CO2 Adsorption Measurements Research Articles

Lewis Acid Catalysis of TiO4 Tetrahedra on Mesoporous Silica in Water

TiO4-deposited mesoporous silica (TDMS) was studied as a water-tolerant solid Lewis acid catalyst. TDMS prepared by a simple postgrafting technique using Ti(i-pro)4 has a large BET surface area (ca. 450 m2 g–1) and ordered mesoporous structure. Ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray absorption near edge structure (XANES), and CO adsorption measurements with Fourier transform infrared (FTIR) spectroscopy revealed that isolated TiO4 tetrahedra on TDMS have Lewis acidity, even in the presence of water. Lewis acid centers on TDMS exhibit higher catalytic performance for the hydride transfer of pyruvaldehyde to lactic acid and the Mukaiyama-aldol condensation of benzaldehyde with 1-trimethylsilyloxy-cyclohexene in water than that of conventional heterogeneous and homogeneous Lewis acids, including scandium(III) triflate (Sc(OTf)3), which also works even in water. The high catalytic performance of TDMS can be attributed to Lewis acid catalysis of isolated TiO4 tetrahedra in water.

Nitrogen-Doped Carbons: Remarkably Stable Materials for CO2 Capture

Nitrogen-doped porous carbon (N-carbon) with high nitrogen content was synthesized by carbonization of an ionic liquid. The hydrothermal and chemical stability of N-carbon was investigated by treatment in flowing steam, pure CO2, dry air, and dry SO2 at 130 °C. CO2 adsorption measurements before and after the treatments showed that, even under such severe conditions, in comparison to typical adsorption–desorption cycling, N-carbon was found to be a remarkably stable material for CO2 capture.

Heteroatom-doped carbon gels from phenols and heterocyclic aldehydes: Sulfur-doped carbon xerogels

Sulfur-doped carbon xerogels were obtained through carbonization of resorcinol/2-thiophenecarboxaldehyde organic gels. The acid-catalyzed sol–gel polymerization of resorcinol and 2-thiophenecarboxaldehyde leads to organic gels whose morphology and texture is dependent on the amount of catalyst used. As a result, monolithic organic gels with sulfur content of up to 19.6wt.% and easily tailored properties can be produced. After carbonization, a substantial amount of sulfur is retained and porous carbon xerogels with S-content of up to 10wt.% are produced (at 800°C). Depending on the sol–gel synthesis conditions, monolithic S-doped carbon xerogels with controllable and enhanced mesoporosity, surface areas of up to 670m2/g and enhanced mechanical integrity were obtained. Additional KOH activation of the organic or carbon xerogels enables production of micro–mesoporous carbons with surface areas of up to 2550m2/g while retaining over 5wt.% of sulfur. Preliminary CO2 adsorption measurements were performed. On the basis of resorcinol/2-thiophenecarboxaldehyde gel synthesis a more general approach towards heteroatom-doped carbon gels is proposed: sol–gel polymerization of phenols and heterocyclic aldehydes. Thus a variety of heteroatom-doped porous carbon materials with a tailored pore texture and morphology are available via this procedure.

Effect of Ba and K addition and controlled spatial deposition of Rh in Rh/Al2O3 catalysts for CO2 hydrogenation

The effect of Ba and K addition to Rh/Al2O3 catalysts for CO2 hydrogenation was investigated. Catalysts with preferential deposition of 1wt% of Rh either on the alumina support or the Ba or K component were prepared by the two nozzle flame spray pyrolysis method and characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and scanning transmission electron microscopy. XRD and thermoanalysis combined with mass spectroscopy indicated that the Ba existed mainly as BaCO3, while K was present in the form of KHCO3 and KOH. DRIFTS combined with CO adsorption measurements revealed a strikingly different CO adsorption behavior of Ba- and K-containing catalysts.The pure Rh/Al2O3 catalyst as well as the Ba-containing catalysts showed a high selectivity to CH4 below 500°C with a maximum yield at 400°C. Above 400°C, the reverse water gas shift reaction leading to CO and H2O started to become dominant, in accordance with thermodynamics. In contrast, the K-containing catalysts produced no CH4, all CO2 was directly converted to CO in the entire temperature range (300–800°C). Preferential deposition of the Rh on the additive components (Ba, K) or the alumina support had comparably little effect on the catalytic behavior. The CO2 capturing additives, Ba and K, did not result in enhanced catalytic performance, probably due to the relatively high stability of the corresponding carbonates at the optimal reaction temperatures.

