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Particulate matter (PM) and nitrogen oxides (NOx) emitted from power plant or mobile vehicles are responsible for air pollution and ever more stringent emission limits are proposed. Removal of particulate matter and NOx from diesel exhaust gases is currently achieved via a diesel particulate filter (DPF) and a NOx reduction catalyst (NOx storage and reduction catalyst (NSRC) or selectively catalytic reduction (SCR) catalyst). Particulate matter is trapped in the filter while the exhaust gases pass through the walls of the filter. Due to the increasing back pressure, particulate matter needs to be removed periodically by oxidizing trapped particles into CO2 and H2O. Nitrogen dioxide (NO2, “passive regeneration”) and O2 (“active regeneration”) are used as the oxidants for carbon (main component of particulate matter) oxidation during the filter regeneration. However, reactions of carbon with NO2 or O2 occur at high temperatures over 250 oC and 500 oC respectively. The decreasing trend of vehicle exhaust gas temperature (below 250 oC) makes these reactions unfavorable. Additional heating to increase the exhaust temperature is achieved by combustion of fuel injected in the exhaust gas, representing a fuel penalty. Nitric oxide (NO) is the main product after reaction of carbon with NO2 necessitating the implementation of a selective catalytic reduction catalyst after the filter for NO reduction to dinitrogen. Selective catalytic reduction uses a vanadium catalyst or iron/copper zeolite to reduce NOx in an oxidative atmosphere using ammonia as the reductant.In this work, photocatalysis which does not need thermal activation is investigated for simultaneous soot oxidation and NOx reduction in simulated exhaust gases. A homemade gas phase photoreactor was used to simulate the composition of exhaust gas and monitor the relevant components (NO, NO2, N2O, NH3, CO2, CO). First, the photocatalytic activity of titanium dioxide (TiO2) under UVA light has been investigated in carbon oxidation using nitric oxide as the only oxidant. Titanium dioxide is a widely investigated photocatalyst for water splitting, removal of organic compounds and self-cleaning materials. Both photocatalytic soot oxidation and NOx removal has been reported using titanium dioxide. However, photo-oxidation of carbon using nitrogen oxides has never been reported before. In this study, photocatalytic carbon oxidation with nitric oxide in the absence of oxygen was investigated on TiO2 surface at relatively low temperature (150 oC). In the absence of oxygen carbon was photocatalytically converted mainly to carbon dioxide, and nitric oxide primarily reduced into dinitrogen. Carbon oxidation rates and NO conversions under different reaction conditions were compared. The highest carbon oxidation rate of 2.0 μg carbon per hour per mg TiO2 with 98% NO conversion was achieved in the presence of 3,000 ppm NO. The effects of water vapor and NO concentration on carbon photo-oxidation rate was thoroughly studied. The addition of water enhances nitrate formation and decrease the NO reduction rate but shows little effect on CO2 formation. Under the investigated experimental conditions catalyst deactivation caused by nitrate formation is negligible. The main drawback is the low reaction rate, which required the experiments to be performed under static conditions rather than under flow through conditions.In the second part of this work, the focus shifted to the NO reduction effects. NO can be continuously reduced to N2 in the presence of solid carbon on TiO2 photocatalyst surface at low flow rate (5 ml/min) under UVA illumination. Batch mode experiments were also performed to investigate the nitrate formation on photocatalyst surface. Nitrate is formed on photocatalyst surface from the reaction of nitric oxide with photo-generated radicals. Samples after reaction were characterized by Fourier Transform Infrared spectroscopy (FTIR) and the nitrate formation on catalyst surface was quantified using a nitrate test kit. The reaction mechanisms of photo-SCR using soot and nitrate formation or decomposition are discussed. NO2, nitrous and nitric acid are assumed to be formed and transferred through the gas phase to carbon surface. These reactive species contribute to the carbon oxidation process. The temporary formation of N2O could be related to the reaction of NO with Ti3+ sites on photoactivated TiO2 before it reaches steady state saturation with nitrate. Formation and decomposition of nitrate can be a dynamic process. HNO3/NO3- can be photocatalytically transformed back to NO2 via the reaction of nitrate and NO in the presence of TiO2 under illumination. The TiO2/carbon sample before and after reaction were characterized by High-Resolution Scanning Electron Microscopy (HR SEM) providing a visual evidence of photocatalytic carbon oxidation. Photo-SCR of NOx using soot achieves the same target as NOx reburn via the reverse prompt NOx reaction in coal combustion. The concept of using soot for reducing NOx is an attractive concept, removing soot and NOx simultaneously. Further research is needed to increase the reaction rate for practical applications.In the last part of this work, the improvement of the carbon oxidation rate was further studied in the presence of oxygen. Photocatalytic oxidation of the most reactive carbon fraction proceeds equally well with O2 and NO. The combination of nitric oxide, oxygen and water was found to be effectively increasing the CO2 formation rate especially in the later phase of the reaction. Therefore a synergetic effect of NO and O2 on refractory carbon photocatalytic oxidation is observed. NO is more effective than O2 on photocatalytic oxidation of the more refractory part of the carbon. During the reaction, carbon is oxidized mainly to CO2 while NOx is mainly reduced to N2. Enhanced O2 and NO concentrations in the gas phase have a positive effect on the carbon oxidation rate. At optimum gas composition with 3,000 ppm NO and 13.3% O2 the highest carbon oxidation rate reaches 5.64 µgcarbon/mgTiO2 h, with formal electron/photon quantum efficiency of 0.052. Nitrate was formed during the reaction. A long term reaction provides the evidence that the catalyst deactivation caused by nitrates is limited. HR SEM was used to observe the carbon particles morphology change during carbon oxidation with oxygen as the only oxidant. Differences of carbon particles morphology change between the reactions with or without NOx are observed in the HR SEM measurements. The carbon particles were oxidized more significantly and uniformly in the presence of nitric oxide compared to the reactions using O2 as the only oxidant under identical reaction conditions. It is evident that the oxidizing species generated in the presence of nitric oxide can migrate longer distance than the hydroxyl radicals or oxygen related radicals which are formed in the presence of oxygen and water.

