Chemical Immobilization of H5PMo10V2O40 (PMo10V2) Catalyst on Nitrogen-rich Macroporous Carbon (N-MC) for Use as an Oxidation Catalyst

Nitrogen-rich macroporous carbon (N-MC) was prepared using melamine-formaldehyde resin as a carbon precursor. The surface of N-MC was then modified to have a nitrogen-derived functional group (amine group), and thus, to provide an anchoring site for heteropolyacid (HPA) catalyst. By taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]^5?, H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) HPA catalyst was chemically immobilized on the N-MC support as a charge matching component. It was found that PMo₁₀V₂ was finely dispersed on the N-MC support. In the model vapor-phase 2-propanol conversion reaction, the PMo₁₀V₂/N-MC catalyst showed a remarkably enhanced oxidation catalytic activity and a suppressed acid catalytic activity compared to the mother catalyst. The PMo₁₀V₂/N-MC catalyst served as an efficient oxidation catalyst in the reaction where both acid and oxidation reactions occurred simultaneously.     

Preparation and Oxidation Catalysis of H5PMo10V2O40 Catalyst Immobilized on Nitrogen-Containing Spherical Carbon

Nitrogen-containing spherical carbon (N-SC) with a diameter of ca. 12 μm was synthesized by a hydrothermal method using melamine-formaldehyde resin as a carbon precursor. The N-SC was then modified to have a positive charge, and thus, to provide a site for the immobilization of H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) catalyst. The PMo₁₀V₂ catalyst was chemically immobilized on the surface-modified N-SC support by taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]^5?. Characterization results showed that nitrogen in the N-SC support played an important role in forming a nitrogen-derived functional group (amine group) and that PMo₁₀V₂ catalyst was chemically immobilized on the nitrogen-derived functional group of N-SC support. PMo₁₀V₂/N-SC catalyst showed a higher 2-propanol conversion than the unsupported PMo₁₀V₂ catalyst in the vapor-phase 2-propanol conversion reaction. Moreover, the PMo₁₀V₂/N-SC catalyst showed an enhanced oxidation catalytic activity (formation of acetone) and a suppressed acid catalytic activity (formation of propylene and isopropyl ether) than the unsupported PMo₁₀V₂ catalyst. The enhanced oxidation activity of PMo₁₀V₂/N-SC catalyst was due to fine dispersion of [PMo₁₀V₂O₄₀]^5? on the N-SC support formed via chemical immobilization.     

Immobilization of H<Subscript>3</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst on the nitrogen-containing mesoporous carbon and its application to the vapor-phase 2-propanol conversion reaction

Nitrogen-containing mesoporous carbon (N-MC) with high surface area (=1,115 m²/g) and large pore volume (=1.18 cm³/g) was synthesized by a templating method. The surface of N-MC was then modified to form a positive charge, and thus, to provide sites for the immobilization of [PMo₁₂O₄₀]³⁻. By taking advantage of the overall negative charge of [PMo₁₂O₄₀]³⁻, H3PMo₁₂O₄₀ (PMo₁₂) was chemically immobilized on the N-MC support as a charge matching component. It was found that the PMo₁₂/N-MC still retained relatively high surface area (=687 m²/g) and large pore volume (=0.67 cm³/g) even after the immobilization of PMo₁₂. It was also revealed that PMo₁₂ species were finely and molecularly dispersed on the N-MC support via chemical immobilization. In the vapor-phase 2-propanol conversion reaction, the PMo₁₂/N-MC showed a higher conversion than the unsupported PMo₁₂. Furthermore, the PMo₁₂/N-MC showed an enhanced oxidation catalytic activity and a suppressed acid catalytic activity compared to the unsupported PMo₁₂. This catalytic behavior of PMo₁₂/N-MC was due to the molecular dispersion of PMo₁₂ on the N-MC support formed via chemical immobilization by sacrificing the proton.     

