First Phenol Carboxylation with CO2 on Carbon Nanostructured C@Fe-Al2O3 Hybrids in Aqueous Media under Mild Conditions.

Feliciano Calvo-Castañera,Nuria Candela,Jesús Álvarez-Rodríguez,Ángel Maroto-Valiente

doi:10.3390/nano11010190

Feliciano Calvo-Castañera, Nuria Candela + Show 2 more

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https://doi.org/10.3390/nano11010190

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Abstract

Novel hybrid materials with integrated catalytic properties and hydrophobic response, C@Fe–Al2O3 hybrid samples, were presented and tested as catalysts for phenol reaction in aqueous solutions at atmospheric pressure and mild temperature conditions, using CO2 as a feedstock. A series of carbon-coated γ-alumina pellets (C@Fe–Al2O3) were synthesized and characterized by TGA, Brunauer–Emmett–Teller (BET) method, Raman spectroscopy, SEM, TEM, and XPS in order to get comprehensive knowledge of their properties at the nanoscale and relate them with their catalytic behavior. The results obtained correlated their catalytic activities with their carbon surface compositions. The application of these materials as active catalysts in the Kolbe–Schmitt reaction for CO2 conversion in aqueous media was proposed as an alternative reaction for the valorization of exhausts industrial effluents. In these early tests, the highest conversion of phenol was observed for the hybrid samples with the highest graphitic characteristic and the most hydrophobic behavior. Carboxylation products such as benzoic acid, p-hydroxybenzoic acid, and salicylic acid, have been identified under these experimental conditions.

Highlights

Most chemical reactions involving CO2 as a reagent are developed in the presence of highly reactive metal catalysts and high pressures and temperatures [1]
The Kolbe–Schmitt reaction is a well-known reaction for the industrial production of aromatic hydroxy acids, in which phenol carboxylation with CO2 is processed under high CO2 pressure (20–100 atm) and temperature (150–200 ◦ C)
C@Fe–Al2 O3 hybrids were prepared by the carbon coating of iron-impregnated spheres (FeAl) via thermal catalytic vapor decomposition (CVD) in a 600 mm-length tubular quartz reactor with an inner diameter of 48 mm

Summary

Introduction

Most chemical reactions involving CO2 as a reagent are developed in the presence of highly reactive metal catalysts and high pressures and temperatures [1]. One of the most classical reactions is the carboxylation of phenol, known as the Kolbe–Schmitt reaction, developed in 1860, when Kolbe obtained salicylic acid through electrophilic substitution by heating a phenol and sodium mixture with carbon dioxide at 80 atmospheres of pressure [15]. Schmitt raised the pressure up to 130 atm to improve the salicylic acid yield [16]. This method has been the milestone for the aromatic hydroxy acid synthesis by carboxylation [17]. The Kolbe–Schmitt reaction is a well-known reaction for the industrial production of aromatic hydroxy acids, in which phenol carboxylation with CO2 is processed under high CO2 pressure (20–100 atm) and temperature (150–200 ◦ C). The Kolbe–Schmitt advance in this reaction is inhibited by the presence of water, since dry phenoxide is considered as the determinant step

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