Jong San Chang

Energy-Efficient Dehumidification over Hierachically Porous Metal–Organic Frameworks as Advanced Water Adsorbents

Water sorption technologies are widely used commercially in many contexts, including industrial or indoor desiccant applications such as desiccant dehumidifiers, gas dryers, adsorptive air conditioning systems, fresh water production, adsorption heat transformation, etc.[1] In recent years, the potential for energy savings through improved efficiency has received increased attention, particularly as low-grade thermal energy or solar energy could be utilized. Currently, silica gel and zeolites are widely utilized commercially, often formed into corrugated honeycomb rotors.[1] As these sorbents typically must be heated above 150 °C during the desorption step, these sorbents are far from ideal in terms of energy consumption. There are additional issues with the level of dehumidification that these materials are able to achieve.[1] Improved energy efficiency requires advanced water adsorbents that can be regenerated together with the removal of a large amount of water vapor from humid conditions.[1] If such materials could operate at or below 80 °C, they could utilize readily available waste heat, leading to further energy savings. Among the existing classes of porous solids, crystalline metal–organic frameworks (MOFs)[2] are currently of great

Design of Hydrophilic Metal Organic Framework Water Adsorbents for Heat Reallocation

A new hydrothermally stable Al polycarboxylate metal-organic framework (MOF) based on a heteroatom bio-derived aromatic spacer is designed through a template-free green synthesis process. It appears that in some test conditions this MOF outperforms the heat reallocation performances of commercial SAPO-34.

Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites

Selective dinitrogen binding to transition metal ions mainly covers two strategic domains: biological nitrogen fixation catalysed by metalloenzyme nitrogenases, and adsorptive purification of natural gas and air. Many transition metal-dinitrogen complexes have been envisaged for biomimetic nitrogen fixation to produce ammonia. Inspired by this concept, here we report mesoporous metal-organic framework materials containing accessible Cr(III) sites, able to thermodynamically capture N2 over CH4 and O2. This fundamental study integrating advanced experimental and computational tools confirmed that the separation mechanism for both N2/CH4 and N2/O2 gas mixtures is driven by the presence of these unsaturated Cr(III) sites that allows a much stronger binding of N2 over the two other gases. Besides the potential breakthrough in adsorption-based technologies, this proof of concept could open new horizons to address several challenges in chemistry, including the design of heterogeneous biomimetic catalysts through nitrogen fixation.

Adsorptive separation of acetylene from light hydrocarbons by mesoporous iron trimesate MIL-100(Fe)

A reducible metal-organic framework (MOF), iron(III) trimesate, denoted as MIL-100(Fe), was investigated for the separation and purification of methane/ethane/ethylene/acetylene and an acetylene/CO2 mixtures by using sorption isotherms, breakthrough experiments, ideal adsorbed solution theory (IAST) calculations, and IR spectroscopic analysis. The MIL-100(Fe) showed high adsorption selectivity not only for acetylene and ethylene over methane and ethane, but also for acetylene over CO2 . The separation and purification of acetylene over ethylene was also possible for MIL-100(Fe) activated at 423 K. According to the data obtained from operando IR spectroscopy, the unsaturated Fe(III) sites and surface OH groups are mainly responsible for the successful separation of the acetylene/ethylene mixture, whereas the unsaturated Fe(II) sites have a detrimental effect on both separation and purification. The potential of MIL-100(Fe) for the separation of a mixture of C2 H2 /CO2 was also examined by using the IAST calculations and transient breakthrough simulations. Comparing the IAST selectivity calculations of C2 H2 /CO2 for four MOFs selected from the literature, the selectivity with MIL-100(Fe) was higher than those of CuBTC, ZJU-60a, and PCP-33, but lower than that of HOF-3.

