Catalytic Aerobic Oxidation of Cyclohexane and Ethyl Benzene Over Chromium-Containing Mesoporous Organosilicas

Abstract

Chromium-containing ethane-bridged hybrid periodic mesoporous organosilicas (Cr-PMO) were synthesized using 1,2-bis(triethoxysilyl)ethane (BTEE) and tetraethyl orthosilicate (TEOS) as silica sources and alkyltrimethyl ammonium salts as surfactants by two different synthesis routes. PXRD and N 2 adsorption-desorption analysis shows that the original structure of the materials is maintained after chromium substitution while spectroscopic study proves the incorporation of chromium in the frame wall positions and show the existence of Cr 2 O 3 species in the mixed silica source (BTEE-TEOS) synthesized chromium samples. The catalytic activity of the newly developed chromium samples was evaluated in the liquid phase oxidation of cyclohexane and ethylbenzene using air as an oxidant. Further, the Cr-PMO samples exhibited better cyclohexane conversion and cyclohexanone selectivity than the conventional Cr-MCM-41 and other metal-containing MCM-41 samples. The exceptional activity of the new chromium-containing molecular sieves is attributed to the hydrophobicity of the materials and to the complementary structural features that facilitates the accessibility of substrate to the active framework chromium sites.

Recent developments in liquid-phase selective oxidation using environmentally benign oxidants and mesoporous metal silicates

“…60 The oxidation of CH with molecular oxygen (air) over mesoporous metal silicate catalysts has been extensively explored. [61][62][63][64][65][66] Table 2 presents a short summary of the results published in the literature. The sponge-like material Co-TUD-1 was shown to be an active and selective catalyst for the…”

Selective oxidation of ethylbenzene to acetophenone over Cr(III) Schiff base complex intercalated into layered double hydroxide

“…Table compares the results of the present work with those for previously reported catalysts . The catalyst and method applied in the present case have advantages in terms of heterogeneous nature and better conversions, selectivity and reusability of the catalyst and separation of acetophenone.…”

“…Heterogeneous catalysts have become very important for ecofriendly industrial processes because these materials are developed with the objective of performing reactions under milder conditions and without hazardous wastes. Many researchers have used Cr(III)‐based heterogeneous catalysts for the oxidation of ethylbenzene using various oxidants . Dapurkar et al .…”

Strong Brønsted acid-modified chromium oxide as an efficient catalyst for the selective oxidation of methacrolein to methacrylic acid

“…In 1940's, the pioneering work on the oxidation of para-substituted ethylbenzene into corresponding acetophenone with air in the presence of Cr2O3 at 403 -433 K was reported [24]. Recently, it was found that supported Cr2O3 [25,26] and Cr 3+ -containing mesoporous materials [27][28][29] and metal-organic framework (Cr-MIL-101, Ref. [30]) effectively promoted oxidation of benzyl alcohol to benzaldehyde [25], cycloalkanes to α,β-unsaturated ketones [28,30], monoterpenic alkenes to epoxide and allylic derivatives [27,30], and autooxidation of cyclohexane into cyclohexanone and cyclohexanol [26,29] in an O2 or air atmosphere.…”