Preparation of H<Subscript>5</Subscript>PMo<Subscript>10</Subscript>V<Subscript>2</Subscript>O<Subscript>40</Subscript> catalyst immobilized on spherical carbon and its application to the vapor-phase 2-propanol conversion reaction

Spherical carbon (SC) with a diameter of ca. 9 μm was synthesized by a hydrothermal method using sucrose as a carbon precursor. The spherical carbon was then modified to have a positive charge, and thus, to provide a site for the immobilization of H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) catalyst. The PMo₁₀V₂ catalyst was immobilized on the surface-modified spherical carbon by taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]⁵⁻. The PMo₁₀V₂ catalyst immobilized on the spherical carbon (PMo₁₀V₂/SC) was applied to the vapor-phase 2-propanol conversion reaction. In the catalytic reaction, the PMo₁₀V₂/SC catalyst showed a higher 2-propanol conversion than the unsupported PMo₁₀V₂ catalyst. Furthermore, the PMo₁₀V₂/SC catalyst showed enhanced oxidation catalytic activity (formation of acetone) and the suppressed acid catalytic activity (formation of propylene and isopropyl ether) compared to the unsupported PMo₁₀V₂ catalyst. The enhanced oxidation activity of PMo₁₀V₂/SC catalyst was due to the fine dispersion of [PMo₁₀V₂O₄₀]⁵⁻ on the spherical carbon formed via chemical immobilization.     

Selective oxidation of methanol to dimethoxymethane over acid-modified V2O5/TiO2 catalysts

Selective oxidation of methanol to dimethoxymethane (DMM) was conducted in a fixed-bed reactor over an acid-modified V₂O₅/TiO₂ catalyst. The influence of the acid modification on its structure, redox and acidic properties, and catalytic performance for methanol oxidation were investigated. The results indicated that the content of vanadia in the catalyst exhibits a vital influence on the dispersion of vanadium species, while the acid modification can enhance its surface acidity. Proper amounts of the acid (W() = 15%) and V₂O₅ (W(V₂O₅) = 15%) components loaded in the acid-modified V₂O₅/TiO₂ catalyst are able to build a bi-functional circumstance that is favorable for the formation of DMM with high activity and selectivity. As a result, for the selective oxidation of methanol, the H₂SO₄-modified V₂O₅/TiO₂ catalyst gives a much higher DMM yield at 150 °C than the unmodified one.     

A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

Preparation, characterization, and oxidation catalysis of H3PMo12O40 heteropolyacid catalyst immobilized on carbon aerogel

Carbon aerogel (CA) with high surface area and large pore volume was prepared by polycondensation of resorcinol with formaldehyde. The surface of CA was then modified to have a positive charge, and thus to provide a site for the immobilization of H₃PMo₁₂O₄₀ (PMo₁₂) catalyst. By taking advantage of the overall negative charge of [PMo₁₂O₄₀]^3?, PMo₁₂ catalyst was chemically immobilized on the surface-modified CA as a charge matching component. It was found that PMo₁₂ catalyst was finely dispersed on the CA support via chemical interaction. In the vaporphase 2-propanol conversion reaction, the PMo₁₂/CA catalyst showed a higher 2-propanol conversion than the unsupported PMo₁₂ catalyst. Furthermore, the PMo₁₂/CA catalyst showed an enhanced oxidation catalytic activity (formation of acetone) and a suppressed acid catalytic activity (formation of propylene and isopropyl ether) compared to the unsupported PMo₁₂ catalyst. The enhanced oxidation activity of PMo₁₂/CA catalyst was due to fine dispersion of [PMo₁₂O₄₀]_3? on the CA support formed via chemical immobilization.     

Methanol selective oxidation to dimethoxymethane on H<Subscript>3</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>/SBA-15 supported catalysts

A series of SBA-15 supported H₃PMo₁₂O₄₀ catalysts were prepared for the one-step oxidation of methanol to dimethoxymethane (DMM). The evaluation and characterization revealed that higher DMM selectivity obtained on the incipient wetness impregnation (IM) catalyst was related to the instability of H₃PMo₁₂O₄₀ on it. Raman spectra showed that 12-molybdophosphoric acid was more stable on the direct synthesis (DS) catalyst than on the IM catalyst and the existence of SBA-15 support enhanced the stability of H₃PMo₁₂O₄₀. Moreover, higher H₃PMo₁₂O₄₀ loading resulted in more acid sites and low DMM selectivity, furthermore the thermal pretreatment on H₃PMo₁₂O₄₀ influenced its structure and thus affected DMM selectivity. This paper was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.     

