Understanding W/H-ZSM-5 catalysts for the dehydroaromatization of methane

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Abstract

Tungsten is the most interesting and promising metal to replace molybdenum in methane dehydroaromatization (MDA) catalysis.

Abstract

Tungsten is the most interesting and promising metal to replace molybdenum in methane dehydroaromatization (MDA) catalysis. Located in the same column of the periodic table, tungsten displays similar chemical features to molybdenum ( i.e., formation and stability of oxidation states, acidity of trioxides, tendency toward formation of polynuclear species, atomic radii, ionic radii, etc.) but shows higher thermal stability. The latter could be an advantage during high-temperature reaction–regeneration cycles. However, the MDA activity of W–ZSM-5 catalysts is much lower than the activity obtained with their Mo counterpart. In order to gain a further understanding of such differences in catalytic activity, we present a thorough investigation of the effect of dispersion and distribution of W sites on the zeolite, their relation with catalytic activity, and the temporal evolution of dispersion with reaction–regeneration cycles. The structure of W sites is elucidated with advanced and detailed characterization techniques, including operando X-ray absorption spectroscopy (XAS). The information obtained can help the catalysis community to design better W catalysts for MDA and other reactions ( i.e., metathesis, hydrocarbon cracking, hydrodesulfurization, isomerization, etc.) where this is the metal of choice.

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The Global Methane Budget 2000–2017

Marielle Saunois, Ann Stavert, Ben Poulter … (2020)

Abstract. Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or 50 %–65 %). The mean annual total emission for the new decade (2008–2017) is 29 Tg CH4 yr−1 larger than our estimate for the previous decade (2000–2009), and 24 Tg CH4 yr−1 larger than the one reported in the previous budget for 2003–2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr−1, range 594–881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (∼ 65 % of the global budget, < 30∘ N) compared to mid-latitudes (∼ 30 %, 30–60∘ N) and high northern latitudes (∼ 4 %, 60–90∘ N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters. Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH4 yr−1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH4 yr−1 by 8 Tg CH4 yr−1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning. The data presented here can be downloaded from https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.

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Strategies for the Direct Catalytic Valorization of Methane Using Heterogeneous Catalysis: Challenges and Opportunities

Emiel J M Hensen, Àgnes Szécsényi, Alma I. Olivos-Suarez … (2016)

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Dehydrogenation and aromatization of methane under non-oxidizing conditions

Yide Xu, Linsheng Wang, Longxiang Tao … (1993)

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Author and article information

Contributors

Mustafa Çağlayan: (View ORCID Profile)

Abdallah Nassereddine: (View ORCID Profile)

Stefan-Adrian F. Nastase: (View ORCID Profile)

Alla Dikhtiarenko: (View ORCID Profile)

Jean-Louis Hazemann: (View ORCID Profile)

Javier Ruiz-Martinez: (View ORCID Profile)

Luigi Cavallo: (View ORCID Profile)

Samy Ould-Chikh: (View ORCID Profile)

Jorge Gascon: (View ORCID Profile)

Journal

Journal ID (publisher-id): CSTAGD

Title: Catalysis Science & Technology

Abbreviated Title: Catal. Sci. Technol.

Publisher: Royal Society of Chemistry (RSC)

ISSN (Print): 2044-4753

ISSN (Electronic): 2044-4761

Publication date Created: May 09 2023

Publication date (Electronic): 2023

Volume: 13

Issue: 9

Pages: 2748-2762

Affiliations

[1 ]KAUST Catalysis Center (KCC), Advanced Catalytic Materials, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia

[2 ]Institut Néel, UPR 2940 CNRS – Université Grenoble Alpes, Grenoble F-38000, France

[3 ]KAUST Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia

[4 ]Institut de Chimie Moléculaire de Grenoble, UAR2607 CNRS Université Grenoble Alpes, Grenoble F-38000, France

[5 ]KAUST Catalysis Center (KCC), Catalysis Nanomaterials and Spectroscopy, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia

Article

DOI: 10.1039/D3CY00103B

SO-VID: 835d958c-988e-4453-aa2c-d375d4810503

License:

http://creativecommons.org/licenses/by-nc/3.0/

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