Steam reforming of acetic acid over Ni-Ba/Al_2O_3 catalysts:Impacts of barium addition on coking behaviors and formation of reaction intermediates

The influence of barium addition to a Ni/Al_2O_3 catalyst on the reaction intermediates formed,the activity,resistance of the catalyst to coking,and properties of the coke formed after acetic acid steam reforming were investigated in this study.The results showed the drastic effects of barium addition on the physicochemical properties and performances of the catalyst.The solid-phase reaction between alumina and BaO formed BaAl_2O_4,which re-constructed the alumina structure,resulting in a decrease in the specific surface area and an increase in the resistance of metallic Ni to sintering.The addition of barium was also beneficial for enhancing the catalytic activity,resulting from the changed catalytic reaction network.The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study of the acetic acid steam reforming indicated that barium could effectively suppress the accumulation of the reaction intermediates of carbonyl,formate,and C=C functional groups on the catalyst surface,attributed to its relatively high ability to cause the gasification of these species.In addition,coking was considerably more significant over the Ba-Ni/Al_2O_3 catalyst.Moreover,the Ba-Ni/Al_2O_3 catalyst was more stable than the Ni/Al_2O_3catalyst,owing to the distinct forms of coke formed (carbon nanotube form over the Ba-Ni/Al_2O_3 catalyst,and the amorphous form over the Ni/Al_2O_3 catalyst).     

A new selective metallochromic reagent for the detection and chelatometric determination of calcium

A new reagent, Calcichrome, which gives a highly sensitive colour reaction with calcium ions in alkaline solution, has been synthesised. Neither barium, strontium nor magnesium react with the reagent, which is therefore proposed as a selective spot-test reagent for calcium. In addition, Calcichrome may be used as a metallochromic indicator for the accurate complexometric titration of calcium in the presence of at least twelve-fold amounts of barium. Trans-1:2-diaminocyclohexane-N:N:N':N'-tetra-acetic acid is used as titrant since it is the only complexan available which is sufficiently selective in its reactivity towards calcium and barium.     

The Ba(II) complex of a crown ether bearing a sulphydryl side-arm as turnover catalyst of ester cleavage

When activated by barium(II), 18-mercaptomethyl-1,4,7,10,13,16-hexaoxacyclononadecane acts as turnover catalyst in the methanolysis of p-nitrophenyl acetate (pNPOAc) under slightly basic conditions in CH₃CN-CH₃OH 9:1 (v/v). The function of the complexed barium ion is to enhance the nucleophilicity of the pendant SH group towards the acetyl group of the ester, and to assist as a built-in electrophile the subsequent transfer of the acetyl group from the acetylated intermediate to the solvent. Besides the above double displacement mechanism of ester cleavage, a direct metal-ion assisted methanolysis involving reaction of pNPOAc with the ternary complex (5·BaOMe)⁺ has been detected.     

Synthesis, crystal structure and thermal decomposition study of a new barium acetato-propionate complex

The present study reports on a novel barium acetato-propionate complex, obtained by the reaction of barium acetate with propionic acid, used as an oxide precursor with applications in superconducting thin films deposition. The molecular structure has been determined by X-ray diffraction on single crystals and demonstrated to be [Ba₇(CH₃CH₂COO)₁₀(CH₃COO)₄·5H₂O]. The barium acetato-propionate is a three-dimensional channel-type polymer. The thermal decomposition of the barium precursor has been studied by simultaneous differential thermal analysis-thermogravimetry-mass spectrometry (DTA-TG-MS) in air at a heating rate of 10 °C/min. Based on these analyses, infrared spectroscopy was further used to characterize the precursor solution by the step-wise addition of the reagents. The X-ray diffraction on the precursor powder at different temperatures was performed.     

Iodometric microdetermination of sulphur in organic compounds by an amplification reaction

A new method is described for the iodometric microdetermination of sulphur in organic compounds, using a 12-fold amplification reaction after oxygen-flask combustion. The method is based on reaction of the resulting sulphuric add with an excess of saturated barium bromate solution. The unreacted barium bromate is precipitated by addition of acetone, filtered off, redissolved in hot water and after addition of an excess of iodide and acid, the iodine liberated is titrated with thiosulphate. The method is simple, rapid, highly accurate, and of wide application in the microanalysis of organosulphur compounds containing other common acid-forming elements.     

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Organomagnesium compounds, represented by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen–magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hand, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with a variety of electrophiles in various reaction modes. In particular, organocalcium, strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.

