Multilayer Catalyst Research Articles

FTIR-investigation of reaction of 2-propanol and acidity of vanadium oxides layered on zirconia and their surface structure

The oxidation of alcohol and adsorption of pyridine on mono- and multi-layer V-Zr oxides prepared by the gas-phase method have been studied by FTIR spectroscopy. Multilayer catalysts exhibit both Lewis and Brönsted acidic sites, while monolayer catalysts exhibit only Lewis sites. The quantitative analysis of the V = O band in the region of 1100-900 cm −1 by band shape analysis indicates that the V = O species in multi-layer catalysts are composed of two types of V = O species, while that in monolayer catalysts are composed of a single V = O species. These surface V = O species of vanadium oxides show different activities and selectivities for both butene and alcohol oxidations.

Ammoxtoation of toluene over TiO 2(B)-supported vanadium oxide catalysts

TiO 2(B) was used as a support for vanadium oxide with loadings in the range 1 4 to 10 theoretical layers. The vanadium could be separated into two parts, which were soluble and insoluble in NH 3(aq), respectively. Insoluble vanadium, in an amount corresponding to a complete monolayer at high loadings, was present as V 4+ in freshly prepared catalysts. Diffuse reflectance FTIR spectroscopy was used to characterize the catalysts. The bands assigned to stretching vibrations of hydroxyl groups on TiO 2(B) were found to decrease in intensity with increasing vanadium loading. Spectra in the VO and V-O-V vibration region revealed a rather complex growth pattern. For a catalyst covered with a complete monolayer, vanadium strongly interacting with the support is present as interconnected tetrahedral V 4+ units. When the loading is increased, several additional layers of V 5+ in tetrahedral coordination can exist on top of the monolayer. At higher loadings, there is an abrupt change in structure, resulting in the formation of an amorphous phase built up from distorted VO 6 octahedra. Also, crystalline V 2O 5 is formed. The catalysts were used in the ammoxidation of toluene to benzonitrile. Multilayer catalysts showed better catalytic performance in comparison with crystalline V 2O 5 and catalysts exposing monolayer species.

Studies on molybdena-alumina catalysts: XII. MoS 2 surface coverage from CO 2 adsorption

Adsorption of CO 2 on a number of sulfided Mo Al 2O 3 catalysts of different Mo contents and Al 2O 3 supports was made by a pulse technique. Uptakes on the catalysts were lower than on their respective supports, from which the surface coverage of the Al 2O 3 by the MoS 2 phase was determined, since CO 2 did not adsorb on MoS 2. It was found that supports calcined up to 500 °C and for Mo loadings up to 8%, the MoS 2 phase was present as a monomolecular layer. However, supports calcined at higher temperatures showed evidence of multilayers of MoS 2. The results are consistent with a model in which the MoS 2 clusters are oriented flatwise to the support. The lower coverage found in monolayer catalysts in the sulfide state compared to the oxide state is attributed to contraction of the coverage per Mo atom rather than to formation of multilayers. ESCA results on multilayer oxide catalysts showed qualitative correlation with calculated average numbers of multilayers present.