Ammonia: A vital additive in the epoxidation of propylene over TS-1 extrudates

Since the discovery of titanium silicate-1 (TS-1) by Enichem several decades ago, the addition in small amounts of ammonia to the feed has been frequently mentioned in the patent literature as being key to improving the catalytic performance in epoxidations. The present study aims to investigate the molecular effect of this promotor. To achieve this, we addressed the mass transfer limitations of the reaction using shaped extrudates. Under the investigated conditions, the addition of 33 ppm of ammonia to the reactor feed increases the epoxide selectivity from 60 % to 100 %. However, the improvement in selectivity is accompanied by a decrease in activity as the concentration of the additive increases. The effect of ammonia was further explored through time-resolved IR experiments and DFT calculations, which reveals an interaction between ammonia and the titanium active sites, leading to the formation of more accessible pentacoordinate titanium active sites. This work highlights the importance of additives in industrial system studies, providing valuable insights for both industrial applications and academic research.