Growth of multi-walled C nanotubes from pre-heated CH4 using Fe3O4 as a catalyst precursor

The present study aims to investigate influence of pre-heating of CH₄ on the growth of multi-walled C nanotubes (MWCNTs) on a Si (100) substrate by chemical vapor deposition technique using Fe₃O₄ powder as catalyst precursor. Reduction behavior of Fe₃O₄ was also studied in a flowing undiluted CH₄ atmosphere in order to gain better insight into MWCNT synthesis. Mass measurements, XRD and thermodynamic analyses were carried out to determine the extent of reduction of Fe₃O₄ by CH₄. It was found that Fe₃O₄ initially transformed to Fe via FeO within 30 min at 1200 K. Fe₃C and C then formed as reaction time increased to 60 min. It was postulated that reduction of Fe₃O₄ took place by H₂, a product of CH₄ decomposition. The overall reactions leading to the formations of Fe and Fe₃C phases were proposed using equilibrium thermodynamic analysis and the experimental results. Undiluted CH₄ was used to synthesize MWCNTs at temperatures in the range of 1050–1300 K. It was observed that a dense carbon coating was formed at 1300 K owing to self pyrolysis of CH₄, while at 1200 K individual MWCNTs were observed on the Si substrate. Growth of MWCNTs did not take place at the temperature range of 1050–1150 K. The use of CH₄ pre-heated at 1200 K, however, yielded MWCNTs at this temperature range. Experimental results and thermodynamic analysis of the C–H system (excluding graphite) indicated that pre-heating treatment of CH₄ promoted Fe₃O₄ reduction by H₂ and C formations from active intermediate hydrocarbon species of high molecular weights (especially C₆H₆).     

Binuclear cyano-bridged complex derived from [MnIII(salpn)] and [FeIII(CN)6]: Synthesis,structure and magnetic properties

The reaction of the neutral [Mn(salpn)C(CN)₃(H₂O)] (salpn^2 − = N,N^′-1,3-propylenebis(salicylideneiminato) dianion) with [Fe^III(CN)₆]^3 − in the presence of strong oxidizer (NH₄)₂S₂O₈ yields a binuclear anion complex [NH₃CH₂CH₂CH₂NH₃]^2 +{[Mn^III(salpn)(H₂O)][Fe^III(CN)₆]}^2 − (1). Its structure, DC and AC susceptibility have been studied. Frequency dependence of the AC susceptibility characteristic for single-molecule magnets has been found.     

Effect of NO on the catalytic removal of N2O over FeZSM-5. Friend or foe

Selective catalytic reduction (SCR) of N₂O with C₃H₈ over FeZSM-5 under excess oxygen is strongly inhibited by NO. The assistance of the hydrocarbon in N₂O reduction vanishes at high partial NO pressures, approaching the activity of the N₂O + NO system at molar NO/N₂O ratios of 1.5–2, with N₂O/C₃H₈=1. This effect differs from the NO promotion in direct N₂O decomposition over Fe-zeolite catalysts. The negative effect of NO on the N₂O reduction has a significant impact in the design and operation of catalytic reactors in tail-gases of nitric acid plants and other sources where NO comes along with N₂O.     

Cu- and Pd-substituted nanoscale Fe-based perovskites for selective catalytic reduction of NO by propene

A series of Fe-based perovskites with high specific surface area was prepared by a new method, reactive grinding, and characterized by N₂ adsorption, XRD, SEM, H₂-TPR, TPD of O₂, TPD of NO + O₂, TPD of C₃H₆, and TPSR of NO + O₂ under C₃H₆/He flow. These materials were then subjected to activity tests in the selective catalytic reduction of NO by propene. The catalytic performance over LaFeO₃ is poor but can be improved significantly by incorporating Cu into its lattice, resulting in N₂ yields over LaFe_0.8Cu_0.2O₃ of 81% at 450 °C and 97% at 700 °C with a reactant mixture containing 3000 ppm NO, 3000 ppm C₃H₆, and 1% O₂ in helium at a space velocity of 50,000 h⁻¹. The enhanced NO reduction after Cu substitution is attributed to the easy formation of nitrate species, which have high reactivity toward C₃H₆. A mechanism was proposed with the formation of nitrate species as the first step and organo nitrogen compounds as important intermediates. Great catalytic performance at low temperature was also achieved over LaFe_0.97Pd_0.03O₃ with a N₂ yield of 67% and C₃H₆ conversion of 68% at 350 °C corresponding to the outstanding redox properties of this catalyst. O₂ can act as a promoter to oxidize NO into strongly adsorbed nitrate species, and also can accelerate the transformation of organo nitrogen compounds and isocyanate to get the desired products. In contrast, at higher concentrations O₂ has a detrimental effect, leading to consumption of the reducing agent by the complete oxidation of C₃H₆.     