In this perspective, we highlight the recent development of metallation protocols of non-polar unsaturated molecules for the generation of organo-alkaline earth metal compounds and their applications in chemical synthesis and catalysis.     

Organic peroxides—XIX: Decomposition of trialkylperoxy triazines

The kinetics of the decomposition of tri-t-butylperoxy-1,3,5-triazine (from trichloro-1,3,5-triazine and barium t-butyl peroxide in situ) follows the 1-order with an activation energy of 24.6 $\text{kcal}\text{mole}$. Isolated products are cyanuric acid and acetone. The reaction of trichloro-triazine with potassium cumyl peroxide yields cyanuric acid, isopropenyl phenyl ether, dicumyl peroxide, acetone and phenol, with barium 2-benzyl-2-propyl peroxide cyanuric acid, benzaldehyde and 2-benzyloxy-2-[2-benzyl-2-propylperoxy]-propane. The mechanism of the decomposition is discussed.     

钡添加剂对二次碱性锌电极性能的影响

采用直接化学合成法制备以钡作添加剂的二次碱性锌电极活性物质,样品的表面形貌及其晶态结构由SEM和XRD表征,并以循环伏安、充放电循环及电化学阻抗谱测定样品的电化学性能.实验表明,锌电极因Ba的添加而生成一种化学式为BaZn(OH)4·xH2O的锌酸钡,改善了电极的电化学性能.此外发现,Zn电极的电化学阻抗谱含有一个对应于电极表面放电产物覆盖率的时间常数.     

Synthesis, characterization and molecular structures of barium(II) trichloroacetate DME/1,4-dioxane compounds

Two new barium(II) trichloroacetate compounds, [Ba(H₂O)(DME)(μ-O₂CCCl₃)₂]_n (1) and [{Ba(H₂O)₂(diox)_0.5(μ-O₂CCCl₃)₂}(diox)]_n (2) were synthesized and characterized by elemental analyses, physiochemical studies, FT-IR, ¹H NMR, thermogravimetric analyses (TG/DTG/DSC) and single crystal X-ray studies. The reaction of hydrated barium(II) trichloroacetate monohydrate with excess DME (1,2-dimethoxyethane) and diox (1,4-dioxane) in methanol at room temperature led to the isolation of the novel compounds 1 and 2, respectively. Bridging trichloroacetate groups are anticipated on the basis of FT-IR studies and this was confirmed by the X-ray studies. Both compounds dissociate to produce ions in water, as shown by molar conductance values. ¹H NMR spectroscopy confirms that DME and 1,4-dioxane are coordinated to the metal ion in these compounds. Single crystal X-ray diffraction studies reveal that the barium cation is coordinated to nine O atoms in a deformed coordination polyhedron in both compounds. Structural data of barium(II) trichloroacetates compounds have been obtained for the first time in the present investigation.     

Synthesis and molecular structure of a novel barium arylspiroboronate ester

The compound barium bis{bis-(4,6-di-tert-butyl[1,2-benzenediolato(2-)-O,O′]borate)} has been prepared by the addition of 3,5-di-tert-butylcatechol to a solution of boric acid and Ba(OH)₂ and characterized by a single crystal X-ray diffraction study. The title compound crystallized in the triclinic space group P-1, with cell parameters a = 13.280(2) Å, b = 15.755(3) Å, and c = 16.980(3) Å, α = 71.691(2)o, β = 79.528(3)o, γ = 80.741(3)o, Z = 1, and V = 3296.1(10) ų. The structure was solved by direct methods and refined to a final R = 0.0459 for 14370 reflections with I > 2σ(I). One of the arylspiroboronate ester counterions is bound to the barium atom in a rare example of the η1 bonding mode via a single oxygen of one of the catecholato groups. The coordination sphere around the barium is complemented by four molecules of water, one molecule of acetone and two bridging water molecules, connecting to an adjacent barium atom.     

Preparation of optically pure cross-conjugated cyclopentadienones

The synthesis of optically pure cross-conjugated cyclopentadienones is readily achieved in two steps via a one-pot alkylcuprate addition/aldol condensation/dehydration sequence using racemic or enantioenriched endo-3a,4,7,7a-tetrahydro-1H-4,7-methano-inden-1-ones followed by microwave-mediated Lewis acid-catalysed retro Diels-Alder reaction. An alternative route involving a modified Baylis-Hillman protocol followed by conjugate addition with alkylcuprates and a retro Diels-Alder reaction was also investigated.     

