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The development of space and time resolved spectroscopic methods to image space and time dependent heterogeneities in catalyst bodies during preparation is of paramount importance for the development of more efficient and sustainable chemical processes. There are a large number of physicochemical parameters that play an important role in the preparation of catalyst bodies, and in order to obtain the optimum and most efficient catalyst material a careful selection of all these must be made. The aim of this work was double. On the one hand, new spatiotemporal spectroscopic methods were developed and their limitations and capabilities to study the different elemental steps of catalyst preparation were investigated. On the other hand, research on the influence of different chemical or physical properties during the preparation of Ni and Pd/gamma-Al2O3 catalysts was conducted by means of the developed spectroscopic techniques. Several spectroscopic techniques have been investigated comprising invasive (UV-Vis and IR micro-spectroscopies) and noninvasive methods (MRI and TEDDI). UV-Vis micro-spectroscopy provides information regarding the surroundings of the metal-ions during the impregnation step. Hence, the dynamics of the metal-ion and potential changes in its coordination sphere while moving towards the core of the catalyst body can be measured. This technique can also be applied to dried samples and, if the sample does not become black, after calcination or thermal treatment. IR micro-spectroscopy can be utilized on dried samples and it yields information regarding the location of organic molecules. On the other hand, magnetic resonance imaging (MRI) and tomographic energy dispersive diffraction imaging (TEDDI) have been investigated as noninvasive methods. 1H-MRI can be used in a very straightforward manner to monitor the impregnation process of paramagnetic metal-ion complexes and, when the ligands surrounding the metal-ion are water molecules, the impregnation process can be monitored quantitatively. The possibility of quantifying impregnation processes is of great importance in catalyst design since understanding the molecular-transport kinetics is crucial to control the preparation of mm-sized catalysts. Finally, the TEDDI technique is, for the moment, the only technique that can be used in situ during the drying and thermal treatment steps of mm-sized catalyst bodies preparation. Thanks to this advantage, the genesis of Ni nanoparticles within gamma-Al2O3 pellets has been visualized for the first time together with the breakdown of the precursor phase and the formation of, until now, unknown intermediate phases. Thus, this method can provide relevant input regarding the shape and size of the active particles in a catalytic material. Moreover, possible gradients of the shape and size of the active component along the catalyst body can be disclosed, which would provide enormous benefits when understanding the performance of the catalyst.

Zeolites are microporous materials with pores that have about the same size as small molecules like water or benzene. They are important catalysts in the petrochemical industry, for example for catalytic cracking, and isomerization- and alkylation reactions. This thesis deals with molecular aspects of the application of zeolite catalysis for the production of cumene via benzene alkylation with propene using Mordenite (MOR-type zeolite). We will use classical force field based molecular simulations to study properties at the atomistic scale. In Chapter 1, an overview is given of the various properties of zeolites, as well as the simulation methods to study the adsorption and diffusion of guest molecules adsorbed in zeolites. In Chapter 2, it is shown that the adsorption and diffusion properties of alkanes in MOR strongly depend on the distribution of non-framework Al atoms. A model is presented to accurately describe this effect. A new method to efficiently compute the heat of adsorption for guest molecules adsorbed in zeolites with non-framework cations is presented in Chapter 3. It is found that this method is much more efficient than the existing methods. Furthermore, it is shown that for the simulation of polar molecules in zeolites, the Ewald summation is superior compared to the recently proposed Wolf-method. In Chapter 4, we study the adsorption selectivity of benzene/propene mixtures in various zeolites, and we evaluate their use as a potential catalysts for benzene alkylation. In Chapter 5, we propose an efficient method to accurately compute pore size distributions. This method is extensively used in Chapter 6, in which we study the dealumination mechanism of MOR-type zeolite using Kinetic Monte Carlo simulations. The results of these dealumination simulations are in very good agreement with various experiments. It is found that the pore size of the main channels is significantly increased. Finally, we propose several criteria for potential catalysts for the production of cumene from benzene and propene.

