Quantum chemical calculation of the catalytic reaction of ethane dehydrogenation on gallium oxide-hydroxide binuclear clusters in oxidized GaO/ZSM-5 zeolite

The catalytic activity of oxidized GaO/HZSM-5 in the reaction of alkane dehydrogenation can be due to hydrogenated gallium oxide clusters stabilized in the cationic positions of the zeolite. The binuclear gallium oxide clusters [Ga₂O₂]²⁺ in oxidized gallium-substituted high-silica zeolite HZSM-5, which are isomeric to two gallyl ions [GaO]⁺ stabilized on two spatially separated lattice aluminum ions, were considered using the DFT method within the framework of a cluster approach. It was found that, even in the case of a relatively large distance between these aluminum ions, gallium oxide particles in oxidized GaO/HZSM-5 can occur as charged planar [Ga₂O₂]²⁺ four-membered rings. These cluster particles exhibited a high affinity to hydrogen, and they were readily hydrogenated with the retention of their structural integrity. It was demonstrated that this partially hydrogenated cluster could be responsible for the catalytic process of ethane dehydrogenation. In the first step, ethane dissociatively added to the [Ga₂O₂H₂]²⁺ cluster. Then, the ethylene molecule was eliminated from the resulting intermediate to leave the [Ga₂O₂H₄]²⁺ cluster. The cycle was closed by the elimination of a hydrogen molecule with the formation of the initial structure of [Ga₂O₂H₂]²⁺.     

Catalytic properties,surface composition,and acidity of Ga-ZSM-5 catalysts for aromatization of lower paraffins

A study has been made of the catalytic and acidic properties together with the surface composition of the zeolite HZSM-5 modified by gallium by hydrothermal treatment with a sodium gallate solution and also by impregnation with gallium nitrate solution. It has been established that the first method of introducing gallium produces a more selective catalyst for aromatization of n-butane. It has been shown that under the conditions of the catalytic reaction several types of active centers incorporating Ga are formed: Ga₂O₃ on the zeolite surface, gallium ions inside the zeolite canals, and gallium atoms at the surface of and in the lattice that are bonded to OH groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2726–2732, December, 1991.     

Kinetics of Oxidation Processes in the System Co/Ga studied by in situ X‐Ray Diffraction

Oxidation processes in the system Co/Ga were studied by in situ X‐ray diffraction at temperatures between 800 and 1000 °C. Experiments were performed with metal powders and planar substrates. Oxidation of cobalt‐rich alloys, Co_1‐xGa_x, results in the formation of mixtures of cobalt‐ and gallium‐containing oxides. During oxidation of the intermetallic compounds CoGa and CoGa₃ only gallium is oxidized, and dense tarnishing layers of β‐Ga₂O₃ are formed. In all cases the oxide products are only intermediate products on the way to thermodynamic equilibrium, i.e. total oxidation of both metals. The kinetics during oxidation of the intermetallic compound CoGa was studied in detail by time resolved in situ X‐ray diffraction. After an induction time the kinetics can be described by a parabolic rate law with an activation energy of 312 kJ mol^—1. From the decrease of the parabolic rate constant with decreasing oxygen partial pressure and the observation of pore formation at the metal‐oxide interface it can be concluded that (i) outward diffusion of Ga‐ions through β‐Ga₂O₃ is the rate determining step during this solid state reaction, and (ii) Ga‐ions are mobile by means of gallium vacancies.     

Oxidation of arenes by molten gallium(III) chloride

Molten, anhydrous Ga₂Cl₆ at 100–130°C readily oxidizes pyrene, anthracene and naphtracene with the concomitant reduction of Ga(III) to Ga(I). Dilute solutions of these arenes (ArH) are oxidized to their radical cations (ArH^+·), which decay very slowly in Ga₂Cl₆, while more concentrated solutions are oxidized to stable arenium ions (ArH₂⁺) with hydrogen derived from aryl-ary] coupling reactions.     

