SI methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading

Confinement of water and methane in mesopores of hydrophobized SBA-15 is demonstrated to promote methane hydrate formation. In comparison to as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics of methane storage in and delivery from the hydrate. C8 grafting density was determined at 0.5 groups nm-2 based on TGA and quantitative NMR spectroscopy. Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close spatial proximity between the grafted C8 chains and pore-intruded water species. X-ray diffraction demonstrates formation of Structure I hydrate on SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on hydrophobized SBA-15 C8 reaches 96 pct. as compared to only 71 pct. on a pristine SBA-15 sample with comparable pore size, pore volume and surface area. The clathrate loading amounted to 14.8 g g-1. 2D correlation NMR spectroscopy (1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of SBA-15 C8 as well as in interparticle volumes. Following the initial crystallization of SBA-15 C8-supported methane hydrate taking several hours, a pressure swing process at 248 K allows to desorb and re-adsorb methane from the structure within minutes and without thawing the frozen water structure. Fast loading and unloading of methane was achieved in 19 subsequent cycles without losses in kinetics. The ability to harvest the gas and regenerate the structure without the need to re-freeze the water represents a 50 pct. energy gain with respect to melting and subsequently recrystallizing the hydrate at 298 K and 248 K, respectively. After methane desorption, a small amount of residual methane hydrate in combination with an amorphous yet locally ordered ice phase is observed using 13C and 2H NMR spectroscopy

Zeolite catalyzed etherification of alpha-olefins and terpenes with alcohols in liquid phase

