Titania-supported catalysts hydrogen effect

The present study revealed effects of various rutile/anatase ratios in titania on the reduction behaviors of titania-supported cobalt catalysts. It was found that the presence of rutile phase in titania could facilitate the reduction process of the orbalt catalyst. As a matter of fact, the number of reduced cobalt metal surface atoms, which is related to the overall activity during CO hydrogenation increased. 

Sipos, E., Farkas, G., Tungjer, A., Figueiredo, J.l. (2002) Enantioselective hydrogenation of isophorone with titania supported Pd catalysts modified with (-)-dihydroapovincaminic acid ethyl ester effect of the support and the reduction method, J. Mol. Catal. A. Chem. 179,107-112. 

The influence of the support is undoubted and spillover was further confirmed by the excess of hydrogen chemisorbed by a mechanical mixture of unsupported alloy and TJ-A1203 above that calculated from the known values for the separate components. It was also observed that the chemisorption was slower on the supported than on the unsupported metal and that the greater part of the adsorbate was held reversibly no comment could be made on the possible mediation by traces of water. On the other hand, spillover from platinum-rhenium onto alumina appears to be inhibited for ratios Re/(Pt Re) > 0.6. In an infrared investigation of isocyanate complexes formed between nitric oxide and carbon monoxide, on the surface of rhodium-titania and rhodium-silica catalysts, it seems that the number of complexes exceeded the number of rhodium surface atoms.The supports have a pronounced effect on the location of the isocyanate bond and on the stability of the complexes, with some suggestion of spillover. 

Also, Marsh and co-workers [145] showed that gold on cobalt oxide particles, supported on a mechanical mixture of zirconia-stabilised ceria, zirconia and titania remains active in a gas stream containing 15 ppm SO2. Haruta and co-workers [207] found that although the low-temperature CO oxidation activity of Ti02-supported Au can be inhibited by exposure to SO2, the effect on the activity for the oxidation of H2 or propane is quite small. Venezia and co-workers [208] reported that bimetallic Pd-Au catalysts supported on silica/alumina are resistant to sulphur poisoning (up to 113 ppm S in the form of dibenzothiophene) in the simultaneous hydrogenation of toluene and naphthalene at 523 K. 

Both catalysts supported on silica produce a small amoimt of propene oxide at the highest temperatures however, the selectivities remain low, proving the necessity of titania on the support to have an effective epoxidation catalyst. Furthermore, these catalysts by far have the lowest hydrogen efficiency because of the direct oxidation of hydrogen into water, making the economics of these catalysts very unattractive. 

A rather effective catalyst proved to be the system of rhodium nanoclusters stabilized with pol5winylpirrolidone (PVP) and supported on finely dispersed oxides (gamma-alumina, silica, or titania) and modified with Cnd (Huang et al. ). With this system EtPy was hydrogenated at 25 C and 70 bar hydrogen in THE with a TOP of 58.6 min and an ee of 65.4%. 

The reaction order a for carbon monoxide was —0.03, while steam had a positive reaction order b of 0.44. Carbon dioxide and hydrogen showed significant inhibition, as indicated by the reaction order of —0.1 for c and —0.44 for d, respectively [306], The effect of the support on the activity of platinum catalysts was investigated by Rosa et al. [251]. Alumina, ceria, titania and mixed ceria/titania were compared, all containing 0.5 wt.% of platinum. As shown in Figure 4.24, the activity ranking was as follows ... 

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