Effect of the rehydration on the acidity and catalytic activity of SAPO molecular sieves

The structural changes occurring in the template-free SAPO-5 and SAPO-34 upon the rehydration are reversible and do not affect their acidity and catalytic activity. The rehydrated SAPO-37 loses irreversibly a considerable part of its initial crystallinity, surface area, acidity and catalytic activity. Nevertheless the remaining acid centers are stable against dehydrationrehydration cycles.     

A catalytic and characterization study of the surface acidity generated on the reduction of copper exchanged Y zeolites

Zeolite acidity, in the form of Bronsted acid sites generated on reducing a range of copper Y zeolites, was probed by infrared spectroscopy. The nature of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) is shown to influence both the acid strength and location of the Bronsted sites. Acid strength decreases in the order CuLiY > CuNaY > CuKY > CuRbNaY > CuCsNaY. The specific effect of the alkali metal co-stations on the level of protonic activity in benzene ethylation and cumene cracking is discussed.     

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity.     

The structure and surface acidity of zirconia-supported tungsten oxides

The structure and surface acidity of zirconia-supported tungsten oxide are studied by using BET, XRD, FT Raman, Tian–Calvet microcalorimetry as well as XPS. Three different crystal forms of ZrO₂ and their hydroxide precursors were prepared in a controllable way. It was found that the starting material and preparing conditions used have a significant effect on the structure of ZrO₂ obtained. The tungstate species on zirconium hydroxide generally promote the transformation of the hydroxide precursor into tetragonal ZrO₂, while the same species on the pre-calcined ZrO₂ has less effect during calcination. A bulk-phase WO₃ existed in the samples prepared by initially impregnating the monoclinic, tetragonal and cubic ZrO₂ or the hydroxide precursors of m- and t-ZrO₂, while no crystalline WO₃ was present in the samples prepared by initially impregnating the hydroxide precursor of c-ZrO₂. Raman results revealed that the surface tungstate(s) on three different zirconium hydroxides or their respective zirconia have similar structural features before calcination. The surface tungsten oxides and some WO₃ bulk phase are the detectable tungsten species in the final samples, the ratio of each component is strongly dependent on the preparation history and the nature of the support. Creation of very strong acidic sites on the zirconia-supported tungsten oxide is related to the crystal form of zirconia itself, the type of tungsten oxide species, and the cooperation between the surface tungsten oxide overlayer and zirconia. The strong acidic sites can be completely poisoned by the remaining sodium ion impurities, but have not been appreciably influenced by added yttrium component. The crystalline WO₃ seems of little importance in building up the strong surface acidity. This revised version was published online in July 2006 with corrections to the Cover Date.     

一种新催化体系的构建及其催化活性研究

用一种配体(5,5,7,12,12,14-六甲基-1,4,8,11-四氮杂环十四烷-N'-乙酸)和镧离子(Ⅲ)构建了一种新的催化体系,并用于催化对硝基苯酚磷酸二酯(BNPP)水解裂解。利用紫外-可见分光光度法研究了BNPP的催化水解的动力学。实验结果表明:这种新催化体系与其他相似的镧离子体系相比表现出更高的活性、水溶性和稳定性,在这一体系作用下,BNPP催化水解的速率比其自水解的速率提高了107倍左右。光谱分析表明,催化体系的活性物种是由镧离子和配体构成的大环配合物。     

甲基磺酸钙催化酯化反应性能的研究

合成了甲基磺酸钙,并用热重和EDTA络合滴定法对其进行了分析。研究了以甲基磺酸钙为催化剂催化氯乙酸与异丙醇的酯化反应中各种因素对酯化率的影响,当醇酸物质的量比1．2：1,催化剂用量1．0％(以酸的物质的量计),反应时间2．5h,反应温度80～85℃,环己烷作为带水剂时,酯化率可达98．1％。用甲基磺酸钙作催化剂合成其他氯乙酸酯,酯化率均在95．0％以上。催化剂甲基磺酸钙可重复使用。     

磺化聚氯乙烯的催化活性

研究了磺化聚氯乙烯在酯化、缩醛或缩酮的合成以及频呐重排反应中的应用。结果表明,此催化剂的催化活性和重复性良好。     

溶液的酸度和浓度对Pd-TiO_2/C催化剂电催化活性的影响

本实验通过采用液相还原法制备Pd-TiO2/C催化剂,然后改变溶液的酸度和浓度对所制备的催化剂进行线性扫描测试。测试结果显示,Pd-Ti O2/C催化剂的电催化活性随着溶液中酸度和浓度改变会产生相应的变化,在一定条件下催化剂的电催化活性可达到最佳效果。     

Effect of calcium carbonate on the preparation of glass ceramic foams from water-quenched titanium-bearing blast furnace slag and waste glass

