Synthesis of 3-fluorobenzaldehyde by gas-phase selective oxidation on Fe–Mo oxide/boralite catalysts

The gas-phase selective synthesis of 3-fluorobenzaldehyde from 3-fluorotoluene over bulk iron molybdate and Fe–Mo oxide in a host boralite sample is described. The latter samples, prepared by adding Fe and Mo by chemical vapor deposition to the boralite, show high selectivity in oxidation, making yields of 3-fluorobenzaldehyde of over 40% possible. The pretreatment of the zeolite to eliminate extra-framework boron improves behavior, and secondary post-addition of molybdenum by CVD to increase the Mo/Fe ratio in the catalyst has a similar enhancing effect. The behavior of Fe–Mo/boralite samples proves significantly better, in terms of both specific activity (per mass of active phase) and selectivity, than bulk Fe₂(MoO₄)₃, but at high conversion lower selectivities are found probably due to the presence of limitations in the backdiffusion of 3-fluorobenzaldehyde. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modification of the surface reactivity of Cu-MFI during chemisorption and transformation of the reagents in the selective reduction of NO with propane and O2

The steady-and unsteady-state catalytic behaviour of Cu-MFI in the conversion of propane and NO in the presence of O₂ is reported, showing how the chemisorption and transformation of reactants may influence the surface reactivity. Various effects were observed: (i) a change in the surface reactivity and kinetics in going from low to high concentrations of NO or propane, (ii) the transformation of NO to N₂ and N₂O promoted at low temperature (250°C) by oxygen in the absence of hydrocarbon, (iii) the influence of NO over the surface reactivity of the catalyst in the conversion of propane and (iv) the influence of surface precoverage with oxidized nitrogen oxides (N_xO_y) or carboxylate species on the catalyst transient reactivity in the reduction of NO to N₂. In particular, Cu-MFI is initially more active when oxidized nitrogen oxides are present, suggesting that the active intermediate in the reduction of NO with propane is a complex formed by the reaction of nitrate with activated hydrocarbon. It is shown, however, that strongly bound oxidized nitrogen oxides may have also additional effects on the surface reactivity: (i) can promote the conversion of NO to N₂ and N₂O in transient conditions and (ii) can give a partial inhibition of the surface reactivity blocking copper ions due to their strong chemisorption. Furthermore, it is shown that NO reacts faster with oxygen than hydrocarbon forming N_xO_y species which are then the oxidizing agent for the hydrocarbon. It is thus suggested that the surface reactivity of Cu-MFI in the reduction of NO with propane/oxygen depends on the surface population of nitrogen oxide adspecies which influence not only the surface reactivity, but also the pathway of hydrocarbon oxidation.     

The use of a solar photoelectrochemical reactor for sustainable production of energy

The conversion of solar energy into H₂ via water splitting process is one of the most attractive ways to obtain clean and renewable energy. Unfortunately, the fast back reaction of recombination and high band gap needed to activate the photo-catalytic materials, strongly limit the performances in conventional slurry photo-reactors. In this context we present a new photoelectrochemical approach with a double-chamber reactor configuration for H₂ production by water photo-electrolysis. The core of the photo-system is a membrane electrode assembly consisting of different layers which hold distinct two areas of the reactor where the generation of O₂ and H₂ occurs separately. Particular attention is given to the development, on a nano-scale level, of the materials to be used as photoanode and electrocathode: nanostructured TiO₂ arrays and carbon nanotubes are used respectively in the form of thin films separated by a proton conductive membrane. Results showed 3.2 mmol h^?1 g^?1 of H₂ evolution that is about one order of magnitude higher with respect to the activity obtained with conventional slurry photoreactors. Moreover, we present the opportunity to recycle CO₂ back to liquid fuels by using the same photoelectrochemical approach.     

