1,721,050 research outputs found
Understanding the catalytic benefits of multi=metallic active sites in microporous aluminophosphates
No full textStructure-property correlations, which direct the formation of specific active-acid sites, in nanoporous materials have been explored with the aim to further the notion of rational catalyst design. It is demonstrated that the influence of the specific zeotype framework extends beyond modulating Brønsted acidity, with the framework topology playing a fundamental role in reaction kinetics. The structural integrity and nature of the active site has been probed using a combined catalysis and multi-technique characterisation study, aimed at optimising the sustainable production of ?-Caprolactam, the precursor of the recyclable Nylon 6 polymer. The effect of bimetallic substitution, with an aim to generate novel acid sites, has been explored using Mg2+, Zn2+ and Si4+ dopants. Through a combined CO and lutidine probed FT-IR study, the nature of the acid site has been examined and correlated to the nature of the dopants present. The presence of multiple dopant atoms has had a significant effect on catalytic activity, modulating the presence of acid sites to allow new active species to be discovered, and prompting synergistic interactions in multi-step pathways. A combined X-ray absorption spectroscopy and ab initio DFT theoretical study was used to probe the nature of the active sites responsible for catalytic synergy in Co-Ti bimetallic nanoporous frameworks. Contrasting the bimetallic and analogous monometallic species has led to the discovery of a unique bimetallic Co-O-Ti bond. The properties of this bond have been explored and contrasted with the analogous monometallic species, with specific reference to their catalytic applicability for sustainable oxidation reactions. The catalytic synergy prompted by the bimetallic substitution in the CoTiAlPO-5 material has been investigated and contrasted to the monometallic system. Specific focus was placed on the in-situ production of hydroxylamine as part of the sustainable aerobic ammoximation of cyclohexanone. Periodic DFT calculations have revealed subtle mechanistic differences between the mono- and bimetallic systems which account for energetic differences in the rate determining step of the reaction pathway
Down the Microporous Rabbit Hole of Silicoaluminophosphates: Recent Developments on Synthesis, Characterization, and Catalytic Applications
No full textSince their invention silicoaluminophosphates (SAPOs) have become by far the most researched class of aluminophosphates due to their commercial use as solid acid catalysts. Currently over 25 different SAPO frameworks have been synthesized, providing a diverse range of confined nanoporous topologies, with distinct acid sites. When combined with emerging synthetic techniques to further modulate these species, there are endless possibilities to tailor SAPO materials for specific catalytic applications. Herein, this Review focuses on developments, and possibilities, from the past decade in the field of SAPO research, with particular attention paid to synthesis, characterization, theoretical studies, and case studies of their catalytic applications. I aim to simultaneously educate and inspire readers at all stages of their career and hope that this Review helps further interest and research into the exciting field of SAPOs
Data for Doctoral thesis'Towards realistic large-scale simulations of fixed bed chemical reactors: Bridging the gap between discrete element and porous media computational fluid dynamics models'
No full textData submitted for doctoral thesis
1) filename: Chapter_3_Fig_Data -> Excel file, with the data for Figure A.10 presented in Appendix C
2) Chapter_4_Fig_Data -> Excel file, data for all figures in Chapter 4 of the thesis.
3) Chapter_5_Fig_Data -> Excel file, data for all figures in Chapter 5 of the thesis.
4) 5S_beds_analysis_Avizo_method -> Excel file, containing all data of the 5S 100-300, 300-500, and 500-700 particles.
5) Bed_Characteristics_Avizo_method_v4 -> Excel file, containing all data of the 1S 100-300, 300-500, and 500-700 particles.
6) Chapter_6_Fig_Data -> Excel file, kinetic data derivation for the Ethanol dehydration reaction used in Chapter 6, shown in Appendix B7.
7) Profiles_Comparison_DEM_SR -> Excel file, containing all data for the radial profiles of all parameters of Chapter 6, for all three DEM, PM, and SR models.
8) Parallel_Profiles_Comparison_DEM_SR -> Excel file, containing all data for the axial profiles of all parameters of Chapter 6, for all three DEM, PM, and SR models.
9) Parametric_Studies -> Excel file, containing all data for the parametric studies related to Chapter 6, i.e., mesh independency study (Sheet "Mesh"), intraparticle porosity (Sheet "Porosity"), temperature (Sheet "Temperature" and "Bed-Temperature" for the 1- and 27-particle cases, respectively), WHSV (Sheet "WHSV" and "Bed - WHSV" for the 1- and 27-particle cases, respectively), and exothermicity (Sheet "Exothermicity").
10) Comp_time_Complete -> Excel file, data for the computational resources of all cases of Chapter 6, i.e., Table 6.2, Figure 6.30, and section F.9
11) Final_cases_DEM_vs_SR -> PowerPoint presentation containing all contour plots of figure 6
Associated publications:
The data of Chapter 4 has been published in the paper: DOI: 10.1039/D0FD00136H
The data of Chapter 5 has been published in the paper: DOI: 10.1016/j.apt.2022.103932
Contributors for data collection:
1) Matthew E. Potter, Orchid ID: 0000-0001-9849-3306, for help with the 5S catalytic beds of Chapter 5
2) Katy Rankin, Orchid ID: 0000-0002-8458-1038, for doing the Computed Tomography (CT) scans of the catalytic beds of Chapter 5.
