Conditions for the appearance of thermal oscillations during the catalytic oxidation of methanol

The experimental conditions in which thermal oscillations may be detected during methanol oxidation on palladium catalyst were determined for methanol concentration, oxygen flow rate, temperature of the gaseous reaction mixture and weight of the catalyst sample. Catalyst powder disposal may influence the characteristics of oscillations.

---

, , , , , , . .

     

On the nature of radicals formed in methanol catalytic oxidation

The quantum-chemical calculations of the hydroxymethyl radical •CH₂OH were performed for the first time and a theoretical EPR spectrum of this radical was constructed. The formation of the hydroxymethyl radical in the reaction of methanol oxidation is thermodynamically favorable. The shape and parameters of the constructed spectrum differed from those for radicals experimentally detected in the catalytic oxidation of methanol using the matrix isolation method. However, they are consistent with the spectrum ascribed to the EPR spectrum of •CH₂OH observed in the direct photolysis of methanol. This result allows one to refine the identification of the nature of radicals formed in the catalytic reaction of methanol oxidation.     

Bifurcation diagrams of the heterogeneous catalytic oxidation of methanol

The experimental bifurcation diagrams of the heterogeneous catalytic oxidation of methanol on Pd have been determined by changing the concentration of methanol or oxygen in the feed. Hopf bifurcations have been obtained.     

Overall kinetic model for oscillating catalytic oxidation of methanol

An overall kinetic model for the deep catalytic oxidation of methanol is presented. It is based on the balance of chemical species and could described self-sustained oscillations.

---

. .

     

The effect of ethanol on the catalytic oxidation of methanol on silver

Thermal desorption, radioactive indicators, and a kinetic method involving frozen radicals were used to study the catalytic oxidation of methanol in the presence of ethanol on silver. The increase in the yield of aldehydes in the combined oxidation of these alcohols on silver is related to a change in the nature of the adsorption and homogeneous steps of this reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1174–1176, May, 1990.     

Activation energy for the ignition of the catalytic oxidation of methanol in oscillatory regime

The overall activation energy for the ignition of thermokinetic oscillations observed (in a dynamic calorimeter) during the heterogeneous catalytic oxidation of methanol on Pd/LiAl₅O₈ were obtained and discussed by a PdO_x redox cycle.     

Fabrication of the catalytic electrodes for methanol oxidation on electrospinning-derived carbon fibrous mats

The carbon fibrous mats with high conductivity (50 S cm⁻¹) formed by carbon nanofibers with an average diameter of ∼150 nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibers. The platinum clusters are electrodeposited on the carbon nanofibrous mats (CFMs) by multi-cycle CV method. In contrast to the catalytic peak current of methanol oxidation on commercial catalyst (185 mA mg⁻¹ Pt), the catalytic peak current on optimum Pt/CFM electrode reaches to ∼420 mA mg⁻¹ Pt despite of the large size (50–200 nm) of the Pt clusters, revealing that the special structure of carbon fibrous mats is favorable to improve the performance of catalyst.     

Thermal stability of MnMoO4-MoO3 catalysts for methanol oxidation

The thermal stability of MnMoO4-MoO₃ catalysts for methanol oxidation has been studied. Formation of eutectic composition of 33 wt.% MnMoO₄ and 67 wt% MoO₃ and a melting point of 969–973K was observed. An attempt has been made to plot a state diagram of the MnMoO₄-MoO₃ system.The thermal stabilities of the Mn-Mo-O and commercial Fe-Mo-O catalysts have been compared. It has been concluded that manganese(II) molybdate catalysts are stable up to 973 K and are of a definite interest in view of their application in practice.

---

Zusammenfassung Es wurde die thermische StabilitÄt von MnMoO₄-MoO₃-Katalysatoren für die Methanoloxidation untersucht. Es wurde die Bildung eines Eutektikum mit der Zusammensetzung von 33m% MnMoO₄ und 67m% MoO₃ und dem Schmelzpunkt von 969–973 K beobachtet sowie versucht, da\ Zustandsdiagramm für das MnMoO₄-MoO₃-System zu erstellen.Weiterhin wurde die thermische StabilitÄt von Mn-Mo-O-Katalysatoren mit der von handelsüblichen Fe-Mo-O-Katalysatoren verglichen. Es wurde festgestellt, da\ Mangan(II)-molybdatkatalysatoren bis zu 973 K hitzebestÄndig und im Hinblick auf ihre praktische Anwendung von eindeutig gro\er Bedeutung sind.

