Influence of Synthesis Conditions on the Physicochemical Properties and Catalytic Activity of Fe/Cr-Pillared Bentonites

Fatma Tomul

doi:10.1155/2012/237853

Abstract

The synthesis of Fe/Cr-pillared bentonites starting from a 2% clay suspension and also from dry clay using ultrasound treatment for both the aging and the intercalation steps of the pillaring solution considerably reduces the time and the amount of water required compared with the conventional synthesis method. The catalysts were characterized using scanning electron microscopy with an energy dispersive system (SEM-EDS), powder X-ray diffraction (XRD), N2and CO2-adsorption/desorption, electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis and the catalytic activity of selected samples was evaluated for the phenol oxidation reaction. The results of XRD analysis showed that delaminated Fe/Cr-pillared bentonite with d001value 68 Å was observed after intercalation a direct mixture of the pillaring solution and dry clay. The adsorption-desorption isotherm analysis showed that the samples synthesized with the proposed methodology in intercalation stage have similar textural properties and these properties do not change remarkably with synthesis conditions. In addition, the characterisation studies showed that the physicochemical properties of samples synthesized by ultrasound were comparable to those of sample synthesized by conventional method in this study. The sample synthesized by conventional method show 50% phenol conversion. This value was higher than those of samples synthesized by the ultrasound.

Highlights

Pillared clays have been studied as potential micro/mesoporous materials for use as catalysts and catalyst supports on the industrial scale because of their well-controlled pore structure and catalytic properties [1,2,3,4]
The excessive amount of water required for the diluted clay suspensions and pillaring agents, combined with long synthesis times for the pillared clays, makes it difficult to produce them on the industrial scale [5, 6]
Chromium is preferable for catalytic applications because of its large range of oxidation numbers despite the major disadvantage that the pillared structure of the chromium-pillared clays is damaged when calcined at high temperatures, decreasing the surface area [22, 23]

Summary

Introduction

Pillared clays have been studied as potential micro/mesoporous materials for use as catalysts and catalyst supports on the industrial scale because of their well-controlled pore structure and catalytic properties [1,2,3,4]. The excessive amount of water required for the diluted clay suspensions and pillaring agents, combined with long synthesis times for the pillared clays, makes it difficult to produce them on the industrial scale [5, 6] For this reason, studies related to developing a more rapid synthesis of these materials have recently become important. Studies related to developing a more rapid synthesis of these materials have recently become important At this point in the development of pillared clay catalysts for the industrial scale, it is important to improve their physicochemical and catalytic properties as well as to develop synthesis methods that decrease their production time and water use [6,7,8,9,10]. Related studies have implied that catalytic activity can be increased by adding a second metal to the structure of the pillared clays produced using the iron pillaring solution [25]

Methods

Results

Conclusion