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Predictive design of engineered multifunctional solid catalysts
No full textThe ability to devise and design multifunctional active sites at the nanoscale, by drawing on the intricate ability of enzymes to evolve single-sites with distinctive catalytic function, has prompted complimentary and concordant developments in the field of catalyst design and in situ operando spectroscopy. Innovations in design-application approach have led to a more fundamental understanding of the nature of the active site and its mechanistic influence at a molecular level, that have enabled robust structure-property correlations to be established, which has facilitated the dextrous manipulation and predictive design of redox and solid-acid sites for industrially-significant, sustainable catalytic transformations
Combining catalysis and computational fluid dynamics towards improved process design for ethanol dehydration
No full textThrough a combined computational fluid dynamics, characterization and catalysis study we have developed, for the first time, a working model of the ethanol dehydration process within a catalytic pelletized fixed bed reactor. The model, constructed from experimental kinetic data on the dehydration of ethanol to ethylene, with the industrial MTO catalyst SAPO-34, provides unique insights on reaction rate, product selectivity and local temperature fluctuations that are pivotal to reactor design towards optimized catalytic processes, and highly relevant for the optimization of industrial chemical processes
The curious effects of integrating bimetallic active centres within nanoporous architectures for acid-catalysed transformations
Full text linkThe resourceful combination of distinct Mg, Zn and Si active-sites within a single aluminophosphate framework, via simultaneous isomorphous substitution, has afforded unique bimetallic nanoporous heterogeneous catalysts. Unique site-specific interactions have been engineered, at the molecular level, to facilitate catalytic modifications and optimize product yield. By the dextrous incorporation of individual transition-metal active centres, we are able to intricately control the precise nature of the Brønsted acid sites, thereby influencing their catalytic behaviour for the industrially relevant acid-catalysed Beckmann rearrangement of cyclohexanone oxime and isopropylation of benzene
The molecular design of active sites in nanoporous materials for sustainable catalysis
No full textAt the forefront of global development, the chemical industry is being confronted by a growing demand for products and services, but also the need to provide these in a manner that is sustainable in the long-term. In facing this challenge, the industry is being revolutionised by advances in catalysis that allow chemical transformations to be performed in a more efficient and economical manner. To this end, molecular design, facilitated by detailed theoretical and empirical studies, has played a pivotal role in creating highly-active and selective heterogeneous catalysts. In this review, the industrially-relevant Beckmann rearrangement is presented as an exemplar of how judicious characterisation and ab initio experiments can be used to understand and optimise nanoporous materials for sustainable catalysis
Quantifying the impact of intraparticle convection within fixed beds formed by catalytic particles with low macro-porosities
No full textComputational fluid dynamics (CFD) modeling plays a pivotalrole in optimizing fixed bed catalytic chemical reactors to enhance performancebut must accurately capture the various length- and time-scales that underpinthe complex particle−fluid interactions. Within catalytic particles, a range ofpore sizes exist, with micro-pore scales enhancing the active surface area forincreased reactivity and macro-pore scales enhancing intraparticle heat andmass transfer through intraparticle convection. Existing particle-resolved CFDmodels primarily approach such dual-scale particles with low intraparticlemacro-porosities as purely solid. Consequently, intraparticle phenomenaassociated with intraparticle convection are neglected, and their impact inthe full bed scale is not understood. This study presents a porous particle CFDmodel, whereby individual particles are defined through two distinct porosity terms, a macro-porosity term responsible for theparticle’s hydrodynamic profile and a micro-porosity term responsible for diffusion and reaction. By comparing the flow profilesthrough full beds formed by porous and solid particles, the impact of intraparticle convection on mass and heat transfer, as well as ondiffusion and reaction, was investigated
Spectroscopic investigation into the design of solid–acid catalysts for the low temperature dehydration of ethanol
Full text linkThe increased demand for bulk hydrocarbons necessitates research into increasingly sustainable, energy-efficient catalytic processes. Owing to intricately designed structure–property correlations, SAPO-34 has become established as a promising material for the low temperature ethanol dehydration to produce ethylene. However, further optimization of this process requires a precise knowledge of the reaction mechanism at a molecular level. In order to achieve this a range of spectroscopic characterization techniques are required to probe both the interaction with the active site, and also the wider role of the framework. To this end we employ a combination of in situ infra-red and neutron scattering techniques to elucidate the influence of the surface ethoxy species in the activation of both diethyl ether and ethanol, towards the improved formation of ethylene at low temperatures. The combined conclusions of these studies is that the formation of ethylene is the rate determining step, which is of fundamental importance towards the development of this process and the introduction of bio-ethanol as a viable feedstock for ethylene production
Understanding catalytic CO2 and CO conversion into methanol using computational fluid dynamics
No full textThe kinetics of methanol synthesis from a mixture of CO2/CO/H2 have been widely studied in the literature. Yet the role of direct CO hydrogenation is still unclear, in terms of predicting and developing an accurate kinetic model. To investigate, a computational fluid dynamics model has been developed, incorporating two distinct kinetic models, one which includes CO hydrogenation and one which does not. Including CO hydrogenation in the kinetic model provides a more complex interaction between the three involved reactions and can better predict potential inhibitions caused by the presence of H2O. This, however, increases the complexity of the kinetic model. The benefit of applying a fluid dynamics model to study fixed bed reactors is demonstrated, as it offers unique insights into the spatial species concentration, temperature variations, and reaction rate magnitudes. The validated model is shown to be a powerful interrogative tool, capable of supporting system optimization across the catalyst and reactor engineering sectors.</p
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