H3PW12O40 and its cesium salts as pentane isomerization catalysts at ambient temperature

The activity of Mg−Al basic heterogeneous catalysts in the reactions of alcohols with ethylene oxide was studied. The kinetics of alcohol oxyethylation was examined. The kinetic equation of the reaction was determined and the structure of products was studied. The distribution coefficients of the oxyethylation reaction products were calculated. A comparison of the catalytic activity of Mg−Al hydroxides and products of their thermal treatment was made.     

Oxidation of isobutane catalyzed by vanadyl, copper and cesium substituted H3PMo12O40

Effects of Cs⁺, H⁺ and Cu²⁺ counterions in the vanadium containing heteropoly compounds Cs_xH_1-xVO[PMo₁₂O₄₀] and Cs_yH_0.5-yCu_0.25VO[PMo₁₂O₄₀] on the catalytic oxidation of isobutane and characterization by TGA, IR and ESR spectroscopies are reported. A high selectivity of 76% for methacrylic acid and methacrolein together has been obtained with Cs_0.75H_0.25VO[PMo₁₂O₄₀] catalysts at a reactivity of 5.3x10^-1 mmol/h cm³.     

Deactivation of H3PW12O40/TiO2 catalyst used in the production of camphene

Summary The deactivation of the H3PW12O40 (HPW) catalyst supported on TiO2 used in the isomerization reaction of a-pinene and its regeneration were studied. The regeneration of the deactivated catalyst was carried out with an air flow at 300 and 500ºC, with an ozone-enriched oxygen flow at 150ºC and by extraction with solvent and acid treatment. Only the last treatment permitted to recover its activity restoring it in 48% of its initial value.     

AC electrical conductivity measurements during H2-TPD experiments on a Pt/Al2O3 catalyst

The kinetics of the reaction of cyclopentanol with PhNCO or OCN(C₆H₁₂)NCO was studied in toluene, di-n-butyl ether and acetonitrile. The results suggest a predominant influence of the aggregation state of alcohol.     

Effect of magnetostrictive phase on structural, dielectric and electrical properties of NiFe2O4 + Pb0.93La0.07(Zr0.60Ti0.40)O3 composites

Particulate composites of NiFe₂O₄ (NFO) and Pb_0.93La_0.07 (Zr_0.60Ti_0.40) O₃ (PLZT) were synthesized by solid-state reaction technique. Structure and surface morphological studies were carried out using X-ray diffraction and scanning electron microscopy techniques, respectively. Frequency dependent variation of dielectric constant (), loss tangent (tan δ) and ac resistivity for (x) NFO + (1−x) PLZT composites in the range 100 Hz–5 MHz at room temperature were studied. The temperature dependence of dielectric constant (′), loss tangent (tan δ) was studied in wide temperature range of measurement at fixed frequencies. Also DC resistivity measurements were carried out in the temperature range of 300 K–923 K. Structural, dielectric and electrical properties show notable change due to presence of magnetostrictive NFO phase along with PLZT.     

Microwave-promoted efficient conversion of acetophenones to 1,3,5-triarylbenzenes catalyzed by H3PW12O40 and nano-silica supported H3PW12O40 as reusable catalysts

H₃PW₁₂O₄₀ and nano-silica supported H₃PW₁₂O₄₀ were found to be efficient heterogeneous catalysts for the preparation of 1,3,5-triarylbenzenes via triple self condensation of acetophenones under microwave irradiation and solvent-free conditions. High yields, short reaction times, easy work-up, easy availability and handling, eco-friendly and reusability of the catalysts are the main aspects of the present method. The catalytic mechanism of 1,3,5-triarylbenzenes synthesis is also proposed.     

Comparison of H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by H MAS NMR

The H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ heteropolyacids supported on silica were studied by ¹H MAS NMR as a function of both the coverage and the dehydroxylation temperature. The signal at ca. 8 ppm attributed to the highly acidic protons of the anhydrous form of the heteropolyacid was never observed in the case of the phosphotungstic polyanion supported on silica while it was clearly present in the case of the silicotungstic species. These results explain the different activities of the two supported heteropolyacids in acid reactions involving strong acid sites. To cite this article: A. Thomas et al., C. R. Chimie 8 (2005).     

