The effect of boron addition on texture and structure of NiMo/Al2O3 catalysts

The effect of support (Al₂O₃) modification with borate ions and the effect of their concentration on the texture and structure of nickel-molybdena catalysts were studied. The surface area and pore volume of the samples were determined using the BET method, whereas pores distribution – besides the BET method also by mercury porosimetry. FT-IR, derivatographic, and diffractometric studies were also performed. Modification with borate ions does not bring about any change in the type of the support pores, nor does it change its crystallic structure. However, a considerable decrease in the surface area of the support was observed. It was shown that modification with borate ions leads to a decrease in thermal stability of catalysts, yet increase in concentration of borate ions raises the thermal stability of the samples. It was found that on the catalyst surface borate ions form a well-dispersed monolayer structure.     

A Study of Porous and Surface Properties of Nickel-Molybdenum Catalyst Incorporated on Alumina Modified with Sodium and Magnesium Ions

A series of nickel-molybdenum samples supported on alumina modified with sodium or magnesium ions was studied by the BET method, differential thermal analysis (DTA) and IR spectroscopy to determine their surface properties, pore volume and distribution. Modification with sodium and magnesium ions causes a decrease of the surface area of the nickel-molybdenum catalysts. The decrease proceeds with increasing concentration of the modifying ions. Incorporation of these ions does not change the type of catalyst pores (the ink-bottle or bottle types), yet it affects the size and distribution of pores. It was found that sodium ions prevent from the formation of aluminum molybdate, while magnesium ions increase the thermal stability of the catalyst.     

Structure and Texture of Nickel-Molybdenum Catalysts on Alumina Support Modified with Fluoride or Chloride Ions

The performed study involves measurements of a specific surface area via a BET method, of the pore volume, FT-IR, and a derivatographic study of a series of Al₂O_3-supported nickel-molybdenum catalysts modified with fluoride and chloride ions. It was found that fluoride ions lead to a decrease in the specific surface area of catalysts, whereas chloride ions have a small effect on this parameter. Modification does not change the type of pores of the catalysts, yet it affects their size and increases concentration of OH groups adsorbed on the surface of the catalysts relative to the carrier and the unmodified catalyst. Addition of fluoride ions decreases the thermal stability of the catalyst, whereas chloride ions does not cause any change.     

Characterization of nickel–alumina aerogels with high thermal stability

The characterization of NiO–Al₂O₃ aerogels prepared from nickel nitrate and aluminum iso-propoxide through a sol–gel processing and subsequent supercritical drying was performed. The UV–visible, XPS and FT–IR investigations revealed that nickel ions were incorporated into alumina spinel structure as nickel aluminate form, not as nickel oxide, after calcination. TEM observations after the subsequent reduction exhibited uniform and fine nickel particles less than 6 nm diameter throughout the alumina aerogel support with high dispersion, by which not only high thermal stability of the metal at elevated temperatures but also high reforming activity and stability should be brought about. The large surface area and pore volume also provided the catalyst stability through the improvement of the thermal stability of alumina support.     

The Effect of Sequence Incorporation of Sodium Ions on Structural and Thermal Properties of CoMo/Al2O3

The alumina supported cobalt-molybdena catalysts containing sodium ions were subjected to X-ray diffraction studies, IR spctroscopy and thermal analysis. Sodium ions were introduced onto Al₂O₃ either simultaneously with the other components, or prior to them or after them. Di- and polymolybdates phases were found to be formed on the support in all samples. In samples obtained in a two-stage process the interaction of Na⁺ ions with the support ions was detected which did not occur in samples obtained in a single-stage process. Nitrate ions introduced simultaneously with the other components undergo a relatively strong thermal decomposition while in the samples synthesised in two stages they are strongly bounded. The greatest number of strongly bound nitrates was found in the sample into which sodium ions were introduced in the second stage of the preparation procedure.     