ABSTRACT

Glass ceramic foams were fabricated with powder sintering technology at a low temperature (900°C), using water-quenched titanium-bearing blast furnace slag (WTS) and waste glass as the primary raw materials. Additionally, calcium carbonate, sodium borate and sodium phosphate were chosen as sintering aids to form excellent performance products. The effects of calcium carbonate additions on foaming process, crystal content, morphology and properties of the prepared samples were systematically researched. The research indicates that increasing the calcium carbonate content made the foaming process harder and the pore size got more uniform. Consequently, the compressive strength and bulk density increased, while the porosity and water absorption decreased. The homogenous porous structures and optimal comprehensive properties were achieved with 5–7?wt-% CaCO₃ addition, including a bulk density of 0.79–0.82?g?cm^–3, porosity of 73.13–75.28%, water absorption of 3.29–3.75% and compressive strength of 13.13–13.85?MPa.     

A method of determining the surface acidity of polymeric and metallic materials and its application to lap shear adhesion

A method has been developed to measure the surface acidity of solids using the contact angles of seven probe liquids. The geometric mean model was used to calculate the surface free energy. Then the value of the solid polarity, from the geometric mean, was compared with the polarity values calculated using the geometric mean dispersive component and the contact angles of two Lewis acids (liquefied phenol and glycerol) and two Lewis bases (formamide and aniline.) The deviation between these values was used to determine a value for the acidity, referred to as D. D was measured for a series of polymeric and metallic materials. Lap shear joints were fabricated and tested using these substrates and two adhesives, a urethane and an epoxy. The acidity of the substrate surfaces was found to affect the lap shear joint strength.     

On the acidity of liquid and solid acid catalysts: Part 1. A thermodynamic point of view

The protonation equilibria of weak bases (B) in solid acids (HClO₄/SiO₂, CF₃SO₃H/SiO₂, H₂SO₄/SiO₂) were studied by UV spectroscopy and the results were compared to those obtained for analogous compounds in concentrated aqueous solutions of strong acids (HClO₄, CF₃SO₃H, H₂SO₄). The behaviour of B in liquid (L) and solid (S) phase was analysed by titration curves, log[BH⁺]/[B] ratios and thermodynamic pK _BH+ values. It has been shown that the proton transfer process acid → base (i.e., from (H+A^-)_(L,S) to (BH+A^-)_(L,S)} can be described by the relationship observed between the activity coefficient terms that are to be taken into account for acid–base equilibria occurring in nonideal systems ( – log(f _B f _B+/f _BH+)_(L,S)= -n _BA log(f _A–f _H+/f _HA)_(L,S)) and can be estimated by the n _BA values. Two “activity coefficient functions” (i.e., Mc(B) = – log(f _B f _B+/f _BH+)and Mc(s) = – log(f _A–f _H+/f _HA)) were used to describe, respectively, the equilibria of B and the equilibria of the acids in concentrated aqueous solutions and the meaning of terms “activity coefficient function” and “protonating ability of an acid” were discussed. The difference between “acidity functions”, determined for solutes (Ac(i)) and solvents (Ac(s)) in aqueous acids, and the H_x acidity functions, the latter developed for solutes in analogous media by the Hammett procedure, was also shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of alumina content on surface area and micropore distribution of porous glass prepared from borosilicate glass

The surface area and micropore distribution of porous glass prepared from borosilicate glass were controlled by the addition of alumina up to 8 wt%. The surface area increased with increased alumina content in the range from 0 to 3 wt%, but it suddenly decreased when the percent alumina exceeded 4 wt%. The mean pore diameter and micropore volume also decreased with increased alumina content. When nickel ion was supported into the porous glass, the surface area decreased to about one-half that of the original glass. Since the amount of nickel supported on the porous glass increased directly with surface area, the silanol group was considered to be uniformly distributed on the glass.     

Solid acidity of metal oxide monolayer and its role in catalytic reactions

Such metal oxide as SO₄²⁻, MoO₃, WO₃, and V₂O₅ spread readily on supports like SnO₂, ZrO₂, and TiO₂ due to the different properties between acid and base oxides to generate the acid site on the monolayer. Number, strength, and structure of the acid site were characterized by temperature-programmed desorption (TPD) of ammonia principally, together with various physico-chemical techniques, and its role for catalytic reactions was studied. Approximately, one to two acid sites were stabilized on 1 nm² of the surface, which consisted of four to eight metal atoms. The limit in surface acid site density was estimated on the monolayer based on the concept of solid acidity on zeolites. Sequence of the metal oxide to show the strong acidity was, SO₄²⁻>WO₃>MoO₃>V₂O₅, and for the support oxide to accommodate the monolayer, SnO₂>ZrO₂>TiO₂>Al₂O₃. From these combinations, the metal oxide monolayer to show the adequate strength of acid site could be selected. Brønsted acidity was observed often, however, the Lewis acidity was prevailing on the reduced vanadium oxide. The structure of acid site, Brønsted or Lewis acid site, thus depended on the oxidation state. Relationship of the profile of solid acidity with various catalytic activities was explained. The solid acid site on the monolayer will possibly be applied to environment friendly technologies.     

