Organogermanium reactive intermediates. The direct detection and characterization of transient germylenes and digermenes in solution

Diphenylgermylene (Ph2Ge) and its Ge=Ge doubly bonded dimer, tetraphenyldigermene (6a), have been characterized directly in solution for the first time by laser flash photolysis methods. The germylene is formed via (formal) cheletropic photocycloreversion of 3,4-dimethyl-1,1-diphenylgermacyclopent-3-ene (4a), which is shown to proceed in high chemical (>95%) and quantum yield (phi = 0.62) by steady-state trapping experiments with methanol, acetic acid, isoprene, and triethylsilane. Flash photolysis of 4a in dry deoxygenated hexane at 23 degrees C leads to the prompt formation of a transient assigned to Ph2Ge (lambda(max) = 500 nm; epsilon(max) = 1650 M(-1) cm(-1)), which decays with second-order kinetics (tau approximately 3 micros), with the concomitant growth of a second transient species that is assigned to digermene 6a (tau approximately 40 micros; lambda(max) = 440 nm). Analogous results are obtained from 1,1-dimesityl- and 1,1-dimethyl-3,4-dimethylgermacyclopent-3-ene (4b and 4c, respectively), which afford Mes2Ge (tau approximately 20 micros; lambda(max) = 560 nm) and Me2Ge (tau approximately 2 micros; lambda(max) = 480 nm), respectively, as well as the corresponding digermenes, tetramesityl- (6b; lambda(max) = 410 nm) and tetramethyldigermene (6c; lambda(max) = 370 nm). The results for the mesityl compound are compared to the analogous ones from laser flash photolysis of the known Mes2Ge/6b precursor, hexamesitylcyclotrigermane. The spectra of the three germylenes and two of the digermenes are in excellent agreement with calculated spectra, derived from time-dependent DFT calculations. Absolute rate constants for dimerization of Ph2Ge and Mes2Ge and for their reaction with n-butylamine and acetic acid in hexane at 23 degrees C are also reported.     

Multicolor Photoluminescence in ITQ-16 Zeolite Film

Exploring the native defects of zeolites is highly important for understanding the properties of zeolites, such as catalysis and optics. Here, ITQ-16 films were prepared via the secondary growth method in the presence of Ge atoms. Various intrinsic defects of ITQ-16 films were fully studied through photoluminescence and FTIR characterizations. It was found that both the as-synthesized and calcined ITQ-16 films displayed multicolor photoluminescence including ultraviolet, blue, green and red emissions by exciting upon appropriate wavelengths. The results indicate that Si-OH and non-bridging oxygen hole centers(NBOHCs) are responsible for the origin of green and red emissions at 540-800 nm, while according to a variety of emission bands of calcined ITQ-16 film, blue emission bands at around 446 and 462 nm are attributed to peroxy free radicals(≡SiO₂·), ultraviolet emissions ranging from 250 nm to 450 nm are suggested originating from a singlet-to-triplet transition of two-fold-coordinated Si and Ge, respectively.     

Synthesis and structure determination of a new microporous zeolite with large cavities connected by small pores

A new small-pore germanosilicate zeolite, named as ITQ-49, has been synthesized using a new ditetraalkylphosphonium dication as an organic structure-directing agent, and its structure has been solved by direct methods applied to the powder X-ray diffraction pattern of the calcined solid. This new zeolite crystallizes in the space group Immm with cell parameters a = 19.6007(8) ?, b = 18.3274(7) ?, and c = 16.5335(6) ?. The pore topology of ITQ-49 consists of large, nonspherical cavities that are connected to each other through small eight-membered-ring windows, resulting in a unidirectional small-pore zeolite that has a relatively large adsorption capacity. Also, ITQ-49 contains double four-membered-ring units where Ge is preferentially located, and fluoride anions are placed inside these units.     