The controlled assembly of materials on the nanoscale has been a major focus of research across many scientific disciplines. In the nanometer size range, materials characteristics can be tuned not only by composition but more importantly by size and shape of constituent phases, giving rise to exceptional optical, magnetic, electric, mechanical and catalytic properties. To gain insight into the relation between a structure and its properties, dedicated characterization techniques are required that provide detailed 3D information with nanometer resolution. One of the most promising and rapidly developing techniques, in this respect, is electron tomography (ET), a method for obtaining 3D structural information from a series of electron micrographs. ET offers, in addition, the possibility to extract quantitative information on constituent phases which is explored in depth in this thesis. From a materials viewpoint the focus is on catalysts which are indispensable to society because of their prominent role in the manufacture of most chemical products. In supported heterogeneous catalysts, the active components such as transition metals and metal oxides are finely dispersed on a high surface area support to maximize the number of catalytically active sites per unit mass of material. The high surface area support anchors the active components to prevent sintering at elevated temperatures. With case studies of nickel oxide supported on ordered mesoporous silica SBA-15, ruthenium supported on carbon nanotubes, and gold supported inside of mesoporous zirconia spheres, manual and automated quantification approaches in combination with structure modeling are presented. It is shown that knowledge of the active phase particle size, location, neighbor distance, and local loading are key facts to understand and improve catalyst preparation and performance by tuning nanoscale morphologies. Another very interesting avenue to nanomaterials is bottom-up assembly of prefabricated building blocks into large, ordered structures, a concept that is shared across several disciplines. With examples of four binary nanoparticles superlattices it is shown that a comprehensive, quantitative, 3D characterization by ET down to the single nanocrystal level can be achieved. ET and image analysis provide accurate lattice parameters of a given superlattice, unambiguously revealing the crystal structure including possible distortions. Furthermore, the ability to detect defects and their effect on the surrounding lattice are considered to be instrumental in a microscopic understanding of emerging materials properties. This thesis illustrates quantitative approaches into the local 3D morphology of complex nanostructured materials by ET that will contribute in the future to a more rational design of this important class of materials.

Automotive catalysis being a mature technology, it can only be improved by the introduction of new breakthroughs. The ideas generating these technical advances in material science can be found thanks to the synthesis and study of model systems with controlled geometries, compositions, interactions and dimensions in well-known environments. This approach limits the amount of possible parameters influencing the experimental results and facilitates their interpretation. The aim of this PhD thesis was to enlarge insight into the fundamental issue of metal-support interactions for Pt- and Rh-based exhaust gas emission catalysts. This has been done by synthesising model catalysts made of well-defined Pt and Rh nanoparticles dispersed on various oxide supports, differing in their chemical composition and pore architecture. The composition effect was mainly examined with a series of zeolite Y supports containing different alkali or alkaline earth metal ions and further confirmed with promoted macroporous SiO2. The impact of the support porosity was investigated thanks to all silica supports varying by their pore size. The electronic properties of the supported Pt and Rh nanoparticles were then studied by Infrared (IR) spectroscopy in combination with CO or NO as probe molecule and, for Pt, further confirmed by X-ray Absorption Fine Structure spectroscopy (XAFS), a direct measurement technique of the electron density. Finally, the impact of the support composition on the catalytic activity of Pt and Rh was evaluated for two simple reactions relevant to the automotive exhaust gas converters: the CO oxidation in excess of oxygen and the NO reduction by CO at stoichiometry. Combining all results, it has been possible to derive relationships between the chemical composition of the support material, the electronic density of the supported metal nanoparticles and their catalytic activity. For all catalyst materials, the IR spectra showed clear differences, the probe molecules were adsorbed on the Pt or Rh surface in linear or bridge positions. It was found that the relative intensity of the bridge bonded probe molecule as referred to the total absorbance of the metal-bonded CO or NO molecules was decreasing for increasing Lewis acidity of the promoting cation, as expressed by the Kamlet-Taft parameter ?. As the CO IR linear-to-bridge band intensity ratio increased, so did the AXAFS peak intensity, while the promoting cation was more acidic and the Pt particles became electron poor. This confirmed that AXAFS is a novel spectroscopic method to directly probe the electronic properties of supported Pt nanoparticles. In general, the pore size effect was small while the support composition had a big impact. Finally, it was possible to correlate the above observations with the activity of the Pt or Rh catalysts for the CO oxidation reaction in excess of oxygen, i.e. the T50% for CO oxidation decreases with electron density on the precious metal nanoparticles. Concerning the stoichiometric NO reduction by CO on Rh, no clear trend could be extracted, probably due to other important factors affecting the Rh catalytic activity, such as its oxidation state and its particle size.