Preparation of H5PMo10V2O40 catalyst immobilized on nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) and its application to the vapor-phase oxidation of benzyl alcohol

Nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) was synthesized by a templating method using mesostructured cellular foam silica (MCF-S) and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MCF-C was then modified to have a positive charge, and thus, to provide a site for the immobilization of [PMo₁₀V₂O₄₀]⁵⁻. By taking advantage of the overall negative charge of [PMo₁₀V₂O₄₀]⁵⁻, H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) catalyst was chemically immobilized on the N-MCF-C support as a charge-matching component. Characterization results showed that the PMo₁₀V₂ catalyst was finely dispersed on the N-MCF-C support via strong chemical interaction, and that the pore structure of N-MCF-C was still maintained even after the immobilization of PMo₁₀V₂. In the vapor-phase oxidation of benzyl alcohol, the PMo₁₀V₂/N-MCF-C catalyst showed a higher conversion and a higher oxidation activity (formation of benzaldehyde) than the unsupported PMo₁₀V₂ and PMo₁₀V₂/MCF-S catalysts.     

In situ synthesis of Au/Ti-HMS and its catalytic performance in oxidation of bulky sulfur compounds using in situ generated H2O2 in the presence of H2/O2

Gold particles are supported on Ti-containing mesoporous silica (Ti-HMS) through an in situ process. The obtained samples were characterized by a series of techniques including ICP, powder X-ray diffraction, N₂ sorption, UV-visible spectroscopy and transmission electron microscopy. The performance of the catalyst in direct synthesis of H₂O₂ from H₂/O₂ in methanol solvent and oxidative desulphurization using the in situ generated H₂O₂ have been systematically investigated. The results show that in situ synthesized Au/Ti-HMS, the organic template of which is eliminated via extraction with ethanol, successfully maintains the typical wormhole structure of HMS and possesses uniform mesopores, which is confirmed by N₂ sorption and TEM. UV-visible spectroscopy result confirms the simultaneous existence of Au and Ti active centers in this bifunctional catalyst. Gold particles supported on Ti-HMS show high activity in the direct synthesis of H₂O₂ from H₂ and O₂ in methanol solvent. Furthermore, high removal rate of bulky sulfur compounds can be obtained using the in situ generated H₂O₂ over Au/Ti-HMS. Final conversion rate of the substrates confirms the dominant role of the in situ H₂O₂ oxidation in deep desulphurization. In addition, this bifunctional catalyst can avoid the insufficiency of H₂O₂ caused by the decomposition comparing with the Ti-HMS/commercial H₂O₂ system.     

Li6V10O28, a novel cathode material for Li-ion battery

A novel cathode material, lithium decavanadate Li₆V₁₀O₂₈ with a large tunnel within the framework structure for lithium ion battery has been prepared by hydrothermal synthesis and annealing dehydration treatment. The structure and electrochemical properties of the sample have been investigated. The novel material shows good reversibility for Li⁺ insertion/extraction and long cycle life. High discharge capacity (132 mAh/g) is obtained at 0.2 mA/cm² discharge current and potential range between 2.0 and 4.2 V versus Li⁺/Li. AC impedance of the Li/Li₆V₁₀O₂₈ cell reveals that the cathode process is controlled mainly by Li⁺ diffusion in the active material. The novel material would be a promising cathode material for Li-ion batteries.     

