Insight into the Nitrilation Reaction as Catalyzed by Titanium Dioxide

While titanium dioxide has displayed excellent capabilities as a catalyst for the nitrilation reaction, the role catalyst polymorphism plays in this reaction has remained largely unexplored. Here, we explore the catalytic capabilities of the anatase and rutile polymorphs regarding the nitrilation reaction. In efforts to clarify structure – activity correlations, sets of these two polymorphs were characterized to determine their polymorphic purity, surface areas, and acidic properties. Initial catalytic investigations encountered considerable challenges, as substantial deactivation was observed when employing ethyl acrylate as a substrate ‐ an issue attributed to the polymerization of the generated acrylonitrile. Stable catalyst performance was achieved using the saturated substrate, ethyl propionate. Investigating the nitrilation reaction using this saturated substrate displayed significantly higher catalytic activity on the anatase polymorphs compared to the rutile. The catalytic activity correlated well with the total acid density, and correlations occurred independently for both anatase and rutile, emphasizing the impact the catalyst polymorph has on this reaction. Finally, the superior catalytic performance of anatase was rationalized through in situ FTIR investigation of adsorbed ethyl propionate.