Academic literature on the topic 'Temperature-programmed reduction (TPR)'

A series of La1−xSrxCrO3(0⩽x⩽0.3) composite oxides were prepared by a modified citric method. These perovskite oxides were further modified with Ru through impregnation. X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and temperature-programmed-reduction (TPR) techniques were adopted to investigate the properties of both the as-prepared perovskite oxides and the surface-Ru-modified La1−xSrxCrO3 samples. XPS results indicated the existence of Cr6+ ions in the fresh samples and transformed to Cr3+ after reduction. The hydrogen consumed by these perovskite oxides during TPR increased with the Sr doping, which was more than twice of the theoretical value according to Kröger-Vink notation. The reduction temperature of Cr ions of Ru∕La1−xSrxCrO3 significantly decreased with an increase of the Ru loading. A small reduction peak at ∼540°C, which was not shifted by increasing Ru loadings, was observed and could be ascribed to the reduction of trace chromate phases. On all TPR profiles of the three doped perovskites with unity of the A-site and B-site ratio, the reduction of Ru species could not be observed at low Ru loadings (0.05% and 0.1%). A reduction peak from RuO2 particles appeared at temperatures prior to the perovskite reduction on the TPR plots of modified La0.9Sr0.1CrO3 and La0.8Sr0.2CrO3 with high Ru loading (0.5% and 1%, respectively), but it did not occur with the Ru modified La0.7Sr0.3CrO3 in the investigated Ru loading range. The TPR results of the Ru modified La0.8Sr0.2Cr0.95O3 depicted that some Ru ions might be stabilized due to the incorporation into the oxide.

Temperature-programmed reduction (TPR) is a widely used method for characterization of oxide-based catalysts, sorbents, and functional materials, but its results lack quantitative assessment. Here, we present a novel approach to kinetic analysis of the TPR that can be applied to a large variety of systems involving multiple limiting stages. Implementation of cubic splines to approximate rate constant vs. conversion dependencies obtained from several TPR curves recorded at different heating rates yields in a set of kinetic parameters (activation energy and preexponential factors) for all reduction stages. Relationship between preexponential factor of the first reduction stage and the specific surface area of the sample has been shown. Reduction of hematite has been studied to prove the performance of the developed kinetic analysis technique.

Alumina-supported palladium vanadium-pentoxide catalysts were studied by means of temperature-programmed surface reaction, temperature-programmed reduction, temperature-programmed oxidation, and by ESR spectroscopy in the complete oxidation of benzene. The surface reaction measurements indicated that 0.5% Pd - 30% V2O5 / Al2O3 produced most oxidation products, compared to 0.5% Pd / Al2O3 or 30% V2O5 / Al2O3 samples. A drastic fall of peak maxima in temperature-programmed oxidation and reduction spectra indicates the decisive role of palladium in the mixed metal metal oxide system in facilitating the vanadium redox transitions. During initial period of catalysts operation, there proceeds formation of vanadium oxide phases which contain clustered V4+ ions in a matrix of vanadium pentoxide. These ions are responsible for the high activity of the palladium vanadium pentoxide catalyst.

Metallic molybdenum was synthesized through reduction of molybdenum trioxide (MoO3) by using hydrogen as a reducing agent. The reduction behavior of MoO3 were investigated by using temperature programmed reduction (TPR). The reduced phases were characterized by X-ray diffraction spectroscopy (XRD). The XRD results indicate that the reduction of MoO3 proceed in two steps reduction (MoO3 → MoO2 → Mo) with formation of intermediate phases of Mo4O11 during first step of reduction. However, the TPR results showed only one broad peak that correspond to all reduction step that was merge into one peak. It seem that, increasing the temperature cause the rapid reduction that correlated with thermodynamic consideration data that show the formation of metallic molybdenum is become feasible by increasing the temperature.