Preparation of Mesoporous V–Ce–Ti–O for the Selective Oxidation of Methanol to Dimethoxymethane

Mesoporous V–Ce–Ti–O oxides were synthesized through the combination of sol–gel and hydrothermal methods and were characterized by different techniques. N₂ adsorption showed that the mesoporous oxides with 0–20 wt.% V₂O₅ possessed the surface areas of about 160 m² g^?1 with narrow pore size distribution centered around 4–5 nm. Vanadium species were highly dispersed in the samples, as confirmed by the wide angle XRD and Raman spectroscopy. The surface acidity of the materials was determined by the microcalorimetric adsorption of NH₃. Temperature programmed reduction and O₂ chemisorption were used to probe the redox property of the materials. It was found that the mesoporous V–Ce–Ti–O possessed bifunctional characters of acidic and redox properties that catalyzed the oxidation of methanol to dimethoxymethane (DMM). These bifunctional characters were further enhanced by the addition of V₂O₅ and SO₄ ^2? onto V–Ce–Ti–O simultaneously. Such supported catalysts exhibited excellent performance for the selective oxidation of methanol to DMM. Specifically, 72% conversion of methanol with 85% selectivity to DMM was achieved at 423 K over a SO₄ ^2?–V₂O₅/V–Ce–Ti–O catalyst.     

Lithium insertion in ultra-thin nanobelts of Ag2V4O11/Ag

In this study, ultra-thin nanobelts of Ag₂V₄O₁₁/Ag were successfully synthesized. The synthesized ultra-thin nanobelts of Ag₂V₄O₁₁/Ag are highly crystalline and the thickness is found to be about 5 nm. A lithium battery using ultra-thin nanobelts of Ag₂V₄O₁₁/Ag as the active materials of the positive electrode exhibits a high initial discharge capacity of 276 mAh g⁻¹, corresponding to the formation of Li_xAg₂V₄O₁₁ (x = 6). With increased cycling, the electrode made of ultra-thin nanobelts of Ag₂V₄O₁₁/Ag tends to loose electrochemical activity due to Ag⁺ ions in the ultra-thin nanobelts of Ag₂V₄O₁₁ were reduced and new phase was formed.     

Vapor phase oxidation of dimethyl sulfide with ozone over V2O5/TiO2 catalyst

The removal of volatile and odorous emissions from pulp and paper industrial processes usually generates secondary pollution which is treated further by scrubbing, adsorption, and catalytic incineration. Studies using a flow reactor packed with 10% vanadia/titania (V₂O₅/TiO₂) catalyst showed complete conversion of dimethyl sulfide (DMS) in the presence of ozone. The molar yields of partial oxidation products were only 10–20%. Small amounts of partial oxidation products, such as and dimethyl sulfone (DMSO₂), dimethyl disulfide (DMDS), and dimethyl sulfoxide (DMSO), were also formed. The results of the oxidation of DMS using ozone only, ozone plus catalyst, and oxygen plus catalyst suggest that the combined use of O₃ with catalyst is essential for the complete destruction of DMS to CO₂ and SO₂. A Box-Behnken design was used to determine the factors that have a significant effect on the conversion and selectivity of the products. It was concluded that product selectivity is strongly influenced by temperature, gas hourly space velocity (GHSV), and ozone concentration. The catalysts were characterized using XRD, surface area measurements, and SEM techniques. Time-on-stream studies carried out in a 500 ppmv gas stream held at 150 °C for 6 h, using 2 g of the catalyst, an ozone-to-DMS molar ratio of 0.9, and a GHSV of 37,000 h⁻¹, yielded 99.9% conversion of DMS. A plausible reaction mechanism has been proposed for the oxidation of DMS based on reaction product distribution and possible intermediates formed.     

Selective oxidation of propylene to acetone by molecular oxygen over Mx/2H5−x[PMo10V2O40]/HMS (M=Cu2+, Co2+, Ni2+)

The transition metal salts (Cu²⁺, Co²⁺ and Ni²⁺) of 10-molybdo-2-vanadophosphoric acid (H₅[PMo₁₀V₂O₄₀]) were supported on hexagonal mesoporous silica (HMS), and the resultant materials were used as catalysts for the selective oxidation of propylene to acetone by molecular oxygen. CuH₃[PMo₁₀V₂O₄₀]/HMS showed a high selectivity for acetone of 84.2% at 17.8% propylene conversion in a tubular fixed-bed reactor system under atmospheric pressure at 423 K. The high yield of acetone over CuH₃[PMo₁₀V₂O₄₀]/HMS at 423 K resulted from the proper acidity and oxidation ability of the heteropoly compound, the nature (acid property, redox property, etc.) of the Cu²⁺ counter-ion, the high surface area of the HMS support and the proper reaction temperature for the propylene oxidation.     

