In situ synthesis of Cu-BTC (HKUST-1) in macro-/mesoporous silica monoliths for continuous flow catalysis.

The metal-organic framework Cu-BTC has been successfully synthesized as nanoparticles inside the mesopores of silica monoliths featuring a homogeneous macropore network enabling the use of Cu-BTC for continuous flow applications in liquid phase with low pressure drop. High productivity was reached with this catalyst for the Friedländer reaction.

Phospholipid-templated silica nanocapsules as efficient polyenzymatic biocatalysts.

Solid polyenzymatic biocatalysts have been designed by combining two immobilized enzymes, the first one allowing the in situ generation of H(2)O(2) from air and the second one performing an oxidation reaction. The in situ H(2)O(2) generation system is based on the reaction of glucose with air using a glucose oxidase (GOx). The optimization of the encapsulation of GOx into phospholipids-templated silica capsules (NPS) was performed. A bienzymatic system made of GOx and horseradish peroxidase (HRP) was studied. Optimal conditions for the activity of the GOx/HRP bienzymatic system have been determined for both homogeneous and heterogeneous conditions. The encapsulation in NPS materials increases the stability of both enzymes. The performance of the encapsulated bienzymatic GOx/HRP system in the model reaction of 4-aminoantipyridine with phenol is similar when the enzymes are immobilized separately in two NPS or coencapsulated in the same NPS. An excess of peroxidase compared to GOx ([HRP]/[GOx] = 5-10) is necessary to obtain the optimal activity. To show the potentiality of bienzymatic systems in real applications, HRP has been replaced by hemoglobin, which is known for its ability to oxidize polycyclic aromatic hydrocarbons (PAH) pollutants through a pseudoperoxidase pathway. A larger excess of Hb compared to GOx ([Hb]/[GOx] = 1000) was necessary to obtain the maximum PAH removal, as Hb is not a real peroxidase as HRP but a hemoprotein with some pseudoperoxidase activity. In opposite to real enzymes, the immobilization of Hb by adsorption in mesoporous silica is preferable as its encapsulation. Therefore, the bienzymatic system made of GOx encapsulated in NPS and Hb adsorbed in mesoporous silica has been used for the removal of 11 PAH from water. This heterogeneous bienzymatic system allows 64% of PAH removal from water using simple air as oxidant.

Theoretical evidence of the observed kinetic order dependence on temperature during the N(2)O decomposition over Fe-ZSM-5.

The characterization of Fe/ZSM5 zeolite materials, the nature of Fe-sites active in N(2)O direct decomposition, as well as the rate limiting step are still a matter of debate. The mechanism of N(2)O decomposition on the binuclear oxo-hydroxo bridged extraframework iron core site [Fe(II)(mu-O)(mu-OH)Fe(II)](+) inside the ZSM-5 zeolite has been studied by combining theoretical and experimental approaches. The overall calculated path of N(2)O decomposition involves the oxidation of binuclear Fe(II) core sites by N(2)O (atomic alpha-oxygen formation) and the recombination of two surface alpha-oxygen atoms leading to the formation of molecular oxygen. Rate parameters computed using standard statistical mechanics and transition state theory reveal that elementary catalytic steps involved into N(2)O decomposition are strongly dependent on the temperature. This theoretical result was compared to the experimentally observed steady state kinetics of the N(2)O decomposition and temperature-programmed desorption (TPD) experiments. A switch of the reaction order with respect to N(2)O pressure from zero to one occurs at around 800 K suggesting a change of the rate determining step from the alpha-oxygen recombination to alpha-oxygen formation. The TPD results on the molecular oxygen desorption confirmed the mechanism proposed.

Functionalized inorganic monolithic microreactors for high productivity in fine chemicals catalytic synthesis.

Highly productive: Grafted monolith silica skeleton microreactors process bulky molecules more efficiently than a batch mode reactor. This efficiency is due to a higher contact area, shorter diffusion path, and lower inhibition by products in the thin monolith skeleton. These materials provide a new approach in the field of heterogeneous catalysis for the synthesis of fine chemicals.

