Fourier transform infrared spectroscopic study of surface acidity by pyridine adsorption on Mo/ZrO2-SiO2(Al2O3) catalysts

Acidity of the oxidic molybdenum catalysts supported on mixed ZrO2-SiO2 and ZrO2-Al2O3 carriers was investigated by Fourier transform infrared spectroscopy of pyridine adsorption. Deposition of molybdenum on ZrO2-SiO2 and ZrO2-Al2O3 supports leads to formation of surface Br?nsted acid sites. The number of the Br?nsted and Lewis acid sites in supported-molybdenum catalysts depends on both the ZrO2 content and the type of the support. With increasing ZrO2 content, the Lewis acid sites increase for both series of catalysts. The Br?nsted acid sites are higher for Mo/ZrO2-SiO2 samples compared to those for Mo/ZrO2-Al2O3 and also increase with zirconia.     

In situ ATR-IR study of prochiral 2-methyl-2-pentenoic acid adsorption on Al2O3 and Pd/Al2O3

Adsorption and desorption of trans-2-methyl-2-pentenoic acid (MPeA) in dichloromethane (CH(2)Cl(2)) were investigated by using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. A liquid flow-through spectroscopic cell allowed for high quality spectra to be obtained from deposited thin films of Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) on a ZnSe internal reflection element. The MPeA molecules adsorb on both Al(2)O(3) and Pd surfaces molecularly and dissociatively under the concentration range examined (2-16 mM). In the case of molecular adsorption, both monomer (ν(C=O) ~ 1720 cm(-1)) and dimer (ν(C=O) ~ 1685 cm(-1)) species are observed to adsorb, with the relative amount of monomer to dimer dependent on the surface and the liquid phase acid concentration. In the case of dissociative adsorption, the acid adsorbs predominantly in a bridged bidentate configuration, as adjudged by the ca. 150-220 cm(-1) separation between asymmetric and symmetric vibrational bands. All of these species are found to be strongly adsorbed on both Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) surfaces, even under pure solvent flow after adsorption.     

In situ studies of butyronitrile adsorption and hydrogenation on Pt/Al2O3 using attenuated total reflection infrared spectroscopy

The adsorption and hydrogenation of butyronitrile (BN) in hexane on a 5% Pt/Al2O3 catalyst has been studied using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. ATR-IR measurements were conducted on thin ( approximately 10 mum) films of catalyst deposited on Ge wave guides. Multivariate analysis involving classical lease-squares (CLS) and partial least-squares (PLS) modeling was used to aid in the interpretation of the spectroscopic data. During the adsorption of BN over a concentration range from 4 to 40 mM in hexane, no clear evidence for adsorbed N-bound end-on species could be detected. However, a feature at approximately 1635-1640 cm-1 indicated the presence of an adsorbed imine species, with the C=N group existing in a tilted configuration involving a strong degree of pi interaction with the surface. This assignment is bolstered by the detection of N-H stretching bands that are consistent with imine vibrations. This imine-type intermediate is very prominent and shows transient behavior in the presence of solution-phase hydrogen, suggesting that, once formed, it can be converted into amine products that adsorb on the catalyst surface. Evidence for amine formation was observed in the form of N-H stretching and NH2 bending vibrations, with assignments confirmed through comparison studies of butylamine adsorption under identical conditions. Comparisons between Pt/Al2O3 and Al2O3 suggest that there may be some adsorption of these amines on the support surface. The mechanistic implications with regard to heterogeneous nitrile hydrogenation on transition metals under mild conditions are briefly discussed in light of these findings.     

Intrinsic viscosity of SiO2, Al2O3 and TiO2 aqueous suspensions

The viscosity of dilute suspensions of several metal oxides (SiO2, Al2O3 and TiO2) was measured at different pH values. The intrinsic viscosity, [eta], was derived from the concentration dependence of the viscosity. This magnitude was pH-dependent. A correlation with the shape of the kinetic unity has been proposed.     