硫酸钠熔盐制备片状α-Al2O3的研究

分别以十八水合硫酸铝和氢氧化铝为γ-Al2O3源,以硫酸钠为熔盐,干法混合熔盐和γ-Al2O3,采用熔盐法制备片状氧化铝.结果表明:以氢氧化铝为γ-Al2O3源,由于氢氧化铝为母盐分解后仍保留球形多面体的母盐假相,熔盐只能溶解球形多面体表面的氧化铝,经过溶解-沉淀过程生长出少量镶嵌于球形多面体的片状氧化铝,不能制备片状氧化铝;以十八水合硫酸铝为氧化铝源,分解后形成的分散程度良好的γ-Al2O3与硫酸钠熔盐摩尔比γ-Al2O3∶Na2SO4=1∶4时能够充分溶解于熔盐中,可制备出分散的片状氧化铝.     

Nano‐sized silver crystals and their dispersion over α‐alumina for ethylene epoxidation

Ethylene oxide catalyst is a high metal loading catalyst, in which silver crystals is impregnated on α‐Al₂O₃ support. In this type of catalyst, metal dispersion plays an important role on catalyst selectivity for desired products. In this work, silver nitrate and silver oxide together with oxalic and lactic acid as the raw materials were used with different impregnation techniques to make catalysts with high silver content and dispersion. It is also known that the use of promoters affect the metal dispersion on the catalyst support and for that cesium was used as the promoter to improve the silver crystal dispersion. Physical and chemical characteristics of the prepared catalysts, i.e., surface area, pore volume, silver content, nano‐sized silver crystals and their dispersion were measured using BET method, Atomic Absorption Spectroscopy, X‐ray diffraction and TEM. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

磷酸盐结合法制备Al2O3多孔陶瓷及性能

以煅烧α-Al2O3粉为骨料、磷酸二氢铝为高温烧成粘结剂、石蜡为成型助剂,通过模压成型、干燥、烧结等工序制备了氧化铝多孔陶瓷,研究了烧成温度和磷酸二氢铝含量对氧化铝多孔陶瓷微观形貌、物相组成、线收缩率、孔隙率和弯曲强度的影响,探讨了磷酸盐结合法烧结机理.结果表明:氧化铝多孔陶瓷物相由α-Al2 O3和AlPO4构成,在较低温度下,氧化铝颗粒仅依靠AlPO4的粘结作用而形成多孔陶瓷,氧化铝多孔陶瓷线收缩率和弯曲强度随磷酸二氢铝含量的增加而缓慢增大,孔隙率则缓慢降低;随着烧结温度的提高,AlPO4的存在促进了氧化铝颗粒间的液相烧结,线收缩率和弯曲强度随烧结温度的升高而显著增大,孔隙率也明显降低.     

Hydrogenation of p-chloronitrobenzene over NiPtB nanoalloy catalysts

NiPtB nanoalloy catalysts with various Ni contents were prepared by chemical reduction method at room temperature using NaBH₄ as reducing agent. Pt and Ni cations were completely reduced to metals, and small amount of boron was also reduced and form alloy with metals. NiPtB formed nanosized alloy structure and X-ray diffraction patterns showed its amorphous nature. The particle size distribution and the surface composition were affected by Ni/Pt ratio in the starting materials and the temperature of heat treatment. The catalytic activity of the nanoalloys was tested for hydrogenation of p-chloronitrobenzene (p-CNB). The activity and selectivity to p-chloroaniline (p-CAN) were affected by the content of Ni in the catalyst. For NiPt_0.01B catalyst, the occurrence of surface segregation of B was driven by the strain energy at high reaction temperature. For NiPt_0.03B and NiPt_0.01B catalysts, Pt segregated to the surface by H₂ affinity. Ni/Pt ratio decreased as the reaction temperature increased. The activity was essentially affected by the addition of Ni on Pt in the NiPtB catalyst, as expected, because Pt is more active than Ni for this reaction. The hydrogenation of p-CNB was very selective and yielded p-CAN exclusively on NiPtB catalysts than that on Pt catalyst.     