A MnII5 tetragonal pyramid stabilized by p-tert-butylcalix[8]arene: Synthesis,structure and magnetic property

A compound, [Mn₅(H₄C8A)(OH)₂(C₃H₆NO₂)(DMF)₅(CH₃O)_1.5(HCO₂) (C₂H₃O₂)_0.5]·2DMF·CH₃OH (1) (H₈C8A = p-tert-butylcalix[8]arene, DMF = N,N′-dimethylformamide), was synthesized by the solvothermal method in the mixed CH₃OH/DMF (1:1) solvent. Compound 1 is featured with a tetragonal pyramid-like Mn^II₅ cluster encircled within a calix[8]arene molecule with a ‘pleated loop’ conformation. Magnetic study indicates that the Mn^II centers exhibit antiferromagnetic interactions.     

Organic–inorganic hybrid oxides: Structure and magnetic properties of [{Cu(terpy)}2Mo6O17(H2O)(O3PCH2NH2CH2PO3)2] · H2O,a bimetallic oxide constructed from novel {Mo6O17(H2O)(O3PCH2NH2CH2PO3)2}4− clusters

The hydrothermal reaction of MoO₃, CuSO₄ · 5H₂O, 2,2′:6′:2″-terpyridine (terpy) and bis-N,N-(methylphosphonic acid) amine (H₂O₃PCH₂NHCH₂PO₃H₂) provided blue crystals of the bimetallic oxide [{Cu(terpy)}₂Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂] · H₂O (1 · H₂O). The three-dimensional structure of 1 is constructed from {Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂}⁴⁻ clusters linked through {Cu(terpy)}²⁺ subunits. The cluster consists of three pairs of edge-sharing {MoO₆} octahedra linked through corner-sharing interactions into a {Mo₆O₆} ring. One phosphonate ligand spans the diameter of the ring, bridging four molybdenum sites and leaving at a pendant {PO} group at each terminus. The second diphosphonate ligand exploits one {–PO₃} unit to cap the hexamolybdate ring and bridge all six molybdenum sites while the second {–PO₃} terminus bridges two molybdenum sites, leaving a pendant {PO} unit. Crystal data: C₃₄H₄₅Cu₂Mo₆N₈O₃₅P₄: monoclinic, P2₁/n, a = 11.9431(7) Å, b = 17.382(1) Å, c = 27.524(2) Å, β = 90.429(1)°, V = 5713.7(6) Å³, Z = 4, D_calc = 2.270 g cm⁻³, R₁ = 0.0466.     

Conversions of fuel-N,volatile-N,and char-N to NO and N2O during combustion of a single coal particle in O2/N2 and O2/H2O at low temperature

Oxy-steam combustion is a promising next-generation combustion technology. Conversions of fuel-N, volatile-N, and char-N to NO and N₂O during combustion of a single coal particle in O₂/N₂ and O₂/H₂O were studied in a tube reactor at low temperature. In O₂/N₂, NO reaches the maximum value in the devolatilization stage and N₂O reaches the maximum value in the char combustion stage. In O₂/H₂O, both NO and N₂O reach the maximum values in the char combustion stage. The total conversion ratios of fuel-N to NO and N₂O in O₂/N₂ are obviously higher than those in O₂/H₂O, due to the reduction of H₂O on NO and N₂O. Temperature changes the trade-off between NO and N₂O. In O₂/N₂ and O₂/H₂O, the conversion ratios of fuel-N, volatile-N, and char-N to NO increase with increasing temperature, and those to N₂O show the opposite trends. The conversion ratios of fuel-N, volatile-N, and char-N to NO reach the maximum values at < O₂ > = 30 vol% in O₂/N₂. In O₂/H₂O, the conversion ratios of fuel-N and char-N to NO reach the maximum values at < O₂ > = 30 vol%, and the conversion ratio of volatile-N to NO shows a slightly increasing trend with increasing oxygen concentration. The conversion ratios of fuel-N, volatile-N, and char-N to N₂O decrease with increasing oxygen concentration in both atmospheres. A higher coal rank has higher conversion ratios of fuel-N to NO and N₂O. Anthracite coal exhibits the highest conversion ratios of fuel-N, volatile-N, and char-N to NO and N₂O in both atmospheres. This work is to develop efficient ways to understand and control NO and N₂O emissions for a clean and sustainable atmosphere.     

