Selective Catalytic Reduction of Nitrogen Oxides with Hydrocarbons at conventional fixed bed catalytic reactors and solid electrolyte membrane reactors

Atmospheric pollution resulted from human activities, is one of the most important problems that the developed countries should confront. Nitrogen oxides, NOx, have been included in the “criteria” pollutants category. The high atmospheric NOx concentration, is directly related with the “greenhouse” effect, depletion of the ozone layer, acid rain and chronic complaints of the human respiratory system. The aforementioned problems along with the increasing industrial development worldwide have triggered research efforts towards the development of methods/techniques capable to reduce NOx emissions. A solution to these problems is expected to be offered using environmental catalysis. The selective catalytic reduction of NOx with hydrocarbons is an attractive technology that is expected to reduce the anthropogenic emissions of NOx. The novelty of this technology lies in the use of unburned hydrocarbons as reducing agents, which co-exist in exhaust streams. In this context, the simultaneous effective removal of both hazardous gases can be achieved. The main goal of the present thesis concerns the development and optimization of metal/Al2O3 catalysts as well as the investigation of the reaction mechanism which describes the reduction of nitrogen oxides (ΝΟ and Ν2Ο) along with the simultaneous oxidation of unburned hydrocarbons. Furthermore the present thesis is also focused in the promotion of the most promising catalysts with alkali ions (Νa+ and Κ+) in order to alter their electronic properties to the desired direction and therefore to increase the achieved activity, stability and durability, both at ideal and practical conditions.Η ατμοσφαιρική ρύπανση αποτελεί σήμερα ένα από τα μεγαλύτερα προβλήματα των ανεπτυγμένων χωρών, λόγω της διατάραξης της φυσικής ισορροπίας που έχει προκληθεί από τις ανθρωπογενείς δραστηριότητες. Τα οξείδια του αζώτου (NOx­) έχουν συμπεριληφθεί στους σημαντικότερους και πλέον επικίνδυνους αέριους ρύπους. Φαινόμενα όπως αυτό του “θερμοκηπίου” και της υπερθέρμανσης του πλανήτη, της μείωσης του στρώματος του όζοντος στην στρατόσφαιρα, της όξινης εναπόθεσης, των χρόνιων παθήσεων του αναπνευστικού συστήματος των ανθρώπων κ.α. συνδέονται άμεσα με τις υψηλές συγκεντρώσεις των NOx στην ατμόσφαιρα. Η επιδείνωση αυτών των προβλημάτων, σε συνδυασμό με την καλπάζουσα βιομηχανική ανάπτυξη, καθιστούν επιτακτική την ανάγκη για τον έλεγχο και την ανάπτυξη τεχνολογιών ικανών να περιορίσουν τις εκπομπές των NOx. Η εκλεκτική καταλυτική αναγωγή των οξειδίων του αζώτου με υδρογονάνθρακες αποτελεί μια τεχνολογία που θεωρείται ότι δύναται να περιορίσει τις ανθρωπογενείς εκπομπές των NOx. Η καινοτομία της τεχνολογίας έγκειται στην χρήση άκαυστων υδρογονανθράκων, οι οποίοι επίσης περιέχονται στα καυσαέρια των διεργασιών και μπορούν να αντικαταστήσουν την ιδιαίτερα τοξική και διαβρωτική ΝΗ3 που χρησιμοποιείται σήμερα σε βιομηχανικές εφαρμογές, ως αναγωγικό μέσο. Με τον τρόπο αυτό επιτυγχάνεται η ταυτόχρονη απομάκρυνσή των επίσης επικίνδυνων για την υποβάθμιση της ατμόσφαιρας υδρογονανθράκων μαζί με τα NOx. Ο στόχος της παρούσας διδακτορικής διατριβής αφορά στην ανάπτυξη και στην βελτιστοποίηση καταλυτικών συστημάτων μετάλλου/Al2O3 καθώς και στην διερεύνηση του μηχανισμού των υπό μελέτη διεργασιών για την αναγωγή των εκλυόμενων, στα απαέρια μονάδων παραγωγής ισχύος, οξειδίων του αζώτου (ΝΟ και Ν2Ο), με την ταυτόχρονη οξείδωση των άκαυστων υδρογονανθράκων, των ίδιων των απαερίων, με σκοπό την αμοιβαία ελάττωση των εκπομπών τους. Σε ένα δεύτερο επίπεδο, η διδακτορική διατριβή εστιάστηκε στην ενίσχυση των επιλεγόμενων καταλυτικών συστημάτων με αλκαλικά ιόντα (Νa+ και Κ+) με σκοπό την μεταβολή των ηλεκτρονιακών τους ιδιοτήτων προς την επιθυμητή κατεύθυνση και κατά συνέπεια την αύξηση της επιτευχθείσας ενεργότητας και σταθερότητάς τους, τόσο σε ιδανικές όσο και σε πραγματικές συνθήκες αντίδραση