Probing Cu(I)-exchanged zeolite with CO: DFT modeling and experiment.

Addition of CO on Cu-exchanged zeolite was investigated by means of quantum chemical calculations based on density functional theory. The aim of this investigation was to get insights about changes of electronic properties of a copper site with zeolite composition by using a CO probe molecule. Calculated nu(CO) frequency values show that various Si/Al ratios of faujasite zeolite reproduce the expected experimental decrease of the nu(CO) values with decreasing Si/Al ratio. These calculations predict that H/Na ratio variations also induce changes in the nu(CO) values. These results illustrate that different compositions of the zeolite change the electronic properties of copper that are reflected in the nu(CO) frequency values. DFT results showed also that different structures and CO adsorption energies are obtained due to various Si/Al and H/Na ratios of the zeolite. Finally, these calculations evidence the possibility for CO to be connected at the same time to Cu(I) and to a close Na cation, Cu being at site II and Na at site II in Cu(I)-exchanged faujasite. A DRIFT experiment on two samples of faujasite, Cu(28)H(51)NaY and Cu(25)H(0)NaY, supports nu(CO) displacements to higher energy values with increasing H/Na ratio.

Theoretical study of N2O reduction by CO in Fe-BEA Zeolite.

Quantum mechanical (QM) and QM/molecular mechanics (MM) studies of the full catalytic cycle of N(2)O reduction by CO in Fe-BEA zeolite, that is, oxidation of BEA-Fe by N(2)O and reduction of BEA-Fe-alphaO by CO, is presented. A large QM cluster, representing half of the channel of the BEA zeolite, is used. The contribution of the MM embedding to the calculated activation energies is found to be negligible. The minimum-energy paths for N(2)O decomposition and reduction with CO are calculated using the nudged elastic band (NEB) method. Calculated and experimental activation energies are in good agreement. The two possible orientations for the gaseous molecules adsorbing on the Fe site that are found lead to different activation energies.

Novel non-hydrolytic synthesis of a V2O5-TiO2 xerogel for the selective catalytic reduction of NOx by ammonia.

A vanadia-titania mesoporous xerogel (10.5 wt% V(2)O(5)) was prepared from chloride precursors using a one-step non-hydrolytic sol-gel route and subsequent drying at ambient pressure; after calcination at 773 K for 5 h no crystalline V(2)O(5) was detected and the resulting mixed oxide exhibited remarkable activity in the selective reduction of NO with NH(3).

Supported choline hydroxide (ionic liquid) as heterogeneous catalyst for aldol condensation reactions.

Choline hydroxide was used as a basic catalyst for aldol condensation reactions to produce new C-C bonds between several ketones and aldehydes. Choline supported on MgO exhibits higher TOF values than other well known basic catalysts in these reactions.

Selective catalytic reduction of NO by NH3 on Cu-faujasite catalysts: an experimental and quantum chemical approach.

The selective catalytic reduction (SCR) of NO by NH3 in the presence of O2 on Cu-faujasite (Cu-FAU) has been studied. Substitution of some Cu2+ with H+ and Na+ cations, compensating for the negative charge of the zeolite framework, forms the various CuHNa-FAU studied. The amount of Cu was held constant and the proportion of H+ and Na+ varied in the sample. The substitution of Na+ for H+ increases sharply the SCR rate by lowering the temperature of reaction by about 150 K. It is proposed that the rate increase mainly comes from an unhindered migration of Cu from hidden to active sites and a modification of the redox properties of Cu species. The former was demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO. The change in redox properties was demonstrated by a faster oxidation of Cu+ to Cu2+ (rate-determining step). Quantum chemical calculations on model clusters of CuHNa-FAU indicate that the faster rate of oxidation can be explained by a higher lability of protons in the absence of Na, which can be then removed from the catalyst more easily to yield H2O during the oxidation process.