Donorstabilisierte Galliumdihalogenide Ga2X4·2D (X = Cl,Br; D = Donormolekül): Ein experimenteller Beitrag zu den Variationsmöglichkeiten der Ga‐Ga‐Einfachbindung

Donor‐stabilized Galliumdihalides Ga₂X₄·2D (X = Cl, Br; D = Donor): An Experimental Contribution on the Variation of the Gallium‐Gallium Single Bond During the disproportionation of metastable GaX‐solutions (X= Cl, Br) donor‐stabilized galliumdihalides are formed as oxidized products. According to X‐ray structure analyses they all exhibit dimeric entities DX₂Ga‐GAX₂D (D= THF, NHEt2, NEt3, 4‐^tButylpyridin or Br^‐), which means these compounds are isoelectronic with ethane and could schematically be regarded as representatives of catenulate or alkane‐like gallium subhalides: Ga_n(X, D)_2n+2. The gallium‐gallium bond in these compounds is shorter than in the organometallic compounds such as R₂Ga‐GaR₂. The comparison of the bonding situation in the galliumdihalides, particularly of the gallium‐gallium bond, shows clearly the influence by donor molecules as well as by halogen ligands.     

Sequential Oxidation and C−H Bond Activation at a Gallium(I) Center

In situ oxidation of the Ga^I compound NacNacGa by either N₂O or pyridine oxide results in the generation of a labile monomeric oxide, NacNacGa(O), which can easily cleave the C?H bonds of aliphatic and aromatic substrates featuring good donor sites. The products of this reaction are gallium organyl hydroxides. DFT calculations show that these reactions start with the formation of NacNac‐Ga(O)(L) adducts, the oxo ligand of which can easily abstract protons from nearby C?H bonds, even for sp²‐hybridized carbon centers. Aliphatic amines do not enter this reaction for kinetic reasons, presumably because of the unfavorable sterics.     

Aromatization over nanosized Ga-containing ZSM-5 zeolites prepared by different methods: Effect of acidity of active Ga species on the catalytic performance

Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO⁺ species ([GaO⁺]^a) that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO⁺]^a species with stronger Lewis acid sites produced a better synergism with moderate Brønsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga₂O₃ phase and small amounts of GaO⁺ species that are mainly located on the external surface ([GaO⁺]^b), which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples (Gax-NZ5) exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield (i.e., 65.4 wt%) was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.     

Adsorption properties of oxidized gallium-modified zeolite ZSM-5 from diffuse reflectance IR and quantum-chemical data: 1. Interaction with hydrogen and ethane

Diffuse reflectance IR spectroscopy was used to study adsorption and subsequent high-temperature hydrogen and ethane transformations on gallium ions in gallium-modified ZSM-5 zeolite. The results were correlated with the corresponding quantum-chemical calculations. From the experimental and calculated data, it follows that trivalent gallium oxo ions are reduced to the univalent state in a hydrogen or ethane atmosphere even at moderate temperatures. Therefore, gallium oxo ions can function as active sites only at the early stages of light-paraffin aromatization. At the later stages, the dehydrogenation of light paraffins involves univalent gallium ions through the formation of intermediate gallium and alkylgallium hydrides.     

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga₂O₃/Al₂O₃ oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X‐ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel‐type structure; also shown by γ‐Al₂O₃ and γ‐Ga₂O₃. The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m² g^?1 for the mixed oxide having Ga:Al = 9:1 up to 370 m² g^?1 for that having Ga:Al = 1:9. High resolution MAS NMR showed that Ga³⁺ and Al³⁺ ions occur at both tetrahedral and octahedral sites in the spinel‐type structure of the mixed metal oxides, although there is a preferential occupation of tetrahedral sites by Ga³⁺ ions. A proportion of penta‐coordinated Al³⁺ ions was also found. IR spectra of carbon monoxide adsorbed at 77 K showed that the mixed metal oxides have a considerable Lewis acidity, related mainly to tetrahedrally coordinated metal ions exposed at crystal surfaces. The characteristic infrared absorption band of coordinated (adsorbed) CO appears in the range 2205–2190 cm^?1, and its peak wavenumber is nearly independent of Ga:Al ratio in the mixed gallia‐alumina oxides.     