Υλοποίηση επεξεργαστή ARM με χρήση γλώσσας Bluespec

Διπλωματική εργασία που υποβλήθηκε στη σχολή ΗΜΜΥ του Πολυτεχνείου Κρήτης για την πλήρωση των προϋποθέσεων λήψης του διπλώματοςΠερίληψη: Ο σκοπός αυτής της διπλωματικής ήταν να δημιουργηθεί ένας επεξεργαστής ARM με τη χρήση της γλώσσας προγραμματισμού Bluespec System Verilog(BSV). Η BSV έχει μία θεμελιωδώς διαφορετική προσέγγιση στη σχεδίαση υλικού, συγκριτικά με άλλες γλώσσες περιγραφής υλικού. Βασίζεται στη δημιουργία κυκλωμάτων από ότι στην απλή περιγραφή κυκλωμάτων και επίσης βασίζεται σε ατομικούς κανόνες συναλλαγών αντί για μια συνολική σύγχρονη άποψη του κόσμου. O επεξεργαστής είναι μέλος της ARM7 οικογένειας επεξεργαστών, έχει 3 στάδια pipeline, χρησιμοποιεί 32-bit αρχιτεκτονική και βασίζεται στο ARMv4 σύνολο εντολών. Επιπλέον ο επεξεργαστής υποστηρίζει όλα τα διαφορετικά modes λειτουργίας. Τα mode λειτουργίας είναι User, Fast Interrupt(FIQ), Interrupt(IRQ), Supervisor, Abort, System και Undefined. Ο αριθμός των τύπων των διαφορετικών εντολών που υλοποιήθηκαν είναι 26. Ο καθένας από αυτούς τους διαφορετικούς τύπους έχει επιπλέον λειτουργίες ανάλογα της συνθήκη της εντολής και το τρόπο με τον οποίο έχει διευθυνσιοδότηθεί. Για την επιβεβαίωσης της σωστής λειτουργίας του επεξεργαστή χρησιμοποιήθηκε κώδικας assembly . Αυτός ο κώδικας παράχθηκε από κώδικα C++ μέσω του ARM gccSummarization: The goal of this thesis was to construct an ARM processor using the Bluspec System Verilog language(BSV). BSV has a fundamentally different approach to hardware design, comparing to other Hardware Description Languages. It is based on circuit generation rather than merely circuit description and is also based on atomic transactional rules instead of a globally synchronous view of the world. The processor belongs to the ARM7 family, it has a 3-stage pipeline, it uses a 32-bit architecture and is based on ARMv4 instruction set. In addition the processor supports all the operating modes. The modes of operation are User, Fast Interrupt(FIQ), Interrupt(IRQ), Supervisor, Abort, System and Undefined. The amount of different types of instructions that were implemented is 26. Each and every one of these types has additional functions depending on the condition codes and the addressing modes of the instruction. For the verification of the design, assembly code was used. This assembly code was produced by C++ code, through the ARM GCC

Αξιολόγηση της πλατφόρμας Intel Harp με χρήση ενός επιταχυντή ARM με πολλαπλούς πυρήνες

Μεταπτυχιακή Διατριβή που υποβλήθηκε στη σχολή ΗΜΜΥ του Πολυτεχνείου Κρήτης για την πλήρωση προϋποθέσεων λήψης του Μεταπτυχιακού Διπλώματος ΕιδίκευσηςSummarization: The purpose of this thesis was to evaluate Intel's platform with scalable Xeon CPU and an integrated Arria 10 FPGA. The communication between CPU and FPGA is done with three physical channels, one QPI (Quick Path Interconnect) coherent channel and two PCIe non-coherent channels. There is also a shared memory between the two sides. The read and write bandwidth of the FPGA to the shared memory is approximately 19 GB/s respectively. The FPGA side consists of a static and a reconfigurable part. The static part implements all the necessary components to establish the communication with the CPU. The reconfigurable part is connected with the static part through the Core Cache Interface protocol (CCI-P) that provides a level of abstraction to the developer for starting developing accelerators. The system consists of software and hardware implementations. The evaluation was done with an ARM many core accelerator. The ARM core has a 3-stage pipeline, it uses a 32-bit architecture and is implements the ARMv4 instruction set. Also it implements a few basic floating point instructions. The RTL for the ARM core was written in Bluespec System Verilog (BSV). The hardware architecture has 16 ARM cores. Each core has a direct-map cache with a variable size. Instruction and data memories of every core can be initialized from software in order to the processors can execute the programs that are defined by the developer. The code and the data for the internal memories of each core are read form binary files. Each core is assigned with buffers with a certain amount of memory space to read and write data from/to it. The hardware can have access to them with the use of physical addresses. For the purpose of measuring the bandwidth of the design STREAM benchmark was used. Plus a matrix multiplication test was made as a way to check how the architecture handles real life applications

