Structured Monolithic Catalysts vs. Fixed Bed for the Oxidative Dehydrogenation of Propane.

The deposition of V-based catalysts for the oxidative dehydrogenation of propane to propene on cordierite honeycomb monoliths was optimised as a strategy to decrease the contact time in a structured reactor with respect to a conventional fixed bed one. 10 wt% VOx supported over SiO₂ or Al₂O₃ were used as catalysts, deposed over the monolith using silica or alumina as primer, respectively. Both the alumina supported catalyst and the bohemite primer precursor were effectively deposed by dip-coating from stable powder suspensions, whereas insufficient adhesion was obtained when loading pre-synthesised SiO₂ over the cordierite. A new method based on sol-gel production of SiO₂ from tetraethylortosilicate (TEOS) over the monolith surface was set up. A correlation was derived for the prevision of the amount of silica deposed depending on the amount of TEOS. Both primer and catalyst loading were optimised as for uniformity and stability of the coating and resulted 0.5⁻1 wt % primer and 0.15 wt % of catalyst. Activity testing confirmed the strong improvement of propene productivity by increasing the time factor (i.e. Ncm³ of flowing reactant/min gcat), which ended in a one order of magnitude increase of productivity for the honeycomb-supported samples with respect to the fixed bed configuration.