AES and FTIR characterization of sol–gel alumina films

In this work we obtained sol–gel alumina coatings on AISI 304 stainless steel substrates. Alumina sols were prepared by using aluminum isopropoxide (AI) as precursor, acetic acid (HOAc) as catalyst, ethanol (C₂H₅OH) or isopropanol (C₃H₈O) as solvent, and water. The as-prepared solutions were deposited on stainless steel substrates by means of the dip-coating technique. The obtained composites were characterized by Fourier transform infrared spectroscopy (FTIR) and Auger electron spectroscopy (AES). We observed that the concentration of AlO type bonds in the obtained alumina coatings depends on the solvent type used, temperature and peptization state of the sol, withdrawal speed, and number of dipping cycles. AES experiments showed that the interface formed between the alumina coating and substrate surface is in general formed by several layers of different chemical compositions.     

Synthesis of nanosized ZSM‐5 using different alumina sources

Alumina sources can influence different aspects of ZSM‐5 crystallization and it leads to change in the properties of the final product. The crystallinity of nanosized ZSM‐5 zeolite from precursors mixtures containing different alumina sources, e.g. sodium aluminate, aluminum sulphate, aluminum hydroxide and alumina has been studied. The produced samples were investigated using XRD, SEM, FT‐ IR and BET surface area. The product obtained by sodium aluminate and aluminum sulphate was ZSM‐5 phase. Whereas, the product obtained by aluminum hydroxide and alumina was the albit phase. As‐synthesized ZSM‐5 was prepared by sodium aluminate, as alumina source was the highest crystallinity. It was found that the average crystallite size increased in the following order; alumina <aluminum hydroxide < aluminum sulphate < sodium aluminate. The surface area increased in the following order; aluminum sulphate < sodium aluminate < aluminum hydroxide < alumina due to increasing in crystallinity percentage of ZSM‐5. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthetic nanodiamonds (SNDs) containing bimetallic Ni(Co)–Fe composites: preparation,characterization and catalytic performance in the reaction of CO2 methanation

Abstract

In this article, we present the preparation, characterization, and catalytic performance of bimetallic Co₉₃Fe₀₇ and Ni₈₀Fe₂₀ active mass loaded on synthetic nanodiamonds (SNDs) in the carbon dioxide (CO₂) methanation. The pristine SNDs possessing a developed specific surface are thermally stable and inert to the reaction mixture of CO₂ and dihydrogen. However, it is shown that 100% conversion of CO₂ into methane can be reached at the lower temperature than that for a massive Co₉₃Fe₀₇ or Ni₈₀Fe₂₀ catalyst when 20?wt.% of the catalyst mass was loaded on the surface of SNDs. The catalytic activity of the prepared bimetallic/SNDs composites is estimated as the minimum temperature at the maximum conversion of CO₂ at atmospheric pressure: it is 325 and 290?°C for Co₉₃Fe₀₇/SNDs and Ni₈₀Fe₂₀/SNDs, respectively. Thermal desorption studies showed that the methanation over Co-Fe/SNDs and Ni-Fe/SNDs catalysts run through the stage of CO₂ dissociation into carbon and oxygen atoms and their subsequent interaction with hydrogen to form methane and water molecules. Scanning electron microscopy studies have shown that the presence of transition metal-rich sites on the surface of the carrier contributes to the improvement of efficiency of the Ni₈₀Fe₂₀ catalyst action.     