N2O abatement over γ-Al2O3 supported catalysts: Effect of reducing agent and active phase nature

Δημοσίευση σε επιστημονικό περιοδικόSummarization: A series of metal catalysts (Pd, Rh, Ru, Cu, Fe, In and Ni) supported on γ-Al2O3 carrier, were evaluated during N2O catalytic conversion to N2 in the absence and presence of excess oxygen and reducing agents (CH4 or C3H8). Among all catalysts tested, Pd-, Ru- and Rh-based samples exhibited the best catalytic performance, in all reaction conditions examined. The reaction was inhibited by O2, in particular at lower temperatures, while its effect was essentially negligible at higher ones. In the presence of reducing agents and under lean reaction conditions, N2O conversion was comparably enhanced, with C3H8 being more efficient than CH4; however even in the presence of hydrocarbons N2O decomposition is the major pathway for N2O abatement, since reducing agents mainly act as oxygen scavengers reducing and concurrently activating the metal sites. The influence of different co-existing gases (CO, H2O and SO2) on the performance of Pd supported catalysts was also investigated, whereas thermal stability tests in the presence of SO2 indicate a gradual irreversible decrease in activity until a new steady state was established.Παρουσιάστηκε στο: Topics in Catalysi

A comparison between electrochemical and conventional catalyst promotion: The case of N2O reduction by alkanes or alkenes over K-modified Pd catalysts

Δημοσίευση σε επιστημονικό περιοδικόSummarization: In the present work, two different methods of catalyst promotion, the electrochemical promotion (EP) and the conventional promotion (CP), were comparatively applied on a catalytic system of significant environmental and practical importance: the N2O reduction by hydrocarbons (alkanes and alkenes), in the presence or absence of O2, over Pd catalysts. A galvanic cell of the type Pd/K+-conducting β″-Al2O3/Au was constructed for the application of the EP concept whereas the CP concept was investigated via a series of highly dispersed Pd/γ-Al2O3 catalysts, conventionally promoted (by impregnation) with K modifier. Given that EP is a straightforward, efficient and in situ way for investigating the effect of a promoter on a catalytic system, the present study is dealing with its prior use as a rapid “research tool” for exploring the effect of K promoter on the catalytic system under consideration. Subsequently, the insight obtained from EP studies is applied to the design of conventional catalysts' composites, i.e. Pd/γ-Al2O3 catalysts conventionally promoted by K at loadings indicated from EP studies. For the system investigated, the optimal promoter loading was in the range of ∼ 0.45–0.55, in terms of K-coverage. In this range of K-loadings significant enhancement on de-N2O activity was obtained under reducing conditions using both methods of K-promotion. However, in the presence of excess oxygen in the reaction mixture the effect of K-promotion was less pronounced, independently of the reducing agent used.Παρουσιάστηκε στο: Solid State Ionic

Correlation of surface characteristics with catalytic performance of potassium promoted Pd/Al2O3 Catalysts: The case of N2O reduction by alkanes or alkenes

Δημοσίευση σε επιστημονικό περιοδικόSummarization: The present study aims at investigating the role of potassium (K) promoter on the surface and catalytic behavior of Pd/Al2O3 catalysts during N2O reduction by alkanes (CH4, C3H8) or alkenes (C3H6). In this context, the surface properties of un-promoted and K-promoted catalysts were evaluated by means of X ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption and FTIR-pyridine adsorption. The results reveal that both the electronic and structural properties of Pd entities can be substantially modified by potassium ions, which are in close proximity with catalyst surface without exhibiting a tendency to accumulate. This in turn results in significant modifications on reactants/intermediates chemisorption bonds, affecting the catalytic performance of K-promoted catalysts. Indeed, it was found that potassium strongly promotes the N2O reduction by propane or propene yielding notably lower N2O light off temperatures (ca. 100 °C) as compared to those obtained over un-promoted catalysts. On the contrary, a slight inhibition upon K-promotion was observed, when using CH4 as reducing agent, implying that the action of the K-promoter is strongly related with the reducing agent used and its’ relative interaction with the catalyst’s surface. The results are discussed in terms of the correlation between the surface chemistry modifications induced by electropositive promoters and the de-N2O performance of K-promoted catalysts.Παρουσιάστηκε στο: Topics in Catalysi