环己烯对噻吩在CuY分子筛上吸附的影响机制

A CuY zeolite prepared by liquid phase ion exchange was characterized by X-ray photoelectron spectroscopy, pyridine in situ Fourier transform infrared (in situ FTIR) spectroscopy, and ammonia temperature programmed desorption. The effect of cyclohexene on the adsorption of thiophene over the prepared CuY zeolite was explored by in situ FTIR. In particular, the role of the zeolite's Br?nsted acidity was investigated in the adsorption process. The results show that the percentage of Cu⁺ on the surface of the CuY zeolite can reach 77%. The surface acidity of the CuY zeolite mainly comprises medium and strong Br?nsted acidity and Lewis acidity. According to the adsorption results, cyclohexene negatively influences thiophene adsorption on the Br?nsted or Lewis acid sites in CuY by competitive adsorption. Although polymerization of thiophene and cyclohexene can occur easily on the HY or REY zeolites, the presence of Br?nsted acids in the CuY zeolite was not sufficient to polymerize either thiophene or cyclohexene. This difference may be caused by an anti-synergistic effect between the Cu ions of the CuY zeolite and neighboring Br?nsted acid sites, the result of which inhibits the polymerization of adsorbed thiophene and cyclohexene.     

Probing the surface acidity of modified γ-alumina with1H and15N high-resolution solid state NMR spectroscopy

¹H MAS NMR and¹⁵N NMR studies of adsorbed N₂ and N₂O molecules were used to characterize Br?nsted and Lewis acidic sites of unmodified γ-Al₂O₃ and γ-Al₂O₃ modified with NaOH. Changes in the concentrations of surface hydroxyls with the increase in the number of more “basic” OH groups for NaOH/γ-Al₂O₃ have been found by¹H MAS NMR experiments. Two different types of Lewis acidic sites in γ-Al₂O₃ have been revealed using¹⁵N NMR studies. The strongest sites are poisoned even at small NaOH concentrations (ca. 0.05 wt.%). Not only the number of electron-accepting sites but also their strength are supposed to decrease for modified γ-alumina.     

Temperature-programmed desorption of water and ammonia on sulphated zirconia catalysts for measuring their strong acidity and acidity distribution

Temperature-programmed desorption (TPD) of water and ammonia over ZrO₂ and sulphated ZrO₂ prepared by different methods has been investigated for measuring strong acidity and acidity distribution on sulphated zirconia-type solid super-acid catalysts. The TPD of water provides a simple reliable method for this purpose because of the high stability of water molecules under redox conditions     

ZSM-5分子筛酸性质对甲醛合成三聚甲醛催化性能的影响

ZSM-5分子筛是合成三聚甲醛的有效催化剂。本工作通过XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等手段对一系列不同SiO₂/Al₂O₃物质的量比的ZSM-5分子筛催化剂进行了表征,研究了ZSM-5分子筛中Brønsted酸中心和Lewis酸中心对其甲醛合成三聚甲醛催化性能的影响。结果表明,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有合适的Brønsted酸中心用于催化甲醛缩聚为三聚甲醛的反应,同时其Lewis酸中心量极少,可有效抑制Cannizzaro或Tishchenko等副反应,提高三聚甲醛的选择性,因而具有最佳的合成三聚甲醛催化性能。寿命实验评价结果显示,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有良好的催化稳定性,单程寿命长达114 h,并且可通过550℃焙烧再生恢复其催化活性。     

Study of Pt and Rh based supported catalysts modified with tetrabutyltin for the selective hydrogenation of 4-methoxyacetophenone

Catalysts based on Pt and Rh modified with Sn(C₄H₉)₄ were studied in the hydrogenation of 4-methoxyacetophenone. The selectivity to 1-(4-methoxyphenyl)ethanol was close to 100% at Sn/(Pt,Rh) = 1.0, however the catalytic activity decreased drastically. With respect to the balance between activity and selectivity the catalyst PtSnOM (Sn/Pt=0.4) showed the best performance.     

