Catalytic thermal reactions of cumene over sepiolite and palygorskite

Abstract

The catalytic activity of sepiolite and palygorskite in cracking and disproportionation reactions of cumene was studied. The formation of benzene, diisopropylbenzene and propylene characterizes Br0nsted acid sites whereas that of ethylbenzene characterizes Lewis acid sites. At 150 and 250~ the reactions are determined mainly by the presence of acid sites in the channels of these clays. The yields are significantly higher in sepiolite as compared to palygorskite. The concentration of acid sites and their strength increase with the thermal loss of zeolitic and part of the bound water. At 350~ the reactions are determined by the acidity of the external surface of both minerals and yields are only slightly higher in sepiolite. At 150~ most acid sites are of the Br6nsted type. With the rise in temperature the relative concentration of Lewis acid sites increases.Clay minerals are used as catalysts in many cracking and disproportionation processes [1, 2]. The catalytic activity, which is mainly determined by the surface acidity of the mineral, results from the presence of surface groups, such as siloxane, silanol, aluminol, -AI-O and -Mg-O, located at the edges of the alumino-and magnesium-silicate frameworks, as well as from exchangeable cations and adsorbed water molecules. Most studies on the catalytic activity of clays, were dealing with swelling smectite minerals and only very little work was carried out with sepiolite and palygorskite [3-18]. These minerals are built of TOT ribbons with a width along the b-axis of three linked tetrahedral chains in sepiolite and two linked chains in palygorskite. The two minerals are characterized by having parallel zeolitic channels into which small molecules can penetrate [19-22]. It has been recently shown by electron microscopy that due to defects some of the chan-

Determination of adsorptive properties of a Turkish Sepiolite for removal of Reactive Blue 15 anionic dye from aqueous solutions

“…3 together with the mass losses in each stage in Table 2. Two endothermic peaks at 25-105 and 180-232 • C on the DTA curves of the Turkish Sepiolite corresponds to the removal of moisture and zeolitic water [19,25] which have mass losses by 1.92 and 0.60%, respectively. An endothermic peak at 232-326 • C which exhibit a mass loss by 1.79%, represents the desorption of bounded water.…”

“…An endothermic peak at 232-326 • C which exhibit a mass loss by 1.79%, represents the desorption of bounded water. In addition, dehydroxylation process and decomposition of the dolomite impurity occur in the temperature ranges 580-720 and 725-823 • C which is followed by a phase change exothermic peak at 851 • C [19,21,[24][25][26].…”

“…The behaviour of the sepiolite when treating with some organic molecules has been studied by the some researchers [17,[19][20][21]. Sorption of organic molecules such as 15 Crown Ether 5, Crystal Violet, Methylene Blue on the sepiolite showed that there are free negative sorption sites (P − ) and neutral sorption sites (N) on its surface [20,22].…”

The Effect of Thermal Treatment on the Structure of Palygorskite Used for Flue Gas SO₂ Removal

“…This particular crystal structure endows it with suitable surface charge, certain ion exchange capacity, large specific surface area and high adsorption capacity [1] and other physical and chemical properties. Owing to these properties, palygorskite is widely used in catalysis [2][3][4], adsorption [5][6][7][8][9][10][11] and other fields. H 2 O, SO 2 , NH 3 and other small polar molecules is able to selective adsorbed on the vertical channels in the crystal structure of palygorskite .…”