A dmp‐type Microporous Cadmium(II)‐Isonicotinate: Synthesis, Structure and CO2 Adsorption Property

AbstractThe 4‐connected dmp‐type cadmium(II)‐isonicotinate framework [Cd(isonic)2(H2O)]n·n(DMA) (1) (isonic = isonicotinate, DMA = N,N′‐dimethylacetamide) was obtained by the solvothermal reactions of Cd(NO3)2 and isonicotinic acid (Hisonic). Compound 1 features a 3D porous framework with the opened channels occupied by the lattice DMA molecules. Thermal analysis reveals that such framework remains much stable after removal the free DMA molecules. CO2 adsorption measurement shows that such framework exhibits notable CO2 adsorption behavior.

Direct synthesis of bi-modal porous structure MCM-41 and its application in CO2 capturing through amine-grafting

A bi-modal porous structure MCM-41 (BPS-MCM-41) was synthesized and functionalized by 3-[2-(2-Aminoethylamino)ethylamino]propyltrimethoxysilane (TRI); also, its performance in amine grafting and CO2 capturing was compared with that of pore-expanded MCM-41 [1]. To create larger pores beside the mesoporous structure of MCM-41, carbon black nanoparticles were used as the solid template. Characterizing the BPS-MCM-41 using the BET and BJH techniques resulted in the surface reduction of 29.3 percent and volume increase of 68.46 percent. The pore size distribution showed two peaks: a narrow peak at 2.24 nm diameter, which belonged to micelles, and a wide one at about 50 nm due to the presence of used nanoparticles. The functionalization confirmed that BPS-MCM-41 is capable of accommodating a large quantity of amine groups. The CO2 adsorption measurement indicated that internal volume of the adsorbent was a critical factor affecting the adsorption capacity of the amine grafted adsorbents.

An Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopic Study of Gas Adsorption on Colloidal Stearate-Capped ZnO Catalyst Substrate

Attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy has been applied in situ to study gas adsorption on a colloidal stearate-capped zinc oxide (ZnO) surface. Infrared spectra of a colloidal stearate-capped ZnO catalyst substrate were assigned at room temperature using zinc stearate as a reference compound. Heating was shown to create a monodentate species that allowed conformational change to occur, leading to altered binding geometry of the stearate ligands upon cooling. CO2 and H2 adsorption measurements demonstrated that the ligand shell was permeable and did not cover the entire surface, allowing adsorption and reaction with at least some portion of the ZnO surface. It has been demonstrated that stearate ligands did not prevent the usual chemisorption processes involved in catalytic reactions on a model ZnO catalyst system, yet the ligand-support system is dynamic under representative reaction conditions.

Synthesis of MOF-199 and application to CO2 adsorption

In this study a metal-organic framework (MOF-199) has been synthesized by solvent-thermal method. The conditions of preparation and activation processes have been investigated. The obtained material was characterized by methods of x-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimatric analysis (TGA) and scanning electron microscopy (SEM). The CO2 adsorption measurements were carried out on a high pressure volumetric analyzer (Micromeritics HPVA − 100). According to experimental results, Cu(NO3)2·3H2O has been shown to be the best copper(II) precursor for the synthesis of MOF-199 and N,N-dimethylformamide (DMF):C2H5OH:H2O with the ratio of 1:1:1 has been chosen as the most suitable solvent. The appropriate activation condition has been determined as follows: activate at 200 °C for 5 h and use CH3OH as the solvent to remove DMF. At the optimal conditions, an octahedral shape and three-dimensional (3D) structure of crystallite of MOF-199 was obtained. The synthesized MOF-199 expressed a high value of specific surface area (1448 m2 g−1 by Brunauer–Emmet–Teller (BET) method and 2028 m2 g−1 by Langmuir method) with Ta porous size of crystal of 11.8 Å and specific volume of 0.693 cm3 g−1; it was still stable up to 332 °C and its CO2 storage capacity reached to 206.59 cm3 (STP) g−1 at 25.76 bar.

Novel silica membrane material for molecular sieve applications

Development of new silica membranes properties, e.g., molecular sieving properties, has been increasingly gaining importance in the last few years. A novel unsupported silica membrane, referred to as hydrophobic metal-doped silica, was developed by cobalt-doping within the organic templated silica matrix. The novel material was prepared by the acid-catalyzed hydrolysis and condensation process of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES), which is the precursor for methyl ligand covalently bounded to the silica matrix. The synthesis and surface properties of the novel unsupported silica membrane as well as the unsupported blank silica and modified silica membranes were revealed by surface and microstructural techniques, such as water contact angle measurement, FTIR, X-ray, Solid-state 29Si MAS NMR, TGA and N2 and CO2 adsorption measurements. The results showed that the thermal stability of the organic templated silica matrix was enhanced by cobalt-doping process. A hydrophobic microporous silica membrane material with high thermal stability up to ∼560°C in oxidizing atmosphere and a narrow pore size distribution centered at 1.1nm was obtained. Therefore, a novel precursor material for molecular sieve silica membranes applications has been achieved and developed.