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Allylic alcohols and functionalized anilines are industrially valuable flavouring and fragrance compounds and important intermediates for pharmaceuticals, polymers and other fine chemicals. These compounds can be synthesised via chemoselective reduction of unsaturated aldehydes and nitro compounds. Reduction of the olefinic group yields saturated aldehydes and nitro compounds, whereas hydrogenation of the carbonyl and nitro group produce allylic alcohols and unsaturated amines. Typically, this reduction is performed under high hydrogen pressure conditions with supported metal catalysts, alternatively transfer hydrogenation with an alcohol as hydride donor and a Lewis acid catalyst can be employed. The former process is most widely applicable, but is not straightforward since olefins are often preferentially reduced, due to thermodynamic and kinetic reasons. To direct selectivity towards the desired products there is thus a strong motivation to develop chemoselective supported metal reduction catalysts. Platinum group metals (Pt, Pd, Ir, Rh, Os and Ru; PGMs) are typically used, but often require complex doping schemes. Silver on the contrary, has a very high intrinsic chemoselectivity towards unsaturated products in reductions of polyfunctional molecules and will thus be explored in this work as chemoselective reduction catalyst.Metal nanoparticle catalysts used for the chemoselective reduction are typically supported on porous materials like silica, alumina and carbon. These supports stabilise the metal nanoparticles preventing their aggregation and hence loss in activity and/or selectivity. Though more interestingly the pores of these support can also be used to control the size of nanoparticles via pore confined synthesis strategies. In this work, chemoselective hydrogenation with a commonly used silver on silica catalyst is investigated first, whereafter the development of a new chemoselective silver catalyst on an innovative material is described and the remarkable transfer hydrogenation catalysing power of this support.In the first experimental chapter (Chapter 2), the chemoselective reduction of 4-nitrostyrene using a silver on silica catalyst, prepared via the standard incipient wetness (IWI) procedure, is explored in detail. In IWI a porous support is filled with a metal precursor solution that equals the pore volume of the support. After drying and calcination, the final supported metal nanoparticle catalyst is obtained. In contrast to the typically used bulk averaging or spatially resolving characterisation techniques, in this work optical microscopy is used as the most important characterisation technique. Optical microscopy proved to be a convenient tool to directly interlink structural and compositional information and hydrogenation performance of individual support particles. This novel correlative imaging approach revealed for the first time how incipient wetness impregnation led to 10-fold variations in silver loading between individual submillimetre-sized silica support granules. Furthermore, this heterogeneity had a profound impact on the catalytic performance: 100-fold interparticle variations in normalized catalytic performance were discovered for the chemoselective 4-nitrostyrene reduction between granules of the same batch. This detailed study revealed the optimal silver loading and based on this information the normalized yield was increased by 38 %.To unravel the origin of this interparticle heterogeneity the impregnation process was dissected into the individual synthesis steps (impregnation, drying & calcination) and the pre-impregnated support, and investigated in detail using optical microscopy (Chapter 3). Examination of the influence of each elementary step on the resulting silver distribution pointed out that every step introduces a minimal degree of interparticle heterogeneity, but the optimised drying procedure has the largest impact on the heterogeneity. More specifically, the position of a support granule in the stagnant drying bed has a large influence on the resulting colour and thus silver distribution. Moving from a static to a fluidized bed drying resulted in an improved homogeneity in silver loading on the different support granules. This optimised drying procedure is easy to implement in the lab and on even larger scales.The importance of generating well-defined and stable silver nanoparticles was an incentive to look into pore confinement in metal organic frameworks (MOFs). These results are described in Chapter 4. Silver nanoparticles were successfully synthesized by pore confinement in UiO-66, a widely used zirconium-based metal-organic framework. A recyclable 10 wt% Ag/UiO-66 catalyst reached complete conversion of cinnamaldehyde after 6 h and 50 bar of H2 with 66 % selectivity for cinnamyl alcohol in the inert solvent N,N-dimethylacetamide (140°C, 25 mg catalyst, 2 mol% Ag). Surprisingly, pure UiO-66 without silver reached complete conversion with > 90 % selectivity after 24 h at 120°C (25 mg catalyst, 8 mol% Zr) in isopropyl alcohol solvent, even in absence of H2. The Lewis acid sites of the Zr-support catalyse transfer hydrogenation of cinnamaldehyde with isopropyl alcohol, a procedure called Meerwein-Ponndorf-Verley (MPV) reduction. The substrate scope of this MPV reduction was successfully extended to citral and carvone, two α,β-unsaturated carbonyl compounds that are harder to reduce selectively. Further catalyst optimisation was possible via the introduction of a NO2-functional group into the UiO-66 linker, increasing the Lewis