Fe-containing pillared clays as catalysts for phenol hydroxylation

An alternative method for the preparation of mixed Fe–Al-pillared clays (Fe–Al-PILCs) derived from two natural smectites, Wyoming SWy-1 and Tunisia-Gafsa VI (an iron-rich sample) based on the use of a mixture of FeCl3 and chlorhydrol is described. The effect of the pH of the pillaring solution and the Al/Fe ratio are studied in order to assess their influence in the characteristics of the resulting solids: specific surface area, porosity and thermal stability. The behaviour of these solids as catalysts has been checked in the hydroxylation of phenol, under conventional heating or microwave irradiation, this last one allowing better yields and shorter reaction times. The presence of redox centers in the layers or in galleries of the materials, together with a Brönsted acid environment in the galleries of the PILCs, (mixed Fe–Al-PILCs and Al-PILCs derived from the Tunisian clay) induces the hydroxylation of phenol reaching conversions close to 70% under microwave irradiation, even at low reaction time (5 min). These values are comparable or even greater than conversions obtained from other catalysts used for these reactions (i.e. modified MCM).