A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

Lithium insertion/deinsertion properties of new layered vanadium oxides obtained by oxidation of the precursor H2V3O8

The electrochemical behavior of the three new vanadium oxides M_yH_1−yV₃^VO₈ (M=Li, Na, K; y=0.6-0.9) towards lithium insertion was studied. For each compound, the main insertion phenomena, and the lithium amount which can be inserted, were determined from galvanostatic studies performed at different rates. In order to better explain the differences between the compounds, the galvanostatic intermittent titration technique was used and chronoamperometry experiments were performed. Cyclability studies have shown that the performances of M_0.6H_0.4V₃O₈ (M=Li, K) are not better than those of H₂V₃O₈. On the contrary, Na_0.9H_0.1V₃O₈ presents very interesting lithium insertion properties, with a specific capacity of 215 mAh g⁻¹ in the 1.5-4 V voltage range at C/10, and a capacity loss at the 40th cycle remaining smaller than 2.5%. Na_0.9H_0.1V₃O₈ is therefore a good candidate as positive electrode material for rechargeable lithium batteries.     

A kinetic study of lithium transport in the sol–gel Cr0.11V2O5.16 mixed oxide

The kinetics of the electrochemical lithium insertion reaction in the sol–gel chromium–vanadium mixed oxide Cr_0.11V₂O_5.16 has been investigated using ac impedance spectroscopy. The chemical lithium diffusion coefficient is found to be in the range 10⁻⁸/10⁻¹² cm²/s depending the Li content over the wide Li composition range 0 < x < 2 in Li_xCr_0.11V₂O_5.16. The evolution of the cathode impedance is investigated as a function of the lithium content and cycles. The results are discussed in relation with the cycling properties of the electrode material and the unusual structural response of the sol–gel mixed oxide which consists of a single phase behaviour with a continuous cell volume expansion of 6–7% in the 0 < x < 2 range for Li_xCr_0.11V₂O_5.16. For x < 1, a comparison with available kinetic data for the parent oxide indicates a very close behaviour. Cr_0.11V₂O_5.16 is shown to be the best V₂O₅-based cathode material with an initial specific capacity of 280 mAh/g at C/10 rate and still 240 mAh/g after 50 cycles in the 3.8–2 V potential range. The present kinetic data seem to indicate its better cycling behaviour mainly originates from its specific structural response rather than from kinetic reasons.     

Direct formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system

Formation of H₂O₂ from H₂ and O₂ and decomposition/hydrogenation of H₂O₂ have been studied in aqueous acidic medium over Pd/SiO₂ catalyst in presence of different halide ions (viz. F⁻, Cl⁻ and Br⁻). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H₂O₂ formation selectivity in the H₂ to H₂O₂ oxidation over the catalyst. The H₂O₂ destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br⁻ was found to selectivity promote the conversion of H₂ to H₂O₂ by significantly reducing the H₂O₂ decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H₂O₂ formation by promoting the H₂ combustion to water and/or by increasing the rate of decomposition/hydrogenation of H₂O₂ over the catalyst. An optimum concentration of Br⁻ ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H₂O₂ yield in the direct synthesis.     

Development of New Cu0–ZnII/Al2O3 Catalyst Supported on Copper Metallic Foam for the Production of Hydrogen by Methanol Steam Reforming

Copper metallic foam with thermal conductive properties, manufactured by S.C.P.S., has been investigated as a support for catalysts to improve thermal exchange inside the reactor for the endothermic steam reforming of methanol. Thus, we have developed a procedure for the in situ preparation of a Cu⁰–Zn^II/Al₂O₃ catalyst onto the copper metallic foam. The foam-based Cu⁰–Zn^II/Al₂O₃ catalyst shows an activity three times as high as commercial catalysts for a conversion of 74% of methanol into hydrogen.