Temperature programmed reduction (TPR) method was introduced to analyze the structural change and thermal stability of LixCoO2 (LCO) cathode material. The reduction peaks of delithiated LCO clearly represented the different phases of LCO. The reduction peak at a temperature below 250 °C can be attributed to the transformation of CoO2–like to Co3O4–like phase which is similar reduction patterns of CoO2 phase resulting from delithiation of LCO structure. The 2nd reduction peak at 300~375 °C corresponds to the reduction of Co3O4–like phase to CoO–like phase. TPR results indicate the thermal instability of delithiated LCO driven by CoO2–like phase on the surface of the delithiated LCO. In the TPR kinetics, the activation energies (Ea) obtained for as-synthesized LCO were 105.6 and 82.7 kJ mol-1 for Tm_H1 and Tm_H2, respectively, whereas Ea for the delithiated LCO were 93.2, 124.1 and 216.3 kJ mol-1 for Tm_L1, Tm_L2 and Tm_L3, respectively. As a result, the TPR method enables to identify the structural changes and thermal stability of each phase and effectively characterize the distinctive thermal behavior between as-synthesized and delithiated LCO.

Highly dispersed CuFe19Ox catalysts with different shapes were prepared and further characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and in-situ XRD. XRD and TEM results showed that the synthesized CuFe19Ox nanoparticles consisted of CuO and Fe2O3, while CuFe19Ox nanorods consisted of CuFe2O4 and Fe2O3. The reduction properties of CuFe19Ox samples were finely studied by H2-TPR, and the phase composition was identified by in-situ XPS, HR-TEM, and surface TPR (s-TPR). In-situ X-ray photoelectroscopy (XPS) indicated that the metallic Cu and Fe3O4 were the main species after reduction. Moreover, s-TPR studies showed that the reduction performance of copper was significantly affected by the shapes of the Fe3O4 supports. Low-temperature water gas shift (LT-WGS) was chosen to characterize the Cu species on the surface. It was found that reduced CuFe19Ox nanorods had no activity. On the contrary, reduced CuFe19Ox particles showed higher initial WGS activity, where the active Cu0 should originate from the reduction of Cu2O at lower temperatures, as confirmed by the s-TPR profiles.

Abstract The aim of the thesis is to expand the knowledge of the catalytic properties of platinum-loaded zeolite catalysts in the reduction of NOx by hydrocarbons. The work is divided into three parts. First the recent literature of zeolite catalysts has been introduced, secondly the adsorption capacity, activity, and acidity of the catalysts have been studied by TPD and IR techniques, and thirdly the derived reaction mechanisms based on the obtained data are presented. Parent and 1 wt-% Pt-loaded ZSM-5, Beta, Y, and Ferrierite zeolite catalysts have been studied in the C3H6-assisted reduction of NO. The Pd/Al2O3-based catalyst was used as a reference material for the reaction mechanistic studies. Several experimental techniques (in situ DRIFT, activity measurements, CO chemisorption, N2 physisorption, TPD, and TEM) have been used for the characterisation of the catalysts properties. The IR technique was used as the main technique for the determination of activities, surface species, and the acidic properties of the zeolite-based catalysts. The activity studies carried out by the gaseous FTIR technique provide information on the desired reaction products as well as the undesired by-products. The detection and identification of the surface species as well as the reaction intermediates formed were done by the DRIFT method. The activity experiments indicate the effectiveness of the Pt-loaded zeolite catalysts. The reduction of NO was found to decrease in the order: Pt/Beta > Pt/Y > Pt/Ferrierite > Pt/ZSM-5 in the conditions with excess O2. Platinum can be concluded to have an effect on O2 and NO dissociation. Oxidation reactions of NO to NO2 and propene to CO2 were observed to be more intense over the platinum-loaded zeolites than over the parent zeolites. In this work the reaction mechanisms for the C3H6-SCR of NO were derived over the Pt-loaded zeolite as well as the Pd/alumina catalysts based on the data obtained by DRIFT and activity experiments. The kinetics for the NO reduction by CO over Pd/Al2O3 was also derived. With the methods employed, the mechanistic steps over the Pt-loaded zeolites and Pd/Al2O3-based catalysts could be derived quite precisely and easily for C3H6-SCR of NO. Reaction routes were determined to go via different formations of intermediates over the two catalysts, i.e. via organonitrogen and isocyanate routes, respectively. The IR techniques were discovered to be effective tools in applied engineering studies.