In situ attenuated total reflection infrared (ATR-IR) study of the adsorption of NO2-, NH2OH, and NH4+ on Pd/Al2O3 and Pt/Al2O3

In relation to the heterogeneous hydrogenation of nitrite, adsorption of NO2-, NH4+, and NH2OH from the aqueous phase was examined on Pt/Al2O3, Pd/Al2O3, and Al2O3. None of the investigated inorganic nitrogen compounds adsorb on alumina at conditions presented in this study. NO2-(aq) and NH4+(aq) on the other hand show similar adsorption characteristics on both Pd/Al2O3 and Pt/Al2O3. The vibrational spectrum of the NO2- ion changed substantially upon adsorption, clearly indicating that NO2- chemisorbs onto the supported metal catalysts. On the contrary, adsorption of NH4+ does not lead to significant change in the vibrational spectrum of the ion, indicating that the NH4+ ion does not chemisorb on the noble metal but is stabilized via an electrostatic interaction. When comparing the adsorption of hydroxylamine (NH2OH(aq)) on Pd/Al2O3 and Pt/Al2O3, significant differences were observed. On Pd/Al2O3, hydroxylamine is converted into a stable NH2(ads) fragment, whereas on Pt/Al2O3 hydroxylamine is converted into NO, possibly via HNO(ads) as an intermediate.     

Preparation of Gold Microcrystal-Doped TiO2, ZrO2 and Al2O3 Films Through Sol-Gel Process

Au-microcrystal-doped TiO₂, ZrO₂ and Al₂O₃ films were made by sol-gel dip-coating method using titanium, zirconium and aluminum alkoxides with HAuCl₄ · 4H₂O. The influence of the oxide matrix composition on the maximum amount of the Au microcrystals that can be incorporated in the oxide film was examined. Some amount of Au microcrystals were exhausted to the surface of Au microcrystal-doped oxide films when an excess amount of HAuCl₄ · 4H₂O was dissolved in the coating solution. The maximum amount of Au that can be incorporated in the oxide film was found to increase with the increase of the pH point at zero charge (PZC) of the matrix oxide. This should be due to the fact that AuCl ₄ ^- ions are charged negative and also Au microcrystals tend to charge negative, so that the oxide gel with high PZC, which has a tendency to charge positive, may fix the ions and/or microcrystals to its interior. A maximum amount of Au microcrystals as high as 12.6 vol% was attained in an Au:Al₂O₃ film.     

In situ investigation of acetonitrile adsorption on Al2O3-coated CaF2 using sum-frequency spectroscopy

Sum-frequency spectroscopy (SFS) has been used to probe the interface between a model catalyst support (Al(2)O(3)-coated CaF(2)) and liquid consisting of neat acetonitrile and acetonitrile in ethanol. Vibrational features associated with both CN stretching ( approximately 2242 and 2281) and C-H stretching ( approximately 2942 and 2989) are observed for adsorbed nitrile. The peak positions are only slightly shifted from the bulk values, indicating weak adsorption to the model support. In the case of the neat liquid, the C-H stretching vibrations have also been probed using various polarization combinations of the sum frequency, visible and infrared beams in order to determine the orientation of the nitrile with respect to the surface. The average molecular angle calculated ( approximately 39 degrees ) shows the off-normal alignment of acetonitrile on the surface of the model support. Finally, an attempt has been made to obtain qualitative information about the adsorption isotherm of acetonitrile on Al(2)O(3)/CaF(2). The lack of curvature in the isotherm indicates the lack of affinity for the surface by acetonitrile in ethanol.     

Adsorption and desorption studies of radiocesium on Al2O3 from aqueous solutions

The adsorption and the desorption of radiocesium from aqueous solutions containing NaNO₃ or CaCl₂ on Al₂O₃ were studied over a wide range of background electrolyte concentration and solution pH by using batch techniques in polyethylene and glass test tubes. It was found that the wall of the glass test tubes has a great effect on the adsorption and desorption data, and the adsorption-desorption hysteresis on the same time scale is negligible by using the same aqueous solutions for both adsorption and desorption in the polyethylene test tubes. The dependences of the distribution coefficient on the pH and background electrolyte concentration and the adsorption mechanism were discussed.     

Gas chromatographic analysis of aromatic,carboxylic acids in the presence of C1−C5 fatty acids and C2−C7 dicarboxylic acids esterified in aqueous solutions as the n-butyl esters

Summary The direct esterification and gas chromatographic analysis of aromatic carboxylic acids as n-butyl esters is described.Derivatization is performed in aqueous solution with n-butanol in the presence of sulfuric acid. The butyl esters of benzoic, phthalic, hemimellitic, trimellitic, trimesic and pyromellitic acids permit their gas chromatographic separation from each other and from fatty acids and alipatic dicarboxylic acids. At mole ratios of [H₂O]/ [n-BuOH]0.04 the water present does not interfere with the esterification reaction. At mole ratios above 0.04 anhydrous sodium sulfate is used for binding the water, at mole ratios of [Na₂SO₄ anh.]/[H₂O]=0.25–0.75.     

