Heterogenization of Porphyrin into PCN‐222 as Oxidation Catalysts: Comparison in Terms of Reusability

Abstract

Although heterogeneous catalysts can be seperated from reaction media easily, catalyst efficiency is often decreased compared to homogeneous counterparts. In this study, catalytic oxidation of thymol and carvacrol were investigated using micron and nano-sized PCN-222(Fe) as heterogeneous catalysts and water soluble Fe-porphyrin complex (FePTC) as homogeneous catalyst in the presence of peroxymonosulfate (PMS). Feporphyrin complexes is well-known catalyst for oxidation reactions. PCN-222(Fe), a Zr-based mesoporous MOFs utilizing porphyrin as organic linker, exhibits similar catalytic performance compared to FePTC for the first use. However, higher conversion values were achieved in PCN-222(Fe) for the second cycles compared to the homogeneous systems highlighting the importance of heterogeneous MOF system. Thymoquinone (TQ) selectivities of the carvacrol oxidation are 5 and 8 times higher than homogeneous system in the second cycle for nano-and micro-PCN222(Fe), respectively. Importantly, PCN-222(Fe) can be used for at least 3 cycles with the reduced PMS: catalyst mole ratio.

The polymerization of carvacrol catalyzed by Mn-porphyrins: obtaining the desired product guided by the choice of solvent, oxidant, and catalyst

“…Thus, we could suggest that MnCl 2 could lead to the formation of oligomers undetectable by gas chromatography analysis. 23 This observation could justify the fact that the presence of a porphyrin macrocycle plays a fundamental role in modulating the metal ion activity to produce thymoquinone, in the case of the already published studies, 10–14 and the polymer (this study and Semerci's study 15 ).…”

“…10,12,14 Also, other studies investigated carvacrol oxidation with Oxone® employing metalloporphyrins or phthalocyanines as oxidants. 9,11,13,15…”

“…After that, they reported the obtaining of this polymer in systems employing an iron( iii )-porphyrin immobilized into a MOF structure. 15…”

“…10–14 There are only two reports in which the FeP systems allowed the identification of thymohydroquinone and a polymeric product, and possibly other non-identified products could have been formed besides thymoquinone. 13,15…”

“…Although Skrobot et al 12 described that FeP heterogenized in the zeolite, in a preliminary system like the one used with their MnP, it did not lead to the oxidation of carvacrol and leaching of MnP from the support, and the search for alternative heterogeneized systems continued and it was performed by Semerci et al 15 They reported the oxidation of carvacrol by KHSO 5 , in homogeneous and heterogeneized systems, using FeP [5,10,15,20-tetra(4-carboxy)phenylporphyrinateiron( iii )] and its respective metal–organic frameworks (MOFs) as catalysts. In these systems, they achieved a substrate conversion close to 100% and a thymoquinone yield close to 30%.…”