Maria N. Timofeeva

Esterification of 2,6-pyridinedicarboxylic acid with n-butanol catalyzed by heteropoly acid H3PW12O40 or its Ce(III) salt

Abstract The liquid-phase esterification of 2,6-pyridinedicarboxylic acid (PA) with n-BuOH is efficiently catalyzed by heteropoly acid H 3 PW 12 O 40 as a homogeneous catalyst and by its insoluble acidic Ce(III) salt, Ce 0.87 H 0.4 PW 12 O 40 , as a heterogeneous catalyst, yielding 100% of PA dibutyl ester. The Ce(III) salt has a lower activity than H 3 PW 12 O 40 but can be easily recovered and reused. Insoluble NH + 4 , K + and Cs + salts also exhibit moderate activities. The activity of the salts decreases in the series: Ce 0.87 H 0.4 PW 12 O 40 ⪢ Cs 2.5 H 0.5 PW 12 O 40 ∼ Cs 3 PW 12 O 40 ∼ Cs 2 HPW 12 O 40 ∼ (NH 4 ) 3 PW 12 O 40 > K 3 PW 12 O 40 .

Novel Zirconocene Hydride Complexes in Homogeneous and in SiO2‐Supported Olefin‐Polymerization Catalysts Modified with Diisobutylaluminum Hydride or Triisobutylaluminum

Reactive species in SiO 2 -supported, zirconocene-based olefin-polymerization catalysts have been characterized by comparison of their UV-vis spectra with those of related, NMR-spectroscopically identified catalyst species in homogeneous solution. Neutral zirconocene dihydride complexes are found to arise in hydrocarbon solutions as well as on SiO 2 supports when catalyst systems that contain rac-Me 2 si(ind) 2 ZrCl 2 and methylaluminoxane (MAO) are modified by addition of diisobutylaluminum hydride or triisobutylaluminum. These complexes, tentatively formulated as adducts with Lewis-acidic alkylaluminum species AlR 2 X, rac-Me 2 Si(ind) 2 ZrH 2 ·{nAlR 2 X}, are reconverted into the initial reactive zirconocene cations upon addition of isobutene to these reaction systems.

Epoxidation of cycloolefins with hydrogen peroxide in the presence of heteropoly acids combined with phase transfer catalyst

Oxidation of cycloolefins (cyclohexene, cyclooctene, and cyclododecene) with a 30% solution of hydrogen peroxide at 65 °C in the presence of heteropoly acids (HPA) H3PW12–xMoxO40 (x = 0—12), which are precursors of active peroxo complexes, and phase transfer catalysts Q+Cl–, where Q+ is the quaternary ammonium cation containing C4—C18 alkyl groups or [C5H5NC16H33]+, was studied. The catalytic activity decreases in the HPA series: H3PW12O40 > H3PW9Mo3O40 > H3PW6Mo6O40 > H3PW3Mo9O40 > H3PMo12O40. The state of the H3PW12O40—I2I2 system was studied using UV, IR, and 31P NMR spectroscopies with variation of the [H2O2] : [HPA] ratio from 2 to 200 during cyclohexene epoxidation. Despite different catalytic precursors, the reaction proceeds through the same peroxo complex.

Esterification of n-Butanol with Acetic Acid in the Presence of H3PW12O40 Supported on Mesoporous Carbon Materials

The adsorption of H3PW12O40 (HPA) from methanol solutions on mesoporous carbon supports (multiwall carbon nanotubes (CFC-3) and CFC modified with nitrogen atoms (N-CFC)) was studied. It was found that up to 10 wt % HPA was irreversibly adsorbed on the surface of CFC. This character of adsorption is indicative of the strong interaction of the adsorbate (HPA molecules) with coal surface groups (carboxylic, lactone, etc.) to form intermolecular hydrogen bonds with π-electron interactions. It was found that N-containing surface centers affected the adsorption of HPA on N-CFC. The acid and catalytic properties of HPA/CFC systems in the esterification reaction of n-butanol with acetic acid were studied ([BuOH]/[HOAc] = 1 : 15 mol/mol; 80°C). It was found that the strength of proton centers, which was determined as proton affinity, decreased upon supporting HPA. The HPA/CFC-3 systems most actively catalyzed the reaction. The catalytic activity of HPA/N-CFC depended on the nature of N-containing groups at the support surface, and it decreased with concentration of pyridine-like structures.

Adsorption of H3PW12O40 by porous carbon materials

Adsorption of H3PW12O40 from water and organic oxygen-containing solvents (AcOH, Me2CO, MeOH) by carbon mesoporous materials, viz., Sibunit and catalytic filamentous carbons (CFC), was studied. The amount of irreversibly sorbed heteropolyacid is 50—100 mg g–1 of support and decreases in the series of solvents: H2O > Me2CO > AcOH > MeOH. The adsorption capacity of CFC depends on the specific surface, total pore volume, and microstructure of the CFC fiber.