The aim of the work described in this thesis was to investigate the role and nature of nanostructured carbon materials, oxygen surface groups and promoters on platinum-based catalysts for the selective hydrogenation of cinnamaldehyde. The selective hydrogenation of cinnamaldehyde to cinnamyl alcohol was chosen as a showcase. To establish structure-activity relations, it is crucial to prepare well-defined carbon nanofibers (CNF) supports and well-defined catalytic metal phases on these supports. In Chapter 2 an exploratory study on the selective hydrogenation of cinnamaldehyde is described. The influence of the reactant concentration, reaction solvent and nature of the metal and support was evaluated. Based on the results, it was decided to use 2-propanol/water as solvent, cinnamaldehyde concentration of 0.1 M and platinum as catalytic metal for further studies. In Chapter 3 the role of the nature and stability of oxygen surface groups in anchoring and stabilizing platinum particles was investigated. To that purpose CNF and platinum-containing CNF with different amounts and types of oxygen surface groups were prepared and analyzed. The decomposition temperature for acidic oxygen surface groups turned out to depend on the presence of platinum. Platinum anchoring occurs on both carboxyl and phenol type groups during catalyst synthesis. In Chapter 4 the influence of graphene orientations on platinum deposition and reduction behavior was analyzed. To that purpose, platinum was deposited on oxidized nanostructured carbon materials, i.e. CNF, carbon nanoplatelets (CNP) and carbon nanotubes (CNT). It was demonstrated that platinum deposited on CNT resulted in 20 K higher reduction temperature as compared to platinum on CNF and CNP. Application of the required higher reduction temperature resulted in complete reduction for that sample, accompanied by sintering of platinum to large agglomerates. The prepared catalysts were tested and Pt/CNP and Pt/CNF turned out to be active catalysts for the cinnamaldehyde hydrogenation, while fully reduced and sintered platinum on CNT was not very active for this reaction. In Chapter 5 particle size effects for cinnamaldehyde hydrogenation using platinum and ruthenium on CNF with similar amounts of acidic oxygen surface groups, i.e. before and after heat-treatment, were investigated. Different sized platinum and ruthenium particles were deposited on CNF and tested for the selective hydrogenation of cinnamaldehyde. Before heat-treatment, the platinum catalysts with larger metal particles turned out to be more selective. After heat-treatment, which resulted in removal of oxygen surface groups, smaller metal particles resulted in a higher selectivity for the platinum and ruthenium catalysts. The reversed particle size effect is ascribed to a changing adsorption mode of the reactant. In Chapter 6, we aimed to characterize platinum-promoter interactions and to relate this to catalytic performance. Therefore, CNF-supported platinum was combined with tin as promoter via incipient wetness impregnation (IWI) and via reductive deposition precipitation (RDP). Via detailed characterization, it was demonstrated that tin became partially reduced when deposited via RDP, thereby resulting in a close contact of the two metals. Via IWI synthesis such a close interaction was not obtained. The prepared catalysts were tested for the selective hydrogenation of cinnamaldehyde and enhanced selectivities towards cinnamyl alcohol were observed when close platinum-promoter interactions were present.

Important limitations in the application of light metal hydrides for hydrogen storage are slow kinetics and poor reversibility. To alleviate these problems doping and ball-milling are commonly applied, for NaAlH4 leading to particle sizes down to 150 nm. By wet-chemical synthesis we have prepared carbon nanofiber-supported NaAlH4 with discrete particle size ranges of 1-10 μm, 19-30 nm, and 2-10 nm. The hydrogen desorption temperatures and activation energies decreased from 186 °C and 116 kJ · mol-1 for the largest particles to 70 °C and 58 kJ · mol-1 for the smallest particles. In addition, decreasing particle sizes lowered the pressures needed for reloading. This reported size-performance correlation for NaAlH4 may guide hydrogen storage research for a wide range of nanostructured light (metal) hydrides.

Research has been carried out to determine the feasibility of chemometric modeling of infrared (IR) and near-infrared (NIR) spectra of crude oils to predict the long residue (LR) and short residue (SR) properties of these samples. A novel method is described to predict short residue properties at different flashing temperatures based on the IR spectrum of a crude oil measured at room temperature. The resulting method is the subject of European patent application number 07251853.3 filed by Shell Internationale Research Maatschappij B.V. The study has been carried out on 47 crude oils and 4 blends, representing a large variety of physical and chemical properties. From this set, 28 representative samples were selected by principle component analysis (PCA) and used for calibration. The remaining 23 samples were used as a test set to validate the obtained partial least squares (PLS) regression models. The results demonstrate that this integrated approach offers a fast and viable alternative for the currently applied elaborate ASTM (American Society for Testing and Materials) and IP (Institute of Petroleum) methods. IR spectra, in particular, were found to be a useful input for the prediction of different LR properties. Root mean square error of prediction values of the same order of magnitude as the reproducibility values of the ASTM methods were obtained for yield long on crude (YLC), density (DLR), viscosity (VLR), and pour point (PP) , while the ability to predict the sulfur contents (S) and the carbon residue (CR) was found to be useful for indicative purposes. The prediction of SR properties is also promising. Modeling of the IR spectra, and to a lesser extent, the NIR spectra as a function of the average flash temperature (AFT) was particularly successful for the prediction of the short residue properties density (DSR) and viscosity (VSR). Similar results were obtained from the models to predict SR properties as a function of the yield short on crude (YSC) values. Finally, it was concluded that the applied protocol including sample pretreatment and instrumental measurement is highly reproducible and instrument and accessory independent.

