Search results for "Heteropolyacids"

Heterogeneous photo-assisted catalytic hydration/dehydration reactions based on Keggin and Wells-Dawson type heteropolytungstates

2021

Polyoxometalates (POMs) are a wide class of metal-oxygen clusters that can be applied in acid and oxidation catalysis, medicine, electrochemistry, materials design, or models for self-assembling nanoscale systems as long as green and cheap photocatalysts. Heteropolyacids (HPAs) are a POM subclass extensively used as homogeneous photocatalysts for the oxidation of organic substrates. Dispersing HPAs onto solid supports with a high surface area increases their specific surface area and hence (photo)catalytic activity. This chapter reports the use of selected HPAs, heteropolytungstates, immobilized on different supports as heterogeneous photocatalysts.

Study of the photocatalytic activity of Keggin and Wells Dawson heteropolyacids: role of the acidity and of the pseudo-liquid phase regime

2017

Study of the photocatalytic activity of Keggin and Wells Dawson heteropolyacids: role of the acidity and of the pseudo-liquid phase regime

Heteropolyacids - Chitosan Membranes for H2/O2 Low Temperature Fuel Cells

2016

Proton exchange membrane fuel cells (PEMFCs) have received much attention in recent years because of their high power density, efficiency and zero-environmental pollution. As one of the key components in fuel cells, the proton exchange membrane is expected to have high proton conductivity and good electrochemical stability. In the attempt to promote PEMCFs commercialization, high cost of fuel cell systems and short lifecycle are the two main issues that need to be addressed, thus large research effort has been devoted in developing new polymer electrolytes that can replace the usually employed proton conductors, e.g. Nafion®, with other membranes of comparable performances but lower cost.A…

Photocatalytic conversion of glucose in aqueous suspensions of heteropolyacid-TiO2 composites.

2015

Photocatalytic conversion of glucose was carried out in aqueous suspensions in the presence of dfifferent commercial and home prepared TiO2 samples functionalized with a commercial heteropolyacid. Different reaction extents and distribution of intermediate oxidation products were observed depending on the photocatalyst.

Heteropolyacids - Chitosan Membranes for H2/O2 Low Temperature Fuel Cells

2016

Proton exchange membrane fuel cells (PEMFCs) have received much attention in recent years because of their high power density, efficiency and zero-environmental pollution. As one of the key components in fuel cells, the proton exchange membrane is expected to have high proton conductivity and good electrochemical stability. In the attempt to promote PEMCFs commercialization, high cost of fuel cell systems and short lifecycle are the two main issues that need to be addressed, thus large research effort has been devoted in developing new polymer electrolytes that can replace the usually employed proton conductors, e.g. Nafion®, with other membranes of comparable performances but lower cost. A…

Local Structure of Supported Keggin and Wells-Dawson Heteropolyacids and Its Influence on the Catalytic Activity

2019

[EN] Keggin [PW12O40]3– and Wells–Dawson [P2W18O62]6– heteropolyanions are nanosized transition-metal-oxygen clusters belonging to the heteropolyacids (HPAs) family. They are widely used as catalysts due to their high Brønsted acidity, and their dispersion on solid supports favors the accessibility to their acid sites generally increasing the catalytic activity. A series of binary materials composed of Keggin or Wells–Dawson HPAs and SiO2, TiO2, and ZrO2 have been prepared by impregnation or solvothermal methods. Remarkable differences have been found in the catalytic activities among the unsupported and supported HPAs. These differences have been correlated in the past to the structural ch…

Improved (photo)catalytic propene hydration in a gas/solid system by using heteropolyacid/oxide composites: Electron paramagnetic resonance, acidity,…

2017

Binary materials composed of the oxides SiO2, TiO2 and N-doped TiO2 and the Keggin heteropolyacid (PW12) were prepared and physicochemically characterized. They were used as catalysts and photocatalysts for the hydration of propene to 2-propanol. The characterization of the samples, particularly the electron paramagnetic resonance (EPR) spectroscopy results and the acidity properties, were useful to explain the key role played by the PW12 in the composite materials in the thermal and photoassisted catalytic processes. The simultaneous pres-ence of heat and UV light improved the activity of PW12 in the thermal process, and the binary materials showed better (photo)catalytic activities than t…

Heteropolyacids supported on C3N4 and BN: Comparison between catalytic and photocatalytic alcohol dehydration

Keggin and Wells-Dawson supported heteropolyacids as heterogeneous (photo)catalysts for gas-solid 2-propanol dehydration

2016

Catalytic and photocatalytic tests for 2-propanol dehydration to propene were successfully carried out by using binary materials obtained by supporting a Keggin or Wells-Dawson heteropolyacids via impregnation method to commercial SiO2 or TiO2. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The heteropolyacid species played a key role both for the catalytic and the photo-assisted catalytic reactions; indicating that the acidity of the clust…

Photocatalytic conversion of glucose in aqueous suspensions of heteropolyacid-TiO2 composites.

2015

Commercial and home prepared TiO2 samples were functionalized with a commercial Keggin heteropolyacid (HPA) H 3PW12O 40 (PW12) or with a hydrothermally home prepared K 7PW11O 39 salt (PW11). All the materials were characterized by specific surface area measurements (BET), XRD analyses, Raman, DRS along with SEM observations and they have been used for glucose photocatalytic conversion in an aqueous suspension. Different reaction extents and distribution of intermediate oxidation products were observed depending on the photocatalyst. Gluconic acid, arabinose, erythrose and formic acid were observed as oxidation products when bare TiO2 or HPA/TiO2 composite materials were used. Glucose isomer…