Characterization and hydrogenation of methyl oleate over Ru/TiO2, Ru–Sn/TiO2 catalysts

The hydrogenation of methyl oleate over 2%Ru/TiO₂, 4.7%Sn/TiO₂ and 2%Ru–4.7%Sn–TiO₂ catalysts was studied. The catalysts were prepared by the impregnation method. The characterization techniques used were: (i) specific surface area (B.E.T. method); (ii) pore volume and mean pore diameter; (iii) thermogravimetric analysis (TGA); (iv) temperature programed reduction (TPR); (v) X-ray diffraction (DRX); and (vi) scanning electron microscopy (SEM). The results indicate that the presence of tin increases the difficulty of the ruthenium reduction, evidencing a possible metal–metal interaction. However, tin addition to the TiO₂ and the catalysts calcinations did not significantly influence the values obtained for the surface area and mean pore diameter. The DRX analyses showed that the catalysts have a crystalline structure, mostly in the anatase form. The metal-support interaction occurred probably due to the formation of RuTi of Ru/TiO₂ catalyst. In Ru–Sn/TiO₂ catalyst, the metal–metal interaction occurs between ruthenium and tin, resulting in Ru₃Sn₇. The catalysts reaction revealed that tin addition in ruthenium affects the activity of catalyst considerably in the hydrogenation of methyl oleate reaction. However, the activity decrease is accompanied by a considerable increase of alcohols yield, in particular of unsaturated alcohols.     

Effects of metal precursor in the sol–gel synthesis on the physicochemical properties of Pd/Al2O3–CeO2 catalyst: CO oxidation

The object of this research was to investigate the effects of various precursors and different fabricating procedures of Pd/Al₂O₃–CeO₂ catalysts by the sol–gel method. The physicochemical properties and structures of catalyst were characterized with BET surface area, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The performance of the Pd/Al₂O₃–CeO₂ catalyst was also evaluated by CO oxidation tests with a continuous quartz reactor. The results indicated that the catalyst prepared with inorganometallic precursors showed a high dispersion of Pd, large surface area and pore volume, and a high activity in CO oxidation. The higher redox interaction between Pd and Ce of the support starting with inorganometallic precursors, as determined from X-ray powder diffraction, is suggested as being responsible for such a catalytic behavior.     

Structural characterization of alumina-supported nickel molybdena catalysts

The object of our studies was a NiMo/Al₂O₃ catalyst thermally activated in oxygen, hydrogen, and in a mixture of hydrogen and hydrogen sulfide. On the surface of the oxide form of the catalyst there are different species, among them dimeric and polymeric octahedrally coordinated Mo⁶⁺ ions containing oxygen bridges are found. The presence of structures resembling α- and β-NiMoO₄ and 6-heteropolymolybdenates was determined. Reduction with hydrogen leads to formation of two nuclear structures with single and double bridges of [Mo₂⁵⁺ O₃] and [Mo⁵⁺ O₄] type, respectively, and partially reduced 6-heteropolymolybdenates. On the other hand, when the reduction and sulfiding take place at the same time, then terminal oxide ions are partially replaced by sulfide ones. The presence of [MoO₂S₂]²⁻ species has been observed, however, there is no evidence of the exchange —OH groups for —SH ones and exchange of oxygen bridged ions for sulfur ions. It has been also noted that the subsurface structures remained intact after reduction and sulfiding.     

Effect of preparation conditions on the phase transformation of mesoporous alumina

A post-hydrolysis method is proposed for the easy-and-fast preparation of mesoporous γ-alumina (MA) at room temperature using an alkyl carboxylate as a chemical template. Water was used as an initiating solvent in the hydrolysis of aluminum alkoxide in the terminal reaction procedure. Hydrolysis and condensation reactions were simultaneously induced. The initial phase of as-made MA was bayerite and/or (pseudo)boehmite, and was transformed into active alumina at 250 °C, which remained thermally stable at temperatures up to 600 °C. The phase transformation of alumina was analyzed with DTA, XRD and ²⁷Al MAS NMR. Based on an ²⁷Al MAS NMR analysis, calcined alumina prepared via a hydrothermal method contained a high ratio of Al^VI to Al^IV (∼4.8), which is not fully transformed into active alumina, and aluminum hydroxide (AlOOH or Al(OH)₃) was detected. These results suggest that high temperature is required to obtain an active form of alumina, when the hydrothermal method is used. Another factor is the ratio of Al^VI to Al^IV in the MA, which is also dependent on the pH of the reactant. Pore size, surface area, and pore structure could be controlled by adjusting the molar ratio of water to aluminum precursor, and the preparation temperature. The pore size of MA was adjustable from 2 to 7 nm, and the MA indicated a large surface area of 300 ∼ 500 m²/g.     