     

Steady state catalytic properties and oxygen binding energy of cadmium-molybdenum catalysts in methanol oxidation

On normal cadmium molybdate the products of methanol oxidation are primarily CO₂ and H₂. After the introduction of excess MoO₃ to reach Mo/Cd=1.2, methanol is oxidized to formaldehyde and carbon monoxide via a consecutive scheme. The oxygen binding energy in the steady state for the first sample is by 30 kcal/mol higher than that for the second catalyst. The activation energies of methanol conversion are 11.5 and 20 kcal/mol, respectively.

---

CO₂ H₂. MoO₃ Mo/Cd=1, 2 . 1- 30 / , , , , 11,5 20 /.

     

Size-controllable carbon spheres doped Ni (II) for enhancing the catalytic oxidation of methanol

Ni(II)/CSs were prepared using a simple two-step hydrothermal method. The morphology and composition of the catalysts were studied with scanning electron microscope, transmission electron microscope, and X-ray diffraction. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the surface of the prepared carbon spheres was rich in hydroxyl groups, which was beneficial to remove CO intermediates, and therefore, improving the catalytic efficiency and the antipoisoning ability of the catalysts. The results of cyclic voltammetry and chronoamperometry showed that the electrocatalytic activity and stability of Ni(II)/CSs were higher than that of unloaded NiAc under alkaline environment. When the nickel content was 5 wt.%, the peak oxidation current density of methanol on Ni(II)/CSs electrocatalyst reached the maximum of 34.54 mA/cm², which was about 1.8 times that of unloaded NiAc. These results indicate that Ni(II)/CSs has potential applications in the electrocatalytic oxidation of methanol.     

Influence of mechanical activation of molybdenum oxide on its catalytic activity in the reaction of the partial oxidation of methanol

The influence of mechanical activation on the structure and catalytic activity of MoO₃ was studied. It was established that as a result of mechanical treatment grinding, secondary aggregation of particles and accumulation of materials from the grinding machine occurred. An increase in the catalytic activity was observed in the oxidation of methanol to formaldehyde.     

Influence of excess MoO3 in a non-stoichiometric cadmium-molybdenum catalyst on the catalytic properties in methanol oxidation

By IR and Raman spectroscopy it has been shown that excess MoO₃ is bound molecularly on the surface of CdMoO₄, presumably on sites of C₂ and C_i symmetry. This increases the activity and selectivity of the catalyst in methanol oxidation to formaldehyde.

---

, , MoO₃ CdMoO₄, C₂ C_i. .

     

Synthesis of polymeric ionic liquid microsphere/Pt nanoparticle hybrids for electrocatalytic oxidation of methanol and catalytic oxidation of benzyl alcohol

Herein, we present a facile approach for the synthesis of polymeric ionic liquids (PILs) microspheres for metal scavenging and catalysis. Crosslinked poly(1‐butyl‐3‐vinylimidazolium bromide) microspheres with the diameter of about 200 nm were synthesized via miniemulsion polymerization, in which 1,4‐di(vinylimidazolium) butane bisbromide was added as the crosslinker. Anion exchange of PIL microspheres with Pt precursor and followed by the reduction of Pt ions produced PIL microsphere supported Pt nanoparticle hybrids. The synthesized Pt nanoparticles with a diameter of about 2 nm are uniformly dispersed and strongly bound to the surface of PIL microspheres. The catalytic performances of PIL/Pt nanoparticle hybrids were evaluated for both the electrocatalytic oxidation of methanol and oxidation of benzyl alcohol. The PIL/Pt nanoparticle hybrids show better electrocatalytic activity towards the electrooxidation of methanol than pure Pt nanoparticles. Furthermore, they are effective and easily reusable catalysts for the selective oxidation of benzyl alcohol in aqueous reaction media, demonstrating that the synthesized PIL microspheres are suitable scaffolds for heterogeneous catalysts Pt. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thermal decomposition of the 1:1 bismuth molybdate and its implications for catalytic oxidation

To study the stability of the 1:1 bismuth molybdate, thin films (300–500 Å) have been prepared by thermal evaporation of the powder samples followed by heating in air or oxygen. Electron diffraction revealed that in an oxidizing atmosphere and at temperatures higher than 400°C or in vacuum and at temperatures higher than about 350°C the 1:1 compound decomposes into the 2:1 bismuth molybdate and MoO₂. These results suggest that during catalytic oxidation and (at least) for temperatures greater than 400°C the 2:1 compound forms near the surface of the 1:1 phase, being responsible for the selective catalytic oxidation.     