Supported 1 wt% Pt-based catalyst materials have been used as model systems to study pore curvature and support composition effects on the electronic properties of supported Pt nanoparticles. For this purpose, Pt nanoparticles have been loaded onto microporous (ITQ-1), mesoporous (Si- MCM-41, Si-MCM-48 and Si-SBA-15), macroporous (SiO2) all-silica supports, as well as onto a macroporous SiO2 support, impregnated with monovalent (Na+, Cs+) and divalent (Mg2+, Ba2+) cations. Time- and temperature-dependent infrared spectroscopy with CO as probe molecule has been used to investigate the adsorption and desorption properties of CO from these supported Pt nanoparticles. At 350 K, a narrow and smooth linear Pt-coordinated CBBO vibration band at 2070 cm 1 was observed for the all-silica catalysts. The IR-CO-TPD results revealed a slightly higher desorption rate for the micro- and mesoporous supports, probably due to larger non-bonding electrostatic interactions between CO and the pore walls. A systematic shift from linear (L) to bridge (B) bonded CBBO upon a decrease of the radius of curvature, which would indicate an increasing electron charge on the supported Pt nanoparticles, is however not observed. In contrast, a relationship between the L:B band intensity ratio and the Lewis acidity of the monovalent and divalent cations, as expressed by the Kamlet-Taft parameter a, was observed for the Pt/SiO2 catalysts. This effect is less pronounced than for zeolite-supported Pt nanoparticles (J. Phys. Chem. B 2005, 109, 3822–3831), but the results demonstrate that the correlation can be easily transferred from one support type to another, thus providing further guidelines for the design of improved automotive catalysts.

Rh particles with an average diameter smaller than 1.5 nm have been supported on a series of zeolite Y samples. These zeolite materials contained different monovalent (H+, Na+, K+, Rb+, and Cs+) and divalent (Mg2+, Ca2+, Sr2+, and Ba2+) cations and were used as model systems to investigate the effect of promoter elements in the oxidation of CO over supported Rh particles in excess of oxygen. Infrared (IR) spectroscopy was carried out to monitor the electronic changes in the local environment of Rh-adsorbed CO. It was found that the bands corresponding to two Rh gem-dicarbonyl species, Rh+(CO)2-(Oz)2 and Rh+(CO)2-(Oz)(H2O), shift to lower wavenumbers with increasing ionic radius/charge ratio of the cation. In addition, the relative intensity of the bridge bonded CO as compared to the total absorbance of Rh-bonded CO species decreases with increasing Lewis acidity, as expressed by the Kamlet-Taft parameter R of the cation. This trend could be directly correlated to the Rh CO oxidation activity, since low temperatures at 50% CO conversion corresponded with catalyst materials with a high contribution of bridge-bonded CO species and hence with small R values. A lower Lewis acidity causes an increased electron density on the framework oxygen atoms and thus an increased electron density on the zeolite-supported Rh particles. Comparable trends have been observed previously on a similar series of cation containing zeolite supported Pt catalyst materials.

Postsynthesis ammonium treatment induces a substantial increase in the catalytic activity of Au/Ti- SBA-15 catalysts for the direct vapor-phase epoxidation of propylene using hydrogen and oxygen. The PO formation rate of a calcined Au/Ti-SBA-15 catalyst prepared by this method increased from 4.3 mgPO h−1 g−1 cat to 37.2 mgPO h−1 g−1 cat at 200 ◦C compared with a catalyst prepared in an identical manner without this treatment. The catalysts were characterized by XRD, N2-sorption, UV–vis–NIR DRS, 29Si MAS NMR, FT-IR spectroscopy, and TEM to gain insight into the relationship between ammonia treatment and catalyst activity. 29Si MAS NMR measurements proved that the ammonium nitrate solution caused hydrolysis of ≡Si–O–Si≡ or ≡Ti–O–Si≡ bonds, resulting in a Ti-SBA-15 surface with a greater amount of surface hydroxyl groups. FT-IR measurements indicated the presence of amine species that favor the homogeneous deposition of Au nanoparticles. This was confirmed by TEM measurements showing greater metal dispersion for NH4NO3-treated Au/Ti-SBA-15 materials.

