 99%

Engineering Thermally Resistant Catalytic Particles for Oxidative Coupling of Methane Using Spray-Drying and Incorporating SiC

Lezcano

Velisoju

Kulkarni

et al. 2021

Ind. Eng. Chem. Res.

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“…However, the one-pass yield is still low, so the development of highly active catalyst for the OCM reaction is required. Some representative OCM catalysts are Mn 2 O 3 /Na 2 WO 4 /SiO 2 [18][19][20], Li/MgO [21,22], and La 2 O 3 /CaO [23,24]. Of these, Mn 2 O 3 -Na 2 WO 4 /SiO 2 has been reported to exhibit high catalytic activity and stability.…”

Section: Introductionmentioning

confidence: 99%

Oxidative Coupling of Methane over Mn2O3-Na2WO4/SiC Catalysts

Kim

Park

et al. 2019

Catalysts

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The oxidative coupling of methane (OCM) is operated at high temperatures and is a highly exothermic reaction; thus, hotspots form on the catalyst surface during reaction unless the produced heat is removed. It is crucial to control the heat formed because surface hotspots can degrade catalytic performance. Herein, we report the preparation of Mn2O3-Na2WO4/SiC catalysts using SiC, which has high thermal conductivity and good stability at high temperatures, and the catalyst was applied to the OCM. Two Mn2O3-Na2WO4/SiC catalysts were prepared by wet-impregnation on SiC supports having different particle sizes. For comparison, the Mn2O3-Na2WO4/SiO2 catalyst was also prepared by the same method. The catalysts were analyzed by nitrogen adsorption–desorption, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The transformation of SiC into α-cristobalite was observed for the Mn2O3-Na2WO4/SiC catalysts. Because SiC was completely converted into α-cristobalite for the nano-sized SiC-supported Mn2O3-Na2WO4 catalyst, the catalytic performance for the OCM reaction of Mn2O3-Na2WO4/n-SiC was similar to that of Mn2O3-Na2WO4/SiO2. However, only the surface layer of SiC was transformed into α-cristobalite for the micro-sized SiC (m-SiC) in Mn2O3-Na2WO4/m-SiC, resulting in a SiC@α-cristobalite core–shell structure. The Mn2O3-Na2WO4/m-SiC showed higher methane conversion and C2+ yield at 800 and 850 °C than Mn2O3-Na2WO4/SiO2.

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“…radicals) oxidation by the molten Na 2 WO 4 phase. Additionally, consistent with this conclusion, a microkinetic modeling study found that the CO oxidation pathway to form CO 2 does not have a rate controlling effect on the overall OCM reaction network for the supported Mn‐Na 2 WO 4 /SiO 2 catalyst in the presence of the molten Na 2 WO 4 phase [16b] . Further, the activation of CH 4 (i.e., breaking of the first C−H bond in CH 4 to form CH 3 .…”

Section: Resultsmentioning

confidence: 54%

New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na₂WO₄/SiO₂ Catalysts

et al. 2021

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The complex structure of the catalytic active phase, and surface‐gas reaction networks have hindered understanding of the oxidative coupling of methane (OCM) reaction mechanism by supported Na2WO4/SiO2 catalysts. The present study demonstrates, with the aid of in situ Raman spectroscopy and chemical probe (H2‐TPR, TAP and steady‐state kinetics) experiments, that the long speculated crystalline Na2WO4 active phase is unstable and melts under OCM reaction conditions, partially transforming to thermally stable surface Na‐WOx sites. Kinetic analysis via temporal analysis of products (TAP) and steady‐state OCM reaction studies demonstrate that (i) surface Na‐WOx sites are responsible for selectively activating CH4 to C2Hx and over‐oxidizing CHy to CO and (ii) molten Na2WO4 phase is mainly responsible for over‐oxidation of CH4 to CO2 and also assists in oxidative dehydrogenation of C2H6 to C2H4. These new insights reveal the nature of catalytic active sites and resolve the OCM reaction mechanism over supported Na2WO4/SiO2 catalysts.

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Micro-kinetic modeling of OCM reactions over Mn/Na2WO4/SiO2 catalyst

Cited by 26 publications

References 26 publications

Engineering Thermally Resistant Catalytic Particles for Oxidative Coupling of Methane Using Spray-Drying and Incorporating SiC

Engineering Thermally Resistant Catalytic Particles for Oxidative Coupling of Methane Using Spray-Drying and Incorporating SiC

Oxidative Coupling of Methane over Mn2O3-Na2WO4/SiC Catalysts

New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na₂WO₄/SiO₂ Catalysts

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Micro-kinetic modeling of OCM reactions over Mn/Na2WO4/SiO2 catalyst

Cited by 26 publications

References 26 publications

Engineering Thermally Resistant Catalytic Particles for Oxidative Coupling of Methane Using Spray-Drying and Incorporating SiC

Engineering Thermally Resistant Catalytic Particles for Oxidative Coupling of Methane Using Spray-Drying and Incorporating SiC

Oxidative Coupling of Methane over Mn2O3-Na2WO4/SiC Catalysts

New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na2WO4/SiO2 Catalysts

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New Mechanistic and Reaction Pathway Insights for Oxidative Coupling of Methane (OCM) over Supported Na₂WO₄/SiO₂ Catalysts