负载铂催化剂中沸石载体酸性对甲烷两步转化的影响

考察了具有相同金属分散度的Pt/NaY、Pt/HNaY、 Pt/HY、Pt/NaBeta和Pt/HBeta催化剂中沸石载体的酸性对在低温下（≤250 ℃）甲烷两步等温转化反应以及由甲烷解离吸附产生的表面碳物种分布的影响。由甲烷等温两步转化生成的C2+烃类产物的总量随着载体酸性的增加而明显增加;C2～C6产物的分布也发生了变化。由表面碳物种的程序升温加氢结果表明,在各种催化剂上碳物种的形式是相似的,其总量和具有活性的Cα物种的量均因载体酸性增加而增加,反应性也增大。这种因沸石载体酸性变化而引起的载体效应是由金属和载体的相互作用造成负载在酸性载体上铂粒子的贫电子性而引起,即由金属粒子电子性质的变化而引起的催化性质的变化。     

The active species of the chromium (phillips type) catalysts for the polymerization of ethylene: A unifying approach

From literature data it is concluded that the rate of the reduction, alkylation, polymer chain growth, and chain transfer reactions of three chromium(II) and one chromium(III) surface species all increase with decreasing electron density at the chromium ion. This electron density has previously been measured by the IR shift of the stretching vibration of one CO molecule terminally adsorbed on these chromium ions. It is observed that the reduction half time decreases proportional to the increasing Lewis acidity and that the rate of the polymer chain growth reaction increases exponentially for three chromium surface species with increasing CO stretching vibration. Due to the large difference of the polymer chain growth rates for the two chromium (II) species (A_d and C_d), common in the normal Phillips catalyst, both contribute almost equally to the polymer product, although the A_d species outnumbers the C_d one by more than 3 to 1.     

Effect of the Al/Si atomic ratio on surface and structural properties of sol-gel prepared aluminosilicates

A series of aluminosilicates with an Al/Si ratio ranging from 0 to ∞ (0 for pure silica and ∞ for pure alumina) was prepared by sol-gel process and characterized by surface and structure techniques. Aluminum trisecbutoxide and tetramethylorthosilicate were used as precursors for the sol-gel synthesis. The acidic properties of the oxides were studied by determination of the zero point charges, through mass titration method, and, for selected samples, by FT-IR spectroscopy of adsorbed pyridine used as a probe for both Brønsted and Lewis acidity. A dependence of the acidity on the Al/Si atomic ratio was found. According to the X-ray diffraction patterns, all the oxides have an amorphous structure except pure alumina exhibiting a γ-alumina pattern. The surface areas of the mixed oxides increase with increasing amount of alumina and are higher as compared to the individual oxides. The surface elemental distribution and electronic properties were investigated by X-ray photoelectron spectroscopy. According to the results, good agreement between the surface Al/Si atomic ratio and the analytical ratio is obtained.     

钾对CuSO4/TiO2脱硝催化剂的失活效应(英文)

为了减少碳排放,在世界各地兴建了越来越多的生物质电厂。钾元素是生物质电厂烟气中的一种典型元素并且可以引起脱硝催化剂的失活。具有优异抗SO₂性能的CuSO₄/TiO₂催化剂被认为是一种有前景的非钒基脱硝催化剂。但是,钾对CuSO₄/TiO₂催化剂的影响仍不清楚。本文研究了钾对CuSO₄/TiO₂催化剂的影响并且与商业V₂O₅-WO₃/TiO₂ (VWTi)催化剂作了比较,采用多种表征方法对催化剂样品进行了表征。钾可以引起CuSO₄/TiO₂和VWTi催化剂的失活,但是CuSO₄/TiO₂催化剂对钾的抵抗能力明显高于商业VWTi催化剂。钾会与CuSO₄/TiO₂催化剂中的CuSO₄发生反应生成CuO和...     

The effect of the nature of included metal cations on the structure and the adsorption and acidic characteristics of VFI aluminophosphates

For a series of metal aluminophosphate zeolites with the VFI structure it was established that the cations of alkaline-earth and transition metals are mostly included isomorphously at the octahedral positions of the framework with substantial deformation of the structure. The strength of the Brönsted acid centers decreases greatly in the series of substituent cations Mg >> Ca > Sr ≥ Ba and increases in the series Cu ≤ Ni ≤ Mn < Co < Zn < Cr < Mg. This is probably determined by the combined effect of the electronegativity and the radius of the metal cation on the Me-O(H)-P bond angle and the strength of the acid centers.     

