Karl Petter Lillerud

A New Zirconium Inorganic Building Brick Forming Metal Organic Frameworks with Exceptional Stability

Porous crystals are strategic materials with industrial applications within petrochemistry, catalysis, gas storage, and selective separation. Their unique properties are based on the molecular-scale porous character. However, a principal limitation of zeolites and similar oxide-based materials is the relatively small size of the pores, typically in the range of medium-sized molecules, limiting their use in pharmaceutical and fine chemical applications. Metal organic frameworks (MOFs) provided a breakthrough in this respect. New MOFs appear at a high and an increasing pace, but the appearances of new, stable inorganic building bricks are rare. Here we present a new zirconium-based inorganic building brick that allows the synthesis of very high surface area MOFs with unprecedented stability. The high stability is based on the combination of strong Zr-O bonds and the ability of the inner Zr6-cluster to rearrange reversibly upon removal or addition of mu3-OH groups, without any changes in the connecting carboxylates. The weak thermal, chemical, and mechanical stability of most MOFs is probably the most important property that limits their use in large scale industrial applications. The Zr-MOFs presented in this work have the toughness needed for industrial applications; decomposition temperature above 500 degrees C and resistance to most chemicals, and they remain crystalline even after exposure to 10 tons/cm2 of external pressure.

Conversion of Methanol to Hydrocarbons: How Zeolite Cavity and Pore Size Controls Product Selectivity

Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2). The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.

Electronic and vibrational properties of a MOF-5 metal–organic framework: ZnO quantum dot behaviour

UV-Vis DRS and photoluminescence (PL) spectroscopy, combined with excitation selective Raman spectroscopy, allow us to understand the main optical and vibrational properties of a metal-organic MOF-5 framework. A O(2-)Zn(2+)[rightward arrow] O(-)Zn(+) ligand to metal charge transfer transition (LMCT) at 350 nm, testifies that the Zn(4)O(13) cluster behaves as a ZnO quantum dot (QD). The organic part acts as a photon antenna able to efficiently transfer the energy to the inorganic ZnO-like QD part, where an intense emission at 525 nm occurs.

Post-synthetic modification of the metal–organic framework compound UiO-66

Post-synthetic modification is a viable route for the introduction of surface sites with new chemical properties in metal–organic framework compounds. Herein we demonstrate that it is possible to perform covalent post-synthetic modifications of the UiO-66–NH2 MOF with four different acid anhydrides. FT-IR is employed to monitor the reactions and the extent of reaction depends on the bulkiness of the anhydrides. For the smallest one, acetic anhydride, 100% conversion to UiO-66–NHCOCH3 was observed.

Hydrogen storage in Chabazite zeolite frameworks

We have recently highlighted that H-SSZ-13, a highly siliceous zeolite (Si/Al = 11.6) with a chabazitic framework, is the most efficient zeolitic material for hydrogen storage [A. Zecchina, S. Bordiga, J. G. Vitillo, G. Ricchiardi, C. Lamberti, G. Spoto, M. Bjørgen and K. P. Lillerud, J. Am. Chem. Soc., 2005, 127, 6361]. The aim of this new study is thus to clarify both the role played by the acidic strength and by the density of the polarizing centers hosted in the same framework topology in the increase of the adsorptive capabilities of the chabazitic materials towards H2. To achieve this goal, the volumetric experiments of H2 uptake (performed at 77 K) and the transmission IR experiment of H2 adsorption at 15 K have been performed on H-SSZ-13, H-SAPO-34 (the isostructural silico-aluminophosphate material with the same Brønsted site density) and H-CHA (the standard chabazite zeolite: Si/Al = 2.1) materials. We have found that a H2 uptake improvement has been obtained by increasing the acidic strength of the Brønsted sites (moving from H-SAPO-34 to H-SSZ-13). Conversely, the important increase of the Brønsted sites density (moving from H-SSZ-13 to H-CHA) has played a negative role. This unexpected behavior has been explained as follows. The additional Brønsted sites are in mutual interaction via H-bonds inside the small cages of the chabazitic framework and for most of them the energetic cost needed to displace the adjacent OH ligand is higher than the adsorption enthalpy of the OH...H2 adduct. From our work it can be concluded that proton exchanged chabazitic frameworks represent, among zeolites, the most efficient materials for hydrogen storage. We have shown that a proper balance between available space (volume accessible to hydrogen), high contact surface, and specific interaction with strong and isolated polarizing centers are the necessary characteristics requested to design better materials for molecular H2 storage.