Focused ion beam implantation of Ga in Si and Ge: fluence‐dependent retention and surface morphology

Focused ion beam implantation of 30‐keV Ga⁺ ions in single‐crystalline Si and Ge was investigated by SIMS, using Cs⁺ primary ions for sputtering. Nine different implantation fluences ranging from 1 × 10¹³ to 1 × 10¹⁷ Ga⁺‐ions/cm² were used, with implanted areas of 40 × 40 µm². The Ga concentration distributions of these implants were determined by SIMS depth profiling. Such 30‐keV Ga implantations were also simulated by a dynamic Monte‐Carlo code that takes into account the gradual change of the near‐surface composition due to the Ga incorporation. In both approaches, an essentially linear increase of the Ga peak concentrations with fluence is found up to ～1 × 10¹⁶cm^?2; for higher fluences, the Ga content approaches a saturation level which is reached at about (1–2) × 10¹⁷cm^?2. The measured and simulated peak concentrations of the Ga distributions are in good agreement. The most probable ranges obtained from the experiments correspond closely with the respective values from the simulations. The surface morphology caused by Ga⁺ implantation was investigated by atomic force microscopy (AFM). The AFM data indicate that for low fluences (<3 × 10¹⁵cm^?2) the surface within the implanted areas is growing outward (i.e. is swelling). For increasingly higher fluences, sputter‐induced erosion of the surface becomes dominant and distinct craters are formed for fluences above ～1 × 10¹⁶cm^?2. At the boundary of the implanted region a wall‐like structure is found to form upon Ga implantation; its height is growing with increasing fluence, reaching a value of ～15 nm at 1 × 10¹⁷ Ga⁺‐ions/cm². Copyright © 2008 John Wiley & Sons, Ltd.     

杂原子分子筛(ⅩⅤ)-含镓ZSM-5型沸石的合成、结构及其性能的研究

以水玻璃、三氯化镓、1,6-己二胺和水为原料,合成了SiO₂/Ga₂O₃为60-38间的含镓ZSM-5型沸石.X-射线谱图表明含镓ZSM-5型沸石与硅铝ZSM-5型沸石相似,电子探针的分析结果表明镓原子进入了沸石骨架。     

Synthesis and crystal structure of unprecedented oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes

Two new polynuclear oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes are obtained upon treatment of Ga(3+)(aq) with pyridine: the supramolecular compound of macrocyclic cavitand cucurbit[6]uril with gallium complex containing 32 metal atoms [Ga(32)(mu(4)-O)(12)(mu(3)-O)(8)(mu(2)-O)(7)(mu(2)-OH)(39)(H(2)O)(20)](PyH subsetC(36)H(36)N(24)O(12))(3)(NO(3))(6).53H(2)O (1) and the tridecanuclear complex [Ga(13)(mu(3)-OH)(6)(mu(2)-OH)(18)(H(2)O)(24)](NO(3))(15).12H(2)O (2). It follows that two modes of nucleation exist when Ga(3+)(aq) is hydrolyzed: one around the tetrahedral GaO(4) units (complex 1) and the other around the octahedral GaO(6) units (complex 2). This is the first time that polynuclear oxo/hydroxo-bridged aqua complexes of Ga(III) have been isolated without the use of other ligands to control or block olygomerization.     

Propriétés des oxinates d'aluminium,de gallium et d'Indium.: Séparation du gallium par extraction par le chloroforme

A study has been made of the solubility in water as a function of pH of oxine and of the oxinatus of aluminium, gallium and indium, as well as their solubility in chloroform.The curves showing the partition between chloroform and water as a function of pu have been established.Gallium can be separated, from aluminium by extraction of the oxinate al pH₂O. It is possible by this means to separate one part of gallium from 10¹ parts of aluminium. The formation of the oxinates serves as a basis of an acidimetric determination of the ions Al⁺³, Ga⁺³ and In⁺³.     

