Hydrogenation, mesoporous catalyst

It is quite evident that if there is no major restriction to the application of mesoporous catalysts as a result of pore accessibility, more serious limitations might arise as a result of their relatively low activity with aqueous hydrogen peroxide. It has been shown that the specific activity of Ti sites in the epoxidation of olefins decreased in the order TS-1 > [Ti,Al]-/ff > Ti-MCM-41 [53]. An analogous, qualitative, trend seems to exist for the hydroxylation of benzene and phenol TS-1 > [Ti,Al]-yS, [Ti,Al]-MOR > Ti-MCM-41, Ti-HMS. Among several reasons. 

In addition to innovative coatings for the protection of the hydrogen dissociation catalyst, mesoporous metal oxide layers for enhanced performance of the sensor elements were investigated. The results demonstrated the suitability of an electrodeposited tungsten oxide (WO3) as a chemochromic layer for hydrogen detection, providing a valuable alternative to vacuum deposition. 

Yasyerh, S., Filizgok, S., Arbag, H., Yasyerli, N., Dogu, G. (2011). Ru incorporated Ni—MCM-41 mesoporous catalysts for dry reforming of methane effects of Mg addition, feed composition and temperature. International Journal of Hydrogen Energy, 56(8),... 

Kusema BT, Faba L, Kumar N, Maki-Arvela P, Diaz E, Orddnez S, et al. Hydrolytic hydrogenation of hemicellulose over metal modified mesoporous catalyst. Catal Today 2012 196 26-33. 

Highly mesoporous carbon supported Pd catalysts were prepared using sodium formate and hydrogen for the reduction of the catalyst precursors. These catalysts were tested in the enantioselective hydrogenation of isophorone and of 2-benzylidene-l-benzosuberone. The support and the catalysts were characterized by different methods such as nitrogen adsorption, hydrogen chemisorption, SEM, XPS and TPD. 

The object of the present study was to use in the above mentioned hydrogenations improved carbon supported catalysts, which could compete with the Pd black catalyst. Carbon materials are common supports, their surface properties can be modified easily and it is possible to prepare carbons with different proportion of micro-, meso- and macropores, which can be key factors influencing their performances. A highly mesoporous carbon was synthesised and used as support of Pd catalysts in the enantioselective hydrogenations. To our knowledge this is the first report on the use of highly mesoporous carbon for the preparation of Pd catalysts for liquid-phase hydrogenation. 

The anchoring and the reduction methods of precious metal precursors influence the particle size, the dispersion and the chemical composition of the catalyst. The results of SEM and H2 chemisorption measurements are summarised in Table 3. The XPS measurements indicate that the catalysts have only metallic Pd phase on their surface. The reduction of catalyst precursor with sodium formate resulted in a catalyst with lower dispersion than the one prepared by hydrogen reduction. The mesoporous carbon supported catalysts were prepared without anchoring agent, this explains why they have much lower dispersion than the commercial catalyst which was prepared in the presence of a spacing and anchoring agent (15). 

Table 4 Enantiomeric excesses in the enantioselective hydrogenation of isophorone and 2-benzyl- 1-benzosuberone on highly mesoporous carbon supported Pd catalysts.

The reduction of the catalyst precursor with sodium formate resulted in a lower Pd dispersion than the catalyst prepared by hydrogen reduction, the particle size is much larger in the former catalyst. The mesoporous carbon supported Pd catalysts are near to those of Pd on titania with respect to their enantiodifferentiating ability. Besides the metal dispersion, the availability of the Pd surface in the pores for the large modifier molecules seems to be the determining factor of the enantioselectivity. 

The carbon templated tin incorporated mesoporous silicalite catalysts with MFI structure were successfully synthesized using microwave and well characterized using all the physico-chemical techniques. The catalytic activity of these catalysts was studied for liquid phase Baeyer-Villiger oxidation of various cyclic ketones using hydrogen peroxide. All the catalyst showed high conversion ( 100%) for bicyclic ketones with 100% selectivity to the corresponding lactone. 

A new class of heterogeneous catalyst has emerged from the incorporation of mono- and bimetallic nanocolloids in the mesopores of MCM-41 or via the entrapment of pro-prepared colloidal metal in sol-gel materials [170-172], Noble metal nanoparticles containing Mex-MCM-41 were synthesized using surfactant stabilized palladium, iridium, and rhodium nanoparticles in the synthesis gel. The materials were characterized by a number of physical methods, showed that the nanoparticles were present inside the pores of MCM-41. They were found to be active catalysts in the hydrogenation of cyclic olefins such as cyclohexene, cyclooctene, cyclododecene, and... 

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