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The capture and storage of the greenhouse gas, CO2, has attracted much interest from scientists in recent years. In this work, density functional theory (DFT) was used to study the adsorption of CO2 in different cation-exchanged molecular sieves. The results show that for the monovalent metal (Li, Na, K, Cu) ion-exchanged molecular sieves (zeolite Y, ZSM-5, CHA and A), the adsorption capacities for CO2 decrease in the order of Li+ > Na+ > K+ > Cu+. Cu+-exchanged zeolites are not suitable as adsorbents for CO2. For the CO2 adsorption capacities in different zeolites with the same exchanged cation, the adsorption energy decreases in the order of Y > A > ZSM-5 ≈ CHA for Li-exchanged zeolites, and ZSM-5 still has the lowest CO2 adsorption energy for both Na- and K-exchanged zeolites. In the cation-exchanged Y zeolites with divalent metals (Be, Mg, Ca and Zn), the CO2 adsorption performance increases in the order of Zn2+ < Be2+ < Ca2+ < Mg2+. Thus, Zn2+-exchanged zeolites are not suitable as adsorbents for CO2.

The methanol-to-olefins (MTO) reaction over zeolite catalysts is very important for both fundamental research and industrial application to produce light olefins. In this study, the influences of the BrOnsted acid strength and pore size effect on the propene elimination in “hydrocarbon pool” (HCP) process over a series of zeolites are systematically investigated by density functional theory (DFT) calculations. The direct mechanism and indirect spiro mechanism with water as the proton transfer reagent in the propene elimination are considered. In the direct mechanism, the reactivity can be enhanced by increasing the acid strength. While, in the indirect mechanism, a moderate acidity is better. The indirect mechanism has a lower activation barrier than the direct one and thus is much more preferable. Because of the pore size effect, the SSZ-13 zeolite with the largest pore has the highest catalytic activity in the indirect mechanism. Following is the ZSM-5 zeolite. While, due to the serious steric hindrance, the reaction is hard to occur in the ZSM-22 zeolite with the smallest pore size.

In this paper, boron, sulfur and phosphor doped g-C3N4 materials (defined as CNBF, CNSF and CNPF, respectively) were successfully prepared by thermal copolymerization of dicyandiamide and imidazole ionic liquids. The CNBF catalysts exhibited significantly enhanced activity in various Knoevenagel condensation of aldehyde with malononitrile, which were typical base-catalyzed reactions, comparing with CNSF and CNPF catalysts. The detailed characterizations of Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), High angle annular dark field-scanning transmission electron microscopy (HADDF-STEM) and 11B solid-state MAS NMR showed that boron was evenly doped in tri-s-triazine rings of g-C3N4 by substituting the carbon sites. In addition, CO2 Temperature programed desorption (CO2-TPD) characterizations indicated that the basic site concentration of CNBF catalysts was proportional to the doped boron content. Excluding the effect of specific surface area, the catalytic activity of CNBF catalysts followed the order CNBF-0.1

Trimethylphosphine (TMP) has been adsorbed in carbon nanotubes and oxidized to trimethylphosphine oxide (TMPO). 31P spin–lattice relaxation T1 measurements at temperatures from 203 to 333 K have been employed to investigate the motions of TMPO. The 31P T1 is found to be monoexponential and isotropic. The activation energy is measured as 4.4 ± 0.3 kcal•mol−1, which is comparable to that of TMP adsorbed on Lewis acid sites in zeolites.

The influences of pore confinement and topology effect on ethylene dimerization over a series of zeolite, like HMOR, HZSM-5, HBEA and HMCM-22, have been systematically studied by density functional theory including dispersion interaction (DFT-D). Both of the stepwise and the concerted mechanisms are considered. Compared to the corresponding 8T models, the calculated activation energies are considerably reduced in the large models of zeolite due to the pore confinement effect. Moreover, the manners of ethylene dimerization are found to be related to the pore structure of zeolite catalyst. In stepwise mechanism, HMCM-22 shows better activity as suggested by the calculated activation energies. In concerted mechanism, the energy barriers in HBEA and HMCM-22 are much lower than that in HMOR and HZMS-5, indicting a better catalytic performance. By comparing the two mechanisms happened in one zeolite, we suggest that the concerted mechanism is preferable in HBEA, HMCM-22 and HMOR zeolite with large pores, while two mechanisms compete to each other in HZSM-5 with medium-size pores.

