Alternative raw materials for methanol oxidative dehydrogenation catalysts

Abstract

Abstract

In this paper the potential of using alkali activated materials as catalyst supports in methanol oxidative dehydrogenation is demonstrated. Dealumination of metakaolin-based alkali activated materials was realized using HCl to increase the specific surface areas and to improve vanadia dispersion. Corresponding supports were prepared from chemically pure raw materials through a sol-gel synthesis. The loading of vanadia was adjusted to reach the same surface VOx surface density (∼0.34 V nm−2) to the materials to be compared. The catalytic performance of the samples was evaluated in methanol oxidative dehydrogenation in the presence of methanethiol. The deeper insight on the reaction was examined using in situ DRIFT experiments. Alkali activated samples showed similar performance to the corresponding catalysts. Optimal formaldehyde production temperature was reached between 400–525°C with low vanadia loading. Better formaldehyde production has connection to lower reduction temperature of dispersed mono/polymeric vanadia species. At the temperature range where vanadia species are completely reduced, formaldehyde further oxidation to CO and CO2 takes place. This is facilitated by higher amount of Si in the support that can retain methoxy species at higher temperatures. Al and Ti in the support results in more easily reducible VOx species leading to better activity. However, these sites are more easily affected by sulphur contaminant. Alkali activated materials offer an interesting alternative to pristine raw materials for catalysts intended for methanol oxidative dehydrogenation.