High selectivity of TiC-CDC for CO2/N2 separation

A series of carbide-derived carbons (CDC) have been prepared starting from TiC and using different chlorine treatment temperatures (500–1200°C). Contrary to N2 adsorption measurements at −196°C, CO2 adsorption measurements at room temperature and high pressure (up to 1MPa) together with immersion calorimetry measurements into dichloromethane suggest that the synthesized CDC exhibit a similar porous structure, in terms of narrow pore volume, independently of the temperature of the reactive extraction treatment used (samples synthesized below 1000°C). Apparently, these carbide-derived carbons exhibit narrow constrictions were CO2 adsorption under standard conditions (0°C and atmospheric pressure) is kinetically restricted. The same accounts for a slightly larger molecule as N2 at a lower adsorption temperature (−196°C), i.e. textural parameters obtained from N2 adsorption measurements on CDC must be underestimated. Furthermore, here we show experimentally that nitrogen exhibits an unusual behavior, poor affinity, on these carbide-derived carbons. CH4 with a slightly larger diameter (0.39nm) is able to partially access the inner porous structure whereas N2, with a slightly smaller diameter (0.36nm), does not. Consequently, these CDC can be envisaged as excellent sorbent for selective CO2 capture in flue-gas streams.

Macro‐ and Microkinetic Simulation of Diesel Oxidation Catalyst: Effect of Aging, Noble Metal Loading and Platinum Oxidation

AbstractIn automotive exhaust aftertreatment simulation, both macro‐ and microkinetic models are commonly used. In this contribution both models are applied for the simulation of diesel oxidation catalysts (Pt/γ‐Al2O3) with different catalyst loading and degree of thermal aging. The study proves that the structure insensitive kinetics of the considered catalysts can be described with the same rate equations only by scaling the rate constants of the different reaction steps with the catalytically active Pt surface, which is accessible by CO adsorption or light‐off measurements. In addition, NO oxidation is strongly influenced by a reversible, slow transformation of Pt into Pt‐oxide.

Construction of three-dimensional metal–organic frameworks in the presence of a tetrahedral ligand and a secondary bidentate linker

Three microporous coordination polymers, namely, [Co2L(DPE)]·2DMF·5H2O (1), [Zn2L(DPE)]·2.5DMF·2H2O (2) and [Cd(H2L)]·3DMF·3.5H2O (3), were solvothermally prepared in the presence of the flexible tetrahedral carboxylate ligand tetrakis[(4-carboxyphenyl)oxamethyl]methane acid (H4L) and a secondary bidentate linker (E)-1,2-di(pyridin-4-yl)ethane (DPE). Compounds 1 and 2 are isostructural and possess a 2-fold interpenetrating (4,4)-pts network. Compound 3 has a 3D structure with a uninodal 4-connected {4.85} topology. All the three compounds consist of large solvent-accessible voids, but only compounds 1 and 2 possess permanent porosity as confirmed by N2, CO2 and CH4 gas adsorption measurements. In addition, compounds 2 and 3 exhibited strong photoluminescent emissions at room temperature with a peak at 495 and 440 nm, respectively, owing to a ligand-centered excited state. The emission intensities of 2 varied upon contact with different solvents or analytes.

Construction of lanthanide metal–organic frameworks with highly-connected topology based on a tetrapodal linker

By using a rigid tetrapodal linker 4,4′,4′′,4′′′-silanetetrayltetrabenzoic acid (H4L) and lanthanide metal ions, three new coordination polymers, namely, [NdL(H2O)][NH2(CH3)2]·(DMF)x·(H2O)y (x ≈ 2, y ≈ 4) (1), [Eu4L3(H2O)6]·(DMF)y·(H2O)x (x ≈ 2, y ≈ 4) (2) and [Er4L3(H2O)6]·(DMF)x·(H2O)z (x ≈ 2, z ≈ 5) (3), were solvothermally synthesized and structurally characterized. Compound 1 is a 3D framework with a (4,8)-connected flu structure, built from distorted cuboid dinuclear neodymium–carboxylate building block and a 4-connected tetrahedral L ligand. Compounds 2 and 3 are isostructural, possessing a non-interpenetrated three-dimensional network with rare (4,4,12) highly-connected topology. In compounds 2 and 3, the fully deprotonated L4− ligands act as pseudotetrahedral 4-connecting nodes and S-shaped tetranuclear lanthanide metal–carboxylate building blocks act as 12-connecting nodes. Compound 1 possesses permanent porosity as confirmed by N2, H2, O2, CO2 and CH4 gas adsorption measurements.