Combined GCMC and MD simulations have been used to investigate the adsorption and diffusion of Xe gases in carbon nanotubes (CNTs) at different conditions. The influences of several factors, such as temperature, pressure and diameter of the CNTs, on the adsorption structure and diffusion rate of Xe atoms have been comprehensively studied. The Xe atoms form an ordered helix structure in the cylindrical radial direction of the CNT, and move in a spiral way. The mean square displacement (MSD) increases with increasing the temperature, while it increases first and then decreases with increasing the pressure. The pore size has a considerable impact on both the structure and number of adsorbed molecules in the CNT, where a smaller pore size accounts for faster diffusion. The Xe atoms diffuse much faster in CNT than zeolite. In contrast to a Fickian motion in zeolite, a ballistic diffusion mechanism is followed in CNTs.

Information of adsorption and diffusion in nanoporous material is helpful to fundamentally understand nanocatalysis and gas sensors. In this work, the adsorption process of benzene in double-walled carbon nanotubes (DWNTs) at the very earliest stages was directly monitored for the first time by using in situ solid-state 13C NMR. The results indicate that benzenes in and out of DWNTs can be conveniently distinguished by 13C MAS NMR. The kinetics of the adsorption process was obtained by integrating the 13C peaks as a function of adsorption time. The kinetic could be interpreted with a model of opposing adsorption–desorption process and the kinetic curves could be satisfyingly fitted by an exponential function.

Functionalized carbon nanotubes (CNTs) play an important role as catalysts in several oxidation reactions. Active centers, present in a catalyst, are mainly associated with oxidizing functional groups. Therefore, determining the concentration of oxidizing centers from the various functional groups present on the surface of CNTs is very important, but it is yet to be achieved. In the present study, solid-state NMR SSNMR techniques were employed to study the adsorption behavior of trimethylphosphine (TMP) in CNTs using TMP as a probe molecule. The results show that TMP gets oxidized to TMPO (trimethylphosphine oxide). The concentration of oxidizing centers was also selectively measured in the order of sub-mmol per g, employing SSNMR. The oxidizing centers comprise a very small portion among the various functional groups present on the surface of CNTs. The concentration of oxidizing centers was found to increase as the degree of functionalization of CNTs increased. Further studies are required to understand the exact structure of oxidizing centers present in CNTs.

MIL-53(Cr) is a well-known and important metal-organic framework material. However, the long synthesis time of MIL-53(Cr) restricts its applications. Herein, we report a facile method to kinetically modulate the crystallization route and decrease the synthesis time of 72 to only 8 h by simply increasing the usage of HF.

Using multinuclear solid-state NMR in combination with probe molecule techniques, we examined the acidic property of SAPO-34 with different Si content. The results show that there are two kinds of Bronsted acid sites in SAPO-34 with the acid strength of one kind higher than that of ZSM-5. The Si species and their distribution in the framework depend on the Si content. A large amount of Si islands are formed when Si content is high, at lower Si content, only isolated Si(OAl)(4) species exists. The Si content has little effects on the Bronsted acid strength of SAPO-34, but does affect the acid concentration. (C) 2012 Elsevier Inc. All rights reserved.

Adsorption of 13C-enriched methanol in multiwalled carbon nanotubes (MWNTs) was systematically studied under well-controlled environment by 13C MAS NMR. The results of variable-pressure experiments indicate that the endohedral adsorption of methanol in carbon nanotubes (CNTs) is preferential over the exohedral adsorption. The exohedral adsorption does not occur until the endohedral adsorption saturates. The 13C chemical shift of endohedral methanol exhibits a large upfield shift due to the strong spatial diamagnetic shielding effect induced by the delocalized electrons of nanotubes under the influence of external magnetic field. The exohedral methanol is also shielded, but to a lesser extent. DFT calculations support these experimental results. The 13C spin–lattice relaxation times, T1, of endohedral and exohedral methanol were also measured, and they have different vapor pressure dependence at room temperature. Furthermore, variable-temperature experiments suggest that methanol molecules inside CNTs may ...

Based on an acidolysis reaction between titanium n-butoxide and carboxyl (COOH) groups, serial highly dispersed TiO(2) photocatalysts were successfully synthesized on COOH-modified mesoporous SBA-15 material. Even after calcined at 550 degrees C to improve the crystallization, the TiO(2)/SBA-15 products possessed high surface area above 400 m(2) g(-1) that should be attributed to the high porosity of mesoporous SBA-15 and the highly uniform COOH group distribution in mesopores. HRTEM images revealed that TiO(2) nanocrystals dispersed well on the surface of SBA-15. The pore channels were partly blocked by TiO(2) nanocrystals, resulting in a bimodal pore size distribution in TiO(2)/SBA-15 compared with SBA-15. XRD and Raman results disclosed the exclusive anatase phase of TiO(2) in the photocatalysts. With adjusting the molar ratio of COOH to TB, the TiO(2)/SBA-15 products displayed different photocatalytic performance using Rhodamine B as probe under UV light. (C) 2010 Elsevier B.V. All rights reserved.

