Synthesis of nanofibrous carbon with herringbone structure on Ni-supported SiC particles using hot CVD apparatus

A nanofibrous carbon material having a herringbone structure was synthesized using Ni-supported silicon carbide (SiC) particles as the catalyst for the hot chemical vapor deposition (CVD) process using CH₄ as carbon source. The amount of the deposits during the CVD process strongly depended on the CVD treatment temperature. The enhancement of weight and the TG data indicated that the quantity synthesis of the deposits was achieved at 823 K. The specific surface area of the deposits was estimated at ca. 120 m² g^− 1. It was confirmed from the TEM images that the deposits synthesized in this study had a herringbone-like structure. From the data of Raman spectra and XRD patterns, the herringbone-like structure started to deposit after 30 minutes in the case of 823 K. The Ni-supported SiC can be used as the catalyst for the synthesis of nanofibrous carbon materials.     

Effect of composition and promoters in Au/TS-1 catalysts for direct propylene epoxidation using H2 and O2

A series of Au/titanium silicalite-1 (TS-1) catalysts with different Si/Ti ratios and promoted with alkali and alkaline earth cations were prepared by deposition–precipitation (DP) and tested for direct propylene epoxidation. It was found that the gold loading and catalytic activity was highly dependent on the pH of the DP synthesis solution and the final composition of the catalyst. Addition of Group 1 metals such as K or Cs had little effect on the gold content, but increased activity, while Group 2 metals such as Mg, Ca, Sr, and Ba increased both the gold content and the catalytic activity. The highest improvement was provided by a Mg promoted catalyst, which at 443 K and 0.1 MPa with a H₂/O₂/C₃H₆/Ar = 1/1/1/7 feed mixture gave a propylene oxide (PO) formation rate of 88 gPO h⁻¹ kg_cat⁻¹, compared to 57 gPO h⁻¹ kg_cat⁻¹ for an unpromoted catalyst, corresponding to a 50% enhancement of activity. Ammonia temperature-programmed desorption (NH₃-TPD) measurements indicated little change in adsorption amount with promotion indicating that the yield increase was not due to the elimination of acidic sites on the catalyst. Instead, the improved catalytic performance was ascribed to increased Au capture efficiency and dispersion by the catalyst. The effect of Si/Ti ratio, pH of synthesis, and the promoter ions on the gold content could be understood from their effect on the surface charge of the support.     

Kinetics studies of nano-structured cobalt–manganese oxide catalysts in Fischer–Tropsch synthesis

The nano-structured cobalt/manganese oxide catalyst was prepared by thermal decomposition of [Co(NH₃)₄CO₃]MnO₄ precursor, and was tested for the Fischer–Tropsch reaction (hydrocarbon forming) in a fixed-bed micro-reactor. Experimental conditions were varied as follow: reaction pressure 1–10 bar, H₂/CO feed ratio of 1–2 and space velocity of 3600 h^?1 at the temperature range of 463.15–523.15 K. On the basis of carbide and/or enolic mechanisms and Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equations, 30 kinetic expressions for CO consumption were tested and interaction between adsorption HCO and dissociated adsorption hydrogen as the controlling step gave the most plausible kinetic model. The kinetic parameters were estimated with non-linear regression method and the activation energy was 80.63 kJ/mol for optimal kinetic model. Kinetic results indicated that in Fischer–Tropsch synthesis (FTS) rate expression, the rate constant (k) has been increased by decreasing the catalyst particle size. The catalyst characterization was carried out using different methods including powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area measurements.     

Aqueous synthesis of high surface area metal oxides

By applying high throughput synthesis and characterization technologies, we have been optimizing common dry or aqueous synthetic routes for the preparation of high surface area metals and oxides, such as precipitation and modified Pechini methods. For wet combustion synthesis, we have been screening a variety of organic acids as dispersants and developed proprietary recipes for individual metals. By resorting to easily decomposable organic acids (as opposed to citric acid in the original Pechini combustion method), such as glyoxylic acid, oxalacetic acid and ketoglutaric acid, it is possible to obtain high surface area materials for many metals after careful optimization of acid/metal ratio and calcination conditions. Examples are Sn, In, Co, Ru, Ni, Fe, Mn, Y, Ce and Rare Earth oxides and their mixtures. After calcination in the temperature range of about 300–400 °C, surface areas >150 m²/g could be obtained for Er, Tm, Co, Ru, and Nb; >200 m²/g for Sn, Fe, Mn, and Y; >300 m²/g for Ce; and >400 m²/g for Ni oxide. Noteworthy are also >140 m²/g for La₂O₃, >80 m²/g for CuO, and 75 m²/g for ZnO. For V, around 40 m²/g was possible for the nearly carbon-free V₂O₅, whereas up to 90 m²/g was obtained for a 90% V–10% carbon composite (by incomplete combustion of the organic acid). Residual carbon helps in stabilizing the porous oxide against sintering. Thus, conventional aqueous routes (precipitation, Pechini) can be competitive to more elaborate and costly methods such as those using organic solvents, sol–gel, supercritical drying or template/hydrothermal synthesis. Combustion synthesis is well suited for the preparation of mixed oxides from mixed metal solutions in aqueous organic acids. Bulk porous Co and CoRu mixed oxides have been screened for liquid phase alcohol oxidations and CoRuCe oxides for CO oxidation and VOC destruction, and doped NiO has been reduced to the metal and tested for various hydrogenations.     