Shape‐Selective Conversion of Methanol to Hydrocarbons Over 10‐Ring Unidirectional‐Channel Acidic H‐ZSM‐22

With the forecasted depletion in global oil reserves, new routes to petrochemical products from natural gas, coal, or biomass are becoming increasingly important. The methanolto-hydrocarbons (MTH) reaction constitutes the final step in one such route. The MTH reaction proceeds over Brønstedacidic zeolite or zeotype catalysts, and near-commercial processes exist for the methanol-to-gasoline (MTG) reaction over ZSM-5, as well as the methanol-to-olefin (MTO) reaction over SAPO-34. A breakthrough in the mechanistic understanding of the MTH reaction was the formulation of the “hydrocarbon pool mechanism” by Dahl and Kolboe, 3] which postulates that methanol is continuously added to aromatic reaction centers, from which light alkenes are split off in later reaction steps. Recently, the importance of methylation and cracking of alkenes over ZSM-5 was highlighted. 6] ZSM-22 (TON) is less well studied as a MTH catalyst. It incorporates one-dimensional non-interacting 10-ring channels with diameters of 0.46 0.57 nm. Song and co-workers reported the failure of ZSM-22 to convert methanol into olefins. Their studies of ZSM-22 showed a low production of olefins during the first pulses of methanol, however the amount of olefin quickly decreased to essentially zero. This failure as an MTH catalyst was ascribed to the narrow pores, which were assumed to be too small to accommodate the complete catalytic cycle of the hydrocarbon pool mechanism. Flow experiments (at 250– 400 8C) afforded relatively constant yields of trace amounts of ethene and propene. The low reactivity was believed to be the result of traces of ZSM-11, impurities in the methanol (acetone) and/or external acid sites. Herein, we report studies of the MTH reaction over ZSM-22 at a wider range of reaction conditions and demonstrate that the previous conclusions are not universally valid. Under suitable conditions, ZSM-22 has a conversion capacity comparable to that of SAPO-34, reaction intermediates reside within the pores, and the product spectrum is intermediate to those found for reactions for the MTO and MTG processes. Several batches of ZSM-22 with different Si/Al ratios were synthesized and all were found to be active catalysts for the MTH reaction. The crystallinity and purity of the product were confirmed by X-ray diffraction. Scanning electron microscopy (SEM) revealed needle shaped crystals of 2–3 mm length. Al NMR spectroscopy indicated that, for the samples discussed here, Al was located exclusively in the framework, both for as-made and calcined/ion-exchanged samples. BET surface areas were in the range 160–207 m g . Two different ZSM-22 catalysts (Si/Al = 30 by inductively coupled plasma atomic emission spectroscopy) with BET surface areas of 173 and 207 m g , denoted ZSM-22 ACHTUNGTRENNUNG(173) and ZSM-22 ACHTUNGTRENNUNG(207) respectively, will be discussed. At temperatures above 350 8C, the initial conversion of methanol over ZSM-22ACHTUNGTRENNUNG(173) (weight hourly space velocity (WHSV) = 2.05 h ) was 100 % and appreciable conversion took place for several hours (Figure 1 a) . However, at 350 8C, deactivation was very rapid. The feed rate in this case was lower than that used in previous studies: WHSV = 48 h 1 was used by Song and co-workers and WHSV = 10 h 1 was used by Li et al.