Κατά τις τελευταίες δεκαετίες παρατηρείται συνεχής αύξηση της έντασης του φαινομένου του θερμοκηπίου γεγονός που προκαλεί σημαντικές συνέπειες στο περιβάλλον και στη ζωή μας γενικότερα. Συνεπώς, είναι απαραίτητη η μείωση της ανθρωπογενούς εκπομπής των αερίων που συμβάλλουν στην αύξηση του φαινομένου αυτού. Η εκμετάλλευση και χρήση των δύο πιο σημαντικών θερμοκηπικών αερίων, του μεθανίου και του διοξειδίου του άνθρακα, μπορεί να επιτευχθεί με την αναμόρφωση του CH4 με CO2 ή αλλιώς ξηρή αναμόρφωση του μεθανίου (Dry Reforming of Methane-DRM). Με τη διεργασία DRM τα δύο συγκεκριμένα αέρια μετατρέπονται σε αέριο σύνθεσης (synthesis gas), το οποίο χρησιμοποιείται είτε για τη σύνθεση πληθώρας οργανικών ενώσεων, είτε για την παραγωγή Η2 για ενεργειακούς σκοπούς. Η DRM παρουσιάζει σημαντικά πλεονεκτήματα: δεν απαιτείται η χρήση ύδατος, φθηνό σχετικά κόστος εγκαταστάσεων, χρησιμοποιείται σε χημικά συστήματα μεταφοράς ενέργειας, ενώ και το αέριο σύνθεσης που παράγεται έχει ακόμα κατάλληλη αναλογία για συνθέσεις Fischer–Tropsch. Παρόλα αυτά η DRM δεν έχει εκτεταμένη βιομηχανική εφαρμογή επειδή αντιμετωπίζει ένα σημαντικό μειονέκτημα: ο καταλύτης μετά από κάποιο χρόνο λειτουργίας απενεργοποιείται λόγω του άνθρακα που αποτίθεται πάνω του. Στην παρούσα εργασία μελετήθηκε ο state of the art καταλύτης Ni/Al2O3, τον οποίο τροποποιήσαμε με βόριο σε διάφορους λόγους [Β/(B+Νi)] με κύριο στόχο τη μείωση των ανθρακούχων αποθέσεων. Οι τροποποιημένοι καταλύτες συντέθηκαν με τη μέθοδο του υγρού συνεμποτισμού και χαρακτηρίστηκαν φυσικοχημικά με διάφορες τεχνικές, ώστε να μελετήσουμε την επίδραση του βορίου στην υφή τους (ΒΕΤ, porosimetry, SEM, TEM), στη δομή τους (XRD, UV-Vis DRS) και στην αναγωγιμότητά τους (H2-TPR). Η καταλυτική συμπεριφορά τους για την αντίδραση της ξηρής αναμόρφωσης του μεθανίου αξιολογήθηκε σε αντιδραστήρα σταθερής κλίνης, για 24h, σε συνθήκες: 973Κ, 1 atm, τροφοδοσία 50%CH4-50%CO2. Ο άνθρακας που αποτέθηκε στους χρησιμοποιημένους καταλύτες μετρήθηκε με τη μέθοδο της θερμοπρογραμματισμένης υδρογόνωσης (TPH). Τα ανηγμένα και χρησιμοποιημένα στην DRM καταλυτικά δείγματα μελετήθηκαν επίσης με ηλεκτρονικό μικροσκόπιο σάρωσης (SEM με αναλυτή EDS) και ηλεκτρονικό μικροσκόπιο διαπερατότητας (ΤΕΜ). Βρέθηκε ότι η παρουσία του Β μειώνει σημαντικά την ποσότητα του αποτιθέμενου άνθρακα στους καταλύτες Ni/Al2O3, σε ποσοστό έως και 86%, χωρίς να επηρεάζει ιδιαίτερα τη δραστικότητα και την εκλεκτικότητα των καταλυτών. Σημαντικό ρόλο παίζει το ποσοστό του Β στον καταλύτη, με τον καταλύτη με λόγο Β/(B+Νi) = 0,5 να εμφανίζει τη βέλτιστη συμπεριφορά. Τα αποτελέσματα μας έδειξαν ότι η ιδιαίτερη θετική επίδραση του βορίου οφείλεται κυρίως στο γεγονός ότι ευνοεί τη διασπορά του μεταλλικού νικελίου. Τροποποίηση με βόριο, σε κατάλληλη περιοχή φορτίσεων, του καταλύτη Ni/Al2O3 μεγιστοποιεί το πλήθος των νανοσωματιδίων νικελίου με μέση διάσταση < 6.0 nm, τα οποία, ως γνωστόν, ελαχιστοποιούν την απόθεση άνθρακα.
The intensity of the greenhouse effect is constantly increasing in the last few decades with an adverse effect both on the environment and the humanity. In order to decrease the effect, human-caused emissions should be minimized. The two most important greenhouse gases, methane and carbon dioxide, can be used in the DRM (Dry Reforming of Methane) process. With this process the above mentioned gases are converted to synthesis gas, which is then used for the synthesis of a great number of organic compounds and synthetic fuels (through the Fisher-Tropsch syntheses) or for the production hydrogen to be used as a fuel (energy purposes). The DRM process presents a number of advantages, namely: no water is required, relatively low cost of process plants,it can be used as a Chemical Energy Transfer System and, finally, the produced synthesis gas has adequate CO/H2 ratio for Fisher-Tropsch syntheses. Although DRM is a promising process, its industrial application is hindered by a major drawback: the catalysts are rapidly deactivating due to coking. In the current study, the state of the art catalyst Ni/Al2O3 was studied and modified with boron, using different ratios of Β/(B+Νi). Our primary objective was to reduce coking. The modified catalysts were synthesized by wet co-impregnation and physicochemically characterized in their oxidic, reduced and used forms, using various techniques, in order to investigate the influence of boron on the texture (BET, Porosimetry, SEM, TEM), structure (XRD, UV-Vis DRS) and reducibility (H2-TPR) of the catalysts. The catalytic performance for the DRM process was studied under stable conditions (973Κ, 1 atm and 50%CH4-50%CO2 undiluted feed), for 24h, using a fixed bed reactor. Carbonaceous deposits on the used catalysts were determined by Temperature Programmed Hydrogenation (TPH). Scanning Electron Microscopy (SEM) with EDS analyser and Transmission Electron Microscopy (TEM) were also used in the study of reduced and used catalytic samples. Modifying Ni/Al2O3 catalysts with boron results in a great decrease of the deposited coke (up to 86%), without any significantly influence on the activity and selectivity of the catalysts. A major factor influencing the catalyst is the B loading, with the ratio Β/(B+Νi)=0,5 giving the best results. Boron’s positive effect was mainly attributed to its ability to increase Ni dispersion. Modification of Ni/Al2O3 catalysts, by using the appropriate boron loading, resulted to an increase of the amount of nickel nanoparticles with an average dimension under 6.0 nm, which are known to minimize coke deposition.