Study of induction period over K2CO3/MoS2 catalyst for higher alcohols synthesis

The K₂CO₃/MoS₂ catalyst for higher alcohols synthesis with synthesis gas as feedstock was prepared. The catalyst was characterized by TPR, in-situ XPS, XRD and SEM. Effects of pretreatment with H₂, CO or synthesis gas on activity and selectivity of the catalyst were investigated. Results showed that there was a remarkable induction period about 180 h at the initial reaction stage for the un-treated catalyst. The catalytic performances for alcohols synthesis changed notably during the induction period. The induction period was confirmed to be resulted primarily from the sulfur losing and K element dispersion on the surface of ADM catalysts. Pretreatment of the catalyst could remarkably shorten the time of induction period as well as promote the catalytic activity. Furthermore, the higher alcohols (C₂ + OH) content in the liquid products were enhanced after the catalyst pretreated by CO or synthesis gas which could be ascribed to the increasing of Mo⁴⁺ content on the surface of the catalyst.     

Ordered Mesoporous Silica (OMS) Supported Vanadium Nitride and Carbide Catalysts

Nanostructured vanadium nitride and carbide catalysts were prepared by the nitridation and carburization of vanadium oxide supported on M41S materials (MCM-41 and SBA-15) and activated carbon. The oxide precursors, V₂O₅/M41S, were obtained in three different synthesis strategies using “in situ” and “ex situ” incorporation of vanadia precursors (V(acac)₃) into the mesoporous host. For the oxide precursors specific surface areas exceeding 1,200 m² g⁻¹ were achieved. After nitridation a slight decrease of surface area was observed. All VN catalysts show a high activity in propane dehydrogenation with a selectivity exceeding 80% towards propene. Impregnation and nitridation conditions have profound influence upon the catalytic activity. The highest activity was observed for VN supported on NORIT A.     

Mesoporous aluminophosphates and Fe-aluminophosphates with highly thermal stability and large surface area templated from semi-fluorinated surfactant

A series of mesoporous aluminophosphates (MAP) and Fe-aluminophosphates (Fe-MAP) with highly thermal stability and large surface area have been successfully synthesized by the use of semi-fluorinated surfactant, which were characterized by XRD, TEM, N₂ adsorption, NMR, UV–Vis, and ESR techniques. These results show these samples are thermally stable up to 600 °C. More importantly, these samples give large surface area (BET, ca. 430–580 m²/g), which has an advantage for the use of catalysts or catalyst supports. In contrast, mesoporous aluminophosphates templated from copolymer surfactants such as F127 show relatively low surface area (<260 m²/g). Furthermore, UV–Vis and ESR spectra suggest that Fe species in Fe-MAP are mainly in tetrahedral coordination. Finally, the tests of hydroxylation of phenol with hydrogen peroxide show that Fe-MAPs are catalytically active.     

Combining molybdenum carbide with ceria overlayers to boost Mo/CeO2 catalyzed ammonia synthesis

The design of an efficient non-noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo₂C/CeO₂ catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low-valent Mo species, as well as high concentration of Ce³⁺ and surface oxygen species. The presence of Mo₂C and CeO₂ overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO₂ catalyst prepared without carbonization, the Mo₂C/CeO₂ catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo-based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis.     

A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

Hydrodeoxygenation of liquefied biomass on urchin-like MoS2

The synthesis of urchin-like crystalline MoS₂ with micron unit size and surface area of 25 m² g^− 1 and its application for the catalytic hydrogenation and hydrodeoxygenation (HDO) of liquefied wood sample are reported. We observed significant increase of deoxygenation rate considering intensities of CO and OH band intensities in liquid phase IR spectra. Prepared catalyst exhibited higher activity compared to commercial MoS₂ powder. Elemental analysis of organic phase after HDO revealed equal elemental compositions for both samples, with higher yield in case of urchin-like MoS₂. Oxygen content decreased from 43.3% to 8.2% (wt.); residual phenolic oxygen is not removable with catalyst described. Observed catalytic performance may provide new solutions in terms of biofuel processing.     

