1,721,019 research outputs found
Advanced catalysts for a low-carbon future exploring new routes for biomass valorisation 291
Full text linkBiomass valorisation is becoming an appealing topic considering the gradual depletion of fossil fuel and the severe environmental deterioration aroused from the massive emission of greenhouse gases (GHGs). Deoxygenation is a fundamental reaction in the upgrading of bio-oil to produce hydrocarbon fuels or high-value chemicals. The removal of oxygen in bio-oil could increase the heating value, enhance the thermal and chemical stability, reduce corrosivity, etc. making the upgraded bio-oil suitable as fuel or blending fuel. Hence, in this thesis, the deoxygenation of raw bio-oil and hydrodeoxygenation of bio-oil model compounds are investigated. Pt/NC are proven to be effective catalysts for the deoxygenation of palm oil to produced bio-hydrogenated diesel (BHD) under optimised reaction conditions. The enhanced interaction between reactants and nitrogen doped support (NC) explains the higher decarbonylation and/or decarboxylation (DeCOx) selectivity. The hydrodeoxygenation of guaiacol with H2 generated from aqueous phase reforming (APR) of methanol and glycerol is conducted in a high-pressure batch reactor. Higher conversion is achieved for methanol as hydrogen source, owing to the higher H2 selectivity from APR process. The interaction of Ni and Pt could enhance the dehydroxylation and hydrogenation in the HDO process, and thus promote deoxygenation efficiency for HDO using methanol as hydrogen source. A novel method for “H2-free” HDO suppressing the external H2 supply is proposed and this concept feasibility is tested over carbon supported non-noble and noble metal catalysts. There is still a large room for improvement in terms of deoxygenation efficiency, but the proposed HDO method is highly recommendable opening new cost-effective alternative for the biomass valorisation. It is worth emphasising the hydrogen transfer route is investigated by the analysis of gas products and the distribution of isotope in isotopic labelling analysis. D/H transfer happens in the catalytic HDO process evidencing the role of the hydrogen donor to produce H2 in-situ. Overall, this thesis showcases appealing strategies for biomass valorisation and how an optimal catalyst design is vital to unlock the potential of bio-resources. In fact, this work is conceived to serve as guidance for the successful design of advanced catalysts to pursue a low carbon future as ultimate goal
The Development of Novel Yolk@Shell Catalysts for the Thermochemical Conversion of CO2
Full text linkCO2 is a plentiful feedstock for reactions that converts this waste material into a valuable source of chemicals and fuels. The current technology used in this field is complex supported metal nanoparticles, popularised by simplistic synthetic routes and reaction applicability. This morphology is highly prone to sintering, which can, in turn, cause carbon deposit formation (coke) on the surface that blocks the active sites.A promising method to improve upon these issues is the variation of the catalytic morphology; encapsulation of the active phase to produce Yolk@Shell particles. Results from the “proof of concept” NiZnO@SiO2 material proved varied; the catalyst demonstrated impressive longevity within the dry reforming of methane, surpassing the internal comparisons by a significant margin, but deactivated. The second chapter sought to improve upon the sample homogeneity and explore their reverse water gas shift reaction performance. The NiCo@SiO2 catalysts performed admirably and suggested advanced product formation after a mass spectrometry study. This finding suggests that the Yolk@Shell structure is capable of increasing internal pressure, allowing new reaction mechanisms to occur. The third catalyst was a reimagining of a traditional catalyst (Cu/ZnO@Mo2C) in the Yolk@Shell morphology. In addition to favourable longevity and reactive selectivity, complex organic product formation was also seen, again linked to the Yolk@Shell structure. The final catalyst developed for this thesis was a preliminary study aiming to combine single-atom catalysts and the encapsulation. Catalytic testing displayed impressive CO2 conversion and longevity, with no sintering or coke. While the XRD results show that single-atom sites were not achieved, however further work could see these two structures combined successfully.Overall, this thesis is based on synthetic development and reactive studies to produce highly effective catalysts for the thermal conversion of CO2, while remaining facile and highly resistant to deactivation. It is hoped that this work will inspire more imaginative methods of catalytic development and investigation to further the field as a whole and not just thermal CO2 utilisation
Catalytic Aspects of Fuel Cells: Overview and Insights
