Tailoring the Catalytic Performance of Sol–Gel‐Encapsulated Tetra‐n‐propylammonium Perruthenate (TPAP) in Aerobic Oxidation of Alcohols

Abstract

Sol-gel nanohybrid silica particles organically modified and doped with the ruthenium species tetra-n-propylammonium perruthenate (TPAP) are highly efficient catalysts for the selective oxidation of alcohols to carbonyl groups with O(2) at low pressure in toluene. The materials are easily prepared by a one-step sol-gel process, and their catalytic performance can be optimised by tailoring the conditions of their synthesis by hydrolytic co-polycondensation of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes R-Si(OMe)(3) in the presence of TPAP. Eventually, heterogeneous catalysts considerably more active than the unsupported perruthenate were obtained, while also being leach-proof and recyclable. The correlation between the materials' activity, surface polarity and textural properties suggests valuable information on the chemical behaviour of sol-gel catalytic materials in oxidation catalysis; this is of interest in view of the importance of efficient solid catalysts for the selective oxidation of alcohols with O(2).

Fluorinated Silica Gels Doped with TPAP as Effective Aerobic Oxidation Catalysts in Dense Phase Carbon Dioxide

“…On the other hand, the cages are heavily fluorinated (Figure 2) despite the low fluoroalkyl: TMS ratio since the terminal fluoroalkyl groups mostly concentrate at the surface of the cages favouring the diffusion of fluorophilic CO 2 . [22] The predominant role of the textural properties in controlling the material×s reactivity in compressed carbon dioxide is consistent with the appreciable reactivity observed with TPAP encapsulated in unmodified SiO 2 , which in toluene was practically inactive [23] and in scCO 2 showed pronounced catalytic activity. [10] The pore-size distribution obtained by N 2 -adsorption reveals clearly that C3F-10 is a microporous glass with type I adsorption isotherm [24] having the largest porosity in the C3-F series (Figure 3).…”

A Mechanistic Study on Alcohol Oxidations with Oxygen Catalysed by TPAP‐Doped Ormosils in Supercritical Carbon Dioxide

“…In conclusion, we have demonstrated that in aerobic oxidation of alcohols in scCO 2 TPAP-doped ormosils exhibit a superior catalytic performance relative to the same homogeneous catalysts used in organic solvent, [16] in terms of selectivity, stability and activity.…”

“…Catalysts with various surface hydrophobicities are easily obtained by varying the relative amount of methyl-modified precursor utilised in the synthesis of the xerogels (i.e., 0%, 25%, 75%, 100% of MTMS), whereas catalytic doped glasses with different pore sizes and entrapment modalities of TPAP are obtained by varying the process employed for the xerogels preparation, i.e., the amount of water and the presence of NaF. [17] The higher suitability of scCO 2 as reaction medium for aerobic oxidation of alcohols with respect to conventional liquid solvents of comparable polarity is revealed by the fact that TPAP encapsulated in unmodified SiO 2 is practically inactive in toluene [16] whereas it exhibits some activity in scCO 2 .…”

“…[13] Similarly to what happens with many catalytic transition metal ion pairs, [14] sol-gel encapsulation of TPAP into ceramic matrices affords heterogeneous aerobic catalysts of different efficiency either for conversions in conventional solvent [15,16] or in carbon dioxide in the supercritical state, [17] an intrinsically non-toxic and environmentally benign reaction medium ideally suited for heterogeneous catalytic applications in the fine chemicals industry.…”

Phosphotungstic Acid Supported on Magnetic Nanoparticle Used As Selective and Reusable Photocatalyst for Aerobic Oxidation of Benzylic Alcohols

“…Many thermal catalytic systems have been designed and developed for the oxidation of alcohols [2][3][4][5][6][7][8][9][10][11][12][13] . Most of these systems are particularly effective for activated (benzylic and allylic) alcohols.…”