Nowadays petroleum, attributed as the ‘mother of all commodities’, accounts for 35% of energy consumption, 95% of the transportation fuels and 100% of a large number of industrially important chemicals and materials. The increasing carbon dioxide concentration in the atmosphere due to fossil hydrocarbon combustion has reached alarming levels urging the use of renewable carbon resources for fuels and chemicals. In chemical industry strategies are being developed for producing chemicals from biomass capable to replace petroleum-derived chemicals. Approaches are typically based on fermentation, gasification and Fischer-Tropsch synthesis from carbon monoxide and hydrogen produced from biomass. Ethers are an important class of chemical compounds that can be derived from biomass. They find lots of applications as fuel additives, inert solvent for specialty applications as well as chemical reactions, fragrance and flavor additives, medical ingredients, anesthetics, etc. Etherification of secondary olefins to produce fuel ethers is reported in both homogeneous and heterogeneous catalytic processes in gas phase as well as liquid phase conditions. But the etherification of α-olefins is less documented in literature. The goal of this work was to develop a liquid phase, heterogeneous catalytic process for the etherification of typical Fischer - Tropsch α-olefins and monoterpenes for use as fuel additives and specialty solvents. Fischer - Tropsch C6-C10 α-olefins are not useful as such and require upgrading process like isomerization for use as fuel. 1-Hexene, 1-octene and 1-decene were selected as model compounds and ethanol as the model bio-alcohol. The reactions were performed at high pressure (6 MPa) to maintain the reaction mixture in liquid state. Zeolites were identified as prospective catalysts. Zeolite beta with Si/Al ratio of 19 was found to be an excellent catalyst for hydroalkoxylation reactions. Identification of reaction products using gas chromatography combined with mass spectrometry (GC-MS) and NMR revealed unique selectivity. Etherification reaction of 1-hexene with ethanol could be performed using an equimolar feed at low temperature, viz. 423K. Ethoxy hexanes were the major product with ca. 90% selectivity with respect to 1-hexene. 2-Ethoxy hexane was the majority product. Side reactions such as dehydration of ethanol to form diethyl ether, oligomerization of hexenes and hydration of 1-hexene to form 2-hexanol were suppressed. Similar product profiles, activities and selectivities were observed for the etherification of 1-octene and 1-decene with ethanol. Etherification of 1-hexene with higher bio-alcohols viz. 1-propanol and 1-butanol was also demonstrated. While selectivity for etherification was always excellent, the conversion did not surpass 60% typically, even with optimized reaction conditions. For the isomerization of 1-hexene to internal isomers, thermodynamic equilibrium composition was achieved in the absence of 1-propanol in the feed while presence of 1-propanol prevented the achievement of equilibrium. For the etherification reaction, a limitation of the maximum achievable conversion by unfavorable thermodynamic equilibrium was evidenced using computational chemistry methods. Terpenes are a class of natural olefins, the ethers of which are valuable to the perfume industry. In view of the immense applications of terpene ethers as fragrance and flavor additives, specialty solvents like in development of photopolymerizable printing plates, etc., etherification of monoterpene β-citronellene with bio-alcohols was also investigated. β-citronellene is a monoterpene containing two types of double bonds, one terminal α-double bond and an internal β-double bond. Among the different zeolites tested, zeolite beta (Si/Al 19) profiled again to be the best. The etherification reaction was found to occur mostly at the β-double bond with a chemoselectivity of ca. 90%, which was found out by Density Functional calculations to be due to the difference in stability of the carbocations formed on protonation of the two double bonds. Under optimized conditions, maximum citronellene conversions of ca. 50% with ca. 80% selectivity for etherification was achieved, which was also found to be limited by thermodynamic equilibrium. Citronellene isomerization and dimerization were the side reactions occurring. In order to identify the reasons for the superior activity of zeolite beta and in general for identifying the prerequisites for a successful hydroalkoxylation catalyst, physicochemical properties of the catalysts were investigated along with performing experiments with selectively poisoned catalysts. Acid site poisons 2,4,6-collidine and 2,6-ditertiarybutyl pyridine cannot enter the channels of the zeolite and hence selectively poison the external surface and pore mouth acid sites. Poisoned catalysts exhibited negligible activity indicating the role of pore mouth and external surface acid sites in etherification reactions. Overall this work highlighted the superior activity and selectivity of zeolite beta in hydroalkoxylation of FT α-olefins and monoterpenes using alcohols which can be produced from biomass via fermentation. Zeolite beta particles are composed of very small crystallites measuring hardly 40 nm each. A zeolite material with such very short channels offers a large number of pore mouths, revealed to be the locus of the catalytic activity. 13C NMR investigations substantiated the occurrence of pore mouth catalysis mechanism induced by competitive adsorption phenomena. The attractiveness of a continuous flow, fixed bed, liquid phase process to produce chemicals out of biomass in replacement of petrochemical derived commodities like fuel additives, specialty solvents, fragrance and flavor additives is an example of greening of the chemical industry.Acknowledgements i Abstract v Samenvatting vii Table of Contents ix List of Abbreviations xi Chapter 1 - Introduction 1 1.1 General Introduction 3 1.2 Ethers and their Applications 4 1.3 Synthesis of Ethers 9 1.3.1 Hydroalkoxylation processes and Catalysts 10 1.3.1.1 Homogeneous Catalysis 10 1.3.1.2 Heterogeneous Catalysis 11 1.3.2 Dependence of Reagent Structure on Reactivity 16 1.3.2.1 Dependence of Olefin Structure on Reactivity 16 1.3.2.1 Dependence of Alcohol Structure on Reactivity 18 1.3.3 Mechanistic Insights 20 1.3.3.1 Ion-Exchange Resin Catalyzed Reactions 20 1.3.3.2 Zeolite Catalyzed Reactions 26 1.4 Terpene Etherification 30 1.5 Aim of the Work 32 1.6 References 33 Chapter 2 - Reactor and Experimental Procedure 39 Chapter 3 - Selective Synthesis of 2-Ethoxy Alkanes through Ethoxylation of 1-Alkenes with Bioethanol over Zeolite Beta Catalyst in a Liquid Phase Continuous Process 49 Chapter 4 - Selective Hydroalkoxylation of 1-Hexene with 1-Propanol and 1-Butanol over Zeolite Beta Catalyst 59 Chapter 5 - Selective Etherification of β-Citronellene Catalyzed by Zeolite Beta 67 Chapter 6 - In situ solid-state 13C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta 83 Chapter 7 - General Conclusions and Perspectives 99 Appendix 1 109 Appendix 2 111 List of Publications 115nrpages: 129status: publishe