To accomplish pH-controllable drug release on mesoporous carrier, one of the best ways is to graft stimuli-responsive organic molecules around mesopore outlets. In this work, the pH-responsive propyldiethylenetriamine groups (abbreviative phrase: multiamine chains) were grafted around mesopore outlets of mesoporous silica spheres (MSS) and expected to act as pH-responsive gates. To this end, three multiamine-grafted MSS (i.e., NM1, NM2, and NM3) were synthesized under different reaction temperatures and reaction times. The reaction temperature and time for multiamine grafting were 25 °C and 12 h for NM1, 100 °C and 1 h for NM2, and 100 °C and 12 h for NM3, respectively. Through systematic investigations of TEM, SEM, N(2) adsorption/desorption, TG, and (29)Si MAS NMR, it was found that NM3 had the highest grafting amount of multiamine chains. It was further confirmed that the multiamine chains around the pore outlets of NM3 played the role of "molecular switch" that could well control the transport of guest drug molecules. In contrast, the multiamine chains around the pore outlets of NM2 and NM3 did not show gate effect. The difference should be decided by the fact whether the grafting amount of multiamine chains around mesopore outlets were sufficient under determined reaction temperature and time. In the tests of in vitro drug release, multiamine-gated MSS (i.e., NM3) showed highly sensitive response to the solution pH. At high pH (pH 7.5), ibuprofen (IBU) in this carrier released rapidly and completely within 2 h; at low pH (pH 4.0 or 5.0), only a small part of the IBU (13 wt %) was slowly released from this carrier and the most of IBU was effectively confined in mesopores.

A novel phase transformation phenomenon that involves two successive phase transformation events was found for the first time in the synthesis of mesostructured aluminophosphate and studied by XRD, TEM, and multinuclear solid-state NMR techniques. The results showed that a hexagonal phase Hex and two lamellar phases, L1 and L2, were formed after hydrothermal treatment for 1, 3, and 50 h, respectively. The status of the surfactant was found to be arrayed interdigitated in a bilayer with a tilt angle in L1 phase but upright in L2 phase. A mechanism that the exciting of the alkane tail of the surfactant together with the condensation of aluminophosphate cooperatively promoted the phase transformation was proposed for the observed phenomenon. Additionally, a ZON microporous structure was found for the first time existing in the framework of the mesostructured aluminophosphate.

The phase transition process from a hexagonal to a lamellar mesostructured aluminophosphate was studied by multinuclear solid-state NMR techniques in combination with low-angle XRD and elemental analysis measurements. The XRD result showed that after hydrothermal treatment for 9 h, the initial hexagonal phase began to transform to a lamellar phase. it was also found by NMR that some initially formed aluminophosphate was hydrolyzed during the earliest 2 In of the hydrothermal treatment, and the inorganic aluminophosphate framework became more and more condensed during the phase transition. The organic surfactant mainly has a gauche conformation in the hexagonal phase, whereas it mainly has a trans conformation in the lamellar phase and is packed more compactly. The Br(-) anion is found to be involved in the phase transition and likely enters into the interface to compensate the lost of negative charges that generated by the condensation of the aluminophosphate. Finally, a mechanism for the phase transition is proposed. (C) 2009 Elsevier Inc. All rights reserved.

Mesoporous silica spheres with controllable particle size were synthesized in mixed ethanol–water solvent. These materials possessed same pore size distribution and pore channel geometry. The amount of ibuprofen (IBU) adsorbed in mesoporous channels increased with the surface area of mesoporous silica spheres. Three kinds of release fluids, simulated intestinal fluid (SIF, pH = 7.4), simulated body fluid (SBF, pH = 7.4), and simulated gastric fluid (SGF, HCl aqueous solution, pH = 1.2) were used to investigate drug release. The effects of particle size and dispersancy of mesoporous spheres on drug release rate were discussed in detail. It was found that larger or agglomerate mesoporous silica spheres could delay the drug release process, which could be attributed to pore-mouth amount and mesopore channel length of mesoporous spheres. Furthermore, to obtain a well controlled drug release system, hydrophobic trimethylsilyl (TMS) groups were functionalized on the surface of mesoporous silica spheres. The release of IBU from TMS-functionalized mesoporous spheres was obviously delayed with the increase of TMS content.