Visible-light-mediated selective thiocyanation/ipso-cyclization/oxidation cascade for the synthesis of thiocyanato-containing azaspirotrienediones

A visible-light-mediated metal-free thiocyanate radical addition/ipso-cyclization/oxidation cascade reaction for the synthesis of thiocyanato-containing azaspirotrienediones from N-phenylpropynamides is described. Cheap and readily available ammonium thiocyanate was used as a precursor to the thiocyanate free radical, which undergoes a radical addition reaction with the alkyne, followed by selective ipso-cyclization and oxidation to afford the dearomatized products. No product of ortho-cyclization was detected. The reaction completes the synthesis of C–S, C–C, and CO bonds in one pot, with abundant and renewable air oxygen as the sole sacrificial reagent and oxygen source.     

Determination of D0o(BaI) from the chemiluminescent reaction Ba + I2

A study is made of the visible chemiluminescence resulting from the reaction of an atomic beam of barium with I_Z under single-collision conditions (～ 10^?4 torr). The resulting spectrum consists of the BaI C²Π → X²Σ emission on top of an underlying “continuum”. The variation of the BaI emission intensity with Ba and I₂ flux is investigated, and it is concluded that the reaction is bimolecular. The total phenomenological cross section for barium atom removal is determined to be 86 A², which agrees well with the total reactive cross section calculated assuming an electron jump mechanism. The short wavelength cutoff is identified as the transition from the υ′ = 41 level of the BaI C²Π_{$\text{3}\text{2}$} state to the υ′ = 41 level of the BaI X²Σ state. A strict lower bound D^o₀(BaI) ? 102 ± 0.7 kcal/mole for the ground state dissociation energy of BaI is obtained from this short wavelength cutoff. The value D^o₀(BaI) = 102 ± 1 kcal/mole is recommended, where the error estimate includes the possible contribution from the final relative translational energy of the products.     

Ba0.15WO3: A bronze with an original pentagonal tunnel structure

The structure of a new barium tungsten bronze, Ba_0.15WO₃, has been established by X-ray diffraction and high-resolution microscopy studies. This bronze is orthorhombic, space group Pbm2 or Pbmm, with a = 8.859(3) Å, b = 10.039(8) Å, and c = 3.808(2)Å. The “WO₃” framework is built up from corner-sharing WO₆ octahedra forming pentagonal tunnels where the barium ions are located. Structural relationships with hexagonal tungsten bronze and tetragonal tungsten bronze structures are discussed.     

Solvent‐free synthesis of polyacrylamide by frontal polymerization

Polymerization and characterization of polyacrylamide prepared by frontal polymerization are described. Frontally polymerized polyacrylamide is imidized and crosslinked during polymerization. Imide formation was determined by elemental analysis. The addition of commercial polyacrylamide or barium carbonate to the monomer (acrylamide) and initiator (potassium persulfate) decreased the reaction temperature from 235 °C to < 100 °C, thereby reducing imide formation. The commercial polyacrylamide‐diluted product, frontally polymerized polyacrylamide‐diluted product, and the barium carbonate‐diluted product were characterized by IR, TGA, and elemental analysis. Molecular weights of barium carbonate‐diluted samples were determined by light scattering and found to be on the order of one million. Conversion of the barium carbonate‐diluted product was determined to be 76 ± 6%, independent of the amount of diluent over the range 0.8:1–1.5:1. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1129–1135, 2000     

The titrimetric determination of carbon dioxide with special reference to the determination of carbon in organic compounds

The titrimetric barium carbonate method for the determination of. carbon in organic compounds has been examined and the various sources of error are discussed. The carbon dioxide from the combustion of the sample is absorbed in excess baryta containing 20% (w/v) barium chloride and the excess is back-titrated with hydrochloric acid in the presence of o-cresolphthalein indicator.The value of this method in conjunction with the previously described determination of water with succinyl chloride, for the simultaneous determination of carbon and hydrogen is assessed     

Reactive barium-promoted Reformatsky-type reaction of alpha-chloroketones with aldehydes

A Reformatsky-type aldol reaction of alpha-chloroketones with aldehydes has been achieved using reactive barium as a low-valent metal in THF; this one-pot process is more effective for obtaining the desired beta-hydroxy ketones in high yields than the stepwise process in which barium enolates are prepared prior to the reaction with aldehydes.     