Ammonia decomposition on tungsten carbide

Decomposition of NH₃ is an important reaction in the cleaning of syngas obtained from the gasification of biomass as well as for the production of hydrogen for fuel cells from easily condensed NH₃. To the best of our knowledge, this paper reports for the first time a detailed study of NH₃ decomposition on tungsten carbide (WC). Results for a commercially available Fe ammonia synthesis catalyst (Amomax-10) are also reported for comparison.The WC catalyst was characterized by BET, XRD, SEM, EDX and temperature programmed reaction (TPRx). The catalytic behavior of WC strongly depended on pretreatment conditions. The highest activity was obtained with WC samples pretreated in an 80/20 mixture of H₂–CO. Complete decomposition of NH₃ was observed at 550 °C for 4000 ppm of NH₃ at a space velocity of 1,884,000 h⁻¹. At lower temperatures, the activity of the WC catalyst reached steady-state after an induction period that decreased in time with increasing temperature. Reconstruction of the surface during pretreatment and during decomposition of NH₃ is suggested to be responsible for the behavior of the catalyst observed during TPRx and time-on-stream (TOS) isothermal reaction. The commercial Fe NH₃ synthesis catalyst, although active for NH₃ decomposition, showed rapid partial deactivation following an induction period with a steady-state conversion of only 35% at 650 °C and the space velocity used. Thus, WC appears to be an excellent catalyst for use in ammonia decomposition.     

Preparation of a highly dispersed Ni2P/Al2O3 catalyst using Ni–Al–CO32 − layered double hydroxide as a nickel precursor

We now report a novel method for the synthesis of a Ni₂P/Al₂O₃-LW catalyst using Ni–Al–CO₃^2 − layered double hydroxide (Ni–Al–CO₃^2 −-LDH) as a nickel precursor and ammonium dihydrogen phosphate as a phosphorous precursor under microwave–hydrothermal (MWH) treatment for 20 min at 363 K. The catalysts were characterized by XRD, TPR, BET, CO uptake and XPS. MWH treatment can promote the formation of smaller and highly dispersed Ni₂P particles and a higher surface area of the catalyst. The Ni₂P/Al₂O₃-LW shows hydrodesulfurization activity of 99.3%, which was much higher than that found for the Ni₂P/Al₂O₃ catalyst obtained via an impregnation method.     

Study on a new iron catalyst for slurry Fischer–Tropsch synthesis

A novel spherical-shaped iron catalyst (100Fe/5Cu/6K/16SiO₂) with 0.24 wt% of SO₄²⁻ loading for slurry Fischer–Tropsch synthesis (FTS) was prepared by spray-drying using cheap industrial iron resource FeSO₄ · 7H₂O. The characterization results from BET, X-ray diffraction and temperature-programmed-reduction (H₂-TPR) show that the sulfate-containing catalyst exhibited higher surface area, more dispersed α-Fe₂O₃ phase and more facility of reduction than a sulfate-free catalyst. The FTS performance in a fixed bed reactor and in a continuous stirred tank reactor indicates that SO₄²⁻ species acts as a promoter by increasing catalyst activity and modifying hydrocarbon selectivity to heavier products.     

Optimization of mesoporous alumina sol-gel synthesis by Taguchi and response surface methodology

Taguchi method (TM) and response surface methodology (RSM) have been employed to optimize three parameters, including the amounts of P123, the amounts of nitric acid and calcination temperature, in order to define an optimal setting for sol-gel synthesis of high surface area mesoporous alumina powder (MA). Herein, the comparison of the both statistical approaches has been examined and discussed considering the nitrogen adsorption as the response variable because this important character for mesoporous materials is exceedingly sensitive to the synthesis parameters. The BET surface area (S_BET) and pore volume of MA under Taguchi optimal condition were 323.5 m² g⁻¹ and 0.551 cm³ g⁻¹, respectively, by conducting confirmation test. Furthermore, the confirmation test showed high S_BET of MA (363.4 m² g⁻¹), which was in a good agreement with calculated S_BET result (431.25 m² g⁻¹) by a quadratic model under RSM optimal condition. Moreover, 3D response surface plots and 2D contour plots of desirability have been discussed to visualize the influence of input factors on response variable. It is also concluded that RSM shows more appropriate (12.33% higher S_BET than TM) and efficient optimal condition with determining a quadratic function as the relationship between S_BET and synthesis parameters.     