Effect of dopant concentration on the catalytic properties of H4SiW12O40 – polyaniline system

Ethanol conversion on polyaniline supported H₄SiW₁₂O₄₀ was investigated at 443 – 483 K. Catalytic activity of the samples expressed as conversion rate per 1 m² exhibits a maximum at H₄SiW₁₂O₄₀ content, equal to about 30 wt.%. The proposed interpretation of these effects is given.     

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H₃PW₁₂O₄₀ (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H₂-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250°C and WHSV of 1.4 h⁻¹, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%. Supported by the Natural Science Foundation of China (Nos. 20306011 and 20476046), the Ph. D. Program Foundation of Chinese University (20040291002), and the Ph. D. innovation Program Foundation of Nanjing University of Technology (BSCX200506)     

H3PW12O40催化水相介质中苯并恶嗪和喹唑啉合成（英文）简

A heteropolyacid efficiently catalyzed the cyclocondensation reaction of 2-aminobenzamide and salicylamide with aldehydes and ketones to afford good yields of benzoxazine and quinazoline ring systems in an aqueous medium. The method gives clean reactions, has simple workup procedure, and uses environment friendly conditions.     

Structural, electrical and reflectance studies of the system ZnMn2-2xNixTixO4

X-ray, electrical conductivity and reflectance studies of the system ZnMn_2-2xNi_xTi_xO₄ have been carried out. The system is tetragonal in the range 0 ≤x ≤ 0.25 and cubic in the range 0.5 ≤x ≤ 1. Electrical resistivity temperature behaviour obeys Wilson’s law for all the compounds and the thermoelectric coefficient values vary between 325 and-290 μV/K. The activation energy and p_RT decrease gradually with increase in concentration of charge carriers atB-site except for ZnNiTiO₄. Reflectance spectral studies indicate the presence of Ni²⁺ at the octahedral site.     

Hydrogen effects on the electric conductivity of a Pt/Al2O3 catalyst

Hydrogen desorption, hydrogen spillover and reduction processes have been evidenced using a new experimental strategy based on AC electric conductivity measurements during TPD and TPR experiments on a 0.5% Pt/Al₂O₃ catalyst.     

MOF derived Co3O4/N-doped carbon nanotubes hybrids as efficient catalysts for sensitive detection of H2O2 and glucose

Developing enzyme-free sensors with high sensitivity and selectivity for H2O2 and glucose is highly desirable for biological science.Especially,it is attractive to exploit noble-metal-free nanomaterials with large surface area and good conductivity as highly active and selective catalysts for molecular detection in enzyme-free sensors.Herein,we successfully fabricate hollow frameworks of Co3O4/N-doped carbon nanotubes(Co3O4/NCNTs)hybrids by the pyrolysis of metal-organic frameworks followed by calcination in the air.The as-prepared novel hollow Co3O4/NCNTs hybrids exhibit excellent electrochemical performance for H2O2 reduction in neutral solutions and glucose oxidation in alkaline solutions.As sensor electrode,the Co3O4/NCNTs show excellent non-enzymatic sensing ability towards H2O2 response with a sensitivity of 87.40μA(mmol/L)^-1 cm^-2,a linear range of 5.00μmol/L-11.00 mmol/L,and a detection limitation of 1μmol/L in H2O2 detection,and a good glucose detection performance with 5μmol/L.These excellent electrochemical performances endow the hollow Co3O4/NCNTs as promising alternative to enzymes in the biological applications.     

N-tert-Butoxycarbonylation of amines using H3PW12O40 as an efficient heterogeneous and recyclable catalyst

The commercially available heteropoly acid H₃PW₁₂O₄₀ (0.5 mol %) is a very efficient and environmentally benign catalyst for N-tert-butoxycarbonylation of amines (primary, secondary) with di-tert-butyl dicarbonate at room temperature in short reaction times (<10 min). No competitive side products such as isocyanates, ureas, N,N-di-tert-butoxycarbonyls, O-Boc and oxazolidinones were observed. Chiral α-amino alcohols and esters afforded the corresponding N-Boc derivatives chemoselectively in excellent yields.     

Study of the acidity of H3PW12O40 supported on activated carbon by microcalorimetry and methanol dehydration reaction

H₃PW₁₂O₄₀/activated carbon catalysts have been studied by microcalorimetry and by the dehydration of methanol to dimethyl ether. It has been shown that the acidity of the polyacid is greatly reduced upon grafting on activated carbon. The decrease is so high that, at low polyanion loadings, the catalysts are relatively inactive in the dehydration of methanol to dimethyl ether.     

