Influence and stability of the surface density of MoOx on TiO2 in deoxydehydration: structure-activity correlations

Titania supported MoOx catalysts containing varying surface densities of Mo were prepared and well-characterized to identify the most effective MoOx species for the deoxydehydration (DODH) reaction of 1,4-anhydroerythritol (1,4-AHE), and eventually close the gap between experimental observations and theoretical predictions. Structure-activity correlations revealed isolated MoOx species to be more active than oligomeric/polymeric/crystalline MoOx species. Decreasing activity with increasing Mo surface density proved to be a result of the increase in strong acidity of the catalysts. These acid sites favored side reactions involving dehydration reaction and ketal formation. Comparative studies with dried and calcined catalysts showed that calcination moderately improves the selectivity of isolated MoOx species while it decreases the selectivity of polymerized MoOx species. This was due to the increased Bronsted acidity of the catalyst, a consequence of calcination. Bronsted acid sites were not present on isolated MoOx species. Regarding leaching, the calcination only benefited the isolated species as the leached species were DODH inactive while for polymerized species, due to their higher loading, the leached species were DODH active. The use of a merely dried catalyst exposed significant leaching of catalytically active species into the reaction medium in the early hours of the reaction. Recycle studies with the most active catalyst demonstrated the stable loading of Mo on TiO2, carbon deposition, and possible acidity regeneration during heat treatments.

Automated summary

Titania supported MoOx catalysts with varying surface densities of Mo were examined for the DODH reaction of 1,4-AHE. Isolated MoOx species were found to be more active than oligomeric/polymeric/crystalline MoOx species. The increase in Mo surface density resulted in strong acidity, favoring side reactions.