Synthesis and characterization of carbon-supported nanoparticles for catalytic applications

Metallic and carburized tungsten nanoparticles have been prepared using WCl₆ as precursor. The synthesis steps lead from tungsten hexachloride to tungsten carbide following the sequence WCl₆ → W⁰ → α-W₂C → WC. These different compounds have been mainly characterized by X-ray diffraction, TEM observations and adsorption measurements. The total reduction of tungsten hexachloride can be completed at T = 973 K. The carburizing of the metallic lattice into carbide WC is observed at 1223 K although incomplete. At this temperature, crystal growth phenomena appear which are not desired for catalysis applications. The synthesis of nanoparticles supported on activated carbon is accompanied by a decrease of the specific surface area of samples, especially during high temperature carburizing.     

Microstructure,mechanical and thermal properties of in situ toughened boron carbide-based ceramic composites co-doped with tungsten carbide and pyrolytic carbon

Boron carbide (B₄C)-based ceramics were pressureless sintered to a relative density of 96.1% at 2150 °C, with the co-incorporation of tungsten carbide and pyrolytic carbon. The as-batched boron carbide power was 7.89 m² g^?1 in surface area. A level of fracture toughness as high as 5.80 ± 0.12 MPa m^1/2 was achieved in the BW-6C composite. Sintering aids of carbon and tungsten boride were formed by an in situ reaction. The toughness improvement was attributed to the presence of thermal residual stress as well as the W₂B₅ platelets. The thermal conductivity and thermal expansivity of the BW-6C composite as a function of temperature are also reported in this work. Our current study demonstrated that the B₄C–W₂B₅ composites could be potential candidate materials for structural applications.     

Synthesis of DME from syngas on the bifunctional Cu–ZnO–Al2O3/Zr-modified ferrierite: Effect of Zr content

The catalytic activity on the coprecipitated Cu–ZnO–Al₂O₃/Zr-ferrierite (CZA–ZrFER) with different Zr content from 0 to 5 wt.% was investigated for the direct synthesis of dimethylether (DME) from H₂-deficient and biomass-derived model syngas (H₂/CO molar ratio = 0.93). The catalytic functionalities, such as CO conversion and DME selectivity, showed their maxima on the bifunctional catalyst with 3 wt.% Zr-modified ferrierite. Detailed characterization studies were conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH₃-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), copper surface area measurements by N₂O titration method, electronic states of copper by IR analysis and particle size measurement by XRD and TEM analysis. The number of acid sites measured by NH₃-TPD on the bifunctional catalysts decreased monotonously with the increase of Zr content, meanwhile, the acidic strength is found to be minimal on the catalyst showing best performance. The reducibility of copper oxide and the surface area of metallic copper also exhibited their maximum values at the same Zr composition indicating that these are responsible for the optimum functionality of the bifunctional CZA–ZrFER catalyst. The role of easily reducible copper species with small particle size and the suppressed strong acidic sites is also emphasized in the consecutive reaction from syngas to DME on the bifunctional catalyst. The different behavior of intrinsic rate of the bifunctional catalysts is also well correlated with the metallic surface area of copper and the amount of acidic sites with their acidic strength.     

Partial methane oxidation into synthesis gas over catalysts supported on meshed metallic materials

Comparative tests of metal catalysts (Pd, Ni, Co, and Cu on a metal gauze and FeCrAl alloy foil) obtained in two ways—thermochemical and electrochemical metal deposition—have been carried out in order to develop efficient catalysts supported on meshed metallic materials for partial methane oxidation into synthesis gas. The tests have been performed in the 680–1000°C range in a flow reactor (10 mm i.d.) with a catalyst in the form of a rolled metal gauze or FeCrAl foil mounted inside. The metallic supports (gauze and foil) with metals (Pd, Ni) supported on them are promising as catalysts for producing synthesis gas by partial methane oxidation in a narrow range of oxygen : methane molar ratios (O₂ : CH₄ = 0.45–0.55). An SEM examination of the catalyst surfaces has demonstrated that the thermochemical deposition of Group VIII metals yields a more branched active metal surface that ensures almost 100% methane conversion at a CO selectivity of >90% even at 900°C.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

A Novel Catalyst Type Containing Noble Metal Nanoparticles Supported on Mesoporous Carbon: Synthesis,Characterization and Catalytic Properties

We report on a method for the controlled synthesis of a new type of high specific surface area mesoporous carbons denoted as the CMH family. By using mixtures of colloidal silica particles as templates it was possible to synthesize samples exhibiting 1,630 m² g⁻¹ specific surface area and 4.37 cm³ g⁻¹ pore volume. CMH materials exhibit high thermal stability in oxygen and can be used as catalyst supports. This function was demonstrated by synthesizing Pt/CMH and Rh/CMH catalysts and testing them in the hydrogenation of cyclohexene. We have found Pt/CMH to be more stable and easier to regenerate than Rh/CMH.