Synthesis and Structure Determination of SCM-15: A 3D Large Pore Zeolite with Interconnected Straight 12×12×10-Ring Channels

A new germanosilicate zeolite named SCM-15 (Sinopec Composite Material No. 15), the first zeolite containing a 3-dimensional (3D) channel system with interconnected 12-, 12-, and 10-ring channels (pore sizes: 6.1×7.2, 6.1×7.4, and 5.2×5.9 Å), has been synthesized using neutral 4-pyrrolidinopyridine as organic structure-directing agents (OSDAs). Its structure has been determined by combining single-crystal electron diffraction (SCED) and synchrotron powder X-ray diffraction (SPXD) data. The unique open framework structure of SCM-15 is related to that of FOS-5 ( BEC ), ITQ-7 ( ISV ), PKU-16 ( POS ), ITQ-26 ( IWS ), ITQ-21, Beta polymorph B, and SU-78B, since all these framework structures can be constructed from similar chains which are connected through shared 4-ring or double 4-ring (d4r) units. Based on this relation, six topologically reasonable 3D large or extra-large pore hypothetical zeolites are predicted.     

The observation of the first vibrational overtone of dihydrogen in the luminescence of zeolites at low temperatures

Dehydrated zeolites NaA, NaY, and barium-exchanged NaY luminesce when irradiated with the 1064 nm laser light of an FT-Raman instrument. When hydrogen is adsorbed in the zeolite, the luminescence is altered in several ways. Most remarkable is the appearance of "absorptions" in the positions of the first vibrational overtones of H(2) and HD. Although these features are in the expected positions with reasonable band profiles for overtone absorptions, the large extinction of the luminescent intensity requires a more efficient mechanism than simple reabsorption of emitted photons. In addition to the appearance of holes in the luminescence spectrum, other luminescent features are substantially quenched by the presence of hydrogen or, in one case, augmented.     

Esterification of Oleic Acid to Produce Biodiesel over 12-Tungstophosphoric Acid Anchored Two-dimensional Zeolite

Biodiesel has emerged as a non-toxic, biodegradable, and renewable fuel substitute that can be readily produced via the esterification reaction of free fatty acids. The present work explores the potential of 12-tungstophosphoric acid(TPA) anchored two-dimensional(2D) ITQ-2 zeolite(TPA/ITQ-2) as heterogeneous acid catalysts for biodiesel production. TPA/ITQ-2 material was prepared by swelling, delamination, and subsequent wetness incipient impregnation approach. The prepared catalysts were comprehensively characterized by powder X-ray diffraction, N₂ adsorption/desorption, temperature-programmed desorption of ammonia, flou-rier transform infrared spectroscopy, and transmission electron microscopy. The catalytic activity of TPA/ITQ-2 for biodiesel production was evaluated by the esterification reaction of oleate acid with methanol. Process parameters, such as reactant molar ratio and TPA loading were optimized. Due to the superior mass transfer and adequate stable acid sites, 2D TPA/ITQ-2 showed a higher catalytic activity and a better recyclable stability than the 3D and layered TPA/zeolites. This work will provide new opportunities for the design of 2D zeolite-based acid catalysts for biodiesel production.     

Toward inorganic electrides

Electrides are materials in which alkali metals (Li through Cs) ionize to form bound alkali cations and "excess" electrons. The electrons reside in large cavities or channels or both in the host lattice. We report here the first synthesis of thermally stable inorganic electrides with cation-to-electron ratios of 1:1 as in organic electrides. Although alkali metal adducts to alumino-silicate zeolites are well known, the cation-to-electron ratio is generally 3:1 or greater because these zeolites contain alkali cations prior to incorporation of the alkali metal. In this work, two pure silica zeolites, ITQ-4and ITQ-7, with pore diameters of approximately 7 A, absorb up to 40 wt % cesium from the vapor phase (even at room temperature). The other alkali metals (except Li) can also be introduced at elevated temperatures. The optical and magnetic properties of the cesium-loaded samples suggest ionization to form Cs+ and e- with substantial electron-spin pairing. The metal-loaded samples are stable to at least 100 degrees C and are able to reduce small aromatic molecules such as benzene and naphthalene to the radical anions within the pores of the zeolite.     

Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH,IWW, and UTL by Substitution of Ge for Al

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post‐synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites ( ITH , IWW , and UTL ) on the post‐synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2–13) and IWW (Si/Ge=3–7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra‐large pore zeolite UTL (Si/Ge=4–6) the hydrolysis of the interlayer Ge?O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two‐step degermanation/alumination procedure by the partial post‐synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.     

Synthesis design and structure of a multipore zeolite with interconnected 12- and 10-MR channels

A new molecular sieve, ITQ-38, containing interconnected large and medium pores in its structure has been synthesized. The rational combination of dicationic piperidine-derivative molecules as organic structure directing agents (OSDAs) with germanium and boron atoms in alkaline media has allowed the synthesis of ITQ-38 zeolite. High-resolution transmission electron microscopy (HRTEM) has been used to elucidate the framework topology of ITQ-38, revealing the presence of domains of perfect ITQ-38 crystals as well as very small areas containing nanosized ITQ-38/ITQ-22 intergrowths. The structure of ITQ-38 is highly related to ITQ-22 and the recently described polymorph C of ITQ-39 zeolite. It shares a common building layer with ITQ-22 and contains the same building unit as the polymorph C of ITQ-39. All three structures present similar framework density, 16.1 T atoms/1000 ?(3).     

Dihydrophenanthrene-type intermediates during photoreaction of trans-4'-benzyl-5-styrylfuran

[structure: see text] Photoreaction of trans-4'-benzyl-5-styrylfuran (trans-BSF) has been studied by the 355-nm laser flash photolysis (LFP) in CH2Cl2 using a Nd3+:YAG laser (30 ps, 5 mJ pulse(-1) or 5 ns, 30 mJ pulse(-1)). Transient fluorescence and absorption spectra assigned to the singlet excited trans-BSF were observed during the 30-ps LFP, whereas a transient absorption spectrum with two peaks at 400 and 510 nm, assigned to the trans-fused dihydrophenanthrene (DHP)-type intermediate (DP1), was observed during the 5-ns LFP. It is clearly suggested that a two-photon absorption process is involved in the formation of DP1. The first photoreaction is the photoisomerization of trans-BSF, which occurs to give cis-BSF. The second photoreaction process is photocyclization of cis-BSF, which occurs to give DP1 decaying with the half lifetime (tau1/2) of 2.8-4.0 micros to produce another DHP-type intermediate (DP2) with an absorption peak at 400 nm in the absence of O2, through [1,9]-hydrogen shift. DP2 decayed with tau1/2 > 500 micros to give the product through aromatization. In O2-saturated CH2Cl2, DP1 decayed with tau1/2 = 250 ns to give a radical intermediate (X) with two peaks at 410 and 510 nm, through hydrogen abstraction of DP1 by O2. X decayed with tau1/2 = 150 micros to give the product through successive hydrogen abstraction.     

Synthesis, characterization, and framework heteroatom localization in ITQ-21

ITQ-21 has been synthesized in a wide range of compositions. By rationally modifying the synthesis variables and zeolite composition, it is possible to fine-tune the crystallite size from nanocrystals (<80 nm) up to microns and to avoid the competition of other phases such as CIT-5, SSZ-24, or a laminar phase that can also be synthesized with the same organic structure directing agent. By means of XRD and (19)F MAS NMR, Ge and Si have been localized among the different crystallographic positions, and it is shown that Ge preferentially occupies T1 positions at the D4R cages, avoiding formation of Ge-O-Ge pairs. However, at high Ge loadings (Si/Ge = 1.7), a new (19)F MAS NMR signal at -14 ppm has been observed and assigned to the presence of Ge-O-Ge in Ge-rich D4R cages. Energetic configurations obtained by theoretical calculations fully agree with experimental observations, with the following increasing order in energy for Ge substitution: T1 < T2 < Ge-O-Ge in T1 < T3.     

Pure silica ITQ-32 zeolite allows separation of linear olefins from paraffins

ITQ-32 is able to separate propene from propane and represents a clear improvement with respect to previous zeolites in achieving the separation of trans-2-butene and 1-butene from the C(4) fraction using only one zeolite.     