Water as a tuneable solvent: a perspective

Water is the sustainable solvent of excellence, but its high polarity limits the solubility of non-polar compounds. Confinement of water in hydrophobic pores alters its hydrogen bonding structure and related properties such as dielectric constant and solvation power. Whether this special state of confined water can be rendered useful in chemical processes is hitherto underexplored. Confining water in hydrophobic nanopores could be a way to modulate water solvent properties, enabling the use of water as a tuneable solvent (WaTuSo). Applying pressure forces a heterogeneous mixture of poorly soluble molecules and water into hydrophobic nanopores of a host material where the lowered polarity of water enhances dissolution. Decompression after reaction causes expulsion of the solution from the pores and spontaneous demixing of reaction products because water returns to its normal polar state. Temporary dissolution enhancement during confinement is expected to be advantageous to chemical reaction and molecular storage. Nano-confined water offers a potential alternative to compression for storing CH$_4$ and H$_2$ gas, and opens new opportunities for green chemistry such as aqueous phase hydrogenation reactions which benefit from enhanced hydrogen solubility. Unprecedented control in time and space over H$_2$O solvation properties in a WaTuSo system will enable new technologies with major scientific and societal impact

Creation of gallium acid and platinum metal sites in bifunctional zeolite hydroisomerization and hydrocracking catalysts by atomic layer deposition

Atomic layer deposition (ALD) is a vacuum technology for the deposition of a small number of atoms on surfaces. Its use in catalysis is growing. Here, we explored the use of ALD for introducing acid and metal sites in zeolites for performing bifunctional catalysis. Plasma-enhanced ALD involving cyclic exposure of a sample to tris(2,2,6,6-tetramethyl-3,5-heptanedionato)gallium (Ga(TMHD)(3)) vapor and O-2 plasma (Ga-ALD) was used for introducing acid sites. Interestingly, Ga-ALD was found to cause preferential deposition of Pt nanoparticles via incipient wetness impregnation on the edges of COK-14 crystal plates, in contrast to previously published results on Al-ALD. Benefiting from the optimum proximity between the Ga acid and Pt metal sites, it is shown here that Ga-ALD is a way to introduce sufficient acidity into all-silica zeolite COK-14 for obtaining bifunctional catalytic behavior. Hydrogenation-dehydrogenation activity in bifunctional catalysts is typically provided by trace amounts of platinum dispersed on the zeolite. Pt-ALD was applied for finely dispersing platinum on ZSM-5 zeolite. Pt-ALD involved alternating exposure to the trimethyl(methylcyclopentadienyl)platinum(iv) (MeCpPtMe3) precursor and ozone. The Pt-ALD method proved to be an efficient way to uniformly disperse ultra-small Pt nanoparticles onto the zeolite. The bifunctional catalytic behavior of ALD-functionalized zeolites was confirmed in the hydroconversion of the n-decane model molecule

Selective Hydroalkoxylation of 1-Hexene with 1-Propanol and 1-Butanol over Zeolite Beta Catalyst

Etherification of 1-hexene with 1-propanol and 1-butanol representative of bioalcohols was performed in a liquid-phase continuous-flow process over a fixed bed of zeolite beta catalyst. Contact time and reaction temperature were optimized to maximize conversion and limit deactivation. The catalyst was stable for at least 14h on stream. In the conversion of 1-hexene with 1-propanol, zeolite beta catalyst showed over 90% selectivity for 2-propoxyhexane. In the conversion of 1-hexene and 1-butanol, 2-butoxyhexane was selectively formed. Dialkyl ether from the alcohol and dodecenes and hexanol from 1-hexene were the main side products. As 1-alkenes and terminal alcohols can be synthesized from biomass, this hydroalkoxylation process could be used for grading up green chemicals to high-boiling solvents and renewable ethers for the diesel pool. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.status: publishe

Water as a tuneable solvent: a perspective.