ZrO2和Al2O3在金红石型TiO2表面的包覆研究

以(NaPO3)6为分散剂,用化学沉积法对金红石型TiO2进行了锆、铝氧化物包膜。研究了包覆过程中,TiO2的分散、ZrO2和Al2O3用量、反应pH值以及时间对二氧化钛的亨特白度(Wh)和光泽度(L)的影响,并采用扫描电镜(SEM)、透射电镜(TEM)、X光电子能谱(XPS)和沉降性试验对包覆前后的二氧化钛进行了表征,得到包锆、包铝氧化物的优化工艺条件。研究了二氧化钛表面包锆、铝氧化物的包覆机理和表面结构。经过其表面包膜处理,二氧化钛的颜料性能得到明显改善。     

One-stage conversion of aromatic carboxylic acids into 2, 5-diaryl-1, 3, 4-oxadiazoles

A method has been developed for the one-stage conversion of aromatic carboxylic acids into symmetrical 2, 5-diaryl-1, 3, 4-oxadiazoles by heating them with hydrazine hydrochloride in polyphosphoric acid.     

负载型纳米ZrO2/Al2O3复合载体的制备和表征及其Ni/ZrO2/Al2O3催化性能的研究

以大孔Al2O3为基载体，采用沉积-沉淀法和溶胶-沉积法制备了负载型纳米ZrO2/Al2O3复合载体．用XRD、TEM和比表面与孔径测定等手段对载体进行了表征．结果表明，负载型纳米ZrO2/Al2O3复合载体具有较大的比表面积和适宜的孔径分布，纳米ZrO2在载体上呈单层均匀分布．以CH4-CO2重整制合成气为探针反应，考察了Ni/ZrO2/Al2O3催化剂的活性和选择性．     

Rules governing vapor-phase extraction of carboxylic acids and phenols from aqueous solutions

The influence of the molecular structure of the components to be extracted and the type of the extractant used on the effectiveness of vapor-phase extraction from water was studied for the example of low-molecular-weight carboxylic acids C₂-C₆ and phenols. Extraction parameters were found to depend on the length of the analyte molecule and its polarity. The experimental data and correlations observed substantiated the validity of the suggested mechanism of vapor-phase extraction. Changes in the Gibbs energy of extraction equilibrium as the length of the analyte molecule (in the homologous series of organic acids C₂-C₆) and molecule polarity (for the example of cresol isomers) increased were evaluated.     

In situ infrared spectroscopic studies on the mechanism of the selective catalytic reduction of NO by C3H8 over Ga2O3/Al2O3: high efficiency of the reducing agent

The partial oxidation of propane and the mechanism of selective catalytic reduction (SCR) of NO by propane over Ga2O3/Al2O3 in excess of O2 have been investigated using in situ Fourier transform infrared spectroscopy. An optimized Ga2O3/Al2O3 catalyst shows high activity and efficiency of the reducing agent propane (100% conversion of NO at 623 K, GHSV: 10,000 h(-1)). One molecule of propane converts more than 4 NO molecules to N2. The reaction starts with the partial oxidation of C3H8 by O2 and carboxylates (acetate, formate) are formed on the catalyst surface above 573 K. This oxidation represents the rate-determining step of the SCR reaction. These surface carboxylates represent a dominating intermediate and (easily) react with (adsorbed) NO forming nitrogen-containing organic species. The latter are proposed to react with NO to form N2. Total oxidation of propane was enhanced at temperatures above 773 K leading to decreased reductant efficiency. Surface nitrite and nitrate species can also be observed, but they were found to be spectators only. This could be concluded from the electron balance (conversion of propane relative to NO) and from the relative rates of the single reaction steps. On the basis of these investigations and stoichiometric calculations, a conclusive reaction mechanism is proposed.     