Bi-porous metal–organic framework with hydrophilic and hydrophobic channels: selective gas sorption and reversible iodine uptake studies

A new three-dimensional (3D) bi-porous metal–organic framework (MOF), {[(Me2NH2)2]·[Cd3(5-tbip)4]·2DMF}n (1) (5-tbipH2: 5-tert-butylisophthalic acid) has been synthesized. The 5-tbip ligand containing a hydrophobic t-butyl group and hydrophilic carboxylate groups is used to synthesize the bi-porous framework. This 3D MOF contains two types of channels, a wide mouth hydrophilic channel of dimension 7.448 × 7.676 A2 and a narrow mouth hydrophobic channel of dimension 2.33 × 1.926 A2. Hydrophilic channels are lined with the orderly arranged dimethyl ammonium (DMA) cations which neutralize the anionic 3D framework. The guest-free form of the MOF (1′) showed interesting CO2 selectivity over other gases such as N2, CH4, and H2. Since the effective pore size of the desolvated compound 1′ (∼0.6 nm: from the pore size distribution curve of CO2 adsorption measurement) is much more than the kinetic diameter of all measured gases (CO2 = 3.3 A, CH4 = 3.76 A, N2 = 3.64 A and H2 = 2.8 A), selective capture of CO2 by 1′ could be ascribed to the strong electrostatic interaction of CO2 with the framework. Compound 1′ also shows reversible iodine uptake (1′ ⊂ 4I2: based on the sample weight measurements and TGA data) with visible color change of the compound. Interestingly, the iodine-loaded MOF showed ∼76 times increase in electrical conductivity compared to 1′.

Coordination Polymers of Copper and Zinc Ions with a Linear Linker Having Imidazole at Each End and an Azo Moiety in the Middle: Pedal Motion, Gas Adsorption, and Emission Studies

The imidazole donor ligand bis(4-imidazol-1-yl-phenyl)-diazene (azim) reacts readily with M(ClO4)2·6H2O [M(II) = Zn(II) and Cu(II)] salts at room temperature to afford {[Zn(azim)2]·(ClO4)2·3DMF}n (1) and {[Cu(azim)2(DMF)2]·(ClO4)2·2DMF}n (2) (DMF = N,N′-dimethylformamide). With MCl2·6H2O [M(II) = Zn(II) and Cu(II)] salts under solvothermal conditions, compounds {[Zn(azim)(HCOO)2]}n (3) and {[Cu(azim)(Cl)]}n (4) are obtained in moderate yields. Complexes 1 and 2 crystallize as 2D four-connected 44 sql networks with rectangular and rhombus grids, respectively. The frameworks are stabilized by an intricate array of hydrogen bonding interactions with guest molecules that also results in overall 3D frameworks. On the other hand, complexes 3 and 4 form 1D zigzag infinite chain structures. All compounds have been characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD) measurements. The TGA and PXRD measurements reveal that the integrity of the frameworks 1 and 2 is maintained upon guest removal. N2 and CO2 adsorption measurements were carried out for evacuated frameworks 1 and 2, and the adsorption studies show CO2 selectivity over N2 at low pressure in the case of 2. Interestingly, heat and guest induced bicycle pedal motion of the azo moiety can be observed in 1 and 4 without loss of crystallinity. Upon excitation at 304 nm, compounds 1–4 and 4′ exhibit solid-state luminescence at room temperature.

New insights into the development of Brønsted acidity of niobic acid

The development of Brønsted acidity and the relationship between acidity, catalytic performance and structure of niobium oxide were investigated for a series of samples prepared by calcination of niobic acid at temperatures between 423 and 823K. All solids were active for propan-2-ol dehydration. The Brønsted acidity was monitored by adsorption of lutidine and CO followed by FT-IR. Low temperature CO adsorption measurements showed that all solids exhibit essentially the same medium Brønsted acid strength. A direct relationship between the abundance of Brønsted acid sites monitored by lutidine adsorption followed by desorption at 523K and propan-2-ol dehydration activity was observed.