On the synthesis of erionite—offretite intergrowth zeolites

Abstract A partial exploration has been made of factors affecting crystallization of offretite—erionite type zeolites from aluminosilicate gels. The effect of the type of template-ion, the Si Al ratio and the Na K ratios in the gel, on offretite crystallization and on erionite inter-growth formation in offretite has been studied. The ionic contribution from the aluminium cation interaction is important for the stability of the structure. Therefore, offretite, which can adapt to more cations and crystallize with a higher Si Al ratio than erionite, forms more easily. The zeolites have been characterized using X-ray diffraction, scanning electron microscopy, EDX-analysis and chemical analysis.

In Situ Infrared Spectroscopic and Gravimetric Characterisation of the Solvent Removal and Dehydroxylation of the Metal Organic Frameworks UiO-66 and UiO-67

Herein, the desolvation, dehydroxylation and rehydroxylation of the metal organic frameworks UiO-66 and -67 are followed by in situ DRIFTS and TG–DSC. The spectra recorded on UiO-66 feature multiple bands corresponding to chemically inequivalent isolated hydroxyl groups, whereas UiO-67 has the expected single μ3-OH band from the Zr6O4(OH)4 cornerstone. Complete rehydration is demonstrated on both materials. Based on further experimental insights, hypotheses are given to explain the observed differences between UiO-66 and -67. Quantum chemical calculations are employed in order to deduce the feasibility of one possible explanation for the observed behaviour on UiO-66.

Chromium transport through Cr2O3 scales I. On lattice diffusion of chromium

Cr specimens preoxidized at 1100–1300°C to give Cr2O3 scales with varying thicknesses and microstructures have been treated at temperature in high vacuum. During the high vacuum treatment the specimens lose weight due to outward Cr transport through the Cr2O3 scales. The initial rate of weight loss gradually diminishes, but eventually the weight loss reaches a linear rate. Concurrently the Cr2O3 scale exhibits grain growth and densifies. It is concluded that the mode of outward chromium transport gradually changes during the high vacuum treatment: from lattice and grain-boundary diffusion and possibly vapor transport along microcracks during the initial stage to lattice diffusion only for the densified scales. It is concluded that chromium diffuses by an interstitial type mechanism. Self-diffusion coefficients of Cr in Cr2O3 at the Cr-Cr2O3 phase boundary have been calculated from the linear rates of chromium transport for different defect structure situations.

Sulfate-induced hot corrosion of nickel

Nickel specimens with layers of Na2SO4 deposited on the metal surface have been reacted in O2+4% SO2 in the temperature range 660–900°C. At temperatures from 671°C (the eutectic temperature of Na2SO4+NiSO4 liquid solutions) to 884°C (the melting point of Na2SO4), molten Na2SO4+NiSO4 is formed in the scales above critical pressures of SO3, and the molten sulfate causes accelerated hot corrosion of nickel. The rapid hot corrosion is preceded by an incubation period during which Na2SO4+NiSO4 solid solutions and eventually molten sulfate are formed. The critical SO3 pressures for formation of molten sulfate as a function of temperature have been delineated through experimental observations, and these are in agreement with theoretical estimates. When only solid solutions of Na2SO4+NiSO4 can be formed, the reactions are slower than specimens with no Na2SO4 layer. The reaction mechanism is concluded to involve inward transport of SO3/NiSO4 and of oxygen through the molten sulfate distributed as a network in the NiO layer of the outer part of the scale. Beneath the NiO/molten sulfate layer, the scale consists of NiO with a network of Ni3S2. Sulfur, present as (Ni-S)liq, is enriched at the metal/scale interface. Nickel diffuses outward through the Ni3S2 network in the inner layer to the boundary of the NiO/molten sulfate layer, where it reacts with the inwardly diffusing oxygen and SO3/NiSO4. The enrichment of sulfur next to the metal is concluded to be due to inward sulfur transport in the NiO+Ni-sulfide layer.