One-Step Catalytic or Photocatalytic Oxidation of Benzene to Phenol: Possible Alternative Routes for Phenol Synthesis?

Abstract

Phenol is an important chemical compound since it is a precursor of the industrial production of many materials and useful compounds. Nowadays, phenol is industrially produced from benzene by the multi-step “cumene process”, which is energy consuming due to high temperature and high pressure. Moreover, in the “cumene process”, the highly explosive cumene hydroperoxide is produced as an intermediate. To overcome these disadvantages, it would be useful to develop green alternatives for the synthesis of phenol that are more efficient and environmentally benign. In this regard, great interest is devoted to processes in which the one-step oxidation of benzene to phenol is achieved, thanks to the use of suitable catalysts and oxidant species. This review article discusses the direct oxidation of benzene to phenol in the liquid phase using different catalyst formulations, including homogeneous and heterogeneous catalysts and photocatalysts, and focuses on the reaction mechanisms involved in the selective conversion of benzene to phenol in the liquid phase.

TiO2 Photocatalysis for the Transformation of Aromatic Water Pollutants into Fuels

“…Many other investigations have documented the H 2 formation during the photocatalytic transformation of benzene; however, they have mainly discussed the H 2 formation as a secondary product. These reports focused on other purposes, such as the mechanistic studies of the photocatalytic reaction [12,13,[249][250][251] and the chemical synthesis [162,250,252], rather than the transformation of the aromatic water pollutants into fuels.…”

Zeolite-Based Catalysis for Phenol Production

“…One of them concerns the use of mesostructured materials (i.e., amorphous silica-based phases with ordered mesoporosity) suitably modified by addition in the synthesis phase or by postsynthesis functionalization with transition metals active in the reaction, without however leading to great advantages, mainly due to the poor control of the characteristics of the active sites and the easy leaching of the metal. 147 Remaining in the field of crystalline-porous solids, the most interesting aspect concerns the extension to the direct oxidation reaction of benzene to phenol of the zeolites with hierarchical porosity, that is, consisting of a microporous (zeolite) system interconnected with a generated mesoporous inside the crystal. In this way, on the one hand, the properties of the zeolite structure are preserved (regular and constant porous system in the entire crystalline domain, characteristics and distribution of the active sites), on the other hand the diffusion limitations of reactants and products are significantly reduced thanks to the presence of the mesoporous system.…”

“…This reaction is extensively studied, using different catalytic systems, both homogeneous and heterogeneous mainly based on transition metals (e.g., Fe, Cu, Ti, V), using different oxidants such as O 2 , N 2 O, H 2 O 2 . − An exhaustive treatment of the huge amount of data reported in the literature is outside the scope of this review, so the focus will be placed only on processes using zeolite-based catalysts that have reached a precommercial level. Two direct oxidation processes of benzene to phenol have been developed, which employ N 2 O and H 2 O 2 as oxidizing agents in the presence of zeolite catalysts containing elements with redox properties (Fe and Ti), which proved to be particularly efficient.…”

“…The strategies examined focus on the reduction of mass-transfer limitations characterizing the classical zeolite catalysts. One of them concerns the use of mesostructured materials (i.e., amorphous silica-based phases with ordered mesoporosity) suitably modified by addition in the synthesis phase or by postsynthesis functionalization with transition metals active in the reaction, without however leading to great advantages, mainly due to the poor control of the characteristics of the active sites and the easy leaching of the metal …”

Reusable citric acid modified V/AC catalyst prepared by dielectric barrier discharge for hydroxylation of benzene to phenol

“…For this reaction, the heterogenous and homogeneous catalysts involving transition metals such as vanadium, iron and copper have been extensively investigated. 1–7 Among which, heterogeneous vanadium catalysts have attracted significant attention owing to their higher activity and the convenience of recovery. 8–16 However, like other heterogeneous catalytic systems, the supported vanadium catalysts always suffer from the leaching of vanadium species.…”