Abstract
Catalytic transfer hydrogenation reactions (CTHs) produce value-added chemicals in the most economical, safe, green, and sustainable way. However, understanding the reaction mechanism and developing stable, selective, and cheap catalysts has been a significant challenge. Herein, we report the hydrogenation of cinnamaldehyde utilising glycerol as the hydrogen donor and metal oxides (SnO2, LaFeO3 and LaSnO3) as catalysts. The perovskites-types were used because they are easy to synthesise, the metal components are readily available, and they are good alternatives to noble metals. The catalysts were synthesised through the nanocasting (hard-template) method with SiO2 (KIT-6) as a template. The template was synthesised using the soft-template (sol-gel) method resulting in a high surface area of 624 m2/g. Furthermore, catalytic evaluations gave high cinnamaldehyde conversions of up to 99%. Interestingly, these catalysts were also found to catalyse the etherification of glycerol in one pot. Therefore, we propose competitive surface catalytic reactions driven by the transition metal cations as the binding sites for both the cinnamaldehyde and the sacrificial alcohol, glycerol. On the other hand, dyes are a growing environmental concern because of their toxicity. Herein, the rapid kinetic evaluation of p-nitrophenol (p-NP) reduction and oxidation of morin using inorganic perovskites as catalysts is reported. The perovskites were synthesised using the hard template method with KIT-6 as a template resulting in high surface areas (~ 687m2/g). The kinetic analysis was done with the aid of an open-source Opentrons liquid handling robot, a microplate reader with 96 wells. In four hours, twelve variations with three replicates were conducted for four different catalysts, a time-efficient and reproducible approach. The reduction of p-nitrophenol and oxidation of morin followed the pseudo-first-order reaction kinetics. The best catalyst for reducing p-nitrophenol was LaSnO3 with an observed rate constant of 3.5 x 10-2 s-1, and for the oxidation of morin was LaFeO3 with 3.9 x10-3 s-1. We postulate that this was dependant on the surface area, oxidising strength, and reducibility of the B cation of the perovskite's ABO3 crystal structure, determining their binding affinity to the reducing agent. Also, the as-synthesised catalysts showed good stability and recyclability of up to four cycles. Therefore, the rapid kinetics system can screen different catalysts for different reactions at minimum time and cost.
M.Sc. (Chemistry)