Evidence for through-framework electron transfer in intrazeolite photochemistry. Case of Ru(bpy)3(2+) and methylviologen in novel delaminated ITQ-2 zeolite

A sample of novel delaminated zeolite ITQ-2 containing Ru(bpy)3(2+) on the external cups and MV2+ included in the independent and not connected channels has been prepared; emission and time-resolved laser flash photolysis has shown unambigously that photoinduced electron transfer from Ru(bpy)3(2+) to MV2+ occurs through the zeolite framework.     

A simplified model of the ECD

A simplified model of the ECD is presented, which is based on the assumption that only a change in the concentration of electron is generating a signal. The model allows to determine four different time constants related to: the collection of electrons (tau(1)), the loss of electrons in the capture process by the impurity molecules (tau(2)), the loss of sample molecules by electron capture (tau(n)) and the removing rate of molecules from the detector volume by the carrier gas (tau(v)). The values of these time constants have been estimated to be in the range of micros for tau(1), ms for tau(2), a part of a second for tau(n) and a few seconds for tau(v). The electron capture efficiency coefficient (p) and the detection coefficient (S(d)) have been defined. These coefficients serve in the model for the coulometric calculation of the mass of analyzed compounds, if the detector works using the conditions described.     

MCM-22和ITQ-2分子筛负载型催化剂加氢裂化性能的对比研究

 以MCM-22和ITQ-2分子筛为载体, WNi为活性组分,制得两种负载型催化剂,考察了两种催化剂的加氢裂化性能,并通过N2吸附、氨程序升温脱附和原位红外光谱对催化剂进行了表征. 减压瓦斯油加氢裂化反应结果表明, WNi/ITQ-2的加氢裂化活性高于WNi/MCM-22, 并且前者的反应温度相对较低. WNi/ITQ-2具有高催化活性是因为ITQ-2分子筛具有空旷的次级结构和较多的可接近的酸性位; 中油选择性高是因为空旷的次级结构使裂化产物快速离开酸性位而避免了二次裂化.     

Study of the interaction between triplet riboflavin and the alpha-, betaH- and betaL-crystallins of the eye lens

Time-resolved photolysis studies of riboflavin (RF) were carried out in the presence and absence of alpha-, betaH- and betaL-crystallins of bovine eye lens. The transient absorption spectra, recorded 5 micros after the laser pulse, reveal the presence of the absorption band (625-675 nm) of the RF neutral triplet state (tau = 42 micros) accompanied by the appearance of a long-lived absorption (tau = 320 micros) in the 500-600 nm region due to the formation of the semireduced RF radical. The RF excited state is quenched by the crystallin proteins through a mechanism that involves electron transfer from the proteins to the flavin, as shown by the decrease of the triplet RF band with the concomitant increase of the band of its semireduced form. Tryptophan loss on RF-sensitized photooxidation of the crystallins when irradiated with monochromatic visible light (450 nm) in a 5% oxygen atmosphere was studied. A direct correlation was found between the triplet RF quenching rate constants by the different crystallin fractions and the decomposition rate constants for the exposed and partially buried tryptophans in the proteins. The RF-sensitized photooxidation of the crystallins is accompanied by the decrease of the low molecular weight constituents giving rise to its multimeric forms. A direct correlation was observed between the initial rate of decrease of the low molecular weight bands corresponding to the irradiated alpha-, betaH- and betaL-crystallins and the quenching constant values of triplet RF by the different crystallins. The correlations found in this study confirm the importance of the Type-I photosensitizing mechanism of the crystallins, when RF acts as a sensitizer at low oxygen concentration, as can occur in the eye lens.     

Synthesis of a new zeolite structure ITQ-24, with intersecting 10- and 12-membered ring pores

A new 10- and 12-membered ring zeolite, named ITQ-24, has been synthesized, and its structure has been solved. It has been found that this zeolite structure is topologically identical to that proposed for the hypothetical polymorph C of the SSZ-33/SSZ-26/CIT-1 family. This new zeolite has been achieved by using a rational approach of introducing Ge in the framework that has a directing effect toward zeolite structures with double-four-membered rings as secondary building units. Notoriously, active catalytic centers, such as Ti and Al, have been incorporated into this new zeolite, demonstrating that it is catalytically active for alkylation of aromatics.     

