Pillared clay catalysts

The Physical Chemistry of Materials Energy and Environmental Applications 

Starting from clays, it is possible to develop an additional group of materials with large pores, whose framework is composed of layered structures with pillars in the interlamellar region [122], These materials are the so-called pillared clays (PILCs). 

The creation of Bronsted acidic sites in a di-octahedral clay such as beidellite, or a tri-octahedral smectite, such as saponite, is carried out using the same methodology previously explained for zeolites  

Besides the Bronsted acidic sites created by the above explained methodology, in PILCs that are ion exchanged with multivalent cations and are partially dehydrated, Lewis acidic sites are produced [132], The main interest in developing acid PILCs was due to their potential applications as cracking catalysts. Certainly the prospect of making PILCs in which the big gaseous oil molecules can diffuse and meet the active acidic sites was a motivation for the development of these catalysts [122], 

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Preparation of Pillared Clay Catalysts. PAG products are used for the preparation of zeolite-like catalysts by intercalation, the insertion of Al polycations molecules between the alurninosiHcate sheets of clay (3,33). Aqueous clay suspensions are slowly added to vigorously stirred PAG solutions, and the reaction mixture is aged for several hours. The clay is separated from the PAG solution and washed free of chloride ion. The treated clay is first dried at low temperature and then calcined in air at 450—500°G, producing a high surface area material having a regular-sized pore opening of about 0.6 to... 

K. Lourvanij and G. L. Rorrer, Dehydration of glucose to organic acids in microporous pillared clay catalysts, Appl. Catal. A Gen., 109 (1994) 147-165. 

Fast deactivation rates due to coking and the limited hydrothermal stability of pillared clays have probably retarded the commercial development of these new type of catalysts and prevented (to date) their acceptance by chemical producers and refiners. However, there is a large economic incentive justifying efforts to convert inexpensive (i.e. 40-100/ton) smectites into commercially viable (pillared clay) catalysts (56). Therefore, it is believed that work on the chemical modification of natural (and synthetic) clays, and work on the preparation and characterization of new pillared clays with improved hydrothermal stability are, and will remain, areas of interest to the academic community, as well as to researchers in industrial laboratories (56). 

In conclusion, pillared clays catalysts are not as good as initially predicted for the cracking of heavy gas oils, mainly because of the iron contamination of natural clays. There is a probability that they could be applied for the conversion of hydrotreated gas oils, giving a slightly lower gasoline yield, but higher octane number than REY zeolites. 

Table 2. Microactivity test results for several pillared clay catalysts after calcination in air at 400 C for lOh. The zeolitic cracking catalyst has been aoed for 5 hours at 760 C with 100% steam at 1 atm. ...

At MAT conditions, montmorilIonites pillared with alumina clusters, and having similar surface area, generate (at a given conversion level) similar amounts of coke (when used to crack gas oil) irrespective of the iron content of the parent bentonite. Thus, the presence of iron cannot be used to explain the high tendency for coke (and light gas) make of pillared clay catalysts. 

The activity advantage of zeolite catalysts over amorphous silica-alumina has well been documented, Weisz and his associates [1] reported that faujasite Y zeolite showed 10 to 10 times greater activity for the cracking of n-hexane than silica-alumina. Wang and Lunsford et al. [2] also noted that acidic Y zeolites were active for the disproportionation of toluene while silica-alumina was inactive. The activity difference between zeolite and silica-alumina has been attributed to their acidic properties. It is, however, difficult to explain the superactivity of zeolite relative to silica-alumina on the basis of acidity, since the number of acid sites of Y-type zeolite is only about 10 times larger than that of silica-alumina. To account for it, Wang et al. [2] proposed that the microporous structure of zeolite enhanced the concentration of reactant molecules at the acid sites. The purpose of the present work is to show that such a microporous effect is valid for pillared clay catalysts. 

