Zinc Powder as an Effective Reducing Reagent during Liquid-Phase Oxidation of Benzene to Phenol Using Molecular Oxygen over V-Substituted Heteropoly Acid Catalysts

Abstract

The liquid-phase oxidation of benzene to phenol in an aqueous acetic acid solvent over a V-substituted heteropolyacid catalyst was attempted using zinc powder as the reducing reagent and gaseous oxygen as the oxidant. Phenol, an oxygenation product, was selectively obtained. Zinc powder, together with the use of gaseous oxygen as the oxidant, was found to be an effective reducing reagent for phenol formation. The influences of the phenol yield on the reaction temperature, the amount of zinc powder, the concentration of acetic acid, and the amount of the V-substituted heteropolyacid catalyst were investigated. The yield of phenol had a maximum value using an aqueous solvent of acetic acid of about 60 vol %. The reuse of the used V-substituted heteropolyacid catalyst caused a decrease in the phenol yield. The reduction of part of the V species in the used V-substituted heteropolyacid catalyst was suggested to be a cause of the deactivation of the phenol formation based on the observation of the diffuse reflectance spectra of the fresh and used catalysts. The generation of hydrogen peroxide (H2O2) was confirmed in the aqueous acetic acid solvent in the presence of both zinc powder and gaseous oxygen. The dependence of the amount of generated H2O2 on the concentration of acetic acid in the aqueous solvent was found to be fairly well correlated with that of the yield of phenol on the concentration of acetic acid.

Highly Selective Synthesis of Phenol from Benzene over a Vanadium‐Doped Graphitic Carbon Nitride Catalyst

“…In weak acidity, the hydrogen peroxide was relatively stable. In contrast, in the strong acidity environment, the self‐decomposition rate of hydrogen peroxide is accelerated,49, 50 which leads to decreased activity and the gradual decrease in the yield of phenol. The two opposite effects of acetic acid resulted in the phenomenon that the yield increased first and then declined with increasing acetic acid (Table 3).…”

High-performance recyclable V–N–C catalysts for the direct hydroxylation of benzene to phenol using molecular oxygen

“…Consequently, developing low-temperature liquid-phase oxidation of benzene to phenol catalyzed by highly efficient nonnoble metal catalysts, mainly containing Cu or V species, is drawing more and more attention from an economic and environmental point of view. 9,[31][32][33][34] To date, the highest phenol yield of more than 20% could be achieved by the synergy between copper and vanadium oxide species on the support SBA-15. 27 Aer then, the Cu ion-exchanged HPMCM-41 catalysts were proved to be more active than the corresponding Cu catalysts supported on SiO 2 , TiO 2 , MgO, or NaY, even though with less than the phenol yield of 2%.…”

Structure of the Active Platinum Cluster and Reaction Pathway of the Selective Synthesis of Phenol from Benzene and Oxygen Regulated with Ammonia on a Platinum Cluster/β‐Zeolite Catalyst Studied by DFT Calculations

“…Therefore, a direct synthesis of phenol from benzene with molecular oxygen as the sole oxidant is desired, and realization of this ideal process has long been a challenge. In previous studies, many oxidants have been used for the direct synthesis of phenol from benzene, including O 2 , H 2 O 2 , N 2 O, H 2 +O 2 , O 2 /CO, and O 2 /NH 3 . In the H 2 +O 2 , O 2 /CO and O 2 /NH 3 systems, O 2 cannot directly transform benzene into phenol, but it is activated by reduction with H 2 (to form H 2 O 2 ), CO (as a sacrificial reagent), and NH 3 (to form N 2 O).…”