Semi-rigid N-para-ferrocenyl(benzoyl)amino-acid esters for biomaterials: synthesis and characterization of Fc-C6H4CONHCH(R)CO2Me where Fc = (η5-C5H5)Fe(η5-C5H4) and R=H,CH3,CH2CH(CH3)2,CH2C6H5 and the X-ray crystal structures of Fc-C6H4CO2Me and the l-alanine derivative Fc-C6H4CONHCH(CH3)CO2Me

A series of N-para-(ferrocenyl)benzoyl amino-acid esters, para-Fc(C₆H₄)CONHCH(R)CO₂CH₃ {Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄); R = H, CH₃, CH₂CH(CH₃)₂, CH₂C₆H₅}, 3–6 have been prepared by coupling para-(ferrocenyl)benzoic acid to the amino-acid esters (gly, l-Ala, l-Leu, l-Phe) using the standard 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol. The compounds were fully characterized by a range of spectroscopic techniques including FAB-MS. The X-ray crystal structures of the parent para-(ferrocenyl)benzoyl methyl ester, Fc-C₆H₄CO₂Me, 1 and a chiral derivative N-{para-(ferrocenyl)benzoyl}-l-alanine methyl ester, Fc-C₆H₄CONHCH(CH₃)CO₂Me, 4 have been determined.     

HC-SCR reaction pathways on ion exchanged ZSM-5 catalysts

Metal cation (metal = Cu, In and La) ion exchanged ZSM-5 zeolites as catalysts for the NO selective reduction by propane and propene in excess oxygen. The surface reactions of HC-SCR over catalysts were investigated through in situ DRIFTS method. For C₃H₈-SCR, adsorbed nitrate species (–NO₃) were observed as main reaction intermediates and they could react with gaseous propane to produce N₂, H₂O and CO₂. While for C₃H₆-SCR, adsorbed amine species (–NH₂) were observed as main reaction intermediates and they could react with NO or NO₂ to produce the final products. The different reaction pathways for C₃H₈-SCR and C₃H₆-SCR over catalysts were proposed based on the DRIFTS results and the main factors controlling the activities of catalysts were discussed in details. The competing adsorption between NO–O₂ and HC–O₂ on the Brønsted acid sites of catalysts was responsible for the different reaction pathways in HC-SCR.     

Syntheses,structures, and magnetic properties of ethoxy-bridged dinuclear iron(III) complexes containing tetradentate ligands

Dinuclear iron(III) complexes, [(phenO)Fe(SO₄)]₂·2CH₃OH (1) and [(bpmapO)Fe(NO₃)]₂(NO₃)₂·3CH₃OH (2) have been prepared by the reaction of phenOH/bpmapOH and FeSO₄·7H₂O/Fe(NO₃)₃·9H₂O in methanol, respectively (phenOH = N-(2-pyridylmethyl)-N′-(2-hydroxyethyl)ethylenediamine, bpmapOH = N-(bis(2-pyridylmethyl)amino)-2-methylpropan-2-ol). Both complexes are ethoxy-bridged dinuclear species and the iron(III) ions in 1 and 2 have distorted octahedral geometries. Both complexes show strong antiferromagnetic interactions through the bridged ethoxy groups within the dimeric units.     

pH-dependent assembly of 1D–2D structures based on both {V10O28} and [NiMo6O24H6]4 − units: Synthesis,structure and magnetic properties

Two novel complexes [H₂N(CH₂CH₂)₂O]₄[Na(H₂O)₂{O(CH₂CH₂)₂NH₂}]₂[Na(H₂O)₄]₂[V₁₀O₂₈][NiMo₆O₂₄H₆]·8H₂O (1) and [H₂N(CH₂CH₂)₂O]₆[Na(H₂O)₃]₂[V₁₀O₂₈H₂][NiMo₆O₂₄H₆]·4H₂O (2) containing both isopolyvanadate {V₁₀O₂₈} and [NiMo₆O₂₄H₆]^4 − units have been synthesized and structurally characterized for the first time, showing that the pH value of the reaction plays a key role in structure control of self-assembled processes. Compound 1 exhibits a novel one-dimensional (1-D) chain-like structure consisting of Anderson-type [NiMo₆O₂₄H₆]^4 − and isopolyvanadate [V₁₀O₂₈]^6 − anions linked by Na⁺ ions. In compound 2 with the lower pH value, [NiMo₆O₂₄H₆]^4 − and [V₁₀O₂₈H₂]^4 − anions are bridged by [Na₂O₁₀] units to form the 2D extended layer. The magnetic properties of 1 and 2 are presented.     

