Selectivity In Methanol Oxidation Research Articles

MOF-808: a novel solid-acid catalyst for methanol conversion to environmentally clean fuel dimethyl ether

In this study, metal–organic frameworks (MOFs) based on zirconium which are called MOF-808 were synthesized by solvothermal method. A series of Zr-MOF were synthesized at different temperatures and reaction times to find the best synthesis samples to produce dimethyl ether from dehydration of methanol. As synthesized MOFs were characterized with x-ray diffraction, standard electron microscopy, and BET, they showed high methanol conversion and selectivity for methanol oxidation. The relationship between crystallinity, reactivity and relation catalysts life was discussed. For the first time, this MOF was used as a solid catalyst in the conversion of methanol to dimethyl ether due to its thermal stability and moderate acidity. The results show that all samples had a crystalline structure and were properly synthesized. The performance of the synthesized catalysts, the selectivity, and the effect of reactor temperature in the conversion of methanol to dimethyl ether in a tubular reactor with weight hourly space velocity = 5 h−1 were investigated. The highest surface area is nearly 1360 m2/g, size dimension of samples is in the range of 200–800 nm, and the highest Langmuir surface area is 1530 m2/g.

Methanol oxidation on AuAg-Zn/MCM-36 – The effect of catalyst components and pretreatment

• ZnO loaded on MCM-36 played a role of structural and electronic promoter. • Alloy was identified after thermal treatment of AuAg-zeolites in Ar and H 2 flows. • Zinc favored the deeper alloying of noble metals in hydrogen reduction conditions. • Zinc on MCM-36 directed the selectivity of Au- and AuAg-catalysts to formaldehyde. • Alloy rich in silver favored the total oxidation of methanol. MCM-36 and Zn/MCM-36 layered zeolites were used as supports for gold and silver. The calcined samples prepared were treated in inert gas or hydrogen flow at 673 K. The effect of gold, silver, zinc and Au-Ag alloy on the surface properties, activity and selectivity of the catalysts in methanol oxidation was studied. The catalysts were fully characterized by XRD, TEM, UV–vis and XPS techniques. The surface acidity of catalysts was measured by pyridine adsorption combined with FTIR studies. The results showed that metallic gold dominated on the surface of calcined catalysts and the amount of negative charge on metal particles was dependent on the chemical composition of the matrix and the active phase. Au-Ag alloy was identified on the surface of bimetallic catalysts after their treatment in argon and hydrogen flow. It was proved that zinc on the surface of MCM-36 promoted the deep alloying of noble metals in strong reducing (hydrogen flow) conditions with the formation of gold-silver alloy rich in silver. The species on the surface of the catalysts, dependent on the activation treatments, determined their activity and selectivity in methanol oxidation. The presence of zinc in the support (Zn/MCM-36) significantly improved the activity of Au-Zn/MCM-36 due to the effect of zinc on the electronic and structural properties of gold. In bimetallic AuAg-samples, the influence of gold-silver alloy on the increase in their activity was dependent on the content of silver in the alloy. Zinc on MCM-36 support increased the selectivity to formaldehyde, whereas the alloy rich in silver favoured the total oxidation of methanol because of the segregation of alloy during the reaction.

Ternary Pt[sbnd]Ru[sbnd]C co-sputtered electrocatalysts having reaction selectivity for anodes and cathodes in direct methanol fuel cells

In the present study, the reaction selectivity of methanol oxidation and O2 reduction at PtRuC co-sputtering samples has been described. The samples were prepared using the polygonal barrel-sputtering method and tested by linear sweep voltammetry in 0.5 mol/L H2SO4 containing methanol and O2. When sputtering was performed at a constant Ar gas pressure of 3 Pa, methanol oxidation became highly selective for the samples prepared at AC powers of 30 and 50 W. This characteristic was likely induced by the existence of O2 reduction intermediates, which can enhance the oxidation of CO, a methanol oxidation intermediate. The samples displaying O2 reduction selectivity were obtained at Ar gas pressure ranging between 0.4 and 3 Pa (AC power: 100 W). The O2 reduction selectivity may be attributed to the deposition of the electron-rich metallic Ru, which exhibits poor methanol oxidation performance. Based on these results, PtRuC samples that show reaction selectivity in methanol oxidation and O2 reduction are independently prepared by the polygonal barrel-sputtering method.

