Hydrophobic Modification of Microenvironment of Highly Dispersed Co₃O₄ Nanoparticles for the Catalytic Selective Oxidation of Ethylbenzene

Abstract

Microenvironments in enzymes play crucial roles in controlling the activities of active centers. Here, hexagonal mesoporous silicas (HMS) with hydrophobic microenvironment was used to mimic the enzymes on the hydrocarbon oxidation with cobalt oxides incorporated as active sites. The variation of the structure and surface properties of the materials with phenyl group incorporation and the state of the supported cobalt oxides were carefully studied. It showed that cobalt oxides presented as Co3O4 distributed evenly among the support, and the catalytic microenvironment was modified by the neighboring phenyl groups to be hydrophobic. This novel catalyst showed enhancement in the adsorption of ethylbenzene and in turn promoted the catalytic conversion than the hydrophilic one. 55.1 % conversion of ethylbenzene and 86.1 % selectivity for acetophenone could be obtained at 393 K for 6 h under 1.0 MPa of O2 with free solvent. Hydrophobic microenvironment of pore surface was considered as an important factor for the better catalytic activity.

Photo- and Solvent-Mediated Production of the Highly Reactive N-Oxyl Radical and Its Efficient Catalytic Oxidation of Hydrocarbons at Ambient Temperature

“…To accurately quantify the selectivity of PEHP, after the first GC determination, the reaction mixtures were treated with excess Ph 3 P for 20 min to quantitatively decompose PEHP into PEA. Also, the Selectivity of PEHP could be calculated after the second GC determination. ,, Ph-CHO is the deep oxidation product due to the C–C cleavage.…”

Oxygen Vacancy Promoted O2 Activation over Mesoporous Ni–Co Mixed Oxides for Aromatic Hydrocarbon Oxidation

“…Fine chemical production with a controlled partial aerobic oxidation of hydrocarbons has received an astonishing degree of attention, both in view of environment and economy. − Selective catalytic oxidation of hydrocarbons to alcohols or ketones is considerably difficult, not only because of the relatively hard activation of the inert C benzyl –H bond but also because of the easy further oxidation of alcohols or ketones to byproducts. − One of the most economical and environmentally used methods for producing alcohols or ketones is the catalytic oxidation of hydrocarbons with O 2 . , In early works, most of the catalysts described for this oxidation reaction are Co-based homogeneous catalysts (such as cobalt cyclolkane carboxylate and cobalt acetate) with some additives (such as manganese and bromide species) in an acetic acid medium. − However, the industrial application of these methods is limited by the harsh reaction conditions (>120 °C, >1 MPa), corrosion of equipment caused by additives Cl – or Br – , and the difficult separation of homogeneous catalysts. − In contrast to these drawbacks of the homogeneous process, numerous heterogeneous catalysts have been extensively studied for the efficient catalytic oxidation of hydrocarbons under mild conditions without additives. − As reported, noble-metal-based catalysts, such as Au, Pd, Pt, and Au–Pb alloy, show preferable catalytic activity for aromatic oxidation but are restricted by their high price and limited reserves. − , …”

CeO2 Nanoparticle-Decorated Co3O4 Microspheres for Selective Oxidation of Ethylbenzene with Molecular Oxygen under Solvent- and Additive-Free Conditions

“…Thus, to meet the requirements of green and economical production in the selective EB oxidation reaction, it is a great challenge to develop a suitable catalyst to attain a favorable performance with molecular oxygen as the oxidant in the absence of any solvents and additives. In recent years, some researchers have attempted to achieve this goal with a few kinds of catalysts, such as the Mn/N–C/Al 2 O 3 catalyst, ternary Cu–Ce–Co catalyst, CoO-containing zeolite beta catalyst, hollow MnO x /TS-1 catalyst, hexagonal mesoporous silica-supported Co 3 O 4 catalyst, Co–N–C-immobilized carbon nanotube catalyst, and nitrogen-doped carbon nanotube-encapsulated cobalt nanoparticle catalyst . Unfortunately, these catalysts are associated with one or more disadvantages of the complicated and tedious preparation process, insufficient activity and/or AcPO selectivity, and poor recycling performance.…”