Selective catalytic reduction of nitrogen oxides by ammonia on iron oxide catalysts

In this study, new Fe₂O₃ based materials are developed for the selective catalytic reduction (SCR) of NO_x by NH₃ in diesel exhaust. As a result of the catalyst screening, performed in a synthetic model exhaust, ZrO₂ is considered to be the most effective carrier for Fe₂O₃. The modification of the Fe₂O₃/ZrO₂ system with tungsten leads to drastic increase of SCR performance as well as pronounced thermal stability. These results show that tungsten acts as bifunctional component. The highest catalytic activity is observed for ZrO₂ that is coated with 1.4 mol% Fe₂O₃ and 7.0 mol% WO₃ (1.4Fe/7.0W/Zr). By the use of this catalyst quantitative conversion of NO_x is obtained between 285 and 430 °C with selective formation of N₂. Here, the turnover frequency of NO_x per Fe atom is found to be 35 × 10⁻⁵ s⁻¹ that indicates a high catalytic performance. The SCR activity of the 1.4Fe/7.0W/Zr material is decreased in the presence of H₂O and CO₂, whereas it is increased by NO₂.Temperature programmed reduction by H₂ (HTPR) analyses show that the Fe sites of the 1.4Fe/7.0W/Zr catalyst are mainly in the form of crystalline Fe₂O₃, whereby relatively small oxide entities are also present. The strongly aggregated Fe₂O₃ species are associated with the presence of the promoter tungsten. Based upon stationary catalytic examinations as well as diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies we postulate an Eley Rideal type mechanism for SCR on 1.4Fe/7.0W/Zr catalyst. The mechanistic model includes a redox cycle of the active Fe sites. As first reaction step, we assume dissociative adsorption of NH₃ that leads to partial reduction of the iron as well as to production of very reactive amide surface species. These amide intermediates are supposed to react with gaseous NO to form N₂ and H₂O. In the final step, the reduced Fe sites be regenerated by oxidation with O₂. As a side reaction of SCR, imide species, originated from decomposition of amide, are oxidized by NO₂ or O₂ into NO.     

Partial hydrogenation of propyne over copper-based catalysts and comparison with nickel-based analogues

The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al₂O₃ and Cu/SiO₂). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N₂ adsorption, H₂-TPR, XPS, and N₂O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523 K using H₂:C₃H₄ ratios of 1–12 and were complemented by operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C₃H₆ selectivity up to 80% at full C₃H₄ conversion and stable performance in long-run tests at T ? 473 K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites [S. Abelló, D. Verboekend, B. Bridier, J. Pérez-Ramírez, J. Catal. 259 (2008) 85] exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.     

Copper–cobalt heterobimetallic ceramic oxide thin film deposition: Synthesis,characterization and application of precursor

Thin films of halide free Cu–Co mixed metal oxide have been prepared at 390 °C from the heterobimetallic complex Co₄(THF)₄(TFA)₈(μ-OH)₂Cu₂(dmae)₂ · 0.5C₇H₈ (1) [dmae = N,N-dimethylaminoethanol ((CH₃)₂NCH₂CH₂O⁻), TFA = triflouroacetate (CF₃COO⁻), THF = tetrahydrofurane (C₄H₈O)] which was prepared by the reaction of [Cu(dmae)Cl]₄ and Co(TFA)₂ · 4H₂O. The precursor was characterized for its melting point, elemental composition, FTIR and X-ray single crystal structure determination. Thin films grown on glass substrate by using AACVD out of complex 1 were characterized by XRD and SEM. TGA and AACVD experiments reveal it to be a suitable precursor for the deposition of halide free Cu–Co mixed-metal oxide thin films at relatively low temperatures.     

Influences of NH3 pre-treatment and radicals on the growth of carbon nanotubes

A triple-layered catalyst (Al/Fe/Mo) undergoes considerable restructuring of surface morphology during NH₃ annealing prior to carbon nanotube (CNT) growth. The diameter (or density) of Al_xO_y–Fe clusters formed during the annealing is found to be dependent on the concentration ratio of NH₃ to H₂O present inside the chamber, which is confirmed by in-situ mass spectroscopy. The different diameter clusters then affect the types of CNTs (i.e. single or multi-walled CNTs) during the growth. Here, a growth model is also presented, where hydrocarbon radicals (C₅H₉, C₆H₉, and C₆H₁₃) generated from C₂H₂ pyrolysis (~ 800 °C) can be used as effective precursors to synthesize CNTs.     

