Size- and support-dependency in the catalysis of gold

https://dr.ntu.edu.sg/bitstream/10356/96770/1/30.%20Application%20of%20Layered%20Double%20Hydroxides%20for%20Removal%20of%20Oxyanions.pdf

Application of layered double hydroxides for removal of oxyanions: A review

Catalytic removal of NO

Publisher Summary This chapter describes the essence of the catalytic chemistry of heteropoly compounds in solution and in the solid state. The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by successhl large-scale applications and by promising laboratory results. Heteropolyanions are polymeric oxoanions formed by condensation of more than two different mononuclear oxoanions. Heteropolyanions formed from one kind of polyanion are called isopolyanions. Acidic elements such as Mo, W, V, Nb and Ta, which are present as oxoanions in aqueous solution, tend to polymerize by dehydration at low pH, forming polyanions and water.Heteropoly catalysts can be applied in various ways. They are used as acid as well as oxidation catalysts. They are used in various phases, as homogeneous liquids, in two-phase liquids (in phase-transfer catalysis), and in liquid-solid and in gas-solid combinations, etc.

Catalytic Chemistry of Heteropoly Compounds

Bulk gold is chemically inert and is generally regarded as a poor catalyst. However, when gold is in very small particles with diameters below 10 nm and is deposited on metal oxides or activated carbon, it becomes surprisingly active, especially at low temperatures, for many reactions such as CO oxidation and propylene epoxidation. The catalytic performance of Au is defined by three major factors: contact structure, support selection, and particle size. The role of the perimeter interfaces of Au particles as the sites for reactions is discussed as well as the change in chemical reactivity of Au clusters composed of fewer than 300 atoms.

When Gold Is Not Noble: Catalysis by Nanoparticles

Textural properties of layered double hydroxides: effect of magnesium substitution by copper or iron

Butadiene formation reaction from ethanol over various kinds of silica-magnesia having different MgO contents were studied from the standpoint of its acid-base catalysis. Maximum acidity was obtained at 50% MgO, while basicity increased with the MgO content. Silica-magnesia (85% MgO) having adequate acidity and basicity gave the maximum activity. The reaction mechanism and the roles of acidic and basic sites are discussed. The rate controlling step is the acetaldehyde formation catalyzed by basic sites.

Butadiene Formation from Ethanol over Silica-Magnesia Catalysts

Mg–V–Al mixed oxides with mesoporous properties using layered double hydroxides as precursors: catalytic behavior for the process of ethylbenzene dehydrogenation to styrene under a carbon dioxide flow

Hydrogen Transfer Reaction between Alcohols and Acetone

Layered double hydroxides (LDHs) in which magnesium was partially substituted by copper or iron in the hydrotalcite-like layer were synthesized by a coprecipitation method. The effects of the substitution on the physicochemical properties of the samples were studied by using various techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption, scanning electron microscopy (SEM), thermogravimetry (TGA), X-ray photoelectron spectroscopy (XPS). After the thermal treatment the samples were tested as catalysts for the process of methylamines (MAs) synthesis from methanol and ammonia. The catalytic behaviors of the substituted samples are defined by a non-equilibrium distribution of MAs with monomethylamine (MMA) the favored product for the catalytic sample derived from CuLDH and dimethylamine (DMA) the main product for the catalyst derived from FeLDH. Reduction increases the selectivity to lower substituted amines: at 85% conversion of methanol the MMA contribution in the MAs distribution is 67% for the reduced catalytic sample containing copper whereas the DMA contribution is nearly 78% for the reduced catalytic sample containing iron. On the contrary when MgAlLDH is used as a catalyst precursor trimethylamine (TMA) has the main contribution in the characteristic MAs distribution. The nature of the substituted metal and the bifunctionality of the samples contribute in establishing the catalytic properties for the process of MAs synthesis from methanol and ammonia.

Hiroo Niiyama

Papers

Textural properties of layered double hydroxides: effect of magnesium substitution by copper or iron

Butadiene Formation from Ethanol over Silica-Magnesia Catalysts

Mg–V–Al mixed oxides with mesoporous properties using layered double hydroxides as precursors: catalytic behavior for the process of ethylbenzene dehydrogenation to styrene under a carbon dioxide flow

Hydrogen Transfer Reaction between Alcohols and Acetone

Copper and iron substituted hydrotalcites: properties and catalyst precursors for methylamines synthesis