Influence of H3PMo12O40/SiO2 thermal treatment on adsorbed forms of formaldehyde and formic acid

Effect of the H₃PMo₁₂O₄₀/SiO₂(P-Mo-HPA) thermal treatment on adsorbed forms of HCOOH and H₂CO has been studied by IR spectroscopy. On the sample pretreated at 150°C, HCOOH adsorbed mainly as hydrogen-bonded complexes. The HPA calcination at 350°C resulted in the formation of surface formates along with hydrogen-bonded complexes. This proves the formation of coordinatively unsaturated surface cations (Lewis acid sites) during HPA dehydration. Alteration of the surface composition due to dehydration was found to have a major influence on the H₂CO adsorbed forms.     

Hydroformylation of alkyl alkenes catalyzed by rhodium supported on MCM-41: The effect of H3PW12O40 on the catalytic activity and recycling

Heteropolyacids impregnated with rhodium(I) or (III) complexes were prepared and used as supported catalysts in the hydroformylation of alkyl alkenes. Two general types of catalysts were prepared and tested: rhodium(I) or (III) in the presence and in the absence of the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (adopted as HPW₁₂) supported on MCM-41 (30 Å). 1-Octene was chosen as a model substrate. Different types of supported catalysts were tested in the hydroformylation of 1-octene and other alkyl alkenes. The effects of the temperature and the type of solvent on the reaction were studied. The results showed that the supported catalysts containing the heteropolyacid H₃PW₁₂O₄₀, 25H₂O (HPW₁₂) along with rhodium(I) or (III) gave higher catalytic activity. In addition, the recycling of the supported catalysts was studied and the results showed again the important effect of the presence of HPW₁₂ on the recycling of the rhodium catalysts.     

超临界水热极速合成异质结构H4SiW12O40/Bi2WO6光催化剂及其脱氮性能

采用超临界水热合成方式极速合成一种H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂,通过X射线衍射(XRD)、场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)、比表面积及孔隙度(BET)测定对所合成催化剂的结构和性质进行了考察,并以吡啶含量为15 mg/g的模拟油对光催化剂的脱氮效果进行评价。结果表明,该光催化剂为二维纳米片自组装成的三维球状结构,其中,H_4SiW_(12)O_(40)与Bi_2WO_6不是简单的固载关系而是在超临界水热条件下生成一种新的晶相,正是由于这种晶相的存在,使得H_4SiW_(12)O_(40)牢固固载在Bi_2WO_6光催化剂本体上的同时,对光生载流子进行了有效疏导,提升了H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂的使用寿命和光催化活性。本研究针对光催化剂制备周期与晶形发育的矛盾,将超临界水热技术与光催化剂模板导向合成技术有机结合,在获得良好晶形异质结构H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂的同时明显缩短了光催化剂的制备周期,从而降低了催化剂的制备成本,攻克了光催化剂工业化应用的主要矛盾,所制备的H_4SiW_(12)O_(40)/Bi_2WO_6光催化剂轻质油脱氮效率达97%以上。     

Conductivity properties of Na2SO4/CaCO3 catalysts and their effect on catalytic activities for oxidative coupling of methane

A series of Na₂SO₄ doped CaCO₃ catalysts were prepared. It was observed that the C₂ yields and selectivities of Na₂SO₄/CaCO₃ catalysts for OCM are intimately related to their conductivities. The effect of conductivity on the catalytic activity is discussed together with the conductivities and catalytic activities of the catalysts. The higher the conductivities, the higher the C₂ yields and selectivities are.     

The effect of Ag addition on electrical properties of the thermoelectric compound Ca3Co4O9

Ca₃Co₄O₉/Ag composites incorporating different amounts of Ag were synthesized by solid-state reaction. Scanning electron microscopy revealed Ag particles dispersed among and combined with Ca₃Co₄O₉ grains several times larger in size. The electrical resistivity (ρ) of the composites is favorably lower than that of Ca₃Co₄O₉ alone and decreases with increasing Ag content. It can thus be inferred that the highly conductive Ag particles between the oxide grains contribute to the reduction of ρ. Although minimal in smaller amounts, the addition of Ag also seems to have a negative impact on the Seebeck coefficient (S) of the composites due to its poor S. Since the reduction of ρ is more significant than the degradation of S, the power factor is found to be improved by the addition of 10 wt% Ag.