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BaCO 3 and Pt/BaCO 3 nanoparticles with high specific surface area (SSA) were prepared by flame spray pyrolysis (FSP). Their structure and behaviour during NO x storage were investigated with special focus on the mechanistic and kinetic details. NO exposure of BaCO 3 (BET: 45 m 2 g −1 ) at various temperatures resulted in simple NO adducts. Low NO storage rate and NO x storage capacity (NSC) were observed up to 400 °C. In the presence as well as the absence of oxygen, NO was stored on BaCO 3 showing the same IR-adsorption bands at 100–300 °C. Higher NSC and storage rates were observed for NO 2 adsorption. DRIFT spectra showed that NO 2 adsorption is accompanied by the formation of small amounts of NO which could be stored and subsequently oxidised again to NO 2 adducts. Pt/BaCO 3 prepared under identical conditions resulted in higher SSA (110 m 2 g −1 ) and showed increased NSC especially at higher temperatures. Enhanced DRIFT adsorption bands indicated the same NO adducts as obtained for the Pt-free BaCO 3 during NO treatment. In the presence of oxygen and above the light-off temperature for NO oxidation, the consecutive reaction of stored nitrite to nitrate could be observed by in situ DRIFTS. NO 2 adsorption led again to the highest NSC and storage rate. An optimal operation temperature window around 300 °C was found where the NO 2 storage rate was high and the catalysed competing NO 2 conversion to NO was low enough to afford maximal NSC. Structural investigations indicate that only prolonged NO x treatment leads to bulk barium nitrate: solid state conversion occurs after few hours. This supports the contention that the main contribution to NO x storage during technical application in NSR catalysis occurs in the surface and subsurface regions of BaCO 3 .

For the partial oxidation of acrolein to acrylic acid, a series of catalysts with the general formula Mo 8 V 2 W c O x and a varying amount of tungsten (0 ≤ c ≤ 5) was investigated. Catalysts were prepared starting from aqueous solutions of ammonium heptamolybdate, metavanadate and metatungstate, which were dried, employing spray drying and crystallisation followed by calcination. The resulting precursors and catalysts were characterised by XRD, SEM and TG/DTA–MS. Additionally, kinetic experiments were applied. Spray drying results in the formation of amorphous structures, whose temperature stability shows a tendency to rise with an increasing amount of tungsten. Spray dried samples in general show a better catalytic performance than crystallised ones. In TP-reactions the spray dried mixed oxides were investigated with regard to their catalytic properties: conversion of acrolein, yield and selectivity regarding the partial oxidation to acrylic acid. The best performance could be assigned to the minor tungsten doped catalysts. The oxygen pathways were investigated with the so-called steady state isotopic transient kinetic analysis (SSITKA). After the replacement of 16 O 2 against 18 O 2 in the feed gas, the rate of oxygen incorporation into the reactants and the isotopic distribution of the oxidation products were analysed depending on temperature and tungsten content. Tungsten doping has a significant influence on the amount of 16 O removed from the catalyst under 18 O 2 . The amount of oxygen made available by the catalysts correlates with the catalysts’ activity.

The storage of NO, NO/O2-mixtures and NO2 on CeO2 and BaO/CeO2 was investigated by in situ DRIFT-spectroscopy. The NOx-storage capacity, as well as the kinetic and the mechanism of the NOx-storage process are influenced by the temperature and the BaO-loading as well as the oxygen partial pressure. The addition of oxygen into NO containing gas mixtures results in the oxidation of the stored nitrite to nitrate species. Adsorption of NO2 leads to in the formation of nitrite and nitrate species, where the nitrite species are completely oxidized to nitrate in the progress of storage.

The dynamic behaviour of the NO SCR-reaction on Fe-exchanged zeolites was investigated by the transient response method (TRM). The results were used to develop a mathematical model for catalysts containing Fe-exchanged zeolites capable of describing the dynamic phenomena observed.

Different global kinetics for the oxidation of NO on platinum are compared in this work. The general form of the equation for the reaction rate is $r = k \cdot c_{NO}^\alpha \cdot c_{O_2 }^\beta \cdot c_{NO_2 }^\gamma \cdot TD^\delta$ with $TD = \left( {1 - c_{NO_2 } \cdot c_{NO}^{ - 1} \cdot c_{O_2 }^{ - 0.50} \cdot K^{ - 1} } \right)$ . Furthermore steady-state and temperature-programmed experiments were performed. The best results of simulation coupled with parameter estimation were obtained using α = 0.28, β = 0.49, γ = 0 and δ = 1, along with an activation energy of 47.5 kJ mol−1.