Full text linkHeterogeneous catalysis plays a central role in the global energy paradigm, with practically all energy-related process relying on a catalyst at a certain point. The application of heterogeneous catalysts will be of paramount importance to achieve the transition towards low carbon and sustainable societies. This book provides an overview of the design, limitations and challenges of heterogeneous catalysts for energy applications. In an attempt to cover a broad spectrum of scenarios, the book considers traditional processes linked to fossil fuels such as reforming and hydrocracking, as well as catalysis for sustainable energy applications such as hydrogen production, photocatalysis, biomass upgrading and conversion of CO2 to clean fuels. Novel approaches in catalysts design are covered, including microchannel reactors and structured catalysts, catalytic membranes and ionic liquids. With contributions from leaders in the field, Heterogeneous Catalysis for Energy Applications will be an essential toolkit for chemists, physicists, chemical engineers and industrials working on energy
CO2 conversion via reverse water-gas shift using multicomponent catalysts
Full text linkThe continuous increase of carbon dioxide (CO2) level, nowadays, has become a knotty problem and life-threatening which is envisaged as the next pandemic. The question is: Can we use it as a plentiful feedstock instead of leaving it as a waste gas? The answer is Yes. Recently, more and more scientists and researchers put their efforts into this topic, converting CO2 into a valuable source of chemicals and fuels. Within current technologies, reverse water-gas shift (RWGS) reaction has attracted wide attention because the produced carbon monoxide (CO) is the versatile compound within the field of C1 chemistry, having the potential to be applied in large-scale when coupled to downstream processes (e.g. Fischer-Tropsch and methanol synthesis). However, due to its endothermic nature, RWGS requires high temperatures and it has kinetic limitations in terms of CO2 conversion at lower temperature regions. Besides, methane (CH4) production from the competitive methanation process is produced at low and moderate temperatures. Therefore, further efforts must be put into the development of active catalysts to overcome the slow kinetics and improve the production distribution towards carbon monoxide.In this present research work, firstly, a comprehensive literature review was done in order to guide the catalyst selection. Following this, Ni, Fe, and Cu oxides have been chosen as active metals, supported on the homemade CeO2-Al2O3 mixed oxide matrix for catalysts synthesis. Catalysts were tested in fixed-bed continuous flow reactors and multiple characterisation techniques were applied. Results indicate that Ni-based catalysts present outstanding CO2 activation, but they also favour CH4 formation and thermal sintering. Effects of selected promoters FeOX and CrOX were studied. Results show that FeOX promoted Ni/CeO2-Al2O3 has better activity/stability balance under critical reaction conditions due to Ni-Fe interaction, as well as the textural property/thermal stability supplied by FeOX. As for Fe-based catalysts, they show less activity, especially at lower temperatures. But their catalytic performance can be largely improved by adding CuOX and NiOX as promoters. Among promoted catalyst systems, Fe-Cu/CeO2-Al2O3 catalyst reveals a considerable CO2 conversion at 500oC for about 40% with nearly 100% CO selectivity. Then, we focused on the study of Fe/Cu oxides ratio effects, developing a bimetallic Fe-Cu catalytic system. Results indicate that when the CuOX increases to 75% (based on the total amount of active metals), 0.25Fe0.75Cu shows the best CO selectivity. And the electronic interaction between Fe and Cu has proven to be important for CO2 activation and H2 dissociation. Besides, the Cu species are found to be partially incorporated into CeOX lattice, which is the key to produce CO. Based on these findings, a new series of FeOX promoted Cu/CeO2-Al2O3 (Fe2O3:CuO = 0.25:0.75) was developed. Catalysts were calcined at three different temperatures (400oC, 600oC, and 800oC) and tested in direct CO2 hydrogenation to methanol. To unravel the reaction pathway of this reaction over our prepared catalysts, advanced technique in-situ Diffusive Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) was applied. CO and formate species were detected simultaneously, evidencing the co-existence of the redox pathway, the RWGS + CO-hydro pathway, and the formate pathway during the reaction. In any case, the calcination temperature has a great impact on the product distribution. Besides, the final experimental chapter suggests a Cu-Fe/CeO2-Al2O3 catalyst calcined at 600oC, which shows the highest CO2 conversion and considerable methanol selectivity due to highly dispersed CuOX and FeOX particles, and the existence of CuCeOX structure.Overall, this thesis is based on rational design and reactive studies to produce highly effective catalysts for CO2 conversion via RWGS. It is hoped that this work will inspire more investigation in this field