After introducing fundamentals of catalysis with noble metal surfaces especially Pt metal for CO oxidation and subsequent developments on nano-crystalline Pt metals supported on oxide supports, an idea of Pt ion in reducible oxide supports acting as adsorption sites is proposed in chapter 1. Idea of red-ox cycling of an ion in an oxide matrix is presented taking Cu ion in YBa2Cu3O7 as an example. Noble metal ions in reducible oxides such as CeO2 or TiO2 acting as adsorption sites and hence a red-ox catalyst was arrived at from chemical considerations. Among several reducible oxide supports, TiO2 was chosen from crystal structure and electronic structure considerations. A good redox catalyst for auto exhaust and related applications should have high oxygen storage capacity (OSC). Any new material that can work as a redox catalyst should be tested for its OSC. Therefore we designed and fabricated a temperature programmed reduction by hydrogen (H2¬TPR) system to measure OSC. This is presented in chapter 2. We have synthesized a number of oxides by solution combustion method. Structures were determined by powder XRD and Rietveld refinement methods. Fe2O3, Fe2-xPdxO3-δ, Cu1-xMnAl1+xO4, LaCoO3, LaCo1-xPdxO3-δ, CeO2, Ce1¬xPdxO2-δ, TiO2, Ti1-xPdxO2-δ and many other oxide systems were synthesized and their structures were determined. OSC of these systems were determined employing the H2/TPR system. TPR studies were carried out for several redox cycles in each case. Except Pd ion substituted CeO2 and TiO2 other oxide systems decomposed during redox cycling. Pd ion substituted TiO2 gave highest OSC and also it was stable paving way to choose this system for further study. In chapter 3, we have described lattice oxygen of TiO2 activation by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01 to 0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst as seen by XPS. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ‘amount of oxygen that is used reversibly to oxidize CO’ is as high as 5100 μmol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature. Rate of CO oxidation is 2.75 μmol.g-1.s-1 at 60 0C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62 and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that bond valence of oxygens associated with both Ti and Pd ions in the lattice is 1.87. A low bond valence of oxygen is characteristic of weak oxygen in the lattice compared to oxygens with bond valence 2 and above in the same lattice. Thus, the exact positions of activated oxygens have been identified in the lattice from DFT calculations. Pt has two stable valencies: +2 and +4. Ti ion in TiO2 is in +4 state. Is it possible to substitute Pt exclusively in +2 or +4 state in TiO2? Implications are that Pt in +2 will have oxide ion vacancies and Pt in +4 states will not have oxide ion vacancies. Indeed we could synthesize Pt ion substituted TiO2 with Pt in +2 and +4 states by solution combustion method. In chapter 4, we have shown the positive role of an oxide ion vacancy in the catalytic reaction. Ti0.97Pt2+0.03O1.97 and Ti0.97Pt4+0.03O2 have been synthesized by solution combustion method using alanine and glycine as the fuels respectively. Both are crystallizing in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are only +2 state in Ti0.97Pt0.03O1.97 (alanine) and only in +4 state in Ti0.97Pt0.03O2 (glycine). CO oxidation rate with Ti0.97Pt2+0.03O1.97 is over 10 times higher compared to Ti0.97Pt4+0.03O2. The large shift in 100 % hydrocarbon oxidation to lower temperature was observed by Pt2+ ion substituted TiO2 from that by Pt4+ ion substituted TiO2. After reoxidation of the reduced compound by H2 as well as CO, Pt ions are stabilized in mixed valences, +2 and +4 states. The role of oxide ion vacancy in enhancing catalytic activity has been demonstrated by carrying out the CO oxidation and H2 + O2 recombination reaction in presence and in absence of O2. There is no deactivation of the catalyst by long time CO to CO2 catalytic reaction. We analyzed the activated lattice oxygens upon substitution of Pt2+ ion and Pt4+ ion in TiO2, using first-principles density functional theory (DFT) calculations with supercells Ti31Pt1O63, Ti30Pt2O62, Ti29Pt3O61 for Pt2+ ion substitution in TiO2 and Ti31Pt1O64, Ti30Pt2O62, Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens and these oxygens are responsible in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of oxide ion vacancy and weakly bonded lattice oxygen. In