Serial of trimethylsilyl-carboxyl bifunctionalized SBA-15 (TMS/COOH/SBA-15) have been studied as carriers for controlled release of drug famotidine (Famo). To load Famo with large capacity, SBA-15 with high content of carboxyl groups was successfully synthesized by one-pot synthesis under the assistance of KCl. The mesostructure of carboxyl functionalized SBA-15 (COOH/SBA-15) could still be kept even though the content of carboxyl groups was up to 57.2%. Increasing carboxyl content Could effectively enhance the loading capacity of Famo. Compared with pure SBA-15, into which Famo could be hardly adsorbed, the largest drug loading capacity of COOH/SBA-15 Could achieve 396 9 mg/g The release of.. Famo from mesoporous Silica Was Studied ill simulated intestine fluid (SIF, pH = 7.4). For COOH/SBA-15, the release rate of Famo decreased with narrowing pore size. After grafting TMS groups Oil the Surface of COOH/SBA-15 with hexamethyldisilazane, the release of Famo was greatly delayed with the increasing content of TMS groups. (C) 2008 Elsevier Inc. All rights reserved.

A comprehensive study has been made to probe the spatial proximities among different acid sites in dealuminated H-Y zeolites modified with various degrees of calcination, steam, and acid treatments by using a variety of different solid-state NMR techniques, including multinuclear MAS NMR and two-dimensional 1H double-quantum (DQ) MAS NMR spectroscopy. The effects of dealumination treatments on the nature, concentration, and location of extraframework Al species in H-Y zeolites were followed by 1H DQ MAS NMR of hydroxyl protons in conjunction with 1H, 27Al, and 29Si MAS NMR results. It was found that the extraframework AlOH species (Lewis acid sites) are always in close proximity to the bridging AlOHSi hydroxyls (Bronsted acid sites) on the framework of dealuminated H-Y zeolites prepared by thermal and hydrothermal treatments, indicating the presence of a Bronsted/Lewis acid synergy effect. However, such an effect is absent in acid-treated H-Y zeolites, as also confirmed by 13C CP/MAS NMR of adsorbed 2-13C...

Solid-state NMR techniques have been employed to investigate the surface acidic properties of TiO(2) and sulfated TiO(2), as well as their photocatalytic activities toward 2-propanol. The multinuclear MAS NMR experiments clearly revealed that three different types of Bronsted acid sites with much stronger acid strength were generated after the sulfation of TiO(2). Due to the enhanced Bronsted acidity, the protonation of 2-propanol can occur more easily, preferentially leading to the formation of Ti-bound 2-propoxy species on the SO(4)(2-)/TiO(2) catalyst. The 2-propoxy species can be directly converted to CO(2) and thus the photocatalytic activity of sulfated TiO(2) catalyst is remarkably enhanced. For comparison, both hydrogen-bonded 2-propanol and Ti-bound 2-propoxy species are present on the TiO(2) catalyst with the former being predominant. The hydrogen-bonded 2-propanol species are oxidated into acetone molecules that are difficult to further convert into CO(2), and the conversion of 2-propoxy species to 2-propanol hampers the direct mineralization of 2-propoxy species on the TiO(2) catalyst.

In order to disclose the dominant interfacial interaction between amino acids and ordered mesoporous materials, the adsorption behaviors of five amino acids on four mesoporous materials were investigated in aqueous solutions with adjustable amino acid concentration, ion strength, and pH. The selected amino acids were acidic amino acid glutamic acid (Glu), basic amino acid arginine (Arg), and neutral amino acids phenylalanine (Phe), leucine (Leu), and alanine (Ala), and the selected mesoporous materials were SBA-15, Al-SBA-15, CH3(10%)-SBA-15, and CH3(20%)-SBA-15. The adsorption capacities of Glu and Arg were strongly dependent on pH and surface charge of the mesoporous adsorbent. The adsorption of Phe showed pH insensitivity but depended on the surface organic functionalization of mesoporous adsorbent. On the basis of the theoretical analysis about the interaction between amino acid and adsorbent, such a remarkable difference was attributed to the different nature of the interaction between amino acid and adsorbent. Arg could be readily adsorbed on the surface of SBA-15, especially Al-SBA-15, under appropriate pH in which the electrostatic interaction was predominant. The driving force of Phe adsorption on mesoporous adsorbent mainly came from the hydrophobic interaction. Therefore, the adsorption capability of Arg decreased with increasing ion strength of solution, while the adsorption capability of Phe increased with the increasing degree of CH3 functionalization on SBA-15. For neutral amino acid Phe, Ala, and Leu, the adsorption capability increased with the increase of the length of their side chains, which was another evidence of hydrophobic effect. Thus, all the adsorption of amino acids on mesoporous silica materials can be decided by the combined influence of two fundamental interactions: electrostatic attraction and hydrophobic effect.

