Activated Carbon-Supported Ruthenium as a Catalyst for the Solvent- and Initiator-Free Aerobic Epoxidation of Limonene

Abstract

The activity and selectivity of ruthenium catalysts supported on various activated carbons have been investigated in the epoxidation of limonene using molecular oxygen, the greenest oxidizing agent, under solvent/reductant- and initiator-free reaction conditions. The catalysts were prepared via different methods including impregnation, sol immobilization, and cation exchange. Supported Ru catalysts with a metal particle size ranging from 1.8 to 21 nm were obtained. The catalyst prepared by cation exchange using Darco G60, with the highest mesopore surface area and pore volume and the lowest Ru particle size (1.8 nm), was found to give the best combination of limonene conversion of 35% and higher selectivity for epoxidation products (S epox) of 57% at 80 °C and 3 bar oxygen pressure, compared to the total selectivity of 25.5% for allylic oxidation products (S allyl). Other activated carbon supports, e.g., Darco MRX, Norit RB4C, and Norit RX3, were found to yield less effective catalysts. In addition, the sol immobilization method led to the highest conversion of limonene (40.4%) but with a lower total selectivity toward epoxidation products (S epox) of 36.8% and that toward allylic oxidation products (S allyl) of 33.6%. The textural parameters of carbon-supported Ru catalysts were determined by BET, TEM, SEM, TPR, and CO chemisorption. Highly dispersed Ru particles were found to promote the formation of limonene epoxides via the reaction of limonene hydroperoxide with limonene instead of hydroperoxide decomposition to allylic radicals. Finally, the appropriate reaction conditions to maximize the selectivity of the epoxides and the reusability of the catalyst were established.

Copper-complexed dipyridyl-pyridazine functionalized periodic mesoporous organosilica as a heterogeneous catalyst for styrene epoxidation

“…[9][10][11][12][13][14] Nowadays, the development of efficient heterogenized catalytic systems for the epoxidation of olefins remains a challenge. 4,[15][16][17] Different types of porous materials, such as zeolites, 18 polymers, 19 mesoporous silicas, 14 activated carbons 20 or MOFs, 21 have been employed as supports of transition metal complexes for liquid phase epoxidation of olefins.…”

Incorporating of Oxidized Cellulose Nanofibers@d-Limonene Pickering Emulsion into Chitosan for Fully Biobased Coatings toward Fruits Protection

“…This is primarily due to the pronounced alteration of D-Limonene caused by its degradation through free radical reactions in the ultraviolet range. 28 Additionally, the amino group (−NH 2 ) in the chitosan backbone creates cationic functional sites in the OCNF, increasing the adsorption of UV protection. As a result, the exceptional UV-blocking properties of the resultant films will significantly expand their potential applications in the field of UV protection.…”

“…Nevertheless, as d -Limonene contents increase gradually, impressive UV-blocking abilities of the films (CFL-1, CFL-2, CFL-3, and CFL-4) against UVB with blocking rates as high as 90.8%, 96.5%, 98.6%, and 98.5%, and UVA radiation at the rates of 50.0%, 50.1%, 69.3%, and 66.9%, respectively, are ultimately achieved, indicating that the d -Limonene has a positive effect on UV-blocking. This is primarily due to the pronounced alteration of d -Limonene caused by its degradation through free radical reactions in the ultraviolet range . Additionally, the amino group (−NH 2 ) in the chitosan backbone creates cationic functional sites in the OCNF, increasing the adsorption of UV protection.…”

Recent advances in catalytic and non-catalytic epoxidation of terpenes: a pathway to bio-based polymers from waste biomass

“…A study investigated the direct epoxidation of limonene using highly dispersed ruthenium (Ru) supported on activated carbon (AC) prepared by several immobilisation techniques, without the use of solvents. 52 The study found that in mild reaction conditions, Ru/AC showed excellent efficacy in the solvent-free epoxidation of limonene. Furthermore, the selectivity of the catalyst towards epoxidation was significantly impacted by the method of catalyst preparation.…”