Photoinduced Formation and Characterization of Electron–Hole Pairs in Azaxanthylium‐Derivatized Short Single‐Walled Carbon Nanotubes

2‐Azaxanthone, a nitrogenated derivative of the well‐studied organic chromophore xanthone, has been covalently bound through 2‐(ethylthio)ethylamido linkers to the carboxylic acid groups of short, soluble single‐walled carbon nanotubes (CNTs) of 450 nm average length, and the resulting azaxanthylium‐functionalized CNTs (AZX‐CNT, 8.5 wt % AZX content) characterized by solution ¹H NMR, Raman and IR spectroscopy and thermogravimetric analysis. Comparison of the quenching of the triplet excited state of AZX (steady‐state and time‐resolved) and of the transient optical spectra of CNTs and AZX‐CNT shows that the covalent linkage boosts the interaction between the azaxanthylium moiety and the short CNT units. The triplet excited state of the azaxanthylium derivative is quenched by CNT with and without covalent bonding, but when it is covalently bonded, the singular transient spectrum is compatible with the photogeneration of electron holes through electron transfer from CNT to excited azaxanthylium units.     

Effects of ITQ-21 and ITQ-24 as zeolite additives on the oil products obtained from the catalytic pyrolysis of waste tire

The effects of ITQ-21 and ITQ-24 as zeolite additives on the catalytic pyrolytic oil using HMOR were investigated. The research was started by studying the effect of HMOR and its amount represented by the catalyst-to-tire ratio, and then followed by the effects of addition of the two ITQ zeolites into HMOR. The results showed that, with increasing the catalyst-to-tire ratio, the gasoline and kerosene yield increased in accordance with the reduction of the heavier fractions, and the concentration of the saturated hydrocarbons in the pyrolytic oil was found to be higher. However, increasing the catalyst-to-tire ratio decreased the yield of liquid product. The two ITQ zeolite additives have strong effects on the pyrolytic oil. For example, as compared with the case of pure HMOR, adding ITQ-21 enhanced the production of kerosene whereas the introduction of ITQ-24 resulted in the higher concentration of aromatic compounds in the derived oil. In addition, the use of catalyst was found to enhance the selectivity of mono-aromatic in the light fraction, but adding ITQ zeolites caused a reduction in the selectivity of HMOR toward the production of mono-aromatics. The differences on the effects of the two ITQ zeolites were explained in relation with the catalyst characterization results. It was found that, the acid properties and topology played very important roles on the influences of these additives.     

Hot-Electron Photodynamics in Silver-Containing BEA-Type Nanozeolite Studied by Femtosecond Transient Absorption Spectroscopy

Silver cations were introduced in nanosized BEA-type zeolite containing organic template by ion-exchange followed by chemical reduction towards preparation of photoactive materials (Ag⁰-BEA). The stabilization of highly dispersed Ag⁰ nanoparticles with a size of 1–2 nm in the BEA zeolite was revealed. The transient optical response of the Ag-BEA samples upon photoexcitation at 400 nm was studied by femtosecond absorption. The photodynamic of the hot electrons was found to depend on the sample preparation. The lifetime of the hot electrons in the Ag−BEA samples containing small Ag nanoparticles (1–2 nm) is significantly shortened in comparison to bear Ag nanoparticles with a size of 10 nm. While for the larger Ag nanoparticles, the energy absorbed in the conduction band is decaying by electron-phonon coupling into the metal lattice, the high surface-to-volume ratio of the small Ag nanoparticles favors the dissipation of the energy of the hot electrons from the metal nanoparticles (Ag⁰) towards the zeolitic micro-environment. This finding is encouraging for further applications of Ag-containing zeolites in photocatalysis and plasmonic chemistry.