Superior Efficacy of Selenium-Promoted Cobalt Titanate in Dual Catalysis: Bisindole Synthesis and Acetophenone Hydrogenation

Non-metal-promoted metal titanates were synthesized using a novel surface-loading method, wherein varying weight percentages of non-metals (NMs (C, P, S, or Se)) were loaded onto preformed metal titanates, followed by calcination at their respective melting temperatures. This study investigates the promotional effect of these non-metals on cobalt titanate (CoTiO₃) in the bisindole synthesis and transfer hydrogenation of acetophenones. The catalytic activity decreased in the following order: Se-CoTiO₃ ≈ S-CoTiO₃ > C-CoTiO₃ > P-CoTiO₃. This finding correlates with the surface charge characteristics of the catalysts. Notably, both selenium- and sulfur-promoted CoTiO₃ exhibited comparable catalytic activity during optimization. However, the sulfur-modified catalyst suffered from poor reusability and a significant decrease in yield, likely due to active site blockage. In contrast, the selenium-promoted CoTiO₃ catalyst demonstrated excellent activity and superior reusability, retaining its performance for seven consecutive cycles. The stable incorporation of selenium was confirmed through X-ray photoelectron spectroscopy (XPS), highlighting its robustness and potential as a sustainable promoter in catalytic systems.