acidity.Based on the high activity and chemoselectivity in the reduction of unsaturated carbonyl compounds using the Lewis acid Zr-sites in UiO-66, a large pore Zr-based MOF, MOF-808-P, was explored as MPV reduction catalyst with isopropyl alcohol as solvent and hydride donor. These large pores of MOF-808-P facilitate the formation of the six-membered ring transition state and more importantly, the Zr-atom in the MOF-cluster is undercoordinated which should lead to an increased number and strength of the Lewis acid sites compared to UiO-66. MOF-808-P catalysed MPV reduction obtained already 99 % cinnamyl alcohol yield after only 2 h (120 °C, 20 mg catalyst, 8 mol% Zr) (Chapter 5). The highly active MOF-808-P was furthermore a good catalyst for the selective reduction of more challenging substrates such as carvone and β-ionone. The activity for the former was 20-fold increased with respect to UiO-66. Two strategies were successfully used to shift the equilibrium reaction towards the desired allylic alcohol products: 1) evaporation of formed acetone when using isopropyl alcohol and 2) the use of the more strongly reducing 1-indanol. Via these approaches the carveol yield was increased to > 70 %.

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Metal-organic frameworks (MOFs) are crystalline nanoporous materials that consist of inorganic metal-containing nodes connected by polytopic organic linkers. MOFs are promising materials for novel applications in various industries because of their high specific surface area, synthetic flexibility and tunable structure-property relationships. For many application areas, such as catalysis, molecular separation and gas storage, MOFs can be utilized as bulk materials. For fabrication of solid-state integrated MOF devices, by contrast, immobilization of MOFs directly on substrates is required, i.e. material synthesis by thin film deposition. Examples of promising applications of this type are chemical sensors, microelectronic chips, supercapacitors or other (opto)electronics. Research on the latter applications is recently emerging and gives rise to a growing need for suitable MOF integration routes.In this Ph. D. research project, novel integration routes for MOFs are explored in order to increase the industrial feasibility of MOF integration into applications such as solid-state devices. The main text of the manuscript is a compilation of five peer reviewed papers and their supporting information in the as-published form. The articles are complemented by an introduction and a general conclusion providing background information on the position of the project in the overarching research fields.The first part of the manuscript focuses on integration of zirconium (IV) carboxylate MOFs. These materials are interesting for applications because of their robustness and flexible chemistry. However, their deposition as films on substrates is challenging due to difficult-to-control crystallization kinetics. Electrochemical deposition is demonstrated as a novel route for their integration, permitting stimulated deposition on conductive surfaces via two distinct mechanisms. Moreover, a synthesis modulation approach can be utilized to regulate the morphology and adhesion of the films. As a proof-of-concept of the beneficial integration of these materials, application in a sorbent trap for analytical sampling of volatile organics is demonstrated. In a subsequent phase, the extraordinary potential of zirconium (IV) carboxylate covered electrodes for field effect gas sensing devices is evidenced by Kelvin probe sensing experiments. Parts-per-billion trace levels of volatile phosphonates are reproducibly detected on a background of dry or humid air, owing to strong physisorption of these analytes at lattice defects in the confined cages of the MOF. Furthermore, this study demonstrates that there is general potential in judicious design of MOFs for high-sensitivity detection of specific analytes.The second part of the manuscript discusses the transformation of deposited metal oxides into MOF films. Metal oxides are promising sacrificial precursor materials for MOF integration, owing to their controlled deposition on substrates by well-established techniques. Whereas transformation of metal oxides into MOFs can be conducted using solution methods, eliminating the role of the solvent during film deposition is interesting for numerous reasons (e.g. sustainability, industrial compatibility, avoidance of dissolution issues). Therefore, solvent-free routes are explored for the conversion of zinc oxide to zeolitic imidazolate framework (ZIF) films. In a first approach, zinc oxide films are reacted with a melted imidazole-based linker for formation of ZIF films. Precise replication of patterns and mesoscopic architectures is achieved, demonstrating spatial localization of the crystallization process by the solid zinc ion source. In a second approach, deposition of nanoscale metal-organic framework films is achieved through heterogeneous vapor-solid reaction between vaporized organic linkers and ultrathin sacrificial metal oxide films. The solid-vapor reaction method, MOF-CVD, is the first demonstrated vapor-phase deposition method for crystalline nanoporous network solids. Moreover, conformal deposition on high-aspect-ratio features and microscopic patterning by additive photolithography is accomplished based on the unique properties of this method. MOF-CVD shows potential for extension to various different MOF classes and will become an important new direction in research on fabrication of MOFs for integrated applications.