Influence of calcination temperature on surface acidity of the solid superacid of sulfated alumina

The acidity of sulfated alumina catalysts was studied by analyzing DTG and heat of Ar adsorption together with the isomerization of pentane. The initial acid sites were Brönsted-type, and converted into Lewis-type upon increasing the pretreatment temperature. The heat of Ar adsorption of the most active sulfated alumina was 18.9 kJ mol^–1, this value being a little smaller than that of sulfated zirconia (23.6 kJ mol^–1).This revised version was published online in December 2005 with corrections to the Cover Date.     

Effect of water on the performance of Pd-ZSM-5 catalysts for the combustion of methane

Palladium-based catalysts were prepared using impregnation （I） and ion-exchange method （E） with ZSM-5 as support. Pd-ZSM-5（I） and Pd-ZSM-5（E） catalysts presented the high activity for the combustion of methane. The order of activity was consistent with Brcnsted acidity of the catalysts： Pd-ZSM-5（I）〉Pd-ZSM-5（E）. It was shown by FT-IR that methane was adsorbed on the acidic bridging hydroxyl groups of ZSM-5-supported Pd catalysts. The effect of water on the activity of Pd-ZSM-5 was investigated. The inhibition effect of water on the conversion of methane was observed. However, water promoted the stability of Pd-ZSM-5 obviously during extended time periods. XPS measurement showed that Pd/Si ratio near the surface of Pd-ZSM-5（E） decreased more pronouncedly with time in dry stream than that of Pd-ZSM-5（I）, this is attributed to the dispersion of Pd into the micropores. The addition of water, however, retarded Pd dispersion. And high partial pressure of methane reduced this effect of water vapor. The decrease in activity during the stability test can be explained on the basis of the reduction of Pd/Si ratio.     

Effect of Tin Precursor on the Catalytic Properties of Pt-Sn/Al2O3 Sol-Gel Prepared Catalysts

Tin-alumina supports were prepared by cogelation of aluminum tri-sec-butoxide and tetrabutyltin or tin tetrachloride. Aqueous or acetone platinum solutions were used for impregnation. The results show that the specific surface area and the acidity of the catalysts were only slightly modified by the metal precursors used. On cyclohexane dehydrogenation andn-hexane conversion, high selectivity to olefins and low cracking products were detected.     

Effect of phosphate ions in the properties of titania sol-gel

Sol-gel titania was phosphated in two different ways: i) “in situ” phosphation using phosphoric acid as hydrolysis catalyst in the titanium butoxide gelling system, and ii) gelling with nitric acid and impregnation with ammonium phosphate solution. In calcined samples at 600°C a positive effect on the specific surface area for the “in situ” phosphated sample was found. X-ray diffraction patterns showed that the presence of phosphates ions stabilized the anatase phase. FTIR-pyridine adsorption identified only Lewis acid sites in phosphated samples. In the isopropanol decomposition for “in situ” phosphated titania, the activity was six times higher than that obtained for titania phosphated by impregnation, showing strong acidity for the in situ phosphated TiO₂ catalyst.     

Effect of different donors on kinetics of Zn catalysts and molecular weight of the obtained polypropylene

This paper studies MgCl₂/internal donor/TiCl₄//external donor/AlEt₃ catalytic systems where ethyl benzoate (E.B.) or 2,2,6,6 tetramethylpiperidine (TMPiP) are used as internal and external donors. E.B. as external donor does not change the molecular weight of the product with TMPiP as internal donor. The molecular weight of polypropylene decreases drastically and global productivity and stereoselectivity are very low with MgCl₂/internal Donor/TiCl₄//external donor/AlEt₃ when TMPiP is the external and internal donor. In this case the insoluble fraction in n-heptane is highly stereospecific and the molecular weight is similar to commercial products. We present a new explanation of these results, based on Ystenes proposal, comparing both precatalysts.     

