Impact of Oxide Support Crystallinity on Microwave-Assisted Direct H₂S Decomposition

(PI: Prof. Cafer T. Yavuz)

Oxide & Organic Nanomaterials for Energy & Environment (ONE) Laboratory, Physical Science & Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia

eziz.naryyev@kaust.edu.sa | https://www.yavuzlab.com/

Abstract

High levels of hydrogen sulfide (H₂S) in natural gas and petroleum reservoirs pose significant challenges, often making resource extraction and processing unfeasible. Conventional approaches, such as the Claus process, convert H₂S to elemental sulfur through multiple energy-intensive steps while wasting valuable hydrogen entirely^1,2. Similarly, thermal direct decomposition methods require extreme temperatures, suffer from equilibrium constraints, and often trigger unwanted methane (CH₄) cracking, causing catalyst coking and deactivation³. These drawbacks severely limit the long-term operation of refineries and high-H₂S feedstocks.

This study presents a microwave-assisted catalytic process for direct H₂S decomposition into valuable hydrogen and sulfur, achieving high conversion efficiencies at lower temperatures, while suppressing side reactions such as methane cracking.

The key finding of this work is the dominant role of catalyst support crystallinity in determining microwave-catalyst interactions, energy coupling, and reaction kinetics. Single crystal (SC) magnesium oxide (MgO) supports, when impregnated with Ni, Mo, or in-situ formed MoS₂ species, exhibit significantly higher dielectric loss factors (δ) than commercial polycrystalline counterparts, enabling superior microwave absorption and localized heating at catalytic active sites. Comparative experiments conducted in a continuous-flow microwave reactor over a wide temperature range revealed a clear performance advantage for SC MgO supports, consistently achieving higher H₂S conversion.

Overall, this study establishes microwave-assisted H₂S decomposition over SC MgO-supported catalysts as a scalable and energy-efficient route for simultaneous hydrogen recovery and sulfur management, highlighting crystallinity engineering as a critical parameter in designing next-generation catalysts for microwave-assisted industrial desulfurization and hydrogen production.

References

1. Lou et al., Renewable and Sustainable Energy Reviews 199 (2024) 114529
2. Sassi et al., American Journal of Environmental Sciences 4 (2008)
3. Zaman, J.; Chakma, A., Fuel Processing Technology 41 (1995) 2
4. Song et al., Science 367 (2020) 777–781

Biography

Eziz Naryyev received his B.S. degree in Chemistry from Turkmen State University in 2011. Following graduation, he spent two years teaching at a high school, where he prepared talented students for international Chemistry Olympiads. In 2019, he was awarded an Erasmus Mundus scholarship to pursue a Master’s degree in Chemical Nano-engineering, a joint program offered by Aix-Marseille University (France), Wroclaw University of Science and Technology (Poland), and Tor Vergata University of Rome (Italy). His Master’s research focused on nanostructured composite membranes for water decontamination.

Since 2023, he has been a Ph.D. student in Chemistry at KAUST under the supervision of Prof. Cafer T. Yavuz, in collaboration with the Saudi Aramco Research & Development Center, Saudi Arabia. His research focuses on microwave chemistry, design, and synthesis of catalysts for H₂S decomposition. During high school and undergraduate years, Eziz represented his country at the 43^rd International Chemistry Olympiad and the 7^th, 8^th, and 9^th International Chemistry Science Olympiads (undergraduate level), winning one silver and three bronze medals.

Activator-Free Silica supported Group(IV)-Hydride based catalyst for synthesis of Ultrahigh Molecular Weight Polyethylene

Abstract

Production of bulk plastics such as polyethylene and polypropylene primarily relies on metal catalyzed olefin polymerization reactions. However, for generating the active species, most of the catalysts requires use of an activator, and usually in large quantities. Alkyl aluminum based activators are most commonly used. Apart from being vital for activation of the catalyst, these activators are expensive, pyrophoric and often used in large quantities. In order to tackle these major hurdles, developing an activator-free catalyst would be more economical and desired pathway for the olefin polymerization. In this study, we explored pathway to develop an activator-free Group(IV) metal based hydride silica-supported catalyst. The developed catalyst was active towards ethylene polymerization reaction without the need for further activation and resulted in synthesis of linear ultrahigh molecular weight polyethylene (UHMWPE) with low polydispersity index (PDI), high T_m (melting temperatures) and crystallinity without any reactor fouling. The developed UHMWPE then subjected towards solid state processing below their T_m. To improve activity and solid state processing of UHMWPE into high strength tapes, we also studied the effect of dehydroxylation temperature and size effect with different types of silica’s such as Aerosel Silica, SBA-15 and Nano-Silica. We found that the activity was directly proportional to dehydroxylation temperature of silica support. In addition, size of the support played significant role in solid state processing and improving the polymer processing and mechanical properties. Ultimately, UHMWPE synthesized using Nano-Silica supported system was found to be solid-state process able. The resulting tape was found to have tensile strength >1.4 GPa and tensile modulus of >130 GPa.

Biography

I, Akash Singh, Joined KAUST in 2023. I am currently a PhD. Candidate in Prof. Magnus A. Rueping group. I studied MSc. Chemistry from IIT Palakkad, India (2020-2022) and BSc.(Hons.) Chemistry from Delhi University, India (2017-2020). I have interest in developing heterogeneous catalyst utilizing the concept of Surface Organometallic Chemistry (SOMC) for various catalytic reaction. Currently I am working on developing silica and zeolite based catalysts by exploring structure-activity/selectivity relationship via concepts of SOMC for activation of ethylene.

Designing Novel Porous Organic Cages for Type II Porous Liquids in Helium/Methane Separation

Abstract

Porous liquids represent an emerging class of materials that combine the permanent porosity of solids with the fluidity of liquids, offering unique opportunities for selective gas separation. In this work, we report the design and synthesis of a novel porous organic cage that forms a type II porous liquid through dissolution in a size-excluded solvent. The resulting system retains accessible internal cavities while exhibiting liquid-like processability. We investigated its potential for gas separation, focusing on the industrially relevant challenge of helium and methane separation, which remains difficult due to the small size and similar properties of these gases. Preliminary studies demonstrate that the porous liquid exhibits preferential uptake of helium over methane, suggesting that molecular-scale control within the organic cage framework can be leveraged to tune gas selectivity. These findings highlight porous organic cages as versatile building blocks for next-generation porous liquids and establish a foundation for developing efficient, solution-processable materials for challenging gas separations. Beyond helium/methane separations, this approach offers a pathway toward designing tailored porous liquids for a broad range of molecular separations and energy-related applications.

Biography

Haochen Wang is a current Ph.D. student under the supervision of Prof. Niveen Khashab at King Abdullah University of Science and Technology (KAUST). He obtained his Master of Chemistry degree (2021) from the University of Oxford under the supervision of Dr. Malcolm Stewart. Wang's research interests are focused on synthetic organic cages and their application in smart materials.