yMorphology control of silicalite-1 (Si-MFI) crystals was achieved by employing microwave-assisted solvothermal synthesis in the reaction system TEOS-TPAOH-alcohol using dipolar alcohols as a co-solvent. The influences of various experimental parameters, such as dielectric parameters of the alcohols, aging time, and the amount of the alcohols in the reaction mixture on the morphology of the resulting Si-MFI crystals were investigated. Our studies show that self-stacked Si-MFI crystals could be prepared by using alcohols with low dielectric constants as a co-solvent with short aging time and high concentration in the reaction mixture under microwave radiation. The resulting products were further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Si-29 MAS NMR analyses. (C) 2007 Elsevier Inc. All rights reserved.

Using trimethylphosphine(TMP) and d(5)-pyridine (deuterated pyridine) as the basic probe molecules, the concentrations of Bronsted acid sites on both HY zeolite and dealuminated HY zeolite have been quantitatively determined using solid-state H-1 and P-31 magic-angle spinning (MAS) NMR. After the adsorption of the probe molecules, the concentration of Bronsted acid sites on the dealuminated HY zeolite increases by about 25%, whereas the parent HY sample remains almost unchanged. The increase in the concentration of Bronsted acid sites is due to the appearance of base-induced Bronsted acid sites in the dealuminated HY zeolite. The terminal SiOH in the vicinity of the aluminum atom is "induced" to form a bridging hydroxyl group (SiOHAl) in the presence of the basic probe molecules. The mechanism of formation of the induced Bronsted acid sites has also been discussed.

The intactness and spatial proximity of acid and base groups in bifunctional mesoporous SBA-15 has been studied by various NMR techniques. The NMR results show that Bronsted acid and Lewis base groups coexist peacefully on the surface of the same support and maintain their acidity and basicity, respectively. Meanwhile, the acid groups and the base groups are in close proximity with suitable distance.

Extra-framework aluminium (EFAL) species in hydrated dealuminated HY zeolite were thoroughly investigated by various two-dimensional solid-state NMR techniques as well as density functional theoretical calculations. (27)Al MQ MAS NMR experiments demonstrated that five-coordinated and four-coordinated extra-framework aluminium subsequently disappeared with the increase of water loading, and the quadrupole interaction of each aluminium species decreased gradually during the hydration process. (1)H double quantum MAS NMR revealed that the EFAL species in the hydrated zeolite consisted of three components: a hydroxyl AlOH group, and two types of water molecule (rigid and mobile water). (1)H-(27)Al LG-CP HETCOR experiments indicated that both the extra-framework and the framework Al atoms were in close proximity to the rigid water in the fully rehydrated zeolite. The experimental results were further confirmed by DFT theoretical calculations. Moreover, theoretical calculation results further demonstrated that the EFAL species in the hydrated zeolite consisted of the three components and the calculated (1)H NMR chemical shift for each component agreed well with our NMR observations. It is the rigid water that connects the extra-framework aluminium with the four-coordinated framework aluminium through strong hydrogen bonds.

We demonstrate here a concept that chemical reactions can be enhanced by utilizing the confined hydrophobic environment of carbon nanotube (CNT) channels to separate products from reactants during a reaction and hence shift the reaction equilibrium. Taking the hydroxylation of benzene to phenol as an example, we observed that benzene is enriched inside CNT channels while the product phenol was discriminatively expelled out of the channels, as shown by solid state NMR studies. Consequently, the reaction over a CNT-confined Re catalyst exhibited a 4 times higher activity than the same catalyst dispersed on the outer walls of the same CNTs. The effect of this selective enrichment of benzene on the reaction was further confirmed by varying the amount of benzene in the reaction over commercial activated carbon-supported catalyst. CNT channels discriminating hydrophobic from hydrophilic molecules are expected to be a general feature. It is of significance for many synthetic organic processes involving molecules with different hydrophobicity in the reactants and products.