Use of the differential charging effect in XPS to determine the nature of surface compounds resulting from the interaction of a Pt/(BaCO<Subscript>3</Subscript> + CeO<Subscript>2</Subscript>) model catalyst with SO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Changes in the chemical composition of the surface of a Pt/(BaCO₃ + CeO₂) model NO _x storage-reduction catalyst upon its interaction with SO _x (SO₂ (260 Pa) + O₂ (2600 Pa) + H₂O (525 Pa)) followed by regeneration in a mixture of CO (2100 Pa) with H₂O (525 Pa) were studied by X-ray photoelectron spectroscopy (XPS). Model catalyst samples were prepared as a thin film (about several hundreds of angstrom units in thickness) on the surface of tantalum foil coated with a layer of aluminum oxide (～100 Å). It was found that the Pt/BaCO₃ and Pt/CeO₂ catalyst constituents acquired different surface charges (differential charging) in the course of photoelectron emission; because of this, it was possible to determine the nature of surface compounds formed as a result of the interaction of the catalyst with a reaction atmosphere. It was found that barium carbonate was converted into barium sulfate as a result of reaction with SO _x on the surface of BaCO₃ at 150°C. As the treatment temperature in SO _x was increased to 300°C, the formation of sulfate on the surface of CeO₂ was observed. The sulfatization of CeO₂ was accompanied by the reduction of Ce(IV) to Ce(III). The regeneration reaction of the catalyst treated in SO _x at 300°C resulted in the consecutive decomposition of cerium(III) sulfate at ≤500°C and then barium sulfate at 600–700°C. Upon the decomposition of BaSO₄, a portion of sulfur was converted into a sulfide state, probably, because of the formation of BaS.     

Synthese und Charakterisierung heterobimetallischer Bis(trimethylsilyl)phosphanide von Barium und Zinn

Synthesis and Characterization of Hetero-bimetallic Bis(trimethylsilyl)phosphanides of Barium and Tin The reaction of barium bis[bis(trimethylsilyl)amide] with one equivalent of bis(trimethylsilyl)phosphane in 1,2-dimethoxyethane (dme) yields the heteroleptic dimeric (dme)barium bis(trimethylsilyl)amide bis(trimethylsilyl)phosphanide. This colorless compound crystallizes in the monoclinic space group P2₁/n with a = 1 259.1(3), b = 1 822.7(4), c = 1 516.1(3) pm, β = 110.54(3)° and Z = 4. The central moiety of the centrosymmetric molecule is the planar Ba₂P₂-cycle with Ba? P-bond lengths of 329 and 334 pm. In the presence of bis[bis(trimethylsilyl)amino]stannylene hetero-bimetallic bis(trimethylsilyl)phosphanides of tin(II) and barium are isolated. If the reaction of Ba[N(SiMe₃)₂]₂ and Sn[N(SiMe₃)₂]₂ in the molar ratio of 1:2 with six equivalents of HP(SiMe₃)₂ is performed in toluene, barium bis{tin(II)-tris[bis(trimethylsilyl)phosphanide]} can be isolated. This compound crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 1 265.1(1), b = 2 290.1(3), c = 2 731.9(3) pm and Z = 4. The anions {Sn[P(SiMe₃)₂]₃}^? bind as two-dentate ligands to the barium atom which shows the extraordinary low coordination number of four. The addition of tetrahydrofuran (thf) to the above mentioned reaction solution leads to the elimination of tris(trimethylsilyl)phosphane and the formation of thf complexes of barium bis{tin(II)-bis(trimethylsilyl)phosphanide-trimethylsilylphosphandiide}. The derivative crystallizes from toluene in the monoclinic space group P2₁/c with a = 1 301.9(2), b = 2 316.3(3), c = 3 968.7(5) pm, β = 99.29(1)° and Z = 8.     

A study of the Arrhenius behavior of the co-precipitation of radium, barium and strontium sulfate

Co-precipitation of radium, barium and strontium is an important process in many contexts, such as uranium mining, oil extraction and in the safety assessment of a final repository for used nuclear fuel. Co-precipitation to a solid solution is possible since radium, barium and strontium act as chemical analogues. In this work the co-precipitation of radium, barium and strontium was studied and the kinetic behavior of the co-precipitation process was investigated. It was shown that radium, barium and strontium co-precipitate congruently and that the precipitation followed an Arrhenius behavior and the Arrhenius parameters for the systems was determined. When studying the differences of the Arrhenius constants by using a student t test (95 % confidence interval) it was observed that the only significant difference in the activation energy, E _a, is between radium and barium and between radium and strontium respectively, the pure strontium having the larger activation energy in comparison. This is most likely coupled to the metal ion size; since the hydration waters are more strongly bound, which leads to them having a slower exchange rate, which in turn effects the rate of co-precipitation to the metal these reactions will be slower.