Direct conversion of cellulose to glucose and valuable intermediates in mild reaction conditions over solid acid catalysts

The direct hydrolysis of cellulose to glucose, HMF and other soluble by-products at 190 °C in water solution using zeolites (H-BEA, H-MOR), sulphated zirconia supported over mesoporous silica (SBA-15), Amberlyst^®15, heteropolyacids and AlCl₃·6H₂O as acid catalysts was studied using a high cellulose to catalyst ratio (10), not-pretreated (neither mechanically nor chemically) cellulose and a static (not mixed) autoclave. Under these conditions, not usually considered, but relevant for industrial applications, micro and mesoporous solid acid catalysts are active in the direct hydrolysis of cellulose to glucose, HMF and other soluble by-products. The reactivity in crystalline cellulose conversion is determined on one side from the need to realize an efficient solid-solid interaction between the external surface of the catalyst and the crystalline cellulose, and on the other side on the need to limit the secondary reactions of the formed products. Microporous materials, due to the presence of shape-selectivity effects limiting the polymerization of glucose to humic-type species show the highest formation of glucose and HMF with respect to the sulphated zirconia supported over mesoporous silica (SBA-15) and homogeneous heteropoly acids.     

Selective heterogeneous oxidation of light alkanes. What differentiates alkane from alkene feedstocks?

Some aspects of the reactivity of vanadyl pyrophosphate catalysts inn-butane andn-pentane oxidation and propane ammoxidation are discussed in order to illustrate differences and peculiarities of the catalysts for the selective oxidation of alkanes in comparison to the catalysts for the selective oxidation of alkenes. The formation of alkenes as reaction intermediates, the catalytic and mechanistic differences in alkane and alkene conversion, their different effects in changing the active surface configuration, the relationship between surface concentration of adspecies and catalytic behavior, and the problem of the surface isolation of the active intermediates are discussed. Some brief economic considerations about the advantages of the various processes of alkane oxidation as compared to alkene or aromatic oxidation are also given.     

On the polyfunctional nature of (VO)2P2O7

The catalytic behavior of vanadyl pyrophosphate in the conversion of decalin, tetrahydro phthalic anhydride, naphthalene, 3-methyl tetrahydrophthalic anhydride, and benzene is reported in order to evidence some basic key catalytic properties of this catalyst and to discuss the possible surface pathways in the synthesis of phthalic anhydride from n-pentane, a characteristic specific catalytic property of this system.On leave from the Institute of Catalisis y Petroleoquimica, Serrano 119, Madrid, Spain.     

Influence of hydrocarbon chemisorption on the NO x adspecies over supported noble-metal catalysts

Topics in Catalysis - In situ and time-resolved DRIFT methods were used to monitor the change in NO x adspecies on Pt(1%)–TiO2 and Rh(1%)–TiO2 catalysts during interaction with propene...     

Preparation, performances and reaction mechanism for the synthesis of H2O2 from H2 and O2 based on palladium membranes

A series of new tubular catalytic membranes (TCM's) have been prepared and tested in the direct synthesis of H₂O₂. Such TCM's are asymmetric -alumina mesoporous membranes supported on macroporous -alumina, either with a subsequent carbon coating (CAM) or without (AAM). Pd was introduced by two different impregnation techniques. Deposition–precipitation (DP) was applied to CAM's to obtain an even Pd particles distribution inside the membrane pore network, whereas electroless plating deposition (EPD) was successfully applied to AAM's to give a 1–10 μm thick nearly-dense Pd layer. Both type of membranes were active in the direct synthesis of H₂O₂. Catalytic tests were carried out in a semi-batch re-circulating reactor under very mild conditions. Concentrations as high as 250–300 ppm H₂O₂ were commonly achieved with both CAM's and AAM's after 6–7 h time on stream, whereas the decomposition rate was particularly high in the presence of H₂. Important features are the temperature control and pre-activation. In order to slow down the decomposition and favor the synthesis of H₂O₂ a smooth metal surface is needed.