Diesel soot abatement via diesel particulate filters composed of so-called wall-flow monoliths is well established. Today, due to recent improvements in the production technology full-featured catalyst functionality can be implemented in the filter walls. This work focuses on a comparison of the reactor performance of the wall-flow filter and the conventional flow-through monolith. To this end a two-dimensional numerical model is set up for each of the two reactor configurations. Concentration profiles in the wall-flow filter systematically change as a function of flow velocity. At high flow velocities transport from the inlet channel into the porous wall is nearly entirely dominated by convection. This leads to uniform axial concentration profiles in the inlet and outlet channel and a steep gradient in the porous wall. At low velocities radial transport into the porous wall is dominated by diffusive transport. This leads to a negligible radial concentration gradient between the inlet and the outlet channel. Under most operating conditions relevant for an automotive exhaust catalyst the flow velocity is in an intermediate range with contributions of diffusive and convective transport. The transition from entirely convection dominated transport at high space velocities to increasingly diffusion dominated transport at lower flow velocities is similarly found for first order kinetics and a generalized Langmuir–Hinshelwood–Hougen–Watson (LHHW) rate law. Wall-flow filters show systematic conversion advantages over the conventional monolith for a first order reaction. For a reaction with LHHW-type kinetics this effect is not generally observed. It is one major result of this work that the relative performance of the two reactor configurations depends on the kinetics of the catalyzed reaction.

This paper presents experiments and model predictions for the oxidation of CO over a platinum catalyst in a monolith reactor. Experimental behavior is broadly consistent with previously reported work on CO oxidation. Ignition–extinction (light-off) curves demonstrated the presence of multiple steady states with a hysteresis effect. The two branches corresponding to the two states of predominantly CO covered or oxygen covered. Admission of CO pulses to an oxygen covered surface results in reaction, indicating the occurrence of adsorption of CO on an oxygen covered surface. A model based on adsorption and surface reaction using the classical Langmuir–Hinshelwood (LH) approach qualitatively was able to reproduce the light-off behavior. The best model assumes dissociative chemisorption of oxygen on two surface sites. It was superior to a model proposing molecular adsorption of oxygen followed by rapid dissociation. Addition of steps allowing CO adsorption on an oxygen filled surface via an “oxygen compression” mechanism enable the qualitative description of the reactor response to step inputs of CO to an oxygen rich feed stream. Some parameter adjustment remains to allow a better fit between experiment and model predictions.

This paper presents experimental and modelling results for the oxidation of mixtures of hydrogen and carbon monoxide in a lean atmosphere. Transient light-off experiments over a platinum catalyst (80 g/ft 3 loading) supported on a washcoated ceramic monolith were performed with a slow inlet temperature ramp. Results for CO alone agree with earlier results that predict self-inhibition of CO; that is an increasing light-off temperature with increasing CO concentration. Addition of hydrogen to the feed causes a reduction in light-off temperature for all concentrations of CO studied. The most significant shift in light-off temperature occurs with the addition of small amounts of hydrogen (500 ppm, v/v) with only minor marginal enhancement occurring at higher hydrogen concentrations. Hydrogen alone in a lean atmosphere will oxidise at room temperature. In mixtures of hydrogen and CO, the CO was observed to react first until a conversion of about 50% was observed, at which point the conversion of hydrogen rapidly went from 0 to 100%. Simulations performed using literature mechanistic models for the oxidation of these mixtures predicted that hydrogen ignites first, followed by CO, a direct contradiction of the experimental evidence. Upon changing the activation energy between adsorbed hydrogen and oxygen, the CO was observed to oxidise first, however, no enhancement of light-off was predicted. The effect cannot be explained by the mechanistic model currently under discussion.

Mixed oxide catalysts on the basis of molybdenum and vanadium are industrially important catalysts for the partial oxidation of acrolein to acrylic acid. For a better understanding of the oxygen pathways for an optimised model catalyst with the stoichiometric composition Mo 7.5 V 2.5 W 0.5 O x , the so-called Steady State Isotopic Transient Kinetic Analysis (SSITKA) method was employed. After switching from 16 O 2 to 18 O 2 the formation of 18 O-labelled acrolein was observed. Acrolein exchanges its carbonyl oxygen with oxygen from the solid catalyst. This exchange is also reflected in the isotopic distribution of the oxidation products (acrylic acid and combustion products). Subsequent desorption of acrolein, as well as further reaction to the oxidation products, can take place. Compared to the partial oxidation the incorporation of the isotopic tracer oxygen into the combustion by-products is much slower. This might be an indicator of an intermediate layer in the combustion pathway. To obtain activation parameters SSITKA experiments were performed over a temperature range between 322 and 391 °C. Based on the observations, a macro kinetic model was adapted upon. The activation energy for the exchange of the carbonyl oxygen of acrolein was found to be approximately 30 kJ mol −1 .