Distribution of the cobalt-containing component in the pore space of HZSM-5 upon a postsynthetic modification of the zeolite with hydroxo compounds of Co<Superscript>2+</Superscript>

The distribution of the cobalt-containing modifying component in the pore space of zeolite HZSM-5 depending on the total cobalt content of the samples (0.5–5.0 wt %) was quantitatively studied for the first time. At cobalt concentrations to 3.0 wt %, the cobalt-containing modifying component mainly occurred as isolated Co _Oh ²⁺ ions in the micropores (channels) of HZSM-5 at the ion-exchange positions of the zeolite and in one-dimensional CoO and CoAl₂O₄ nanoclusters. A further increase in the cobalt concentration to 5.0 wt % resulted, in addition to the filling of micropores, in the partial filling of the mesopore space of the zeolite with a small amount of three-dimensional CoO and CoAl₂O₄ nanoparticles. Using sorption data and electronic diffuse reflectance spectra, we were the first to find that the effective density of a cobalt-containing modifying component in the pore space of a zeolite matrix was lower than the density of a bulk CoO phase by a factor of 6.     

Synthesis of high-purity GaP nanowires using a vapor deposition method

High-purity gallium phosphide (GaP) nanowires were successfully synthesized on the nickel monoxide (NiO) or the cobalt monoxide (CoO) catalyzed alumina substrate by a simple vapor deposition method. To synthesize the high-purity GaP nanowires, the mixture source of gallium (Ga) and GaP powder was directly vaporized in the range of 850–1000 °C for 60 min under argon ambient. The diameter of GaP nanowires was about 38–105 nm and the length was up to several hundreds of micrometers. The GaP nanowires have a single-crystalline zinc blend structure and reveal the core-shell structure, which consists of the GaP core and the GaPO₄/Ga₂O₃ outer layers. We demonstrate that the mixture of Ga/GaP is an ideal source for the high-yield GaP nanowires.     

The distinction of gallium(I) tetrachloroaluminate,Ga[AlCl4], from gallium dichloride

Ga[AlCl₄] is obtained as single crystals via the reduction of gallium trichloride with aluminum and slow cooling of the melt. It crystallizes in the monoclinic system, space group p2₁/n, with a = 716.4(1), b = 1017.9(2), c = 926.7(1) pm, β = 93.21(1)°. Unlike in gallium dichloride, Ga[GaCl₄]], where Ga⁺ has a dodecahedral, eight-coordinate surrounding, a 6 + 2 + 1 coordination is adopted in Ga[AlCl₄] that is similarly observed not only in Ga₂[Ga₂Br₆] and in tin (II) and lead (II) chalcogenides but also in (the almost isotypic) K[AlCl₄].     

Catalytic Oxidation of Methane by Nitrous Oxide on H[Al]ZSM-5 Zeolite, Silicalite, and Amorphous SiO2 Modified by Iron, Silver, and Gadolinium Ions

Methane oxidation by an excess of N₂O on the catalytic sites formed in HZSM-5 zeolite, silicalite, and SiO₂ after modification with iron, silver, and gadolinium cations in different combinations is studied. Introduction of iron and silver ions into H[Al]ZSM-5 zeolite is shown to result in the formation of the sites that are active in methane oxidation, while the systems obtained on the basis of crystalline silicalite or amorphous SiO₂ demonstrate poor or no catalytic activity, respectively. Complete oxidation of methane with 100% conversion is observed on the Fe/HZSM-5 and Ag/HZSM-5 catalysts at temperatures higher than 350 and 450°C, respectively. A decrease in the reaction temperature and in the methane conversion is accompanied by coking of the catalysts and, in the case of Fe/HZSM-5, by the appearance of trace amounts of methanol and formic acid in the gas phase. The temperature dependence of the activity and selectivity for the Ag/HZSM-5 and (Ag + Gd)/HZSM-5 catalysts exhibits a pronounced hysteresis at 330–480°C, and the formation of coke proceeds much faster than in the case of iron-containing samples. Catalytic properties of (Fe + Ag)/HZSM-5 are similar to those of Fe/HZSM-5. The introduction of Gd does not influence significantly the activity and selectivity of the catalysts. ESR and TG–DTA were used to determine the state and distribution of Fe, Ag, and Gd in the samples and to examine the processes of coke formation.     