Nitrogen-containing carbon nanotubes (NCNT) were grown from acetonitrile, pyridine or N,N-dimethylformamide over a supported Fe-, Co- or Ni catalyst in the temperature range 823–1123 K. The physico-chemical properties of the obtained NCNT, such as the C/N ratio or the nitrogen type, were related to the synthesis parameters. It was found that the C/N ratio increased with increasing temperature which could be related to the thermodynamic stabilities of the metal-carbides and metal nitrides. Also the type of nitrogen present in the graphene layer changed with increasing temperature from predominantly pyridinic- to quaternary nitrogen. NCNT obtained with the Fe catalyst showed bamboo morphology regardless of the C/N source or growth temperature while straight tubes were obtained with the Co- or Ni catalyst. We propose that this difference in morphology can be explained by the thermodynamic stabilities of the different metal-carbides, leading to a ‘pulsating’ growth in the case of Fe as opposed to a more continuous growth in the case of Co or Ni.

An explanation is put forward for the beneficial effect of thermal decomposition of supported Ni3(NO3)2(OH)4 in NO/He flow (0.1–1 vol%) that enables preparation of well-dispersed (3–5 nm particles) 24 wt% Ni-catalysts via impregnation and drying using aqueous [Ni(OH2)6](NO3)2 precursor solution. Moreover, combining electron tomography, XRD and N2-physisorption with SBA-15 support yielded a clear picture of the impact of air, He and NO/He gas atmospheres on NiO shape and distribution. TGA/MS indicated that NO2, N2O, H2O products evolved more gradually in NO/He. In situ XRD and DSC revealed that NO lowers the nitrate decomposition rate and appears less endothermic than in air supposedly due to exothermic scavenging of oxygen by NO, which is supported by MS results. The Ni/SiO2 catalyst prepared via the NO-method displayed a higher activity in the hydrogenation of soybean oil as the required hydrogenation time decreased by 30% compared to the traditionally air calcined catalyst.

The elemental preparation steps of impregnation and drying of Ni/g-Al2O3 catalyst bodies have been studied by combining UV-vis and IR microspectroscopy. The influence of the number of chelating ligands in [Ni(en)x(H2O)6-2x]2+ precursor complexes (with en ) ethylenediamine and x ) 0-3) has been investigated. UV-vis measurements after impregnation showed that, regardless of the en:Ni2+ ratio in the precursor solution, Ni2+ was already detected in the core of the pellets 5 min after impregnation. The alumina support did bring about, however, gradients in the nature of the Ni2+ species upon first contact with the lowest en:Ni2+ ratio solutions, but these gradients disappeared after 30-60 min of impregnation. After 60 min, UV-vis seemed to indicate Ni-O-Al interactions between Ni2+ and the support, when water was initially part of the first coordination sphere of Ni2+, which was supported with the results obtained after drying. For dried samples, UV-vis showed a gradient of [Ni(en)x(H2O)6-2x]2+ inside the pellets, with an en-poor region in the core and an en-rich region in the edges of the catalyst bodies, when [Ni(en)3]2+ or [Ni(en)2(H2O)4]2+ were the starting complexes. IR microspectroscopy confirmed these en radial profiles, while EDX measurements showed that an Ni2+ egg-shell distribution goes hand-in-hand with an egg-shell distribution of en. The number of en ligands determined the interactions of Ni2+ with the support after impregnation and controlled the redistribution of metal-ion species during drying. Moreover, when redistribution of Ni2+ occurred during drying, its transport toward the outer rim of the extrudates came about together with changes of the local en:Ni2+ ratio.

The selective hydrogenation of cinnamaldehyde was studied over carbon nanofibers (CNF) supported platinum and ruthenium catalysts. The catalysts differed independently in their metal particle sizes and amount of acidic oxygen groups on the CNF surface. For the catalysts with oxygen on the CNF surface, the larger metal particles ( 3.5 nm) displayed the highest selectivity towards cinnamyl alcohol. Surprisingly, when the oxygen groups were removed from the catalyst surface, the smaller particles ( 2.0 nm) exhibited the highest selectivity to cinnamyl alcohol. Also the hydrogenation activity increased for all catalysts after oxygen removal. A model is proposed to account for the role of the metal particle size and oxygen surface groups in the hydrogenation of cinnamaldehyde.