Water is the sustainable solvent of excellence, but its high polarity limits the solubility of non-polar compounds. Confinement of water in hydrophobic pores alters its hydrogen bonding structure and related properties such as dielectric constant and solvation power. Whether this special state of confined water can be rendered useful in chemical processes is hitherto underexplored. Confining water in hydrophobic nanopores could be a way to modulate water solvent properties, enabling the use of water as a tuneable solvent (WaTuSo). Applying pressure forces a heterogeneous mixture of poorly soluble molecules and water into hydrophobic nanopores of a host material where the lowered polarity of water enhances dissolution. Decompression after reaction causes expulsion of the solution from the pores and spontaneous demixing of reaction products because water returns to its normal polar state. Temporary dissolution enhancement during confinement is expected to be advantageous to chemical reaction and molecular storage. Nano-confined water offers a potential alternative to compression for storing CH4 and H2 gas, and opens new opportunities for green chemistry such as aqueous phase hydrogenation reactions which benefit from enhanced hydrogen solubility. Unprecedented control in time and space over H2O solvation properties in a WaTuSo system will enable new technologies with major scientific and societal impact.status: publishe

Alumina: Discriminative Analysis using 3D Correlation of Solid-State NMR Parameters

Synthetic transition aluminas (χ, κ, θ, γ, δ, η, ρ) exhibit unique adsorptive and catalytic properties leading to numerous practical applications. Generated by thermal transformation of aluminium (oxy)hydroxides, structural differences between them arise from the variability of aluminium coordination numbers and degree of dehydroxylation. Unequivocal identification of these phases using X-ray diffraction has proven to be very difficult. Quadrupolar interactions of 27Al nuclei, highly sensitive to each site symmetry, render advanced 27Al solid-state NMR a unique spectroscopic tool to fingerprint and identify the different phases. In this paper, 27Al NMR spectroscopic data on alumina reported in literature are collected in a comprehensive library. Based on this dataset, a new 3D correlative method of NMR parameters is presented, enabling fingerprinting and identification of such phases. Providing a gold standard from crystalline samples, this approach demonstrates that any sort of crystalline, ill crystallized or amorphous, mixed periodic or aperiodically ordered transition alumina can now be assessed beyond the current limitations of characterisation. Adopting the presented approach as a standard characterisation of alumina samples will readily reveal NMR parameter-structure-property relations suitable to develop new or improved applications of alumina. Methodological guidance is provided to assist consistent implementation of this characterisation throughout the fields involved.status: publishe

Does Water Enable Porosity in Aluminosilicate Zeolites? Porous Frameworks versus Dense Minerals

International audienc

A Pyrrolidine Functionalized Poly[(Ethylene Glycol) Methacrylate] Resin as a Heterogeneous Catalyst for Aqueous Aldol Reactions

The development of a performant aminated catalyst for aldol condensations requires the combined tuning of the active site, support and solvent system. For this purpose, a pyrrolidine group was immobilized on a swellable polymer resin. Favorable interactions between the support and water (in its role as solvent) resulted in a turnover frequency (TOF) amounting to 3.0 ± 1.5 × 10−3 s−1, despite potential inhibition of the active sites by formation of iminium species. The affinity of the solvent for the poly[(ethylene glycol) methacrylate] support resulted in efficient swelling of the catalytic material, which was shown to be key to the observed catalytic performance.</jats:p

3D Correlation of Solid-State NMR Parameters for Alumina - interactive chart

Synthetic transition aluminas (χ, κ, θ, γ, δ, η, ρ) exhibit unique adsorptive and catalytic properties leading to numerous practical applications. Generated by thermal transformation of aluminium (oxy)hydroxides, structural differences between them arise from the variability of aluminium coordination numbers and degree of dehydroxylation. Unequivocal identification of these phases using X-ray diffraction has proven to be very difficult. Quadrupolar interactions of 27Al nuclei, highly sensitive to each site symmetry, render advanced 27Al solid-state NMR a unique spectroscopic tool to fingerprint and identify the different phases. In this paper, 27Al NMR spectroscopic data on alumina reported in literature are collected in a comprehensive library. Based on this dataset, a new 3D correlative method of NMR parameters is presented, enabling fingerprinting and identification of such phases. Providing a gold standard from crystalline samples, this approach demonstrates that any sort of crystalline, ill crystallized or amorphous, mixed periodic or aperiodically ordered transition alumina can now be assessed beyond the current limitations of characterisation. Adopting the presented approach as a standard characterisation of alumina samples, will readily reveal NMR parameter – structure – property relations suitable to develop new or improved applications of alumina.edition: 1.0status: accepte