Emissions to liquid fuels: Development of advanced heterogeneous catalysts for CO2 valorisation
Full text linkCO2 utilisation is becoming an appealing topic in catalysis science due to the urgent need to deal with greenhouse gases (GHG) emissions. Herein, the dry reforming of methane (DRM) represents a viable route to convert CO2 and CH4 (two of the major GHG) into syngas, a highly valuable intermediate in chemical synthesis. Nickel-based catalysts are economically viable materials for this reaction, however they show inevitable signs of deactivation mainly caused by the agglomeration of the active phase and carbon deposition on the surface of the catalyst. In this work, stabilisation of Ni in a pyrochlore-perovskite structure is reported as a viable method to prevent fast deactivation. Substitution of Zirconium by Ni at various loadings in the lanthanum zirconate pyrochlore La2Zr2O7 is investigated in terms of reactant conversions under various reaction conditions. Crystallographic analysis of the catalysts showed the formation of phases corresponding to the pyrochlore structure La2Zr2-xNixO7-δ and an additional La2NiZrO6 perovskite phase at high Ni loadings. The pyrochlore mixed oxide shows high basicity and surface oxygen availability, leading to a material with high CO2 activation potential. In particular, the formation of lanthanum oxycarbonate is occurring upon CO2 activation. The best formulated catalyst shows excellent activity for various reforming reactions at temperatures as low as 600 °C and displays great stability over 350 hours of continuous dry operation. Versatility in feed ratio and syngas production was demonstrated. Carbon formation although inevitable, is limited using this formulation strategy. The presence of nanosized Ni particles contributes to the excellent performance of the catalyst. Exsolution of Ni from the host lattice is believed to occur upon activation pre-treatment of the catalyst and leads to small, well dispersed and highly active Ni clusters. Overall, this work showcases an appealing strategy to design economically viable advanced catalysts for chemical CO2 recycling via reforming reactions
First-principles based mechanistic understanding of CO2 utilisation reactions over advanced heterogeneous catalysts.
Full text linkIt has become increasingly important to control carbon dioxide (CO¬2) emissions and at the same time generate fuel sources to meet the growing global energy consumption need. CO2 (dry) reforming of methane (DRM) is a viable process as it generates fuel (syngas) and utilises greenhouse (CH4 and CO2) gas at the same time. The success of this process relies on the development of suitable noble-metal free catalysts. First principle’s based computational methods, such as density functional theory (DFT), has become a powerful predictive tool for catalyst development in modern science. Therefore the main objective of this thesis work has been to investigate suitable catalysts using computational methods for gas–phase CO2 utilisation reactions.
In this research work, DFT calculations provided us with the fundamental insights into the DRM mechanism over bimetallic Sn/ Ni (111) periodic model surfaces. This analysis showed that low Sn concentration on Ni surface effectively mitigates carbon formation without compromising the CO2 conversion and the syngas production, showcasing superior characteristics of the bimetallic catalyst towards carbon tolerance stability. Other heterogeneous catalysts such as Ni2P and MoP have also been studied in this thesis. Theoretical analysis of DRM reaction on the unexplored nickel phosphide Ni2P (0001) surface showcased suitable syngas production under DRM reaction temperatures with low carbon deposition formation on the surface. This was mainly attributed to a lower number of active sites available for carbon adsorption compared to oxygen on the Ni2P (0001) surface.
DFT study on activation of CO2 and CO on MoP (0001) and Ni2P (0001) surfaces showcased selective CO production from CO2 to be possible on both the surfaces. Further, direct CO activation is favoured on the MoP (0001) surface. Surface bounded oxygen removal on Ni2P (0001) is reasonably favourable.
Findings from this thesis work will be beneficial in developing more robust catalysts for gas phase CO2 utilisation reactions and could contribute to a better understanding of CO2 conversion processes, catalysts deactivation and thus helping to develop new families of powerful catalysts for a greener societ
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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