Subvalente Galliumtriflate – mögliche Ausgangsverbindungen für Clusterverbindungen des Galliums

Subvalent Gallium Triflates – Potentially Useful Starting Materials for Gallium Cluster Compounds By reaction of GaCp* with trifluormethanesulfonic acid in hexane a mixture of gallium trifluormethanesulfonates (triflates, OTf) is obtained. This mixture reacts readily with lithiumsilanides [Li(thf)₃Si(SiMe₃)₂R] (R = Me, SiMe₃) to afford the cluster compounds [Ga₆{Si(SiMe₃)Me}₆], [Ga₂{Si(SiMe₃)₃}₄] and [Ga₁₀{Si(SiMe₃)₃}₆]. By crystallization from various solvents the gallium triflates [Ga(OTf)₃(thf)₃], [HGa(OTf)(thf)₄]⁺ [Ga(OTf)₄(thf)₃]⁻, [Cp*GaGa(OTf)₂]₂ and [Ga(toluene)₂]⁺ [Ga₅(OTf)₆(Cp*)₂]⁻ were isolated and characterized by single crystal X ray structure analysis.     

Pair distribution function and 71Ga NMR study of aqueous Ga3+ complexes

The atomic structures, and thereby the coordination chemistry, of metal ions in aqueous solution represent a cornerstone of chemistry, since they provide first steps in rationalizing generally observed chemical information. However, accurate structural information about metal ion solution species is often surprisingly scarce. Here, the atomic structures of Ga³⁺ ion complexes were determined directly in aqueous solutions across a wide range of pH, counter anions and concentrations by X-ray pair distribution function analysis and ⁷¹Ga NMR. At low pH (<2) octahedrally coordinated gallium dominates as either monomers with a high degree of solvent ordering or as Ga-dimers. At slightly higher pH (pH ≈ 2–3) a polyoxogallate structure is identified as either Ga₃₀ or Ga₃₂ in contradiction with the previously proposed Ga₁₃ Keggin structures. At neutral and slightly higher pH nanosized GaOOH particles form, whereas for pH > 12 tetrahedrally coordinated gallium ions surrounded by ordered solvent are observed. The effects of varying either the concentration or counter anion were minimal. The present study provides the first comprehensive structural exploration of the aqueous chemistry of Ga³⁺ ions with atomic resolution, which is relevant for both semiconductor fabrication and medical applications.

With changing pH four different structural regions in Ga³⁺ aqueous solutions are observed. In contrast the effects of different anions and concentrations are minimal.     

Equilibrium study of the systems of aluminium(III), gallium(III) and indium(III) with mercaptoacetate, 3-mercaptopropionate and 2-mercaptobenzoate

Equilibrium studies were carried out by pH-potentiometry on the systems of aluminium(III), gallium(III) and indium(III) with mercaptoacetate (MerAc^2?), 3-mercaptopropionate (MerPr^2?) and 2-mercaptobenzoate (MerBe^2?). It was found that the complex-forming properties of the Al³⁺ ion towards these mercaptocarboxylic acid ligands differ from those of Ga³⁺ and Al³⁺. Under the conditions of the study, Al³⁺ forms only hydroxo complexes, while Ga³⁺ and In³⁺ form relatively stable complexes involving the simultaneous coordination of the carboxylate and the deprotonated mercapto group. In all cases the equilibrium systems can be described without the assumption of polynuclear complexes. The complexes Ga(MerAc)₂ and Ga(MerBe)₂ show marked stability; this was interpreted in terms of back-coordination and of interaction between the d¹⁰ electrons of the Ga³⁺ ion and the empty d orbitals of the S donor atom. Complexes of composition ML_i are not formed in the Ga³⁺-MerPr^2? system; this points to the importan roles of the number of atoms in the chelate ring and the higher stability of the Ga(III)-hydroxo complexes.