Enhanced catalytic activity of ternary NiCoPd nanocatalyst dispersed on carbon nanotubes toward methanol oxidation reaction in alkaline media

Ternary NiCoPd nanocatalyst dispersed on multi-walled carbon nanotubes (CNTs), NiCoPd/CNTs, was synthesized using a simple and green sonochemical method. The as-prepared NiCoPd/CNT hybrids were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The electrochemical measurements revealed that the ternary NiCoPd/CNTs exhibited an enhanced electrocatalytic activity for the methanol oxidation reaction (MOR), much superior to those of the binary NiPd/CNT and CoPd/CNT, as well as monometallic Pd/CNT counterparts, which likely resulted from the synergistic function of the dopant metals of Ni and Co.     

Electrochemical oxidation of alkyl-substituted allenes in methanol

Mono-, di- and tri-alkyl-substituted allenes were potentiostatically oxidized in methanol at graphite and Pt anodes. At the former electrode, α-methoxylated ketones (due to 4F/mole electricity consumption) and esters (6F/mole) were the major products. At a Pt anode, intermediate products such as vinyl-ether derivatives (2F/mole) were characterised too. Unlike the anodic oxidation of alkenes and alkynes previously reproted in the literature, dimerisation is not a typical process in the allenes' oxidation, since of all the products obtained only a sole dimer has been observed. The mechanism for the formation of most products is discussed.     

Platinum catalysts prepared with functional carbon nanotube defects and its improved catalytic performance for methanol oxidation

Carbon nanotube (CNT) supported Pt nanoparticle catalysts have been prepared by spontaneous reduction of PtCl6(2-) ion as a result of direct redox reactions between PtCl6(2-) and oxygen-containing functional groups at defect sites of CNTs, which were introduced by chemical and electrochemical oxidation treatment of CNTs. The electrocatalytic properties of as-prepared Pt-CNT catalysts for methanol oxidation were investigated by chronopotentiometry and cyclic voltammetry. Compared with Pt catalysts prepared by hydrogen reduction and electrochemical deposition methods, Pt catalysts synthesized by functional CNT defects show excellent antipoisoning ability and long-term cycle stability.     

In silico studies of the mechanism of methanol oxidation by quinoprotein methanol dehydrogenase

The mechanism of bacterial methanol dehydrogenase involves hydride equivalent transfer from substrate to the ortho-quinone PQQ to provide a C5-reduced intermediate that subsequently rearranges to the hydroquinone PQQH(2). We have studied the PQQ reduction by molecular dynamic (MD) simulations in aqueous solution. Among the five simulated structures, either Asp297 or Glu171 or both are ionized. Reasonable structures are obtained only when both carboxyl groups are ionized. This is not unexpected since the kinetic pH optimum is 9.0. In the structure of the enzyme.PQQ.HOCH(3) complex, the hydrogen bonded Glu171-CO(2)(-).H-OCH(3) is in a position to act as a general base catalyst for hydride equivalent transfer to C5 of PQQ. We thus suggest that Glu171 plays the role of general base catalyst in PQQ reduction rather than Asp297 as previously suggested. The reduction is assisted by Arg324, which hydrogen bonds to the ortho-quinone moiety of PQQ. The rearrangement of the C5-reduced intermediate to provide hydroquinone PQQH(2) is also assisted by proton abstraction by Glu171-CO(2)(-) and the continuous hydrogen bonding of Arg324 throughout the entire reaction. These features as well as the mapping of the channel for substrate and water into the active site entrance are the observations of major importance.     

Synergy in selective catalytic oxidation

Summary A strong synergy between separate oxide phases A and B is observed in the oxidation of isobutylene to methacrolein. This is explained by the continuous activation of potential centers on A by spill-over oxygen emitted by B (remote control). This activation corresponds to the creation of Brönsted sites in the case where A is MoO₃. We discuss some details of the mechanism and the consequences with respect to catalyst design and process.