Research has been carried out on the formation of cobalt (Co) and molybdenum (Mo) complexes in CoMo-solutions, which are used for the preparation of Al2O3-supported hydrodesulphurization (HDS) catalysts. Aim of this study was to obtain more insight into possible Co–Mo interactions and their implications for the impregnation process. For this purpose, Raman and UV–vis–NIR spectroscopy has been carried out on different impregnation solutions at various pH. In addition, multivariate curve resolution (MCR) of the Raman spectra has been applied to obtain information on the molecular structure and speciation of the different complexes present in solution. Furthermore, Raman microscopy and SEMEDX were applied on Al2O3 extrudates after impregnation, to obtain information on the distribution of the different metal-ions into the catalyst body as a function of time. It is demonstrated that an interaction between Co(II)-cations and different molybdate anions is indeed present in CoMosolutions. Two different CoMo-complexes are proposed in which Co2+-cations are bound to the outside of HxMo7O24 (6 x) complexes, resulting in a simultaneous transport of the Co and Mo metal–precursor complexes. Since Co acts as a promotor, a close interaction between Co and Mo in the final catalyst is of major importance for the catalytic activity. As such, the interaction should also be taken into account in the preparation of supported CoMo–HDS catalysts.

The influence of catalyst particle size, stirring rate, catalyst mass (0.2–0.6 g), reaction temperature (60–70 C), and reactant concentration (1.3–4 mmol/L, with constant reactant/catalyst ratio) on the hydrogenolysis of the lignan hydroxymatairesinol (HMR) to matairesinol (MAT) was studied under hydrogen atmosphere using a carbon nanofibre supported palladium catalyst. When the temperature or HMR concentration was increased, the reaction rate increased as expected. However, the reaction rate was inversely dependent on the stirring rate, e.g., was influenced by external mass transfer, which was explained by the fact that the reaction rate decreases at higher hydrogen concentrations.

We report here a simple one-pot directed synthesis of an oxomolybdate urea composite in which elementary molybdenum oxide building blocks are linked together with the aid of urea. This type of directed material design resulted in large rod-like crystals of an inorganic-organic hybrid extended structure of {MoO3(NH2-CO-NH2)}∞ consisting of right- and left-handed helical units. In the crystal structure urea acts both as a glue that links the inorganic molybdenum units into a helix and as a supramolecular linker for the stabilization of the crystal structure as a whole. This type of molecular topology resulted in an unexpectedly high thermal stability.

Chlorinated hydrocarbons (CHCs) remain important industrial chemical intermediates and solvents, especially for the exploration of the potential of La-based materials for the conversion of chlorinated waste compounds.[1] The production of industrially important CHCs frequently occurs with concurrent formation of less desirable side-products. For example, mixtures of chlorinated C1 and C2 hydrocarbons are still formed as by-products in industrial processes such as the production of vinyl chloride monomer (VCM).[2, 3] Another example is carbon tetrachloride (CCl4) formation in the production of chloroform (CHCl3) and other chlorinated methanes. The United States Clean Air Act and the Montreal Protocol limit the production and sale of CCl4,[4,5] therefore methods to effectively recycle chlorinated side-products, in particular CCl4, would be advantageous. The hydrogen– chlorine exchange of CCl4 with other CHCs, such as CH2Cl2, for the recycling of less desirable compounds into valuable products would be of particular interest.

By the combination of electron tomography with image segmentation, the properties of 299 NiO crystallites contained in 6 SBA-15 pores were studied. A statistical analysis of the particle size showed that crystallites between 2 and 6 nm were present with a distribution maximum at 3 and 4 nm, for the number-weighted and volume-weighted curves, respectively. Interparticle distances between nearest neighbors were 1-3 nm with very few isolated crystallites. In the examined pores, a local loading twice the applied average of 24 wt % NiO was found. This suggests that a very high local loading combined with a high dispersion is achievable.