Acid-base properties and catalytic activity of metal-organic frameworks: A view from spectroscopic and semiempirical methods

ABSTRACT This article summarizes several approaches for understanding the catalytic chemistry and “structure-surface acidity-reactivity” relationships in a multiplicity of catalytic applications of a continually increasing assemblage of metal-organic frameworks (MOFs) structures. The various spectroscopic techniques for acid-base characterization of MOFs are reviewed. The experimental requirements and the type and nature of probe molecules available are also discussed. Special emphasis is given to the revealing of the surface acid-base effect on the catalytic performance of MOFs.

Regulating the Physicochemical and Catalytic Properties of Layered Aluminosilicates

Basic methods of the introduction of metal ions into the interlayer space of natural layered aluminosilicate (LAS) are considered. The physicochemical and structural properties of pillared LAS’s depend on the nature of the cation, as well as on the cation intercalation method and conditions. The catalytic properties and stability of an LAS in acid-catalyzed and oxidation reactions may depend on its textural and physicochemical properties.

Scanning thermal microscopy with heat conductive nanowire probes

Scanning thermal microscopy (SThM), which enables measurement of thermal transport and temperature distribution in devices and materials with nanoscale resolution is rapidly becoming a key approach in resolving heat dissipation problems in modern processors and assisting development of new thermoelectric materials. In SThM, the self-heating thermal sensor contacts the sample allowing studying of the temperature distribution and heat transport in nanoscaled materials and devices. The main factors that limit the resolution and sensitivities of SThM measurements are the low efficiency of thermal coupling and the lateral dimensions of the probed area of the surface studied. The thermal conductivity of the sample plays a key role in the sensitivity of SThM measurements. During the SThM measurements of the areas with higher thermal conductivity the heat flux via SThM probe is increased compared to the areas with lower thermal conductivity. For optimal SThM measurements of interfaces between low and high thermal conductivity materials, well defined nanoscale probes with high thermal conductivity at the probe apex are required to achieve a higher quality of the probe-sample thermal contact while preserving the lateral resolution of the system. In this paper, we consider a SThM approach that can help address these complex problems by using high thermal conductivity nanowires (NW) attached to a tip apex. We propose analytical models of such NW-SThM probes and analyse the influence of the contact resistance between the SThM probe and the sample studied. The latter becomes particularly important when both tip and sample surface have high thermal conductivities. These models were complemented by finite element analysis simulations and experimental tests using prototype probe where a multiwall carbon nanotube (MWCNT) is exploited as an excellent example of a high thermal conductivity NW. These results elucidate critical relationships between the performance of the SThM probe on one hand and thermal conductivity, geometry of the probe and its components on the other. As such, they provide a pathway for optimizing current SThM for nanothermal studies of high thermal conductivity materials. Comparison between experimental and modeling results allows us to provide direct estimates of the contact thermal resistances for various interfaces such as MWCNT-Al (5×10(-9)±1×10(-9)Km(2)W(-1)), Si3N4-Al (6×10(-8)±2.5×10(-8)Km(2)W(-1)) and Si3N4-graphene (~10(-8)Km(2)W(-1)). It was also demonstrated that the contact between the MWCNT probe and Al is relatively perfect, with a minimal contact resistance. In contrast, the thermal resistance between a standard Si3N4 SThM probe and Al is an order of magnitude higher than reported in the literature, suggesting that the contact between these materials may have a multi-asperity nature that can significantly degrade the contact resistance.

Acidity of Solutions of Heteropoly Acids with Various Structures and Compositions

Hammett acidity functions H0 of solutions of heteropoly acids H5PW11XO40 (X(IV) = Ti, Zr), H3PW12O40, H4SiW12O40, H6P2W21O71, and H21B3W39O132, as well as HClO4 and CF3SO3H, in water and 90% aqueous acetone and acetonitrile, are measured at 20°C by the indicator method. In aqueous solutions all acids under study have the same strength, and in organic solvents their acidities differ. A correlation between the catalytic activity and acidity of the solution is found for the condensation of acetone to mesityl oxide.

Catalytic Properties of Fe-Cu-Al-Montmorillonites in the Oxidation of Acid Chrome Dark Blue Azo Dye

Interlayer cations in the sodium form of the aluminosilicate montmorillonite (Mt) have been exchanged by mixed, bulky, polynuclear hydroxo cations (Al: (Fe + Cu) = 10, Cu: Fe = 0–1, OH: (Fe + Cu + Al) = 2), and the product has been heat-treated to obtain Fe-, Fe-Al-, and Fe-Cu-Al-containing materials (Fe-Cu-Al-Mt). The chemical composition and textural characteristics of the materials depend on the Cu: Fe molar ratio. The catalytic properties of the materials in the oxidation of acid chrome dark blue (ACDB) azo dye with hydrogen peroxide have been investigated. The activity and stability of the Fe-Cu-Al-Mt systems are determined by the quantity of copper and iron atoms introduced into the structure of the material. As the iron ion content is increased, the specific catalytic activity of the system increases and the system becomes less resistant to the leaching of iron ions into the solution. Raising the copper content of the system above 0.07 wt % reduces its activity and stability. The effects of the catalyst content, pH of the solution being oxidized, and reactant ratio (H2O2: ACDB) on the reaction rate have been studied. The ACDB oxidation conditions have been optimized.