Combinatorial Synthesis and Characterization of Metal-Open Frameworks in Mild and Friendly Conditions: Application to CO2 Adsorption

Combinatorial screening using precipitation methods at room temperature can lead to a great diversity of carboxylate based Metal Organic Frameworks (MOFs) including already known or original porous solids. The investigation of the synthesis of MOFs in different solvent and solvent mixtures includes the use of solvents such as alcohols and tetrahydrofuran (THF) which would greatly facilitate large scale production. We also show the application of Principal Component Analysis (PCA) and clustering techniques on large libraries of XRD diffraction files in order to identify classes of similar phases and peculiar phases. The combinatorial screening of 105 samples in the La/btc system has led to the identification of two phases which are solvent depending. On the La(btc) compound, the CO₂ adsorption measurements reveal a guest-host interactions as supported by XRD phase transformation upon thermal treatment. The mass transport can be assigned to a "single file diffusion" regime due to the one dimensional channel porous structure associated to small pore size.

Synthesis of Pd nanoparticles on heteropolyacid-supported silica by a photo-assisted deposition method: an active catalyst for the direct synthesis of hydrogen peroxide

A simple and unique methodology to synthesize active Pd nanoparticles using Cs2.5H0.5PW12O40 heteropolyacid-supported silica (CsHPA/SiO2) under UV-light irradiation has been developed. By the photo-assisted deposition (PAD) method, a Pd2+ precursor in aqueous solution can be deposited and easily reduced by the [PW12O40]4− species generated by photolysis of [PW12O40]3− species in the presence of iPrOH as a sacrificial reagent, to afford nanosized Pd0 metal particles (Pd/CsHPA/SiO2). No direct Pd metal deposition was observed on either pure SiO2 without the CsHPA phase under UV-light irradiation or on CsHPA/SiO2 without UV-light irradiation. The catalytic activity for the direct synthesis of hydrogen peroxide (H2O2) using H2 and O2 gases under atmospheric pressure was strongly dependent on the preparation conditions, variation of CsHPA content, and the type of catalyst support. In addition, the Pd/CsHPA/SiO2 catalyst prepared by the PAD method exhibited significantly better activity than the conventionally prepared impregnation catalyst. The Pd surface area from CO adsorption measurements, and also the suppression of undesired side reactions were determined as the crucial factors to achieve efficient catalytic performance.

Facile strategy for synthesis of mesoporous crystalline γ-alumina by partially hydrolyzing aluminum nitrate solution

The facile synthesis of mesoporous γ-alumina is developed through the partial hydrolysis of Al(NO3)3 aqueous solution with (NH4)2CO3 without organic surfactants. In this synthesis, the stable NH4NO3/Al species (AN/Al) hybrid containing Keggin-Al13 polycations is first prepared, which is the key for the successful formation of mesoporous γ-alumina. XRD, 27Al MAS NMR, TEM, and N2 adsorption and desorption results demonstrate that the as-prepared AN/Al hybrid can be transformed to γ-alumina by treatment at 200 °C and exhibit a wormhole-like mesoporous structure with large surface area up to ∼450 m2 g−1, pore volume of ∼0.3 cm3 g−1 and narrow pore size distribution peaked at ∼3.9 nm after completely removing NH4NO3 at 300 °C. The obtained mesoporous γ-aluminas have high thermal stabilities up to 900 °C and excellent hydrothermal stability. The investigation shows that the synergetic effect of NH4NO3 and Al13 species promotes crystallization of Al species to γ-alumina, which may have a unique mechanism distinct from the mesoporous aluminas reported previously. CO2 adsorption measurements indicate that these mesoporous γ-aluminas have a much higher CO2 adsorption capacity than ordered mesoporous alumina synthesized by the surfactant-templating method and conventional γ-alumina derived from aluminum oxyhydroxides. We believe that this research should be useful for providing new insights into the transformation of transition alumina phases and for synthesizing mesoporous γ-alumina with promising properties for various chemical applications.

A robust microporous metal–organic framework constructed from a flexible organic linker for acetylene storage at ambient temperature

By using an octadentate ligand tetrakis[(3,5-dicarboxyphenoxy)methyl] methane (H8L), a new microporous metal–organic framework [Cu4L(H2O)4](H2O)31 (1) was solvothermally synthesized and structurally characterized. MOF 1 is built from the 4-connected square planar [Cu2(O2CR)4] cluster and 8-connected cube ligand L to have a highly open framework with scu topology. It possesses permanent porosity as confirmed by N2, H2, C2H2, CO2 and CH4 gas adsorption measurements and exhibits high acetylene storage of 193 and 154 cm3 g−1 at 273 and 296 K under 1 atm, respectively.