Selective Catalytic Oxidation of Ethylbenzene to Acetophenone: A Review of Catalyst Systems and Reaction Mechanisms

Acetophenoneis an important chemical intermediate often employedin the production chain of many pharmaceuticals, agrochemicals, food,and cosmetic products. It is industrially produced as a byproductof the Hock process. However, a growing demand for acetophenone hasnecessitated consideration of alternative production routes. The oxidationof ethylbenzene to acetophenone (OEB-A) is one of the most consideredalternatives due to the low cost and availability of ethylbenzene(EB). The EB is one of the products of refinery downstream processesthat is obtained from the xylene/EB isomerization unit. Although theOEB-A reaction is considered inexpensive, it has not been of greatinterest due to the inert behavior of C-H bond, relativelylow acetophenone selectivity, and cumbersome separation strategiesfor extracting acetophenone from other reaction byproducts. In thisReview, we discuss the recent advances in the OEB-A reaction coveringboth homogeneous and heterogeneous systems. Advances in catalyst designand development including ligand design and coordination strategiesand tuning of support properties have, over the years, proven to beeffective in increasing acetophenone selectivity during the OEB-Aprocess. Exploring a single-atom catalyst's definitive activecenters and high atom efficiency in the OEB-A reaction has demonstratedhigh-throughput results, even though not well harnessed due to thechallenges of controlled synthesis of single-atom metal catalyst.Solvent-free, the OEB-A reaction has demonstrated to be attractivedue to its ease of product collection and environmental friendliness.Green synthesis strategies such as metal-free OEB-A reaction and CO2-assisted OEB-A reaction have been reviewed. The CO2 assisted OEB-A reaction has not received the desired attention,even though considerable improvement in catalytic performance wasreported. Considering the importance of carbon circular economy andthe ready availability of CO2, the CO2 assistedOEB-A reaction could be an interesting research focus in the nearfuture.