chapter 5, we have shown high rates of H2 + O2 recombination reaction by Ti0.97Pd0.03O1.97 catalyst coated on honeycomb monolith made up of cordierite material. This catalyst was coated on γ¬Al2O3 coated monolith by solution combustion method using dip-dry-burn process. This is a modified conventional method to coat catalysts on honeycombs. Formation of Ti0.97Pd0.03O1.97 catalyst on monolith was confirmed by XRD. Form the XPS spectra of Pd(3d) core level in Ti1-xPdxO2-δ, Pd ion is the formed to be +2 state. Ti0.97Pd0.03O1.97 showed high rates of H2 + O2 recombination compared to 2 at % Pd(metal)/γ-Al2O3, Ce0.98Pd0.02O2-δ, Ce0.98Pt0.02O2-δ, Ce0.73Zr0.25Pd0.02O2-δ and Ti0.98Pd0.02O1.98. Activation energy of H2 + O2 recombination reaction over Ti0.97Pd0.03O1.97 is 7.8 kcal/mole. Rates of reaction over Ti0.97Pd0.03O1.97 are in the range of 10 – 20 μmol/g/s at 60 0C and 4174 h-1 space velocity. Rate is orders of magnitude higher compared to noble metal catalysts. From the industrial point of view, solvent-free hydrogenation of aromatic nitro compounds to amines at nearly 1 bar pressure is an important process. In chapter 6, we showed that Ti0.97Pd0.03O1.97 is a good –nitro to –amine conversion catalyst under solvent-free condition at 1.2 – 1.3 bar H2 pressure. Nitrobenzene, p-nitrotoluene and 2-chloro-4-nitrotoluene are taken for the catalytic reduction reaction. The amine products were analyzed by gas chromatography and mass spectrometry (GCMS). Further, confirmation of compounds was done by FTIR, 1H NMR and 13C NMR. In presence of alcohol as solvent, 100% conversion of aromatic nitro compounds to amines took place at higher temperature and it required more times. In n-butanol solvent, 100% conversion of nitrobenzene and p-nitrotoluene occurred within 10 h and 12 h at 105 °C respectively. We have compared solvent-free reduction of p-nitrotoluene over different catalysts at 90 °C. Catalytic activity for reduction of p¬nitrotoluene over Ti0.97Pd0.03O1.97 is much higher than that reaction over 3 atom % Pd on TiO2 and Pd metal. Turnover frequencies (TOF) for nitrobenzene and 2-chloro-4-nitrotoluene conversion are 217 and 20 over Ti0.97Pd0.03O1.97 respectively. With increase of temperature, TOF of aromatic nitro compound reduction is also increased. We have compared the solvent-free reduction of aromatic nitro compound over Ti0.97Pd0.03O1.97 with others in the literature. Upto 3 cycles of reduction reaction, there was no degradation of Ti0.97Pd0.03O1.97 catalyst and stability of catalyst structure was analyzed by XRD, XPS and TEM images. Catalyst is stable under reaction condition and the structure is retained with Pd in +2 state. Finally, we have proposed the mechanism of -nitro group reduction reaction based on the structure of Ti0.97Pd0.03O1.97. Instead of handling nano-crystalline materials we proceeded with coating our catalysts on cordierite honeycombs. In chapter 7, we have shown high catalytic activity towards Heck reaction over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith. XRD patterns of Ce0.98Pd0.02O2¬δ coated on cordierite monolith were indexed to fluorite structure. Heck reaction of aryl halide with olefins over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith were carried out at 120 °C. The products were first analyzed by GCMS and for the confirmation of compounds, we have recorded 1H NMR and 13C NMR. Heck reaction was carried out with different solvents and different bases for choosing the good base and a solvent. Hence, we have chosen K2CO3 as base and N,N¬dimethylformamide (DMF) as solvent. We have compared the rates of Heck reactions over these two catalysts and Ti0.97Pd0.03O1.97 catalyst showed much higher catalytic activity than Ce0.98Pd0.02O2-δ. With increase of temperature from 65 °C to 120 °C, the catalytic activity of Ti0.97Pd0.03O1.97 on Heck reaction is also increased. The catalyst was reused for next Heck reaction without significant loss of activity. A mechanism for Heck reaction of aryl halide with alkyl acrylate has been proposed based on the structure of Ti0.97Pd0.03O1.97. In chapter 8, we have provided a critical review of the work presented in the thesis. Critical issues such as noble metal ion doping in TiO2 vs noble metal ion substitution, difficulty of proving the substitution of low % noble metal ion in TiO2, need for better experimental methods to study noble metal ion in oxide matrix have been discussed. Finally, conclusions of the thesis are presented.