纳米ZrO2/Al2O3复合载体及Ni/ZrO2/Al2O3催化剂的性能研究

 采用溶胶-凝胶法在经过扩孔处理的Al2O3基载体上制备了纳米ZrO2/Al2O3复合载体,并通过浸渍法制备了NiO/ZrO2/Al2O3催化剂. 用XRD,TPR,TPD和N2吸附等技术分别考察了载体和催化剂的结构及表面性能,研究了复合载体对Ni/ZrO2/Al2O3催化CO2重整CH4反应性能的影响. 结果表明,纳米ZrO2/Al2O3复合载体具有较大的比表面积、适宜的孔径分布及稳定的t-ZrO2结构,Ni/ZrO2/Al2O3催化剂具有较好的CO2重整CH4反应活性和稳定性.     

Application of the method of images on electrostatic phenomena in aqueous Al2O3 and ZrO2 suspensions

A new solution for the Poisson equation for the diffuse part of the double layer around spherical particles will be presented. The numerical results are compared with the solution of the well-known DLVO theory. The range of the diffuse layer differs considerably in the two theories. Also, the inconsistent representation of the surface and diffuse layer charge in the DLVO theory do not occur in the new theory. Experimental zeta potential measurements were used to determine the charge of colloidal Al2O3 and ZrO2 particles. It is shown that the calculated charge can be interpreted as a superposition of independent H+ and OH- adsorption isotherms. The corresponding Langmuir adsorption isotherms are taken to model the zeta potential dependence on pH. In the vicinity of the isoelectric point the model fits well with the experimental data, but at higher ion concentrations considerable deviations occur. The deviations are discussed. Furthermore, the numerical results for the run of the potential in the diffuse part of the double layer were used to determine the electrostatic interaction potential between the particles in correlation with the zeta potential measurements. The corresponding total interaction potentials, including the van der Waals attraction, were taken to calculate the coagulation half-life for a suspension with a particle loading of 2 vol%. It is shown that stability against coagulation is maintained for Al2O3 particles in the pH region between 3.3 and 7 and for ZrO2 only around pH 5. Stability against flocculation can be achieved in the pH regime between 4.5 and 7 for Al2O3, while the examined ZrO2 particles are not stable against flocculation in aqueous suspensions.     

In_2TiO_5/In_2O_3异质结构的制备及光催化性能

以酞酸丁酯和硝酸铟为起始物,甘氨酸为燃料,脱脂纤维为模板,采用自蔓延燃烧法制备了In2Ti O5/In2O3异质结构半导体光催化剂.利用X射线衍射仪、扫描电子显微镜、X射线能量色散谱仪、热重-差热分析仪、紫外-可见漫反射光谱仪和氮气吸附-脱附仪等对样品进行了表征.以罗丹明B(Rh B)为目标降解物,考察了催化剂的光催化性能.结果表明,在In/Ti摩尔比为2∶1、焙烧温度为800℃、焙烧时间为2 h条件下制备的介孔In2Ti O5/In2O3光催化材料在高压汞灯(125 W)辐照下,120 min可使10 mg/L Rh B的脱色率达到92.1%,降解过程服从一级动力学模型.在相同的光催化条件下,In2Ti O5/In2O3的光催化性能明显优于In2Ti O5,且In2Ti O5/In2O3光催化剂还具有一定的可见光催化活性.     

Calibration of the Probing Depth by Total Electron Yield of EXAFS Spectra in Oxide Overlayers (Ta2O5, TiO2, ZrO2)

Calibration of the probing depth by x-ray absorption spectroscopy (XAS) in oxide materials is intended by measurement of the total electron yield (TEY) of electrons ejected by absorption of the radiation. Measurements have been carried out for three series of electrolytic metal oxide overlayers with different thickness. The experiments have been conducted at the Ti K, Ta L_III and Zr K edges. Analysis of the XAS spectra is carried out by factor analysis and conventional Fourier transformation and fitting analysis. The data showed that the information depth by XAS follows the order ZrO₂>TiO₂>Ta₂O₅ at the Ti K, Ta L_III and Zr K edges. As an alternative, the absorption spectra of the same samples were measured in the conversion electron yield (CEY) mode: i.e. by measuring the current of He⁺ ions produced by the ejected electrons in an atmosphere of He in contact with the sample. Here, the information depth is slightly different from that obtained by TEY. © 1997 by John Wiley & Sons, Ltd.