Interfacial impregnation chemistry in the synthesis of nickel catalysts supported on titania

The interfacial chemistry of the impregnation step involved in the preparation of nickel catalysts supported on titania is presented. Several methodologies based on deposition data, pH measurements, potentiometric mass titrations, and microelectrophoresis have been used in conjunction with diffuse reflectance UV/Vis/NIR spectroscopy, simulations, and semiempirical quantum chemical calculations. Three mononuclear inner-sphere complexes were formed at the compact layer of the "titania/electrolyte solution" interface: A monosubstituted, dihydrolyzed complex above a terminal oxo group, a disubstituted, dihydrolyzed complex above two terminal adjacent oxo groups, and a disubstituted, nonhydrolyzed complex above one terminal and one bridging adjacent oxo groups. The monosubstituted, dihydrolyzed complex predominates. The contribution of the disubstituted configurations is also important at very low Ni(II) surface concentration, but it decreases as the Ni(II) surface concentration increases. In addition, bi- and trinuclear inner-sphere complexes were formed. The receptor site involves one bridging and two terminal oxo groups in the first case and two bridging and three terminal oxo groups in the second case. The relative surface concentrations of these configurations increase initially with Ni(II) surface concentration and then remain practically constant. The understanding of these interfacial processes at a molecular level is very important to shift the catalytic synthesis from an art to a science as well as to obtain strict control of the impregnation step and, to some extent, of the whole preparative sequence. This study is very relevant to the synthesis of submonolayer/monolayer nickel catalysts supported on TiO(2) following equilibrium deposition filtration (otherwise called equilibrium adsorption).     

Influence of platinum on the reducibility of rare earth oxides supported on alumina

XPS experiments on alumina supported Pt–CeO₂ catalyst have shown AlCeO₃ formation during the initial treatment. This aluminate is very stable and remains unaffected by further treatment. TPR was used in tandem to characterize the reducibilities of both platinum and several rate earth oxides. The appearance of a new peak in the TPR profile reveals that there is a preferential interaction between the rare earth oxide and the platinum.     

Chemistry and key structural features of oxyhydroxy-fluorides: relationships with the acidic character, thermal stability and surface area

The stability of Al, Cr and Fe hydroxy-fluorides MF_3−x(OH)_x which adopt the hexagonal-tungsten-bronze (HTB)-type structure has been discussed by considering the lability of water coordinated to metals from a kinetic point of view. Thus, in the case of Al or Fe compounds, the easy departure of water contributes to the stabilization of fluoride ions as well as isolated hydroxyl groups around the metal, leading to the formation of the HTB structure. The stabilization of the HTB structure with respect to another structural type, the pyrochlore, with a lower density, is governed by this kinetic feature as well as the ability of fluorinated salts used as precursors to attract hydroxyls. Al(III) and Fe(III) represent the strongest acidic cations and the associated HTB-type structure containing isolated OH groups can easily be stabilized. In the case of Cr, a mixture of pyrochlore and HTB-type structure is generally obtained. We have succeeded in preparing, using supercritical medium, new (Fe, Cr) oxyhydroxy-fluorides which exhibit edge-shared octahedra and large 1D tunnels. These compounds can be considered as potential candidates for acid catalysts.     

MCM-22分子筛酸性的DFT理论计算研究

本文利用量子力学中的密度泛函理论(DFT)计算，研究了MCM-22分子筛上骨架Al在8个不同的T位的分布和Br?nsted酸的落位及强度。所有计算基于分子筛的8T簇模型 (H₃SiO)₃Si-O(H)-T(OSiH₃)₃(T=Si，Al)，采用DFT的BLYP方法，所有原子均应用DNP基组。通过计算(Al，H)/Si替代能和质子亲和势，得出推论：MCM-22分子筛中骨架Al的最有利落位在T1，T4，T3和T8位。而形成Br?nsted-酸的最可能的位置为Al1-O3-Si4，Al4-O3-Si1，Al3-O11-Si2和Al8-O10-Si2桥基。Al1-O3H-Si4和Al4-O3H-Si1位的酸性强度接近，Al3-O11H-Si2和Al8-O10H-Si2位的酸性分别略低于和略高于前两个酸位。通过计算模板剂分子六次甲基亚胺(HMI)与B-酸中心的相互作用，进一步探讨了HMI对分子筛中Al落位的靶向作用。     

Effect of particle size in the hydrogenation of crotonaldehyde on supported Pt and Pt-Sn catalysts

The present work reports the effect of metal particle size on the selectivity to crotyl alcohol (S_UOL) in the liquid phase hydrogenation of crotonaldehyde over SiO₂ and a-Al₂O₃-supported Pt and Pt-Sn catalysts. It was demonstrated that, for the monometallic catalysts, a higher particle size led to a higher S_UOL, while for the bimetallic catalysts, this effect was not so important.