This chapter covers a brief review of the definition, structural characteristics and main applications of hydrotalcite, an interesting multifunctional material which finds applicability in different areas. Particularly, some catalytic reactions using hydrotalcite or mixed oxides derived from these materials are addressed (Ethanol Steam Reforming, Photochemical conversions, Hydrodesulfurization). The use of Raman Spectroscopy associated with other techniques, such as powder X-ray diffraction (XRD), Extended X-ray Absorption Fine-Structure (EXAFS), Temperature Programmed Reduction of hydrogen (H2-TPR), Fourier-Transform Infrared (FTIR) and Density Functional Theory (DFT) simulations, to characterize this type of material is addressed through examples described in the current literature. In this sense, multidisciplinary efforts must be made in order to increase the understanding of the properties of these materials and the catalytic behavior in the most varied reactions.

The performance of Cu-Ce-Al-oxide and Cu-Cr-Al-oxide catalysts of varying compositions prepared by co-precipitation method was evaluated for the PEM fuel cell grade hydrogen production via oxidative steam reforming of methanol (OSRM). The limitations of partial oxidation and steam reforming of methanol for the hydrogen production for PEM fuel cell could be overcome using OSRM and can be performed auto-thermally with idealized reaction stoichiomatry. Catalysts surface area and pore volume were determined using N2 adsorption-desorption method. The final elemental compositions were determined using atomic absorption spectroscopy. Crystalline phases of catalyst samples were determined by X-ray diffraction (XRD) technique. Temperature programmed reduction (TPR) demonstrated that the incorporation of Ce improved the copper reducibility significantly compared to Cr promoter. The OSRM was carried out in a fixed bed catalytic reactor. Reaction temperature, contact-time (W/F) and oxygen to methanol (O/M) molar ratio varied from 200–300°C, 3–21 kgcat s mol−1 and 0–0.5 respectively. The steam to methanol (S/M) molar ratio = 1.4 and pressure = 1 atm were kept constant. Catalyst Cu-Ce-Al:30-10-60 exhibited 100% methanol conversion and 152 mmol s−1 kgcat−1 hydrogen production rate at 300°C with carbon monoxide formation as low as 1300 ppm, which reduces the load on preferential oxidation of CO to CO2 (PROX) significantly before feeding the hydrogen rich stream to the PEM fuel cell as a feed. The higher catalytic performance of Ce containing catalysts was attributed to the improved Cu reducibility, higher surface area, and better copper dispersion. Reaction parameters were optimized in order to maximize the hydrogen production and to keep the CO formation as low as possible. The time-on-stream stability test showed that the Cu-Ce-Al-oxide catalysts subjected to a moderate deactivation compared to Cu-Cr-Al-oxide catalysts. The amount of carbon deposited onto the catalysts was determined using TG/DTA thermogravimetric analyzer. C1s spectra were obtained by surface analysis of post reaction catalysts using X-ray photoelectron spectroscopy (XPS) to investigate the nature of coke deposited.

