(269c) Tuning the Selective Oxidation of CH3OH to DMM Over Supported V2O5/TiO2/SiO2 with TiO2 Nanoligands

The selective oxidation of methanol over a catalyst with surface redox sites primarily produces formaldehyde (HCHO) as the reaction product, with low selectivity's to other redox products. The conversion of CH3OH over acid sites, however, primarily yields CH3OCH3 as the reaction product. The selective oxidation of CH3OH to (CH3O)2CH2 (DMM: dimethoxy methane)requires redox sites to initially form HCHO and acid sites to combine HCHO with two methanol molecules to form DMM. Recently, DMM has been investigated for its potential benefit as an oxygenated additive in diesel fuel. The objective of this study was to molecularly design a supported V2O5-WO3/TiO2/SiO2 catalyst whereby methanol could be selectively oxidized to give DMM as the main reaction product by changing the titania domain size.

The experimental results demonstrate that varying the local electron density of oxide nanoligand supports allows tuning of the specific activity characteristics of surface metal oxide catalytic active sites. In the low temperature regime (150°C - 190°C), the selectivity to DMM is highest due to a high concentration of methoxy species present on the surface. These methoxy species are able to react to form HCHO, and still in a high enough concentration on the surface to further react with HCHO to produce DMM. However, in the high temperature regime (200°C - 230°C), the concentration of methoxy species is significantly lower. As a result, it takes longer for two methoxy species to diffuse on the catalyst surface and react with HCHO to produce DMM. Therefore, we find the selectivity decrease as we approach our highest temperature. Ultimately, the ability to engineer the catalyst structure at the nanoscale and the fundamental understanding of the synthesis-structure-property relationships of supported metal oxides enabled the rational design of a supported metal oxide that could selectively oxidize methanol to DMM.