The nature of the active Ti species in TiCl3-doped NaAlH4, a promising hydrogen storage material, was studied as a function of the desorption temperature with Ti K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, Ti K-edge X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray diffraction (XRD). In the freshly prepared sample, Ti was amorphous and surrounded by 4.8 Al atoms divided between two shells at 2.71 and 2.89 Å. In the next shell, 1.9 Ti atoms were detected at 3.52 Å. It was concluded that 30% of Ti was incorporated into the surface of Al crystallites and 70% of Ti occupied interstitials in the NaAlH4 lattice, possibly forming trimeric, triangular Ti entities. After hydrogen desorption at 125 C, NaAlH4 decomposed and the Ti-Al coordination number increased from 4.8 to 8.5. We propose that all Ti is incorporated into the surface layer of the formed Al. After the material was heated to 225 C, the local structure of Ti, as inferred from EXAFS and XANES spectroscopy, was identical to the local structure of a TiAl3 alloy. However, the formed alloy was amorphous and was only detected in XRD by an increase of the background intensity around the Al diffraction. These so-called "TiAl3 clusters" agglomerated in the heat treatment to 475 C, forming crystalline TiAl3. Earlier work has shown that increasing the desorption temperature of NaAlH4 lowers the absorption rate and capacity of hydrogen in the next step. Thus, by comparing our results with absorption properties published in the literature on similar samples, we could rank the activity of the Ti for hydrogen absorption as Ti in the Al surface > TiAl3 cluster > crystalline TiAl3, therewith indicating that Ti incorporated into the surface of Al is the most active for the absorption of hydrogen.

The effect of hydration on the molecular structure of silica-supported vanadium oxide catalysts with loadings of 1–16 wt.% V has been systematically investigated by infrared, Raman, UV–vis and EXAFS spectroscopy. IR and Raman spectra recorded during hydration revealed the formation of V–OH groups, characterized by a band at 3660 cm−1. Hydroxylation was found to start instantaneously upon exposure to traces of water, reflecting a very high sensitivity of the supported vanadium oxide catalysts for H2O. Further hydration resulted in the appearance of a V–O–V vibration band located around 700 cm−1 pointing to the formation of di- or polymeric species. EXAFS analysis at 77 K indicated structural changes as the oxygen coordination changed from four to five. Moreover, a VV contribution was detected for the hydrated species. The IR, Raman and UV–vis data suggested a pyramidal anchoring of the dehydrated VOx species, whereas, the EXAFS data pointed to the presence of single V–O–Si bonded VOx species. This difference is attributed to water condensation effects at 77 K during EXAFS acquisition, resulting in a partial re-hydroxylation of the dehydrated samples, as confirmed by complementary IR and Raman analysis. Combining the results of this study with data from our previous studies [D.E. Keller, F.M.F. de Groot, D.C. Koningsberger, B.M. Weckhuysen, J. Phys. Chem. B 109 (2005) 10223; D.E. Keller, D.C. Koningsberger, B.M. Weckhuysen, J. Phys. Chem. B 110 (2006) 14313] as well as literature led to a reaction scheme in which a monomeric VOx species anchored by three Si–O–V bonds to the silica support (pyramidal-type structure) is transformed into a monomeric VOx species anchored by one Si–O–V bond (umbrella-type structure) by partial hydration of the catalyst material. This results in the formation of both V–O–H and Si–O–H bonds. At higher water pressures, larger vanadium oxide clusters are formed due to full hydration of the catalyst surface and a de-attachment of the vanadium oxide from the support surface. The results of this study provide evidence, that an umbrella-type structure (i.e., Si–O–VO(OH)2) could be present under catalytic conditions where H2O is a reaction product (e.g., partial oxidation of methanol to formaldehyde and oxidative dehydrogenation of alkanes). In other words, both the pyramidal ((Si–O)3–VO) and the umbrella (Si–O–VO(OH)2) model can exist at a support surface, their relative ratio depending on the hydration degree of the catalyst material. This study also illustrates that a corroborative characterization requires the use of multiple spectroscopic techniques applied at the same samples under almost identical measuring conditions.

Al K-edge (1561.1 eV) XANES and EXAFS spectra of unoxidized NaAlH4, a hydrogen storage material, have been recorded in He atmosphere in a special in situ low-energy cell. The XANES spectrum of NaAlH4 is reported and compared to that of oxidized NaAlH4, thus illustrating the power of XANES spectroscopy as a quick qualitative check of the NaAlH4. For the EXAFS data, reliable fits of the Al K-edge spectra could be obtained when all scattering contributions, i.e., Al-H, Al-Na, and Al-Al, were incorporated into the fit. The hydrogen atoms made a significant contribution to the Al K-edge EXAFS signal of NaAlH4, which stresses the importance of hydrogen scattering when analyzing EXAFS data of this metal hydride.