Diesel engines offer excellent fuel economy, but this comes at the expense of higher emissions of nitrogen oxides (NOx) and Particulate Matter (PM). To meet current emissions standards, diesel engines require aftertreatment devices. Concepts using combinations of catalysts are becoming more common in aftertreatment systems to reduce the cost and size of these aftertreatment systems. One combination is an LNT-SCR system where the LNT releases NH3 during a regeneration to be used by the SCR catalyst for further NOx reduction. This involves rich-lean cycling of the exhaust stream, which alters species concentrations in the exhaust. Most notably H2O and CO2 levels can vary from 4%–14% during lean-rich cycling. An investigation was performed using multiple Temperature Programmed Desorption (TPD) experiments to determine how H2O and CO2 affect NH3 storage capacity of an Fe-based zeolite SCR catalyst. It was determined that H2O and CO2 inhibit NH3 storage capacity of the SCR catalyst. This inhibition has shown a linear dependence on H2O and CO2 concentration at constant temperature. It was also determined that H2O is a much stronger inhibitor of NH3 storage capacity then CO2. Additional Temperature Programmed Desorption (TPD) experiments, were run where H2O and CO2 concentration (0%, 6%, and 10%) and the initial storage temperature (200°C, 250°C, 300°C, 350°C) were varied. Results suggest the addition of a reaction that creates competition for active sites on the catalyst between H2O and NH3. The additional reaction allows H2O and NH3 to be stored on open catalytic sites and has improved model accuracy by accounting for large changes in H2O, CO2, and temperature.

<div class="section abstract"><div class="htmlview paragraph">Diesel oxidation catalyst (DOC) is one of the critical catalyst components in modern diesel aftertreatment systems. It mainly converts unburned hydrocarbon (HC) and CO to CO₂ and H₂O before they are released to the environment. In addition, it also oxidizes a portion of NO to NO₂, which improves the NO_x conversion efficiency via fast SCR over the downstream selective catalytic reduction (SCR) catalyst. HC light-off tests, with or without the presence of NO_x, has been typically used for DOC evaluation in laboratory. In this work, we aim to understand the influences of DOC light-off experimental conditions, such as initial temperature, initial holding time, HC species, with or without the presence of NO_x, on the DOC HC light-off behavior. The results indicate that light-off test with lower initial temperature and longer initial holding time (at its initial temperature) leads to higher DOC light-off temperature. Depending on the types of HC used, the presence of NO_x can also influence HC light-off. Overall, the different HC light-off behaviors from different testing conditions are mainly affected by the adsorption of HC on the catalyst during the test as evidenced by HC adsorption and TPO (temperature programmed oxidation) test results.</div></div>