Specific Metal–Support Interactions between Nanoparticle Layers for Catalysts with Enhanced Methanol Oxidation Activity

Oxide supports often play a critical role in metal-supported catalysts owing to their charge transfer phenomena that can alter catalytic performance. Herein, in place of conventional bulk oxide supports, monodisperse oxide nanoparticles (NPs) were exploited as supports for Pt catalysts. Depending on the type of oxide NP, Pt/oxide layered catalysts exhibited dramatic changes in the catalytic activity and selectivity for methanol oxidation. While Pt NPs deposited on MnO, Fe3O4, Co3O4, Cu2O, and ZnO NPs had comparable turnover frequencies to that of the pure Pt NP catalyst, Pt deposited TiO2 NPs changed the reaction rate significantly, with preferential selectivity observed toward partial oxidation products. Facet-specific interactions between Pt and TiO2 NPs were demonstrated by density functional theory calculations and catalytic reactions using shape-controlled TiO2 NPs. When Pt NPs were attached to spherical and rhombic TiO2 NPs with abundant (001) surfaces, methanol conversion was enhanced 10-fold owing to strong charge transfer from TiO2 to Pt.

VOx/Fe2O3 Shell\u2013Core Catalysts for the Selective Oxidation of Methanol to Formaldehyde

Efficient oxidation catalysts are important in many current industrial processes, including the selective oxidation of methanol to formaldehyde. Vanadium-containing catalysts have been shown to be effective selective oxidation catalysts for certain reactions, and research continues to examine their applicability to other reactions of interest. Several VOx/Fe2O3 shell–core catalysts with varying VOx coverage have been produced to investigate the stability of VOx monolayers and their selectivity for methanol oxidation. Catalyst formation proceeds via a clear progression of distinct surface species produced during catalyst calcination. At 300 °C the selective VOx overlayer has formed; by 500 °C a sandwich layer of FeVO4 arises between the VOx shell and the Fe2O3 core, inhibiting iron cation participation in the catalysis and enhancing catalyst selectivity. The resulting catalysts, comprising a shell–subshell–core system of VOx/FeVO4/Fe2O3, possess good catalytic activity and selectivity to formaldehyde.

Formation of Pt–Ag alloy on different silicas – surface properties and catalytic activity in oxidation of methanol

Pt–Ag alloy is formed on silicas if Ag/Pt ≥ 2.5 and gives the highest methyl formate selectivity in methanol oxidation.

The effect of zinc and copper in gold catalysts supported on MCF cellular foams on surface properties and catalytic activity in methanol oxidation

MCF (Mesostructured Cellular Foams) and Zn/MCF were used as supports for gold and copper. The effect of zinc and copper on the surface properties, activity and selectivity of gold catalysts in the methanol oxidation was studied. The catalysts were characterized in detail by XRD, TEM, UV–Vis, XPS, ESR and FTIR-NO. The results showed that zinc oxide species play the role of a structural promoter which protects against agglomeration of gold species and an electronic promoter, decreasing reducibility of copper cations by the strong copper-zinc interaction. These interactions result in the incorporation of copper into the crystal structure of zinc oxide and lead to changes in the surrounding of gold in bimetallic (Au-Cu) catalysts compared to materials without zinc. The composition of the catalysts determines their activity and selectivity in methanol oxidation. Bimetallic (Au-Cu) catalysts, irrespective of the nature of the support (MCF vs Zn/MCF), are much more active than monometallic (Au) samples as a result of synergistic interactions between Au and Cu species. The samples containing zinc are highly selective to formaldehyde due to Au-Zn and/or Cu-Zn interaction, which weakens the adsorption of formaldehyde.

Molecular Understanding of Reactivity and Selectivity for Methanol Oxidation at the Au/TiO2Interface

Goldkatalyse: Experimentell und theoretisch wurde bestätigt, dass die Grenzflächenatome eines Au/TiO2-Katalysators sowohl hoch reaktiv als auch hoch selektiv in der Oxidation von Methanol zu Formaldehyd mit O2 bei niedrigen Temperaturen sind. Der mikroskopische Mechanismus dieser komplexen Reaktion wurde im Detail auf molekularer Ebene aufgeklärt (siehe Darstellung eines Goldclusters auf einer TiO2-Oberfläche).

Molecular Understanding of Reactivity and Selectivity for Methanol Oxidation at the Au/TiO2 Interface

Molecular Understanding of Reactivity and Selectivity for Methanol Oxidation at the Au/TiO₂ Interface

Titanium Oxide/Platinum Catalysis: Charge Transfer from a Titanium Oxide Support Controls Activity and Selectivity in Methanol Oxidation on Platinum

