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Developing Structure-Reactivity Relationships of the Zeolite Catalysed Bio-alcohol Mediated Aromatic Alkylation Processes via a Multi-Spectroscopic Investigative Approach

Periodic Reporting for period 1 - ZeBiolApp (Developing Structure-Reactivity Relationships of the Zeolite Catalysed Bio-alcohol Mediated Aromatic Alkylation Processes via a Multi-Spectroscopic Investigative Approach)

Reporting period: 2016-06-01 to 2018-05-31

Chemical industries should reduce their dependence on fossil fuels. In the petrochemical industry, the current state-of-the-art of zeolite-catalyzed aromatic alkylation process involves olefins as an alkylating agent, which is still mostly derived from fossil fuels. In order to reduce the dependency on the depleted fossil-resources, the chemical industry must utilize bioethanol, instead of ethylene. However, the mechanism of bioethanol mediated zeolite catalyzed ethylation of benzene is highly controversial as well as ambiguous. Therefore, the primary scientific objectives of this project were to elucidate the reaction mechanism, as well as to establish the structure-reactivity relationships of zeolite catalyzed hydrocarbon conversion processes.
In this project, we have developed a complementary multi-modal spectroscopic approach, through employing a combination of the advanced solid-state magic angle spinning nuclear magnetic resonance spectroscopy with operando UV-visible diffuse reflectance spectroscopy coupled to on-line mass spectrometry, to elucidate the reaction mechanism of the two industrially operational hydrocarbon conversions over commercially relevant and ‘industrial grade’ zeolite catalysts. These reactions are (i) bio-ethanol mediated ethylation of benzene and (ii) methyl acetate-to-hydrocarbon reaction. As the research and innovation to reduce the dependency of fossil fuel is a top-priority for European Union within Horizon 2020, we believe that the accumulated knowledge from this project will be useful for the development of superior and upgraded catalyst materials for the conversion of renewables.
In order to do mechanistic investigation under ‘real working condition’, initially, an openado spectroscopic set-up was built by the fellow within the host group, which comprising of UV-visible diffuse reflectance spectroscopy coupled to on-line mass spectrometry. Two zeolites catalyzed hydrocarbon conversion processes, i.e. (i) bio-ethanol mediated ethylation of benzene and (ii) methyl acetate-to-hydrocarbon, have been screened. In the next phase, advanced multi-dimensional solid-state magic angle spinning NMR spectroscopy was measured, after performing the same reaction using 13C-isotope enriched substrate. The use of 13C-enriched substrate not only increased sensitivity but also allowed us to perform 2D and 3D nuclear magnetic resonance spectroscopic experiments to construct molecular structures of the post-reacted zeolite trapped organic species. The acquired nuclear magnetic resonance results were finally corroborated with the operando spectroscopic results to elucidate the reaction as well as deactivation mechanism. The acquired results were communicated to the scientific community through publishing the work in the peer-reviewed highly prestigious and impacted journals, as well as presenting in multiple international conferences, mostly via the oral presentations. The outcome of the project was also communicated to the general public through press releases and social media platforms.
Our approach to utilize advanced multi-dimensional solid-state nuclear magnetic resonance and corroborate its findings with the operando set-up, to accurately construct the structure of trapped organic intermediates during the reaction, eventually proved to be the most crucial factor. This has been achieved via selective isotope labeling of the substrate material(s). The strategy of the utilization of both selective isotope enriched substrate and advanced multi-dimensional solid-state nuclear magnetic resonance for the elucidation of the reaction mechanism of any heterogeneous process is also unique. Also, this approach delicately distinguishes and differentiates between two major types of zeolite-trapped organics based on mobility (i.e. immobilized and mobile species). It is indeed a ground-breaking concept in the heterogeneous catalysis. The success of this strategy could easily be rationalized in terms of its reporting in high-impact and prestigious scientific journals as well as the opportunity to present the work in multiple reputed conferences. In a broader perspective, the results reported herein also contribute to the fundamental understanding of zeolite-catalyzed hydrocarbon conversion chemistry. Due to the generality and applicability of our spectroscopic approach, we believe our protocol will stimulate researchers both in academia and industry to investigate the reaction mechanism of any gas-phase heterogeneous catalytic process. Therefore, we are hopeful that the outcome of this project would accelerate the transition from fossil-based European industries to a sustainable and bio-based counterpart in the near future.
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