The nine-site benzene model of Zhao et al. (J. Phys. Chem. B 2005, 109, 5368-5374) has been used to systematically study the adsorption of benzene, propene, and benzene-propene mixtures in zeolites mordenite, Y, , silicalite, and MCM22. Interaction parameters for the benzene-zeolite interactions have been fitted to available adsorption experiments from literature. As an independent check of our force field, we have performed additional adsorption experiments using the TEOM technique and excellent agreement between simulations and TEOM experiments was found. High adsorption selectivities for benzene in benzene-propene mixtures were found in all zeolites, except for silicalite.

By careful selection of the appropriate preparation parameters we show how it is possible to immobilize transition metal ion complexes within the supercages of zeolite Y to create molecular species, which mimic the active sites of enzymes and their catalytic function. In particular, we demonstrate the use of 3,3-bis(1-methylimidazol-2-yl)propionate (MIm2Pr) combined with Cu2+ to imitate enzyme actives sites based on the 2-His-1-carboxylate facial triad motif and the use of histidine moieties (His) to replicate the active site of galactose oxidase. Characterization of these active site mimics using a variety of advanced spectroscopic techniques, has also been performed in order to understand why they possess this improved catalytic activity.

Magnesium dihydride contains 7.7 wt % hydrogen. However, its application for hydrogen storage is impeded by its high stability and slow kinetics. Bringing the size of Mg(H2) into the nanometer range will not only enhance the reaction rates but has also been theoretically predicted to change the thermodynamic stability and destabilize the MgH2 with respect to Mg. However, the preparation of such small particles is a major challenge. We identified a method to prepare large amounts of nanometer-sized nonoxidized magnesium crystallites. The method is based on infiltration of nanoporous carbon with molten magnesium. The size of the Mg crystallites is directly influenced by the pore size of the carbon and can be varied from 2–5 to less than 2 nm. The majority of the nanocrystallites is not oxidized after preparation. No bulk magnesium was detected in the samples with nanoparticle loadings up to 15 wt % on carbon. These 3D supported nanomaterials present interesting systems to study how nanosizing and support interaction can steer the hydrogen sorption properties of metal hydrides.

The coordination chemistry of the 2-His-1-carboxylate facial triad mimics 3,3-bis(1-methylimidazol-2-yl)propionate (MIm2Pr) and 3,3-bis(1-ethyl-4-isopropylimidazol-2-yl) propionate (iPrEtIm2Pr) towards ZnCl2 was studied both in solution and in the solid state. Different coordination modes were found depending both on the stoichiometry and on the ligand that was employed. In the 2:1 ligand-to-metal complex [Zn(MIm2Pr)2], the ligand coordinates in a tridentate, tripodal N,N,O fashion similar to the 2-His-1-carboxylate facial triad. However, the 1:1 ligand-to-metal complexes [Zn(MIm2Pr)Cl(H2O)] and [Zn(iPrEtIm2Pr)Cl] were crystallographically characterized and found to be polymeric in nature. A new, bridging coordination mode of the ligands was observed in both structures comprising N,N-bidentate coordination of the ligand to one zinc atom and O-monodentate coordination to a zinc second atom. A rather unique transformation of pyruvate into oxalate was found with [Zn(MIm2Pr)Cl], which resulted in the isolation of the new, oxalato bridged zinc coordination polymer [Zn2(MIm2Pr)2(ox)]·6H2O, the structure of which was established by X-ray crystal structure determination.

ECE-pincer palladium(II) complexes {ECE=[C6H3(CH2E)2-2,6]-, E=PPh2 and SPh} thered to a trialkoxysilane moiety through a carbamate linkage were immobilized on ordered mesoporous silicas SBA-15 and MCM-41 using a grafting process. The resulting hybrid materials were characterized by IR spectroscopy, solid-state CP/MAS NMR (13C, 31P, and 29Si), and elemental analyses. These analyses showed the integrity of the pincer-metal complexes on the supports, which highlights their stability under the applied immobilization conditions. An H-bonding interaction between the carbamate carbonyl group of the complex and free silanol groups on the silica surface was also established. The hybrid materials were found to act as Lewis acid catalysts in the aldol reaction between methyl isocyanoacetate and benzaldehyde. SBA-15 modified with the PCP-pincer Pd complex was used in up to five runs without loss of activity. Control experiments showed the true heterogeneous nature of the catalyst in this reaction. Nitrogen physisorption data, XRD, and TEM/EDX analyses of the hybrid materials revealed that the mesoporous structure of these materials was retained during the immobilization process as well as during catalysis.