Diesel particulate filters composed of so-called wall-flow monoliths are well established devices for diesel particulate abatement. Recent improvements in production technology allow implementation of full-featured catalyst functionality in the filter walls. From a reactor engineering point of view such wall-flow reactors with wall-integrated catalyst show fundamental differences compared to conventional flow-through monoliths. The complex interactions of convection, diffusion and reaction in the wall-flow monolith are studied by means of numerical simulation. A two-dimensional model for the flow in one pair of inlet/outlet channels with a generic first order reaction in the catalytic filter wall is developed. Concentration profiles in the reactor and a conventional flow-through catalyst are compared. It is found that in the range of moderate reactor conversion concentration gradients along the inlet channel of the filter are small. Thus the reactor can be described by an approximate one-dimensional model, taking into account only the radial flux through the filter wall and assuming a constant inlet concentration in axial direction along the inlet channel. Light-off curves are computed for the wall-flow and for the conventional flow-through monolith. Significantly better conversion is found for the wall-flow configuration. This can be explained by mass transfer limitation in the conventional flow-through monolith.

This work presents a novel simultaneous method: by coupling a pyrometer—a contactless temperature sensor—to an existing DRIFTS setup such a combination was applied for the first time. During temperature-programmed reduction of silver carbonate with ethylene (as an example), pyrometrically detected processes could be assigned to spectroscopically observed changes. This novel simultaneous method offers the possibility of obtaining kinetic parameters such as activation energies of a system under reaction conditions.

Technical catalysts for partial oxidation of acrolein to acrylic acid are based on Mo/V mixed oxides. Different preparation steps are characterised starting from solutions of ammonium-heptamolybdate and -metavanadate. These were dried, employing spray drying and crystallisation method followed by calcination. The materials formed at each preparation step were studied using X-ray powder diffraction, thermal decomposition, TG/DTA-MS and temperature programmed reduction (with H2 and acrolein). X-ray diffraction revealed that the drying method affects structural composition of the binary Mo/V-oxides. Spray drying results preferably in a hexagonal MoO3-type phase, whereas crystallisation leads to V2O5-type structure. A correlation of the applied drying method and therefore of structural composition with catalytic performance is discussed by means of TPR investigation comparing the activation process of the two probe molecules H2 and acrolein. Generally, spray dried samples are more active. The preparation variant via spray drying of precursor solution establishes a highly reproducible as well as promising basis for a specific focussing on the genesis of mostly metastable structure parts, which play a crucial role in heterogeneous catalysis.

NO adsorption and NO/O2 co-adsorption on CeO2 at different temperatures was studied by DRIFT-Spectroscopy. The results indicate that this oxide plays an important role in storing NO x . FTIR studies show that NO adsorption is dominated by the formation of nitrite species. Furthermore, cis- and trans hyponitrite species are detected. Co-adsorption of NO/O2 leads to the formation of nitrates. The experimental data show that the formation of nitrates is a consecutive reaction: adsorption of NO to form nitrite species (NO2 −), followed by an oxidation to form nitrate species (NO3 −).

The applicability of Mo/V-mixed oxides for the partial oxidation of isobutyraldehyde to methacrolein is examined. The results are compared with the catalytic performance of a heteropolyacid-catalyst.

Mo/V mixed oxides have proven themselves to be reliable for the partial oxidation of acrolein to acrylic acid. Methacrolein which is the homologue of acrolein, reacts with clearly worse selectivity and activity on this catalyst system. By means of transient investigations (TP reduction, CP reduction, CP reaction and 18 O -SSITKA) under reaction conditions, it was possible to provide a contribution towards clarifying the oxygen exchange of the Mo/V mixed oxides during the reaction of both aldehydes to the corresponding carboxylic acids. In the case of both aldehydes, an exchange of carbonyl oxygen and solid oxygen occurs on the Mo/V mixed oxide.

Mo/V oxides are interesting catalyst materials for the selective partial oxidation of unsaturated aldehydes (acrolein and methacrolein) to the corresponding carboxylic acids. Two catalyst systems — a mixed oxide and a heteropolyacid salt — were investigated by in situ DRIFT-spectroscopy. Using a novel DRIFTS cell, in which both the catalyst powder and the reference (KBr) were in the same reaction chamber, we are able to detect different adsorbates of (meth)acrolein and (meth)acrylic acid under reaction gases. The investigations showed that in the case of the adsorption of acrolein and methacrolein a significant difference in the structure of corresponding adsorbates could not be proved. This indicates that the reaction mechanism of the selective partial oxidation should be the same for both aldehydes. With these kind of investigations we gain access to a deeper insight into the reaction mechanism.