Multi-step derivatization and analysis of the surface of nonporous silicate glass

Multi-step heterogeneous phase chemical reaction schemes were used to develop different surface chemistries on nonporous glass substrates. Reliable analysis of the products of reaction was needed, because many of the functional groups introduced to the surface were intended to serve as reactive sites for further chemical tailoring to meet specific applications. Because the mass of the surface derivatization layer was only parts per million of the substrate mass, analysis of the reaction products was daunting. However, surface evaluation was accomplished by using several analysis methods in combination and by using the particular glass geometry most suitable to each analysis method.     

Isomerization of n-butane by sulfated zirconia: the effect of calcination temperature and characterization of its surface acidity

The distributions of Brønsted and Lewis acid sites of different acid strengths on sulfated zirconia calcined at 450–650°C were measured by IR of adsorbed pyridine to elucidate the active sites for butane isomerization. The total numbers of Brønsted acid sites were largest when the catalyst was calcined at 500°C. The total numbers of Lewis acid sites increased with increasing calcination temperature to a maximum at 650°C. The catalytic activity in skeletal isomerization of butane correlated well with the number of Brønsted acid sites but not with the number of Lewis acid sites. The active sites were completely blocked by pyridine irreversibly absorbed at 350°C. We suggest that the strong Brønsted acid sites, which are able to retain pyridine against evacuation at 350°C, act as active sites for butane isomerization on sulfated zirconia.     

银原子修饰铂纳米粒子的制备与其催化活性的研究

以聚乙烯吡咯烷酮（PVP）为保护剂在水溶液中合成了铂（Pt）纳米粒子,利用吸附在Pt纳米粒子表面上的氢还原适量AgNO_3,得到表面修饰了Ag原子的纳米Pt催化剂,并利用苯甲醛的催化加氢反应,考察了Ag原子的修饰量对纳米Pt催化剂的活性影响。实验结果表明：随着Ag原子在Pt纳米粒子表面沉积数量的增加,苯甲醛的转化率先升高后降低,当n（Ag）：n（Pt）为0.005时,纳米Pt催化剂的催化活性最高。     

Synergistically reinforcement of a self-setting calcium phosphate cement with bioactive glass fibers

Calcium phosphate cements (CPCs) are highly promising for clinical uses due to their in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits their uses to non-load-bearing applications. In the present research, first, bioactive glass fibers (BGFs) in the ternary SiO₂-CaO-P₂O₅ system were prepared, and then the fiber composites with compositions based on CPC and BGFs were prepared and characterized. Then, the effect of structure and amount of BGF incorporation into the CPC system, and the effect of mechanical compaction on the fiber-modified system were investigated. The results showed that the compressive strength of the set cements without any BGFs was 0.635 MPa which was optimally increased to 3.69 MPa by applying 15% BGF and then decreased by further addition of it. In addition, both the work-of-fracture and elastic modulus of the cement were considerably increased after applying the fibers in the cement composition. Also, the setting time slightly decreased by applying the fibers. In summary, processing parameters were tailored to achieve optimum mechanical properties and strength. The prepared composite may be useful in surgical sites that are not freely accessible by open surgery or when using minimally invasive techniques.     

New method for the study of surface acidity of zeolites by NH3-TPD, using a pH-meter equipped with an ion selective electrode

Desorbed ammonia is captured by an acetic acid solution whose concentration of ammonium ions formed by neutralization, is continuously recorded by a pH-meter equipped with an ion-selective electrode (ISE). This technique allows the study of both the acidity density and the distribution of acid site strengths. Such “strength profile” was obtained by plotting the relative rate of desorbed NH₃ versus the temperature. Results obtained can be fairly well correlated with those already published. It is shown that by investigating several H-ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios, the data of acid density obtained by the ISE method are very close to those calculated from the Al content. The slight shift of the desorption peaks towards higher temperature suggests a slightly higher strength for more isolated acid sites. Zeolite structures, which are richer in Al, contain weaker acid sites, as evidenced by the H-Y when compared to the H-mordenite, while the acid sites density of the former is much higher. The ultra-stabilized Y zeolite (H-USY) shows a lower acidity density than the parent H-Y owing to the removal of some of the tetrahedral Al atoms from the framework during the preparation. The strength profile of the H-USY is also quite different from that of the H-Y. The new technique appears to be much simpler, more rapid, more informative and quite accurate when compared to the technique using a gas chromatograph equipped with a thermal conductivity detector (GC-TCD).