Parker WO Jr, Millitri R, Kiricsi I (1995) Aluminum complexes in partially hydrolyzed aqueous AICI3 solutions used to prepare pillared clay catalysts. Appl Catalysis A General 121 L7-L 11 Persson P, Karlsson M., Ohman L-O. (1998) Coordination of acetate to Al(III) in aqueous solution and at the water-aluminum hydroxide interface a potentiometric and attenuated total reflectance FTIR study. Geochim Cosmochim Acta 62 3657-3668... 

The XPS results of Ti 2p3/2, V 2p3/2 and S 2p on the vanadia doped sulfated Ti-pillared clay catalysts are summarized in Table 2. A broad XPS band near 459 eV was observed on all samples investigated. This value is almost the same as the binding energy of 2p3/2 of Ti on Ti02 [28]. The intensity of this band increases with the Ti concentration, which reflects an increase of the surface concentration of Ti species. A band centered near 517 eV was detected on the vanadium containing samples. This indicates that vanadium on the fresh... 

Enhancing the mesoporosity of pillared clay catalyst - a study of pillar aggregates and deactivation in alkylation reaction... 

Activity of the pillared clay catalyst at any time t denoted by the term Xt was correlated with initial activity (Xo) and the rate of deactivation, oc employing the following relationship given by Tsai et.al (13,14). 

Amount of surfactant (mmol/meq), aluminium adsorbed (mg/g of clay), pillar density number (PDN), 001 spacings ([Pg.576]

Surface area (S.A.)and pore size distribution of the surfactant treated pillared clay catalyst (before and after calcination). 

However, the activity of these metal-loaded pillared clays is more than 10 times lower that for carbon-supported catalysts (15) for both unsaturated nitriles. This loss of activity could be explained in two ways the first supposes a lower accessibility of the metallic surface in the case of the pillared clays catalyst as compared with carbon based catalysts. We may suppose some strong diffusional effect. This would indicate that, assuming a good repartition of the metal into the layers of the pillared clay, the most active accessible metallic sites would just be those near the outer edge of the clay. 

Sakurai, H., Urabe, K., and Izumi, Y. 1988. New acidic pillared clay catalysts prepared from fluor-tetrasilicic mica. J, Chem, Soc Chem, Common, 23 1519. 

Sakurai, H., K. Urabe, and Y. Izumi. 1989. Acidity enhanced pillared clay catalysts. Modification of exchangeable sites on fluor-tetrasilicic mica by the fixed interlayer cations. Bull. Chem. Soc. Jpn. 62 (10) 3221-8. 

Guelou, E., Tatibouet, J. and Barrault, J. (2010). Fe-Al-Pillared Clays Catalysts for Wet Peroxide Oxidation of Phenol, in A. Gil, S. Korili, R. TmjiUano, et al. (eds). Pillared Clays and Related Catalysts, Springer, Heidelberg, Germany, pp. 201—224. 

Achma, R., Ghorbel, A., Dafinov, A., et al. (2008). Copper-supported Pillared Clay Catalysts for the Wet Hydrogen Peroxide Catalytic Oxidation of Model Pollutant Tyrosol, Appl. Catal. A General, 349, pp. 20-28. 

Caudo, S., Centi, G., Genovese, C., et al (2007). Copper- and Iron-pillared Clay Catalysts for the WHPCO of Model and Real Wastewater Streams from Olive Oil Milling Production, Appl Catal B Environ., 70, pp. 437 46. 

The superior activity of a new type of catalyst with respect to conventional SCR catalysts is often claimed in the literature. Long et al. [40], for example, claimed the superiority of pillared clay catalysts for SCR of nitrogen oxides to control power plant emissions by comparing Ce-Fe-Ti02-PILC (Pillared InterLayer Clay) with a V205-W03/Ti02 catalyst. There are many more examples of this type of claim in the literature. 

Long, R.Q., Yang, R.T., and Zammit, K.D. Superior pillared clay catalysts for selective catalytic reduction of nitrogen oxides for power plant emission control. J. Air Waste Manag. Assoc. 2000, 50, 436-442. 

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