IR spectroscopy is a well-established method in the characterization of heterogeneous catalysts under reaction conditions. Working in transmission modes is the most common of currently applied technologies. Yet, there are problems inherent in both methods (KBr wafers and self-supporting wafers) for the in-situ investigation of heterogeneously catalyzed reactions. These problems can be avoided by using the DRIFT (diffuse reflection infrared Fourier transformation) spectroscopy. As is shown in this study, DRIFT spectroscopy proves to be a suitable method producing not only qualitative but also quantitative results of in-situ examinations of heterogeneous catalysts.

The Mo(10-x)V(x)O(y) solid-solution systems (0≤x≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO(2+) species, whose concentration becomes maximal for Mo(5)V(5)O(y·). A quantitative analysis of the [VO(2+)] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo(10-x)V(x)O(y) system. In this respect, the semi-conducting properties of Mo(10-x)V(x)O(y) are p-type in an interval of Mo(9)V(1)O(y)-Mo(5)V(5)O(y) and switch into n-type because of the conduction electrons in a composition range of Mo(5)V(5)O(y)-Mo(1)V(9)O(y). Highest catalytic activity is obtained when vanadium acts as an acceptor center and oxygen vacancies ν(··)(O) are formed for reasons of charge compensation. In addition to the surface, ν(··)(O) and VO(2+) centers in the bulk have to be considered too for heterogeneous catalysis.

Cuprous oxide agglomerates composed of 4-10 nm Cu2O nanoparticles were deposited on multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNTs to give binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] composites. Di-aqua-bis[2-(methoxyimino)propanoato]copper Cu[O2CCCH3NOMe](2)·2H2O 1 in DMF was used as single source precursor for the deposition of nanoscaled Cu2O. The precursor decomposes either in air or under argon to yield CuO2 by in situ redox reaction. Thermogravimetric coupled mass spectroscopic analysis (TG-MS) of 1 revealed that methanol formed during the decomposition of 1 acts as a potential in situ reducing agent. Scanning electron microscopy (SEM) of the binary [Cu2O/MWCNT] nano-composite shows an increase of cuprous oxide loading depending on the precursor amount, along the periphery of the MWCNTs as well as formation of larger particle agglomerates. Transmission electron microscopy (TEM) of the sample shows crystalline domains of size 4-10 nm surrounded by an amorphous region within the larger particles. SEM and TEM of ternary [Cu2O/ZnO/MWCNT] clearly reveal that Cu2O nanoparticles are primarily deposited on ZnO rather than on MWCNTs. The catalytic activities of the [Cu2O/MWCNT] and [Cu2O/ZnO/MWCNT] binary and ternary composites were studied for the selective partial oxidation of ethanol to acetaldehyde with molecular oxygen. While using binary [Cu2O/MWCNT] (13.8 wt% Cu) as catalyst, acetaldehyde was obtained with a yield of 87% at 355 °C (selectivity 96% and conversion 91%). When nanoscale ZnO is present, the resulting [Cu2O/ZnO/MWCNT] composite shows preferential hydrogen and CO2 formation due to the fact that the dehydrogenation and total oxidation pathway is more favoured compared to the binary composite. Significant morphological changes of the catalyst during the catalytic process were observed.

The major objective of this research project was to reach a microscopic understanding of the structure, function and dynamics of V-Mo-(W) mixed oxides for the partial oxidation of acrolein to acrylic acid. Different model catalysts (from binary and ternary vanadium molybdenum oxides up to quaternary oxides with additional tungsten) were prepared via a solid state preparation route and hydrochemical preparation of precursors by spray-drying or crystallisation with subsequent calcination. The phase composition was investigated ex situ by XRD and HR-TEM. Solid state prepared samples are characterised by crystalline phases associated to suitable phase diagrams. Samples prepared from crystallised and spray-dried precursors show crystalline phases which are not part of the phase diagram. Amorphous or nanocrystalline structures are only found in tungsten doped samples. The kinetics of the partial oxidation as well as the catalysts' structure have been studied in situ by XAS, XRD, temperature programmed reaction and reduction as well as by a transient isotopic tracing technique (SSITKA). The reduction and re-oxidation kinetics of the bulk phase have been evaluated by XAS. A direct influence not only of the catalysts' composition but also of the preparation route is shown. Altogether correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability. A model for the solid state behaviour under reaction conditions has been developed. Furthermore, isotope exchange experiments provided a closer image of the mechanism of the selective acrolein oxidation. Based on the in situ characterisation in combination with micro kinetic modelling a detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed.

Mixed oxides based on molybdenum and vanadium are used as catalysts in partial oxidation reactions. Transient examinations, in particular the concentration programmed reduction method with acrolein, proofs the presence of at least two different oxygen species participating in the reaction. A mechanistic view involving surface- and bulk-oxygen as well as a simulation are given.