Separation of p‐Divinylbenzene by Selective Room‐Temperature Adsorption Inside Mg‐CUK‐1 Prepared by Aqueous Microwave Synthesis

A new Mg(II) -based version of the porous coordination polymer CUK-1 with one-dimensional pore structure was prepared by microwave synthesis in water. Mg-CUK-1 is moisture-stable, thermally stable up to 500 °C, and shows unusual reversible soft-crystal behavior: dehydrated single crystals of the material selectively adsorb a range of organic molecules at ambient temperature and pressure. Both polar and apolar aromatic compounds, including pyridine, benzene, p-xylene, and p-divinylbenzene (p-DVB), are all readily adsorbed, while other isomers from complex mixtures of xylenes or DVBs are selectively excluded. The solvent-loaded structures have been studied by single-crystal X-ray diffraction. Time-dependent liquid sorption experiments using commercially available DVB demonstrate a high and rapid selective adsorption of p-DVB and exclusion of m-DVB and ethylvinylbenzene isomers.

Chemical Conversions of Biomass-Derived Platform Chemicals over Copper-Silica Nanocomposite Catalysts.

Biomass and biomass-derived carbohydrates have a high extent of functionality, unlike petroleum, which has limited functionality. In biorefinery applications, the development of methods to control the extent of functionality in final products intended for use as fuels and chemicals is a challenge. In the chemical industry, heterogeneous catalysis is an important tool for the defunctionalization of functionalized feedstocks and biomass-derived platform chemicals to produce value-added chemicals. Herein, we review the recent progress in this field, mainly of vapor phase chemical conversion of biomass-derived C4 -C6 carboxylic acids and esters using copper-silica nanocomposite catalysts. We also demonstrate that these nanocomposite catalysts very efficiently convert biomass-derived platform chemicals into cyclic compounds, such as lactones and hydrofurans, with high selectivities and yields.

Syntheses and applications of nanocatalysts based on nanoporous materials

Heterogeneous catalysis has always been an inherently nanoscopic phenomenon with important technological and societal consequences for energy conversion and the production of chemicals. In fact, catalysts have been reported to represent the oldest commercial application of nanotechnology. Nanocatalysts are generally defined as nanoscale materials that have at least one nanoscale dimension, or have been subjected to nanoscale structural modification in order to enhance their catalytic activity. They could be classified into four distinct types of catalysts: nanoparticulate, nanoporous, nanocrystalline, and supramolecular catalysts. Most catalysts have consisted of nanometre-sized particles dispersed on a high-surface-area support, but recent advances in synthetic methods are leading to increasingly precise control of the variables affecting catalyst activity and selectivity in the nanoporous catalyst. Widespread applications of nanoporous materials in the fields of catalysis, adsorption and separation have emphasised the need to search for new structures with new framework compositions. This contribution summarises recent results on the synthesis, characterisation, and catalytic performance of new nanoporous catalysts performed by the present authors.

Catalytic Combustion of Effluents from Methane-Based MCFC Device over Cordierite Supported Pd/La-Al2O3 Catalyst

Influence of steam, loading amounts of Pd (viz., 0.7, 2.1, 5.4 wt %) and other process parameters (viz. GHSV and temperature) on methane-based MCFC anodeeffluents over Pd-based La2O3-Al2O3 supported on honeycomb substrate have been investigated. TGA study reveals precise temperature of decomposition of Pd-O in catalytic combustion at high temperature. An increase in methane conversion at elevated temperature is attributable to decomposition of PdO to Pd active phase. The XRD analysis of spent catalysts suggests that the reflections corresponding to PdO gradually become weaker with increase in the Pd loading. The addition of 4% water in the feed decreases the methane conversion due to the reversible reaction of PdO with water adduct resulting in the formation of inactive Pd(OH)2 phase. However, the methane conversion remains unaffected and increases monotonously with 100% water concentration in the feed.

Reflectometry Studies of Mesoporous Silica Thin Films

Reflectometry technique has been successfully applied to investigate the correlation between the porosity and optical property (refractive index) of the ordered mesoporous thin film deposited on silicon wafer substrates. The measured optical spectra were simulated by the Effective Medium approximation model. The reflectometry technique has been found to be appropriate for the measurement of thickness of thin films as well as thick layer films. The mesoporous silica films prepared from tri-block copolymer (F-127) as a surfactant and polypropylene oxide as a swelling agent were subsequently exposed to the ammonia vapors to enhance thermal stability and shrinkage minimization of the film that results in increased film thickness.