Platinum films of 1 nm thickness were deposited by electron beam evaporation onto 100 nm thick titanium oxide films (TiOx) with variable oxygen vacancy concentrations and fluorine (F) doping. Methanol oxidation on the platinum films produced formaldehyde, methyl formate, and carbon dioxide. F-doped samples demonstrated significantly higher activity for methanol oxidation when the TiOx was stoichiometric (TiO2), but lower activity when it was nonstoichiometric (TiO1.7 and TiO1.9). These results correlate with the chemical behavior of the same types of catalysts in CO oxidation. Fluorine doping of stoichiometric TiO2 also increased selectivity toward partial oxidation of methanol to formaldehyde and methyl formate, but had an opposite effect in the case of nonstoichiometric TiOx. Introduction of oxygen vacancies and fluorine doping both increased the conductivity of the TiOx film. For oxygen vacancies, this occurred by the formation of a conduction channel in the band gap, whereas in the case of fluorine doping, F acted as an n-type donor, forming a conduction channel at the bottom of the conduction band, about 0.5–1.0 eV higher in energy. The higher energy electrons in F-doped stoichiometric TiOx led to higher turnover rates and increased selectivity toward partial oxidation of methanol. This correlation between electronic structure and turnover rate and selectivity indicates that the ability of the support to transfer charges to surface species controls in part the activity and selectivity of the reaction.

Selectivity in Methanol Oxidation as Studied on Model Systems Involving Vanadium Oxides

Oxidation catalysts are modeled by oxide single crystals, thin oxide films, as well as supported oxide nanoparticles. We characterize the surface of those materials using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectroscopy, infrared spectroscopy, and thermal desorption spectroscopy. We find temperature dependent structural transformations from V2O5(001) to V2O3(0001) via V6O13(001). V2O3(0001) is found to be vanadyl terminated in an oxygen ambient and it loses the vanadyl termination after electron bombardment. It is shown that the concentration of vanadyl groups controls the selectivity of the methanol oxy-dehydrogenation towards formaldehyde. A proposal for the mechanism is made. The results on single crystalline thin films are compared with similar measurements on deposited vanadia nanoparticles. The experimental results are correlated with theoretical calculations and models.

Physicochemical and catalytic properties of iron-doped silica—the effect of preparation and pretreatment methods

Chemical vapor deposition (1wt% of iron) and wet and wetness impregnations (both giving Fe loading of 1.6 and 2.9 wt%) have been applied for the formation of iron-doped silica. The obtained materials were characterized by means of low-temperature N 2 adsorption, XRD, TEM, H 2-TPR, ESR, and chemisorption of CO and O 2. Their catalytic activity was tested in isopropanol decomposition and oxidation of methanol to formaldehyde. Depending on the preparation procedure various levels and strengths of Fe–silica interactions were observed. The activation conditions determine the nature of the Fe species formed. Fe 3+ isolated species are active in isopropanol dehydration whereas Fe–oxide centers exhibit very high selectivity in methanol oxidation to methylformate and formaldehyde.

Monolayers and double layers of vanadium pentoxide on different carriers: Preparation, characterization and catalytic activities

Reactions of vanadyl triisobutoxide with surface OH groups are used to immobilize mono- and double layers of V 2O 5 on Al 2O 3, SiO 2, MgO, and TiO 2 supports. The Al 2O 3 and SiO 2 carriers exhibit quantitative transformation of the surface hydroxyl groups into VO species, as evidenced by OH group and V 5+ determinations. In contrast, with MgO and TiO 2 only a fraction of the surface hydroxyls was found to react with the impregnant solution. Hydroxyl groups present on the surface of the calcined monolayer catalyst are utilized for immobilization of a second V 2O 5 layer. TPR profiles of the supported V 2O 5 catalysts exhibit one prominent peak and indicate that the reducibility of the V 2O 5 species depends mainly on the carrier, and only weakly on the V 2O 5 load. The temperature of maximum hydrogen consumption in the TPR profiles increases in the sequence TiO 2 < Al 2O 3 < SiO 2 < MgO. The catalytic activity of the pure carriers and supported catalysts is tested for methanol and n-heptanol oxidation in the range 520–670 K. From the pure carriers, TiO 2 exhibits the highest selectivity to formaldehyde (22%), while MgO shows a selectivity of 95% to n-heptanal. From the monolayer supported systems, SiO 2V 5+ is most selective (90%) for formaldehyde formation, whereas for n-heptanal production MgOV 5+ was found to be most selective (>95%). Second-layer impregnation does not lead to enhanced activity and selectivity for methanol oxidation. However, it improves the selectivity to n-heptanal for Al 2O 3 and SiO 2 carriers.

Influence of grain morphology of V 2O 5 on its reducibility and selectivity for methanol oxidation

Influence of grain morphology of V 2O 5 on its reducibility and selectivity for methanol oxidation

Influence of the composition and calcination temperature of Mo−Fe catalysts on their activity and selectivity in methanol oxidation

With increasing atomic ratio M=Mo/Fe from 1,1 to 2.2, the specific activity and selectivity are maximum at M=1.6–1.9. A sample with M=1.52 caicined at 673 K has a minimum activity and selectivity as compared to samples calcined at 573, 773 and 973 K. An explanation is suggested for the above facts.