Effects of Fe addition on the structure and catalytic performance of mesoporous Mn/Al–SBA-15 catalysts for the reduction of NO with ammonia

Mesoporous Al–SBA-15 has been synthesized by a hydrothermal method and used as a support for Mn/Al–SBA-15, Fe/Al–SBA-15, and Mn–Fe/Al–SBA-15 catalysts. XRD, N₂ sorption, XPS, H₂-TPR and activity tests have been used to assess the properties of catalysts. The Mn–Fe/Al–SBA-15 catalyst exhibited a higher SCR activity than Mn/Al–SBA-15 or Fe/Al–SBA-15 due to a synergistic effect between Mn and Fe. After the addition of Fe, the binding energy of Mn 2p_3/2 on Mn–Fe/Al–SBA-15(573) decreased by about 0.4 eV and the Mn^4 +/Mn^3 + ratio decreased to 1.10. The appropriate Mn^4 +/Mn^3 + ratio may have a great effect on the reduction of NO over Mn–Fe/Al–SBA-15(573) catalyst.     

Catalytic partial oxidation of ethane to ethylene and syngas over Rh and Pt coated monoliths: Spatial profiles of temperature and composition

The catalytic partial oxidation of C₂H₆ over Pt and Rh coated monolithic supports (4.7 wt% M/α-Al₂O₃ 45 PPI) was investigated with a capillary sampling technique for a range of C₂H₆/air ratios at constant inlet flow (～8 ms contact time), with and without H₂ addition. Effluent data clearly indicate the differences in product distribution between catalysts and equilibrium. Rh effectively converts the reactant mixtures to syngas with ～80% selectivity, whereas Pt produces C₂H₄ with ～55% C-atom selectivity, while neither produces thermodynamically favored C. Spatially resolved measurements provide direct evidence of the multi-zone nature of the reactors. With Rh, complete conversion of O₂ occurs to produce mostly CO, H₂ and H₂O within the first 3 mm of catalyst, followed by a reforming zone to produce additional syngas. Pt consumes O₂ more slowly, which results in a steady increase in temperature along the reactor. Ethylene formation correlates to reactor temperatures >750 °C, regardless of C/O, in line with the onset of homogeneous reactions. Hydrogen addition tests (C₂H₆/O₂/H₂=2/1/2) clearly exhibit preferential oxidation of H₂ with O₂ over Pt, which shifts the maximum in temperature upstream while preserving a portion of the C₂H₆ for C₂H₄ production. H₂ addition modifies the concentration and temperature profiles minimally on Rh. The main differences between catalysts are the high reforming and O₂ consumption activity with Rh compared to Pt, which are likely responsible for differences in C₂H₄ yields.     

Base-free copper-catalyzed aerobic oxidation of benzylic alcohols with N-benzylidene-N,N-dimethylthane-1,2-diamine and TEMPO

Selective oxidation of alcohols using N-benzylidene-N,N-dimethylthane-1,2-diamine, CuBr₂ and TEMPO as the catalytic system was developed. Catalyzed by this simple catalytic system in the absence of any external base, various benzylic alcohols could be oxidized to their corresponding aldehydes with excellent yields in CH₃CN/H₂O (v/v = 1/1) under 0.2 MPa O₂ at 80 °C.     

Five and six-coordinate silicon complexes with an O,N,O′-chelating ligand derived from o-hydroxyacetophenone–N-(2-hydroxyethyl)imine

The reaction of o-hydroxyacetophenone–N-(2-hydroxyethyl)imine, 1, with suitable chlorosilanes in the presence of triethylamine gives access to five and six-coordinate silicon complexes. The molecular structures of TBPY-5–34-[2-oxy-κO-acetophenone–N-(2-oxy-κO-ethyl)iminato-κN]diphenylsilane, C₂₂H₂₁NO₂Si, 2, and OC-6–22′-bis[2-oxy-κO-acetophenone–N-(2-oxy-κO-ethyl)iminato-κN]silicon · chloroform, C₂₀H₂₂N₂O₄Si · CHCl₃, 3, have been determined as representative examples.