Advanced nanostructure Ti0.7In0.3O2 support enhances electron transfer to Pt: Used as high performance catalyst for oxygen reduction reaction

ABSTRACT

The slow rate of the oxygen reduction reaction (ORR) and the instability of Pt based catalysts are two of the most important issues which must be solved in order to make proton exchange membrane fuel cells (PEMFCs) a reality. Here, we present a new approach by exploring robust non-carbon Ti_0.7In_0.3O₂ used as a novel functionalised co-catalytic support for Pt. This approach is based on the novel nanostructure Ti_0.7In_0.3O₂ support with “electronic transfer mechanism” from Ti_0.7In_0.3O₂ to Pt that can modify surface electronic structure of Pt, owing to a shift in the d-band centre of the surface Pt atoms. The 20 wt% Pt/Ti_0.7In_0.3O₂ catalyst shows high activity than that of that of the commercial 20 wt% Pt/C (E-TEK). Our data suggest this enhancement is a result of both the electronic structure change of Pt upon its synergistic interaction with Ti_0.7In_0.3O₂ and the inherent structural and chemical stability and the corrosion-resistance of the Ti_0.7In_0.3O₂ in acidic and oxidative environments.     

Preparation and characterization of monolithic alumina aerogels

Alumina aerogels were prepared by a sol-gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m²/g. It was transformed to γ-Al₂O₃ after heat treatment at 800 °C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4 MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30 °C and 400 °C were 0.028 W/mK and 0.065 W/mK respectively.     

Phosphate ion removal from a solution by soda-lime borosilicate glass

The excessive phosphate ion content in industrial wastewater causes water eutrophication. The objective of this study is to develop a new method of phosphate ion removal from wastewater using soda-lime borosilicate glass. Soda-lime borosilicate glass with high content of modifiers is reacted in a solution containing phosphate ions. Ca²⁺ ions that are leached out of the glass combine with P⁵⁺ ions in a solution to form hydroxyapatite crystals on the glass surface. The phosphate ions can thereby be removed from the solution. The phosphate ion removal rate was highest when glass containing 20–30 mol% of CaO was reacted in a solution with pH of 3.0. The phosphate ion removal rate was faster when the glass was reacted with the solution under a dynamic condition than under a static condition. The elimination rate also strongly depended on the surface area of the glass.     

Cooling crystallization of aluminum sulfate in pure water modulated by sodium dodecylbenzenesulfonate

This study investigated the cooling crystallization of aluminum sulfate to explore the basic data for the recovery of aluminum resources from coal spoil. Cooling crystallization process of aluminum sulfate with sodium dodecylbenzenesulfonate (SDBS) was investigated experimentally. The effects of operating conditions, namely rotate speed and cooling rate on the crystal size (Median diameter, D_0.5) were studied. Based on single factor experimental results, the response surface method (RSM) with a Box–Behnken design (BBD) was used to determine the key operating conditions, from which a predictive equation was established to quantitatively describe the relationships of D_0.5 and there relative parameters. The optimum operating conditions for cooling crystallization of aluminum sulfate were as follows: rotate speed of 200–300 rpm, cooling rate of 4–5 °C /min and n (SDBS)/n (Al₂(SO₄)₃) of around 5E‐4. Molecular dynamics (MD) results reveal that SDBS decreases the diffusion coefficient (D) of Al³⁺ molecules, which inhibits nucleation and promotes crystal growth.